The term aerology (from Greek ἀήρ, aēr, "air"; and -λογία, -logia) is sometimes used as an alternative term for the study of Earth's atmosphere; in other definitions, aerology is restricted to the free atmosphere, the region above the planetary boundary layer.
Composition diagram showing the evolution/cycles of various elements in Earth's atmosphere
Atmospheric chemistry is a branch of atmospheric science in which the
chemistry of the Earth's atmosphere and that of other planets is
studied. It is a multidisciplinary field of research and draws on
environmental chemistry, physics, meteorology, computer modeling,
oceanography, geology and volcanology and other disciplines. Research is
increasingly connected with other areas of study such as climatology.
The composition and chemistry of the atmosphere is of importance
for several reasons, but primarily because of the interactions between
the atmosphere and living organisms. The composition of the Earth's
atmosphere has been changed by human activity and some of these changes
are harmful to human health, crops and ecosystems. Examples of problems
which have been addressed by atmospheric chemistry include acid rain,
photochemical smog and global warming. Atmospheric chemistry seeks to
understand the causes of these problems, and by obtaining a theoretical
understanding of them, allow possible solutions to be tested and the
effects of changes in government policy evaluated.
Atmospheric chemistry plays a major role in understanding the concentration of gases in our atmosphere that contribute to climate change.
More specifically, when combined with atmospheric physics and
biogeochemistry, it is useful in terms of studying the influence of greenhouse gases like CO2, N2O, and CH4, on Earth's radiative balance. According to UNEP, CO2
emissions increased to a new record of 57.1 GtCO2e, up 1.3% from the
previous year. Previous GHG emissions growth from 2010-2019 averaged
only +0.8% yearly, illustrating the dramatic increase in global
emissions. The Global Nitrous Oxide Budget cited that atmospheric N2O has increased by roughly 25% between 1750 and 2022, having the fasted annual growth rate in 2020 and 2021. Atmospheric chemistry is critical in understanding what contributes to
our changing climate. The warming of our climate is caused when CO2
emissions, constrained by biogeochemistry, are above a 0% increase. In
order to stop temperatures from rising, there must be no CO2
emissions. By understanding the chemical composition and emission rates
in our atmosphere alongside economic factors, researchers are able to
trace back emissions back to their sources. About 26% of the 2023 GtCO2e
was used for power, 15% for transportation, 11% in industry, 11% in
agriculture, etc. In order to successfully reverse the human-driven damage contributing
to global climate change, cuts of nearly 42% are needed by 2030 and are
to be implementing using government intervention. This is one example of
how atmospheric chemistry goes hand-in-hand with social and political
policy, biogeochemistry, and economic factors.
Atmospheric dynamics is the study of motion systems of meteorological
importance, integrating observations at multiple locations and times
and theories. Common topics studied include diverse phenomena such as thunderstorms, tornadoes, gravity waves, tropical cyclones, extratropical cyclones, jet streams,
and global-scale circulations. The goal of dynamical studies is to
explain the observed circulations on the basis of fundamental principles
from physics. The objectives of such studies incorporate improving weather forecasting,
developing methods for predicting seasonal and interannual climate
fluctuations, and understanding the implications of human-induced
perturbations (e.g., increased carbon dioxide concentrations or
depletion of the ozone layer) on the global climate.
Atmospheric physics is the application of physics to the study of the
atmosphere. Atmospheric physicists attempt to model Earth's atmosphere
and the atmospheres of the other planets using fluid flow equations,
chemical models, radiation balancing, and energy transfer processes in
the atmosphere and underlying oceans and land. In order to model weather
systems, atmospheric physicists employ elements of scattering theory, wave propagation models, cloud physics, statistical mechanics and spatial statistics,
each of which incorporate high levels of mathematics and physics.
Atmospheric physics has close links to meteorology and climatology and
also covers the design and construction of instruments for studying the
atmosphere and the interpretation of the data they provide, including remote sensing instruments.
Recent studies in atmospheric physics often rely on satellite-based observation. One example includes CALIPSO,
or the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite
Observation. The CALIPSO mission, engineered by NASA and the Centre
National d'Etudes Spatiales/CNES, studies how clouds and airborne
particles play a role in regulating the weather, climate, and quality of
Earth's atmosphere. According to NASA, this mission uses methods like
retrieval algorithm development, climatology development, spectroscopy,
weather and climate model evaluation, and cloudy radiative transfer
models in addition to atmospheric physics concepts to understand the
physics involved in Earth atmospheric regulation.
Climatology is a science that derives knowledge and practices from
the more specialized disciplines of meteorology, oceanography, geology,
biology, and astronomy to study climate. In contrast to meteorology, which studies short-term weather
systems lasting up to a few weeks, climatology studies the frequency
and trends of those systems. It studies the periodicity of weather
events over timescales ranging from years to millennia, as well as
changes in long-term average weather patterns. Climatologists,
those who practice climatology, study both the nature of climates –
local, regional or global – and the natural or human-induced factors
that cause climate variability and current ongoing global warming.
Additionally, the occurrence of past climates on Earth, such as those
arising from glacial periods and interglacials, can be used to predict future changes in climate.
Oftentimes, climatology is studied in conjunction with another
specialized discipline. One recent scientific study that utilizes topics
in climatology, oceanology, and even economics is entitled "Concerns
about El Nino-Southern Oscillation and the Atlantic Meridional
Overturning Circulation with an Increasingly Warm Ocean." Scientists under New Insights in Climate Science found that Earth is at
risk of El Nino events of greater extremes and overall climate
instability given new information regarding the El Nino Southern Oscillation (ENSO) and the Atlantic Meridional Overturning Circulation
(AMOC). ENSO describes a recurring climate pattern in which the
temperature of waters in the central and eastern tropical Pacific Ocean
changes periodically. AMOC is best described by NOAA as "a system of ocean currents that
circulates water within the Atlantic Ocean, bringing warm water north
and cold water south". This research has revealed that the collapse of the AMOC appears to be
occurring sooner than when earlier models had predicted. It also expands
on the fact that our economic and social systems are more vulnerable to
El Nino impacts than previously thought. The study of climatology is
vital in understanding current climate risks. Research is necessary to
mitigate and monitor the efforts put forth towards are ever-evolving
climate. Strengthening our knowledge within the realm of climatology
allows us to better prepare for the impacts of extreme El Nino events,
such as amplified droughts, floods, and heat extremes.
