Ionospheric storms are

storm A storm is any disturbed state of the natural environment or the atmosphere of an astronomical body. It may be marked by significant disruptions to normal conditions such as strong wind, tornadoes, hail, thunder and lightning (a thunderstorm), ...

s which contain varying densities of energised

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary partic ...

s produced from the sun. They are categorised into positive and negative storms, where positive storms have a high

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematicall ...

of electrons and negative storms contain a lower density. The

total electron content Total electron content (TEC) is an important descriptive quantity for the ionosphere of the Earth. TEC is the total number of electrons integrated between two points, along a tube of one meter squared cross section, i.e., the electron columnar n ...

(TEC) is used to measure these densities, and is a key variable used in data to record and compare the intensities of ionospheric storms. ''Ionospheric storms are caused by

geomagnetic storm A geomagnetic storm, also known as a magnetic storm, is a temporary disturbance of the Earth's magnetosphere caused by a solar wind shock wave and/or cloud of magnetic field that interacts with the Earth's magnetic field. The disturbance that d ...

s.'' Ionospheric storm occurrences are strongly linked with sudden increases of

solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the ...

speed, where solar wind brings energised electrons into the upper

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. ...

of the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...

and contributes to increased TEC. Larger storms form global visibility of

aurora An aurora (plural: auroras or aurorae), also commonly known as the polar lights, is a natural light display in Earth's sky, predominantly seen in high-latitude regions (around the Arctic and Antarctic). Auroras display dynamic patterns of bri ...

s. Auroras are most commonly seen in the arctic circle; however, large ionospheric storms allow for them to be visible in places such as the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

, and

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...

. The most intense ionospheric storm occurred in 1859, commonly named the “ solar storm of 1859” or the “ Carrington Event.” The Carrington Event was named after Richard Carrington, an English astronomer who observed the irregular sun activity that occurred during the Carrington Event. The intensity of the storm brought the visibility of the aurora even closer to the

equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can al ...

, reported to be seen in places near it such as

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, a ...

and the Caribbean. Ionospheric storms can happen at any time and location. X-ray Aurora from POLAR overlay

F-region and D-region ionospheric storms are also considered main categories of ionospheric storms. The F-region storms occur due to sudden increases of energised electrons instilled into Earth's ionosphere. The F-region is the highest region of the ionosphere. Consisting of the F1 and F2 layers, its distance above the earth's surface is approximately 200–500 km. The duration of these storms are around a day and reoccur every approximately 27.3 days. Most ionospheric abnormalities occur in the F2 and E layers of the ionosphere. D-region storms occur immediately after F-region storms, and are referred to as the “Post-Storm Effect," the duration of it spanning for a week after the F-region storm's occurrence.

Historical Occurrences

The largest ionospheric storm occurred during the Carrington event on August 28, 1859 and caused extensive damages to various parts including the sparking of fires in railway signals and telegraph wires. The substantial density of energised electrons produced by the storm caused these electrical overloads and shortages. Occurrences of storms in the last 35 years have been consolidated and measured in maximum Ap which records the average daily geomagnetic activity during ionospheric storms. There are higher levels of geomagnetic activity with high maximum Ap counts. Ap counts in terms of geomagnetic activity from 0-7 are considered "quiet," 8-15 "unsettled," 16-29 "active," 30-49 "minor storm," 50-99 "major storm," and above 100 classified as a "severe storm." Minor storms in the last 35 years ranging from 30-49 Ap occurred on 13 September 1999 (46), 11 October 2008 (34), 11 March 2011 (37), 9 October 2012 (46) and on 19 February 2014 (43). Major storms ranging from 50-99 Ap occurred on 6 April 2000 (82), 7 April 2000 (74), 11 April 2001 (85), 18 April 2002 (63), 20 April 2002 (70), 22 January 2004 (64), 18 January 2005 (84), 5 April 2010 (55), 9 March 2012 (87), 15 July 2012 (78) and on 1 June 2013 (58). Severe storms equalling or exceeding 100 Ap occurred on 8 February 1986 (202), 9 February 1986 (100), 13 March 1989 (246), 14 March 1989 (158), 17 November 1989 (109), 10 April 1990 (124), 7 April 1995 (100), 31 March 2001 (192), 6 November 2001 (142), 18 August 2003 (108), 29 October 2003 (204), 30 October 2003 (191), 20 November 2003 (150), 27 July 2004 (186), 8 November 2004 (140) and on 10 November 2004 (161). In recent accounts, the St Patrick's day storm in March 2013 and 2015 caused a strong negative phase in the F2 ionospheric region. The March 2013 and 2015 storms were also long lasting, spanning for over 6 hours. The June 2015 Southern Hemisphere winter storm had a shorter duration, lasting between 4 and 6 hours, and producing a positive effect in the ionosphere. It is difficult to determine the exact location and time for the occurrences of ionospheric storms, its effects being dependent on

season A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's tilted orbit around the Sun. In temperate and po ...