Aeronomy is the scientific study of the upper atmosphere of the Earth — the atmospheric layers above the stratopause
— and corresponding regions of the atmospheres of other planets, where
the entire atmosphere may correspond to the Earth's upper atmosphere or a
portion of it. A branch of both atmospheric chemistry and atmospheric
physics, aeronomy contrasts with meteorology, which focuses on the
layers of the atmosphere below the stratopause. In atmospheric regions studied by aeronomers, chemical dissociation and ionization are important phenomena.
All of the Solar System's planets have atmospheres. This is because
their gravity is strong enough to keep gaseous particles close to the
surface. Larger gas giants are massive enough to keep large amounts of
the light gases hydrogen and helium close by, while the smaller planets lose these gases into space. The composition of the Earth's atmosphere is different from the other
planets because the various life processes that have transpired on the
planet have introduced free molecular oxygen. Much of Mercury's atmosphere has been blasted away by the solar wind. The only moon that has retained a dense atmosphere is Titan. There is a thin atmosphere on Triton, and a trace of an atmosphere on the Moon.
Planetary atmospheres are affected by the varying degrees of
energy received from either the Sun or their interiors, leading to the
formation of dynamic weather systems such as hurricanes (on Earth), planet-wide dust storms (on Mars), an Earth-sized anticyclone on Jupiter (called the Great Red Spot), and holes in the atmosphere (on Neptune). At least one extrasolar planet, HD 189733 b, has been claimed to possess such a weather system, similar to the Great Red Spot but twice as large.
Hot Jupiters have been shown to be losing their atmospheres into space due to stellar radiation, much like the tails of comets. These planets may have vast differences in temperature between their day and night sides which produce supersonic winds, although the day and night sides of HD 189733b appear to have very
similar temperatures, indicating that planet's atmosphere effectively
redistributes the star's energy around the planet.
Space weather is a branch of space physics and aeronomy, or heliophysics, concerned with the varying conditions within the Solar System and its heliosphere. This includes the effects of the solar wind, especially on the Earth's magnetosphere, ionosphere, thermosphere, and exosphere. Though physically distinct, space weather is analogous to the terrestrial weather of Earth's atmosphere (troposphere and stratosphere). The term "space weather" was first used in the 1950s and popularized in the 1990s. Later, it prompted research into "space climate", the large-scale and long-term patterns of space weather.
History
For many centuries, the effects of space weather were noticed, but not understood. Displays of auroral light have long been observed at high latitudes.
Beginnings
In 1724, George Graham reported that the needle of a magnetic compass was regularly deflected from magnetic north
over the course of each day. This effect was eventually attributed to
overhead electric currents flowing in the ionosphere and magnetosphere
by Balfour Stewart in 1882, and confirmed by Arthur Schuster in 1889 from analysis of magnetic observatory data.
In 1852, astronomer and British Major General Edward Sabine showed that the probability of the occurrence of geomagnetic storms on Earth was correlated with the number of sunspots, demonstrating a novel solar-terrestrial interaction. The solar storm of 1859 caused brilliant auroral displays and disrupted global telegraph operations. Richard Carrington correctly connected the storm with a solar flare
that he had observed the day before near a large sunspot group,
demonstrating that specific solar events could affect the Earth.
Kristian Birkeland explained the physics of aurorae by creating artificial ones in his laboratory, and predicted the solar wind.
The introduction of radio revealed that solar weather could cause extreme static or noise. Radar jamming
during a large solar event in 1942 led to the discovery of solar radio
bursts, radio waves over a broad frequency range created by a solar
flare.
The 20th century
In
the 20th century, the interest in space weather expanded as military
and commercial systems came to depend on systems affected by space
weather. Communications satellites are a vital part of global commerce. Weather satellite systems provide information about terrestrial weather. The signals from satellites of a global positioning system
(GPS) are used in a wide variety of applications. Space weather
phenomena can interfere with or damage these satellites or interfere
with the radio signals with which they operate. Space weather phenomena
can cause damaging surges in long-distance transmission lines and expose passengers and crew of aircraft travel to radiation, especially on polar routes.
The International Geophysical Year increased research into space weather. Ground-based data obtained during IGY demonstrated that the aurorae occurred in an auroral oval, a permanent region of luminescence 15 to 25° in latitude from the magnetic poles and 5 to 20° wide. In 1958, the Explorer I satellite discovered the Van Allen belts, regions of radiation particles trapped by the Earth's magnetic field. In January 1959, the SovietsatelliteLuna 1 first directly observed the solar wind and measured its strength. A smaller International Heliophysical Year (IHY) occurred in 2007–2008.
In 1969, INJUN-5 (or Explorer 40) made the first direct observation of the electric field impressed on the Earth's high-latitude ionosphere by the solar wind. In the early 1970s, Triad data demonstrated that permanent electric
currents flowed between the auroral oval and the magnetosphere.
The term "space weather" came into usage in the late 1950s as the space age began and satellites began to measure the space environment. The term regained popularity in the 1990s along with the belief that
space's impact on human systems demanded a more coordinated research and
application framework.
Programs
US National Space Weather Program
A geomagnetic storm watch issued by Space Weather Prediction Center
The purpose of the US National Space Weather Program is to focus
research on the needs of the affected commercial and military
communities, to connect the research and user communities, to create
coordination between operational data centers, and to better define user
community needs. NOAA operates the National Weather Service's Space Weather Prediction Center.
The concept was turned into an action plan in 2000, an implementation plan in 2002, an assessment in 2006 and a revised strategic plan in 2010. A revised action plan was scheduled to be released in 2011 followed by a revised implementation plan in 2012.
ICAO Space Weather Advisory
International Civil Aviation Organization
(ICAO) implemented a Space Weather Advisory program in late 2019. Under
this program, ICAO designated four global space weather service
providers:
The Australia, Canada, France, and Japan (ACFJ) consortium,
comprising space weather agencies from Australia, Canada, France, and
Japan.
The Pan-European Consortium for Aviation Space Weather User Services
(PECASUS), comprising space weather agencies from Finland (lead),
Belgium, the United Kingdom, Poland, Germany, Netherlands, Italy,
Austria, and Cyprus.
The China-Russian Federation Consortium (CRC) comprising space weather agencies from China and the Russian Federation.
Phenomena
Within the Solar System, space weather is influenced by the solar wind and the interplanetary magnetic field carried by the solar wind plasma. A variety of physical phenomena is associated with space weather, including geomagnetic storms and substorms, energization of the Van Allen radiation belts, ionospheric disturbances and scintillation of satellite-to-ground radio signals and long-range radar signals, aurorae, and geomagnetically induced currents at Earth's surface. Coronal mass ejections are also important drivers of space weather, as they can compress the magnetosphere and trigger geomagnetic storms. Solar energetic particles (SEP) accelerated by coronal mass ejections or solar flares can trigger solar particle events, a critical driver of human impact space weather, as they can damage electronics onboard spacecraft (e.g. Galaxy 15 failure), and threaten the lives of astronauts, as well as increase radiation hazards to high-altitude, high-latitude aviation.
Some spacecraft failures can be directly attributed to space weather;
many more are thought to have a space weather component. For example,
46 of the 70 failures reported in 2003 occurred during the October 2003
geomagnetic storm. The two most common adverse space weather effects on
spacecraft are radiation damage and spacecraft charging.
Radiation (high-energy particles) passes through the skin of the
spacecraft and into the electronic components. In most cases, the
radiation causes an erroneous signal or changes one bit in memory of a
spacecraft's electronics (single event upsets). In a few cases, the radiation destroys a section of the electronics (single-event latchup).
Spacecraft charging is the accumulation of an electrostatic charge
on a nonconducting material on the spacecraft's surface by low-energy
particles. If enough charge is built up, a discharge (spark) occurs.
This can cause an erroneous signal to be detected and acted on by the
spacecraft computer. A recent study indicated that spacecraft charging
is the predominant space weather effect on spacecraft in geosynchronous orbit.
Spacecraft orbit changes
The orbits of spacecraft in low Earth orbit (LEO) decay to lower and lower altitudes due to the resistance from the friction between the spacecraft's surface (i.e. ,
drag) and the outer layer of the Earth's atmosphere (or the
thermosphere and exosphere). Eventually, a LEO spacecraft falls out of
orbit and towards the Earth's surface. Many spacecraft launched in the
past few decades have the ability to fire a small rocket to manage their
orbits. The rocket can increase altitude to extend lifetime, to direct
the re-entry towards a particular (marine) site, or route the satellite
to avoid collision with other spacecraft. Such maneuvers require precise
information about the orbit. A geomagnetic storm can cause an orbit
change over a few days that otherwise would occur over a year or more.
The geomagnetic storm adds heat to the thermosphere, causing the
thermosphere to expand and rise, increasing the drag on spacecraft. The 2009 satellite collision between the Iridium 33 and Cosmos 2251 demonstrated the importance of having precise knowledge of all objects in orbit. Iridium 33 had the capability to maneuver out of the path of Cosmos 2251 and could have evaded the crash, if a credible collision prediction had been available.
The exposure of a human body to ionizing radiation has the same harmful effects whether the source of the radiation is a medical X-ray machine, a nuclear power plant, or radiation in space. The degree of the harmful effect depends on the length of exposure and the radiation's energy density. The ever-present radiation belts extend down to the altitude of crewed spacecraft such as the International Space Station (ISS) and the Space Shuttle, but the amount of exposure is within the acceptable lifetime exposure limit under normal conditions. During a major space weather event that includes an SEP burst, the flux can increase by orders of magnitude. Areas within ISS provide shielding that can keep the total dose within safe limits. For the Space Shuttle, such an event would have required immediate mission termination.
Ground systems
Spacecraft signals
The
ionosphere bends radio waves in the same manner that water in a pool
bends visible light. When the medium through which such waves travel is
disturbed, the light image or radio information is distorted and can
become unrecognizable. The degree of distortion (scintillation) of a
radio wave by the ionosphere depends on the signal frequency. Radio
signals in the VHF band (30 to 300 MHz) can be distorted beyond recognition by a disturbed ionosphere. Radio signals in the UHF
band (300 MHz to 3 GHz) transit a disturbed ionosphere, but a receiver
may not be able to keep locked to the carrier frequency. GPS uses
signals at 1575.42 MHz (L1) and 1227.6 MHz (L2) that can be distorted by
a disturbed ionosphere. Space weather events that corrupt GPS signals
can significantly impact society. For example, the Wide Area Augmentation System operated by the US Federal Aviation Administration
(FAA) is used as a navigation tool for North American commercial
aviation. It is disabled by every major space weather event. Outages can
range from minutes to days. Major space weather events can push the
disturbed polar ionosphere 10° to 30° of latitude toward the equator and
can cause large ionospheric gradients (changes in density over distance
of hundreds of km) at mid and low latitude. Both of these factors can
distort GPS signals.