, their varying starting points, compositional changes in the ionosphere and the travelling ionospheric disturbances (TIDs) in relation to

gravity wave In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium. An example of such an interface is that between the atmosphere an ...

s having varying impacts on different locations.

Phases of Ionospheric Storms

In the commencement of an ionospheric storm, due to geomagnetic disturbances in the ionosphere, the storm will become positive for a brief duration. Then, it will become a negative phase storm, and revert to a recovery phase where electron density neutralises.

Positive Phase

The positive phase of an ionospheric storm will last for around the first 24 hours. In this phase, electron density in the ionosphere, particularly in higher altitude layers such as F1 and F2 will increase. Ionisation in the positive phase will be less apparent due to the increase of electron density. Positive phase ionospheric storms have a longer duration and are more prevalent in winter.

Negative Phase

The negative phase of an ionospheric storm will occur directly after the storm's positive phase and last one to two days after the positive phase decreases in electron density to "below its quiet time reference level." Negative phases decrease the electron density of the storm. They also span for longer durations and appear more often during summer.

Recovery Phase

The recovery phase of the ionospheric storm occurs after the negative phase ends, and neutralises the electron density. A time scale of 12 hours to 1 day can be used in accordance with the

Thermosphere The thermosphere is the layer in the Earth's atmosphere directly above the mesosphere and below the exosphere. Within this layer of the atmosphere, ultraviolet radiation causes photoionization/photodissociation of molecules, creating ions; the th ...

Ionosphere General Circulation Model (TIGCM) as a means of calculating the precise time of electron density restabilising post-storm.

Effects on Ionospheric Layers

The effects of ionospheric storms on different layers in the ionosphere including in the F-region, E-region and D-region vary depending on the magnitude of the storm. F-Region is the most affected layer due to it ranging the highest

altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...

compared to the E-region and D-region. The D-region is the region with the lowest altitude and will receive the least geomagnetic disturbance.

F-Region

The F-region is the highest layer of the ionosphere and inner

, around 200 km above Earth's surface and spanning around 300 km in total layer altitude.The F2-region of the F-region (highest altitude inner atmospheric layer) will be affected through the decrease of

critical frequency In telecommunication, the term critical frequency has the following meanings: * In radio propagation by way of the ionosphere, the limiting frequency at or below which a wave component is reflected by, and above which it penetrates through, an iono ...

and

maximum usable frequency In radio transmission maximum usable frequency (MUF) is the highest radio frequency that can be used for transmission between two points via reflection from the ionosphere (skywave or "skip" propagation) at a specified time, independent of tra ...

, which is necessary for high frequency radio communication. The F-region is affected by the friction of solar wind on the ionospheric boundaries which causes magnetospheric motion that may infiltrate into the ionosphere or exit it, creating disturbances which increase and decrease TEC and electron density. During ionospheric storms, it is more common for "anomalous" increases and decreases of TEC and

electron density In quantum chemistry, electron density or electronic density is the measure of the probability of an electron being present at an infinitesimal element of space surrounding any given point. It is a scalar quantity depending upon three spatial ...

to occur in the F2-layer. Ionisation density is also affected in the F-region, decreasing as the height increases, and as ionisation density increases,

atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas ...

s lose electrons and therefore lower altitudes lose electron density. The lower layers of the F-region such as the F1-layer have higher amounts of ionisation and less electron density.

E-Region

The E-region is the middle layer of the ionosphere, approximately 100 km above the Earth's surface, spanning around 100 km up. Effects on the E-region are mainly associated with the high latitudes of the layer, where more severe geomagnetic disturbances occur. Ionisation in this layer is predominantly derived from the particle

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hai ...

in auroras. Due to its lower latitude, there is greater ionisation density compared to that of the F-region, and less electron density. Increased conductivity of currents is caused by the

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the c ...

electric fields of the magnetosphere that run down the lines of the

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and t ...

in the E-region. The increased conductivity is also from the effects of the ionospheric storm. There is also a maximisation in the E-region of the transfer of energy from plasma to neutral particles which promotes "frictional heating" and is used as a heat source for the thermosphere.