Long-distance radio signals
Radio waves in the HF band (3 to 30 MHz) (also known as the shortwave
band) are reflected by the ionosphere. Since the ground also reflects
HF waves, a signal can be transmitted around the curvature of the Earth
beyond the line of sight. During the 20th century, HF communications was
the only method for a ship or aircraft far from land or a base station
to communicate. The advent of systems such as Iridium
brought other methods of communications, but HF remains critical for
vessels that do not carry the newer equipment and as a critical backup
system for others. Space weather events can create irregularities in the
ionosphere that scatter HF signals instead of reflecting them,
preventing HF communications. At auroral and polar latitudes, small
space weather events that occur frequently disrupt HF communications. At
mid-latitudes, HF communications are disrupted by solar radio bursts,
by X-rays from solar flares (which enhance and disturb the ionospheric
D-layer) and by TEC enhancements and irregularities during major geomagnetic storms.
Transpolar airline routes are particularly sensitive to space weather, in part because Federal Aviation Regulations require reliable communication over the entire flight. Diverting such a flight is estimated to cost about $100,000.
All
passengers in commercial aircraft flying above 26,000 feet (7,900 m)
typically experience some exposure in this aviation radiation
environment.
Humans in commercial aviation
The
magnetosphere guides cosmic ray and solar energetic particles to polar
latitudes, while high-energy charged particles enter the mesosphere,
stratosphere, and troposphere. These energetic particles at the top of
the atmosphere shatter atmospheric atoms and molecules, creating harmful
lower-energy particles that penetrate deep into the atmosphere and
create measurable radiation. All aircraft flying above 8 km (26,200
feet) altitude are exposed to these particles. The dose exposure is
greater in polar regions than at midlatitude and equatorial regions.
Many commercial aircraft fly over the polar region. When a space weather
event causes radiation exposure to exceed the safe level set by
aviation authorities, the aircraft's flight path is diverted.
Measurements of the radiation environment at commercial aircraft
altitudes above 8 km (26,000 ft) have historically been done by
instruments that record the data on board where the data are then
processed later on the ground. However, a system of real-time radiation
measurements on-board aircraft has been developed through the NASA
Automated Radiation Measurements for Aerospace Safety (ARMAS) program. ARMAS
has flown hundreds of flights since 2013, mostly on research aircraft,
and sent the data to the ground through Iridium satellite links. The
eventual goal of these types of measurements is to data assimilate them
into physics-based global radiation models, e.g., NASA's Nowcast of
Atmospheric Ionizing Radiation System (NAIRAS), so as to provide the weather of the radiation environment rather than the climatology.
Ground-induced electric fields
Magnetic storm activity can induce geoelectric fields in the Earth's conducting lithosphere. Corresponding voltage differentials can find their way into electric power grids through ground connections,
driving uncontrolled electric currents that interfere with grid
operation, damage transformers, trip protective relays, and sometimes
cause blackouts. This complicated chain of causes and effects was demonstrated during the magnetic storm of March 1989, which caused the complete collapse of the Hydro-Québec
electric-power grid in Canada, temporarily leaving nine million people
without electricity. The possible occurrence of an even more intense
storm led to operational standards intended to mitigate induction-hazard risks, while reinsurance companies commissioned revised risk assessments.
Geophysical exploration
Air- and ship-borne magnetic surveys
can be affected by rapid magnetic field variations during geomagnetic
storms. Such storms cause data-interpretation problems because the space
weather-related magnetic field changes are similar in magnitude to
those of the subsurface crustal magnetic field in the survey area.
Accurate geomagnetic storm warnings, including an assessment of storm
magnitude and duration, allows for an economic use of survey equipment.
Geophysics and hydrocarbon production
For economic and other reasons, oil and gas production often involves horizontal drilling
of well paths many kilometers from a single wellhead. Accuracy
requirements are strict, due to target size – reservoirs may only be a
few tens to hundreds of meters across – and safety, because of the
proximity of other boreholes. The most accurate gyroscopic method is
expensive, since it can stop drilling for hours. An alternative is to
use a magnetic survey, which enables measurement while drilling (MWD). Near real-time magnetic data can be used to correct drilling direction. Magnetic data and space weather forecasts can help to clarify unknown sources of drilling error.
Terrestrial weather
The amount of energy entering the troposphere and stratosphere from space weather phenomena is trivial compared to the solar insolation
in the visible and infrared portions of the solar electromagnetic
spectrum. Although some linkage between the 11-year sunspot cycle and
the Earth's climate has been claimed., this has never been verified. For example, the Maunder minimum,
a 70-year period almost devoid of sunspots, has often been suggested to
be correlated to a cooler climate, but these correlations have
disappeared after deeper studies. The suggested link from changes in
cosmic-ray flux causing changes in the amount of cloud formation did not survive scientific tests. Another suggestion, that variations in the extreme ultraviolet (EUV) flux subtly influence existing drivers of the climate and tip the balance between El Niño/La Niña events collapsed when new research showed this was not possible. As such, a
linkage between space weather and the climate has not been demonstrated.
In addition, a link has been suggested between high energy charged particles (such as SEPs and cosmic rays) and cloud formation. This is because charged particles interact with the atmosphere to produce volatiles which then condense, creating cloud seeds. This is a topic of ongoing research at CERN, where experiments test the effect of high-energy charged particles on atmosphere. If proven, this may suggest a link between space weather (in the form of solar particle events) and cloud formation.
Most recently, a statistical connection has been reported between the occurrence of heavy floods and the arrivals of high-speed solar wind streams (HSSs). The enhanced auroral energy deposition during HSSs is suggested as a mechanism for the generation of downward propagating atmosphericgravity waves (AGWs). As AGWs reach lower atmosphere, they may excite the conditional instability in the troposphere, thus leading to excessive rainfall. [36]
Observation of space weather is done both for scientific research and
applications. Scientific observation has evolved with the state of
knowledge, while application-related observation expanded with the
ability to exploit such data.
Ground-based
Space
weather is monitored at ground level by observing changes in the
Earth's magnetic field over periods of seconds to days, by observing the
surface of the Sun, and by observing radio noise created in the Sun's
atmosphere.
The Sunspot Number (SSN) is the number of sunspots
on the Sun's photosphere in visible light on the side of the Sun
visible to an Earth observer. The number and total area of sunspots are
related to the brightness of the Sun in the EUV and X-ray portions of the solar spectrum and to solar activity such as solar flares and coronal mass ejections.
The 10.7 cm radio flux (F10.7) is a measurement of RF emissions
from the Sun and is roughly correlated with the solar EUV flux. Since
this RF emission is easily obtained from the ground and EUV flux is not,
this value has been measured and disseminated continuously since 1947.
The world standard measurements are made by the Dominion Radio Astrophysical Observatory at Penticton, BC, Canada and reported once a day at local noon in solar flux units (10−22W·m−2·Hz−1). F10.7 is archived by the National Geophysical Data Center.
Fundamental space weather monitoring data are provided by
ground-based magnetometers and magnetic observatories. Magnetic storms
were first discovered by ground-based measurement of occasional magnetic
disturbance. Ground magnetometer data provide real-time situational
awareness for postevent analysis. Magnetic observatories have been in
continuous operations for decades to centuries, providing data to inform
studies of long-term changes in space climatology.
Disturbance storm time index
(Dst index) is an estimate of the magnetic field change at the Earth's
magnetic equator due to a ring of electric current at and just earthward
of the geosynchronous orbit. The index is based on data from four ground-based magnetic observatories between 21° and 33° magnetic latitude
during a one-hour period. Stations closer to the magnetic equator are
not used due to ionospheric effects. The Dst index is compiled and
archived by the World Data Center for Geomagnetism, Kyoto.
Kp/ap
index: 'a' is an index created from the geomagnetic disturbance at one
midlatitude (40° to 50° latitude) geomagnetic observatory during a
3-hour period. 'K' is the quasilogarithmic counterpart of the 'a' index.
Kp and ap are the average of K and an over 13 geomagnetic observatories
to represent planetary-wide geomagnetic disturbances. The Kp/ap index indicates both geomagnetic storms and substorms (auroral disturbance). Kp/ap data are available from 1932 onward.
AE index is compiled from geomagnetic disturbances at 12
geomagnetic observatories in and near the auroral zones and is recorded
at 1-minute intervals. The public AE index is available with a lag of two to three days that
limits its utility for space weather applications. The AE index
indicates the intensity of geomagnetic substorms except during a major
geomagnetic storm when the auroral zones expand equatorward from the
observatories.
Radio noise bursts are reported by the Radio Solar Telescope
Network to the U.S. Air Force and to NOAA. The radio bursts are
associated with solar flare plasma that interacts with the ambient solar
atmosphere.
The Sun's photosphere is observed continuously for activity that can be the precursors to solar flares and CMEs. The Global Oscillation Network Group (GONG) project monitors both the surface and the interior of the Sun by using helioseismology,
the study of sound waves propagating through the Sun and observed as
ripples on the solar surface. GONG can detect sunspot groups on the far
side of the Sun. This ability has recently been verified by visual
observations from the STEREO spacecraft.
Neutron monitors
on the ground indirectly monitor cosmic rays from the Sun and galactic
sources. When cosmic rays interact with the atmosphere, atomic
interactions occur that cause a shower of lower-energy particles to
descend into the atmosphere and to ground level. The presence of cosmic
rays in the near-Earth space environment can be detected by monitoring
high-energy neutrons at ground level. Small fluxes of cosmic rays are
present continuously. Large fluxes are produced by the Sun during events
related to energetic solar flares.
Total Electron Content
(TEC) is a measure of the ionosphere over a given location. TEC is the
number of electrons in a column one meter square from the base of the
ionosphere (around 90 km altitude) to the top of the ionosphere (around
1000 km altitude). Many TEC measurements are made by monitoring the two
frequencies transmitted by GPS
spacecraft. Presently, GPS TEC is monitored and distributed in real
time from more than 360 stations maintained by agencies in many
countries.
Geoeffectiveness is a measure of how strongly space weather
magnetic fields, such as coronal mass ejections, couple with the Earth's
magnetic field. This is determined by the direction of the magnetic
field held within the plasma that originates from the Sun. New
techniques measuring Faraday rotation in radio waves are in development to measure field direction.
Satellite-based
A host of research spacecraft have explored space weather. The Orbiting Geophysical Observatory
series were among the first spacecraft with the mission of analyzing
the space environment. Recent spacecraft include the NASA-ESA
Solar-Terrestrial Relations Observatory (STEREO) pair of spacecraft
launched in 2006 into solar orbit and the Van Allen Probes, launched in 2012 into a highly elliptical
Earth orbit. The two STEREO spacecraft drift away from the Earth by
about 22° per year, one leading and the other trailing the Earth in its
orbit. Together they compile information about the solar surface and
atmosphere in three dimensions. The Van Allen probes record detailed
information about the radiation belts, geomagnetic storms, and the
relationship between the two.
Some spacecraft with other primary missions have carried
auxiliary instruments for solar observation. Among the earliest such
spacecraft were the Applications Technology Satellite (ATS) series at GEO that were precursors to the modern Geostationary Operational Environmental Satellite
(GOES) weather satellite and many communication satellites. The ATS
spacecraft carried environmental particle sensors as auxiliary payloads
and had their navigational magnetic field sensor used for sensing the
environment.