D-Region

The D-region is the lowest layer of the ionosphere, approximately 60 km above the Earth's surface and its layer's altitude spanning around 30–40 km. The top of the D-region is around 90–100 km above the Earth's surface. When ionospheric storms occur, there is enhanced ionisation of electrons that happens in the D-region and causes a decline in day-night asymmetry (DLPT depth.) DLPT depth is calculated by subtracting average day rate by average night rate and dividing it by the average of the rates. The DLPT depth decreases as Ap increases in the D-layer.

Impacts

Radio Communications

There are strong disturbances to

radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transm ...

communications in the event of an ionospheric storm, where in middle and high altitudes, radio communications are considered “ineffective.” This is due to radio waves being found in the ionosphere where the sudden increase of solar wind and energised electrons will interfere. The impacts of disturbances related to radio communications can include temporary blackouts of signal to radio-wave based technology such as televisions, radios and cordless phones. Global impacts vary, including the detriment of digital broadcasting and the displaying of information through radio-communication technologies which may temporarily eliminate the use of certain technologies.

Aircraft and Electrical Systems

Aircraft passengers and the crew are more prone to dangerous exposure from radiation during an ionospheric storm. Flight altitudes are usually 10 km or more, so when an ionospheric storm occurs during the flight, people on the plane will potentially gain an approximate 0.1% chance of developing a lethal

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bl ...

during their lifetime. The plane when flying at a 10 km or above altitude will have around 300 times more exposure to ionised radiation than on sea level. The energised particles produced by the ionospheric storm will also potentially cause damage and disrupt " microelectronic circuitry" due to single event effect (SEE), when the energised particles interconnect with the semiconductor device and causes system failure. Aircrew and the pilot in this situation during short circuiting of aircraft electrical equipment will be reprioritised of their work and cause detriment to the overall safety and wellbeing of the passengers.

Satellites

Ionospheric storms have a visible effect on

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioiso ...

s and satellite communication.

Solar cell A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon.broadcasting Broadcasting is the distribution of audio or video content to a dispersed audience via any electronic mass communications medium, but typically one using the electromagnetic spectrum (radio waves), in a one-to-many model. Broadcasting began ...

and data communications.

Climate

Earthward solar winds and excessive radiation produced from it has limited effect on the climate. The radiation emitted by solar wind only reaches the highest layers of the Earth's atmosphere, including the ionosphere. In the lower atmospheres, where climate change is able to be recorded and monitored, there are minimal trends supporting an ionospheric storm's impact. It is recorded that the increase of solar wind during March 2012 in the United States “coincided” with the heat waves that occurred at the time. The impact on climate in accordance with ionospheric storms based on modern technology is shown to have little to no impact.

GPS and GNSS systems

Due to the disturbances of signals in the ionosphere caused by ionospheric storms, GPS systems are drastically affected. In the late 20th and 21st centuries GPS signals are incorporated within various phones, so the commonality of its use has majorly increased since its release. It is a significant piece of technology that is almost entirely affected as it serves the purpose of displaying direction, which can disable people from being able to tell directions. Directional equipment in aircraft like Global Navigation Satellite Services (GNSS) is also used, however is compromised by radiation damage on satellites and solar cells which all for this navigation system to work. When aircraft loses access to GNSS in the event of an ionospheric storm, back up aircraft procedures are available.

Storm Detection Technology

During the Carrington Event in 1859 where there were only a limited number of available measuring technologies, the full extent of the impacts could not be precisely recorded apart from recounts in newspaper articles written in 1859. In the late 20th and early 21st century, forecasting technology has been improved. This technology allows meteorologists to detect the highest frequency that can be vertically returned 24 hours in advance with accuracy of 8-13% periods with limited disturbance. PropMan, created by K. Davies in the early 1970s is a program which contains the ionospheric prediction code (IONSTORM), for the purpose of forecasting maximum usable frequencies (MUFs) during ionospheric storms when F-region communication frequencies are negated.

References

{{Reflist Ionosphere