Many of the early instruments were research spacecraft that were
re-purposed for space weather applications. One of the first of these
was the IMP-8 (Interplanetary Monitoring Platform). It orbited the Earth at 35 Earth radii and observed the solar wind for
two-thirds of its 12-day orbits from 1973 to 2006. Since the solar wind
carries disturbances that affect the magnetosphere and ionosphere, IMP-8
demonstrated the utility of continuous solar wind monitoring. IMP-8 was
followed by ISEE-3, which was placed near the L1 Sun-Earth Lagrangian point,
235 Earth radii above the surface (about 1.5 million km, or 924,000
miles) and continuously monitored the solar wind from 1978 to 1982. The
next spacecraft to monitor the solar wind at the L1 point was WIND from 1994 to 1998. After April 1998, the WIND spacecraft orbit was changed to circle the Earth and occasionally pass the L1 point. The NASA Advanced Composition Explorer has monitored the solar wind at the L1 point from 1997 to present.
In addition to monitoring the solar wind, monitoring the Sun is
important to space weather. Because the solar EUV cannot be monitored
from the ground, the joint NASA-ESASolar and Heliospheric Observatory
(SOHO) spacecraft was launched and has provided solar EUV images
beginning in 1995. SOHO is a main source of near-real time solar data
for both research and space weather prediction and inspired the STEREO mission. The Yohkoh
spacecraft at LEO observed the Sun from 1991 to 2001 in the X-ray
portion of the solar spectrum and was useful for both research and space
weather prediction. Data from Yohkoh inspired the Solar X-ray Imager on GOES.
GOES-7 monitors space weather conditions during the October 1989 solar activity resulted in a Forbush Decrease, ground level enhancements, and many satellite anomalies.
Spacecraft with instruments whose primary purpose is to provide data for space weather predictions and applications include the Geostationary Operational Environmental Satellite (GOES) series of spacecraft, the POES series, the DMSP series, and the Meteosat
series. The GOES spacecraft have carried an X-ray sensor (XRS) which
measures the flux from the whole solar disk in two bands – 0.05 to
0.4 nm and 0.1 to 0.8 nm – since 1974, an X-ray imager (SXI) since 2004,
a magnetometer which measures the distortions of the Earth's magnetic
field due to space weather, a whole disk EUV
sensor since 2004, and particle sensors (EPS/HEPAD) which measure ions
and electrons in the energy range of 50 keV to 500 MeV. Starting
sometime after 2015, the GOES-R generation of GOES spacecraft will
replace the SXI with a solar EUV image (SUVI) similar to the one on SOHO and STEREO and the particle sensor will be augmented with a component to extend the energy range down to 30 eV.
The Deep Space Climate Observatory (DSCOVR) satellite is a NOAA
Earth observation and space weather satellite that launched in February
2015. Among its features is advance warning of coronal mass ejections.
Models
Space
weather models are simulations of the space weather environment. Models
use sets of mathematical equations to describe physical processes.
These models take a limited data set and attempt to describe all
or part of the space weather environment in or to predict how weather
evolves over time. Early models were heuristic; i.e., they did not directly employ physics. These models take less resources than their more sophisticated descendants.
Later models use physics to account for as many phenomena as
possible. No model can yet reliably predict the environment from the
surface of the Sun to the bottom of the Earth's ionosphere. Space
weather models differ from meteorological models in that the amount of
input is vastly smaller.
A significant portion of space weather model research and development in the past two decades has been done as part of the Geospace Environmental Model (GEM) program of the National Science Foundation. The two major modeling centers are the Center for Space Environment Modeling (CSEM) and the Center for Integrated Space weather Modeling (CISM). The Community Coordinated Modeling Center (CCMC) at the NASA Goddard Space Flight Center
is a facility for coordinating the development and testing of research
models, for improving and preparing models for use in space weather
prediction and application.
Modeling techniques include (a) magnetohydrodynamics,
in which the environment is treated as a fluid, (b) particle in cell,
in which non-fluid interactions are handled within a cell and then cells
are connected to describe the environment, (c) first principles, in
which physical processes are in balance (or equilibrium) with one
another, (d) semi-static modeling, in which a statistical or empirical
relationship is described, or a combination of multiple methods.
Commercial space weather development
During
the first decade of the 21st Century, a commercial sector emerged that
engaged in space weather, serving agency, academia, commercial and
consumer sectors. Space weather providers are typically smaller companies, or small
divisions within a larger company, that provide space weather data,
models, derivative products and service distribution.
The commercial sector includes scientific and engineering
researchers as well as users. Activities are primarily directed toward
the impacts of space weather upon technology. These include, for
example:
Atmospheric drag on LEO satellites caused by energy inputs into the thermosphere from solar UV, FUV, Lyman-alpha, EUV, XUV, X-ray, and gamma ray photons as well as by charged particle precipitation and Joule heating at high latitudes;
Surface and internal charging from increased energetic particle
fluxes, leading to effects such as discharges, single event upsets and
latch-up, on LEO to GEO satellites;
Disrupted GPS signals caused by ionospheric scintillation leading to
increased uncertainty in navigation systems such as aviation's Wide Area Augmentation System (WAAS);
Lost HF, UHF and L-band radio communications due to ionosphere scintillation, solar flares and geomagnetic storms;
Increased radiation to human tissue and avionics from galactic cosmic rays
SEP, especially during large solar flares, and possibly bremsstrahlung
gamma-rays produced by precipitating radiation belt energetic electrons
at altitudes above 8 km;
Increased inaccuracy in surveying and oil/gas exploration that uses
the Earth's main magnetic field when it is disturbed by geomagnetic
storms;
Loss of power transmission from GIC surges in the electrical power
grid and transformer shutdowns during large geomagnetic storms.
Many of these disturbances result in societal impacts that account for a significant part of the national GDP.
The concept of incentivizing commercial space weather was first
suggested by the idea of a Space Weather Economic Innovation Zone
discussed by the American Commercial Space Weather Association (ACSWA)
in 2015. The establishment of this economic innovation zone would
encourage expanded economic activity developing applications to manage
the risks space weather and would encourage broader research activities
related to space weather by universities. It could encourage U.S.
business investment in space weather services and products. It promoted
the support of U.S. business innovation in space weather services and
products by requiring U.S. government purchases of U.S. built commercial
hardware, software, and associated products and services where no
suitable government capability pre-exists. It also promoted U.S. built
commercial hardware, software, and associated products and services
sales to international partners. designate U.S. built commercial
hardware, services, and products as “Space Weather Economic Innovation
Zone” activities; Finally, it recommended that U.S. built commercial
hardware, services, and products be tracked as Space Weather Economic
Innovation Zone contributions within agency reports. In 2015 the U.S.
Congress bill HR1561 provided groundwork where social and environmental
impacts from a Space Weather Economic Innovation Zone could be
far-reaching. In 2016, the Space Weather Research and Forecasting Act
(S. 2817) was introduced to build on that legacy. Later, in 2017-2018
the HR3086 Bill took these concepts, included the breadth of material
from parallel agency studies as part of the OSTP-sponsored Space Weather
Action Program (SWAP), and with bicameral and bipartisan support the 116th Congress (2019) is
considering passage of the Space Weather Coordination Act (S141, 115th
Congress).
The May 1921 geomagnetic storm, one of the largest geomagnetic storms disrupted telegraph service and damaged electrical equipment worldwide.
The Solar storm of August 1972, a large SEP event occurred. If astronauts had been in space at the time, the dose could have been life-threatening.
The March 1989 geomagnetic storm included multiple space weather effects: SEP, CME, Forbush decrease, ground level enhancement, geomagnetic storm, etc..
April 21, 2002, the Nozomi
Mars Probe was hit by a large SEP event that caused large-scale
failure. The mission, which was already about 3 years behind schedule,
was abandoned in December 2003.
The 2003 Halloween solar storms, a series of coronal mass ejections and solar flares in late October and early November 2003 with associated impacts.
Elon Musk at the 2006 Mars Society
conference. Before founding SpaceX in 2002, Musk had expressed interest
in Mars missions and briefly joined the Mars Society's board of
directors.
SpaceX Mars colonization program (also referred to as Occupy Mars) is the planned objective of the company SpaceX, and particularly of its founder Elon Musk, to send humans to live on Mars.
The plan is to establish a self-sustaining, large scale settlement and
directly democratic, self-governing colony. The motivation behind this
is the belief that colonizing Mars will allow humanity to become
multiplanetary, thereby ensuring the long-term survival of the human race if it becomes extinct on Earth. Colonization is to be achieved with reusable and mass-produced, super heavy-lift launch vehicles called Starship. They have been referred to as the "holy grail of rocketry" for extraplanetary colonization.
These plans for colonizing Mars have received both praise and
criticism. They are supported by public interest in further human
involvement beyond Earth and a desire to extend the lifetime of the
human race, but doubts have been expressed about whether they will work,
how it will be done, and whether humans from Earth could live on Mars.
History
Elon Musk, founder of SpaceX, has advocated colonization of Mars at the Mars Society since at least 2001. As early as 2007, Musk publicly stated a personal goal of eventually enabling humans to explore and settle on Mars. SpaceX has stated that its goal is to colonize Mars to ensure the long-term survival of the human species. Since the 2000s and early 2010s, SpaceX has proposed different methods for reaching Mars, including the use of space tugs.
Red Dragon
Artist's conception of two Red Dragon capsules on Mars, next to an outpost
Red Dragon was a 2011–2017 mission concept which would have used a modified Dragon 2 spacecraft as a low-cost Mars lander. The Dragon 2 would have been launched on a Falcon Heavy rocket, and would have landed by using its SuperDracoretro-propulsion thrusters. Equipping the craft with parachutes would not have been possible without significant modifications.
In 2011, SpaceX planned to use Red Dragon for Discovery Mission #13, which would have been launched in 2022, but the plan was not submitted to NASA. Red Dragon was proposed in 2014 as a low-cost way for NASA to obtain a Mars sample return by 2021. The Red Dragon
capsule would have been equipped with a system for returning samples
gathered on Mars to Earth. NASA did not fund this concept. In 2016,
SpaceX planned to launch two Red Dragon vehicles to Mars in 2018,with NASA providing technical support instead of funding. In 2017 Red Dragon was cancelled in favor of the much larger Starship spacecraft.
The company's current plan was first formally proposed at the 2016 International Astronautical Congress alongside a fully-reusable launch vehicle, the Interplanetary Transport System. Since then, the launch vehicle has been renamed "Starship" and continues in development.
The development program reached several milestones in 2024. On its third test flight, Starship reached its desired trajectory for the first time and on its fourth flight test, both stages of the vehicle achieved controlled splashdown after launch for the first time.
On 7 September 2024, SpaceX announced that it would launch the
first uncrewed Starship missions to Mars by 2026 to take advantage of
the next Earth-Mars transfer window. It was planned to send five Starships, and Elon Musk stated on the social media platform X that these missions
would focus on testing whether Starships could reliably land intact on
Mars. If the missions were a success, the company would begin crewed
flights to Mars within about four years.
On 29 May 2025, Elon Musk provided an update presentation on the
SpaceX Mars program. He stated that the company aims to target the
2026/27 Mars launch window, depending on the successful demonstration of
orbital refuelling capabilities. He estimated a 50% chance of being
ready in time for that window. If it is missed, SpaceX plans to attempt
the subsequent launch opportunity, with the overall timeline shifting by
two years. Musk outlined a launch schedule in the event of a successful
2026/27 mission, including approximately 20 missions during the 2028/29
window, 100 missions during 2030/31, and up to 500 missions by the 2033
launch window.
In 2014 SpaceX began building a facility called Starbase, and later a factory called Starfactory, on the previously populated and wildlife preservation area at Boca Chica (Texas) peninsula in the Rio Grande delta at the Gulf of Mexico, to build and launch a fully reusablesuper heavy-lift launch vehicle named Starship. The vehicle's reusability would greatly reduce launch costs, enabling rapid maintenance between flights. It was intended that when Starship became operational, it would travel to Mars carrying human colonists. Musk has stated that a Starship orbital launch could eventually cost
$2 million, after starting at $10 million within 2–3 years and dropping
with time. Starfactory would eventually build Starships at the rate of one per day.
A scene of astronauts on Mars in a 2016 IAC presentation
Musk has stated that Starship's earliest possible Mars landing could have been 2022, and that a crewed mission to Mars would take place no earlier than 2029. SpaceX's early missions to Mars will involve small fleets of Starship spacecraft, funded by public–private partnerships.
SpaceX has stated that it plans to build a crewed base on Mars which it hopes will grow into a self-sufficient colony. Before any people are transported to Mars, a number of cargo missions would be undertaken in order to transport equipment, habitats and supplies. Equipment that would accompany the early groups would include "machines to produce fertilizer, methane and oxygen from Mars' atmospheric nitrogen and carbon dioxide and the planet's subsurface water ice" as well as construction materials to build transparent domes for growing crops.As of September 2024, SpaceX planned to launch five uncrewed Starships
to Mars during the next available Earth–Mars transfer window in 2026.
Musk's plans for the first crewed Mars mission state that it will
consist of approximately 12 people, with goals to "build and
troubleshoot the propellant plant and Mars Base Alpha power system" and
establish a "rudimentary base".
The company plans to synthesize methane from subsurface water and atmospheric carbon dioxide with the Sabatier reaction so that it can produce enough fuel for return journeys, and use similar technologies on Earth to create carbon-neutral propellant.
Populating Mars
People at SpaceX wearing t-shirts with Occupy Mars written on them. Colonization will depend on many people settling with the harsh reality of Mars, as pointed out by Elon Musk presenting SpaceX's colonial approach.
SpaceX hopes to begin sending colonists once infrastructure
is established on Mars and launch costs from Earth are reduced. After
the first few crewed Mars landings, Musk has suggested that the number
of people sent to Mars could be rapidly increased. Musk's timeline for
the colonization of Mars involves a first crewed mission as early as
2029 and the development of a self-sustaining colony by 2050.
A successful colonization, with a human presence established on
Mars, expanding over many decades, would ultimately involve many more
economic actors than SpaceX. Musk stated in 2024 that being able to make use of local resources on
Mars would be essential for establishing a self-sustaining colony, and
that SpaceX intended a colony to develop self-sufficiency in "seven to
nine years". Current proposals include harvesting CO2 from the atmosphere and splitting into its components. This would involve using O2 as well as CH4 for fuel production, and specifically the O2 in addition to nitrogen (the second-most common gas in the Martian atmosphere) for providing breathable air.
The program aims to send a million people to Mars using 1000 Starships launched during Mars launch windows, which occur approximately every 26 months. The journeys would require 80 to 150 days of transit time, averaging approximately 115 days (for the nine synodic periods occurring between 2024 and 2041).
Reception
Human
colonization of Mars has gained increased interest, both supportive and
critical, since the technical achievements of SpaceX's and Elon Musk's
rise of popularity in the 2010s, and more so into the 2020s.
Support
"We bring you Mars", a rendering of a terraformedMars at SpaceX Headquarters
Others like Saul Zimet have expressed strong support for the
concept, suggesting the possibility that the technological advances that
could be developed on Mars will benefit the whole of Earth.
Criticism
SpaceX's plans for the colonization of Mars have been criticized on ethical
and technical grounds. It has been argued that settling humans on Mars
may divert attention from solving problems on Earth that could also
become problems on Mars, on the basis that plans about Mars are always about plans we have for Earth. Jeff Bezos, founder of Blue Origin, one of SpaceX's competitors in commercial spaceflight, has advocated for moving heavy industry from Earth to Low Earth Orbit as opposed to colonizing Mars. SpaceX's support for extraterrestrial settlement has been considered by someone to perpetuate colonialist mentalities. Zahaan Barhmal of The Guardian has argued that the question of the impact of human settlement on Mars has not been comprehensively addressed.
It has been argued that the physical and social consequences of
attempting long-term survival on the surface of Mars will need to be
addressed. Former U.S. President Barack Obama has said that Mars could be more inhospitable than Earth would be "even after a nuclear war", and others have pointed out that planet Earth and underground shelters could still provide better conditions and protection for more people if it were needed. The colonization of Mars has been called a 'dangerous delusion' by Lord Martin Rees, a British cosmologist/astrophysicist and the Astronomer Royal of the United Kingdom. Musk has stated that staying on Mars would be a life-threatening endeavor that would need to be glorious to be worth it. Zahaan Bharmal in the Guardian
has additionally argued that exploration of Mars is better left to the
already successful robot missions, and that crewed missions would be too
expensive, dangerous and boring.
Plans for SpaceX's Mars program have been criticized as far-fetched because of uncertainties about financing, and because they mostly deal with transportation to Mars and not with
the business of establishing a functioning colony afterwards. As of July
2019, SpaceX had not explained its plans for the spacecraft's
life-support systems and radiation protection, and for making use of
resources once the colonists had landed. George Dvorsky writing for Gizmodo characterized Musk's timeline for Martian colonization as "stupendously unreasonable" and "pure delusion".
Law
SpaceX intends to base the laws governing a Martian colony on self-determination and direct democracy (instead of representative democracy). Some of this policy has appeared in the terms and services agreement for individual users of SpaceX's Starlink
platform, which state the following: "The parties recognize Mars as a
free planet and that no Earth-based government has authority or
sovereignty over Martian activities".
In contrast, internationally agreed space law proclaims space to be the "province of all mankind" and holds that Mars is not available to be claimed as property. Its legal status shares some elements of the legal status of international waters on Earth. In addition, it is thought that the business of technocratic colonizers trying to accomplish direct-democracy and the legal accommodation of a diverse population will be challenging.
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