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NEWS | June 1, 2017

True Impacts of Space Weather on a Ground Force

By LTC(R) Gregory Sharpe and MAJ Kenneth Rich, USA Air Land Sea Application Center

 

Lieutenant Colonel (retired) Gregory Sharpe served as an assistant professor in the Department of Joint, Interagency, and Multinational Operations, Command and General Staff School, Army University, Fort Leavenworth, Kansas. He holds a MA in Organizational Psychology and Leadership from Columbia Teacher’s College at Columbia University and served as the Chief, Space Division.

Major Kenneth Rich was an assistant professor in the Department of Joint, Interagency, and Multinational Operations, Command and General Staff School, Army University, Fort Leavenworth, Kansas.

Introduction

It is July 23, 2012 and your artillery battalion is conducting a training exercise with a partner nation in Cambodia. Your battalion tactical operations center is set up, your joint network node satellite communications (SATCOM) van is operating correctly using the super-high frequency (SHF) band, and you are receiving feeds from your AN/TPQ-53 counter-fire radar observing a live fire exercise. You are able to listen to the forward observers calling for fire on their AN/PRC-117G ultrahigh frequency (UHF) radios. Additionally, you can easily observe the data passed via the Advanced Field Artillery Tactical Data System (AFATDS). All of a sudden, the UHF radio transmission become broken and unreadable, the AFATDS data that does get through has Global Positioning System (GPS) positions hundreds of meters off from previous calls for fire and the Q53 is not picking up any artillery rounds—even though you know the guns are firing. The discrepancies are due to a solar storm.

Luckily, this event is fictional. Although, the largest solar storm recorded, which occurred on July 23, 2012, narrowly missed earth. This solar storm was stronger than the Carrington event of 1859 (the largest storm on record impacted the Earth causing telegraph units to operate without being connected to batteries) and could have caused major damage to interconnected systems of today. Translating space weather events to the impact faced by a ground force is a major obstacle encountered by Army Division Space Support Elements. It is acceptable to discuss generic impacts like “space weather effects radio transmissions and radar” in a basic space weather overview class. Yet, discussion of generic impacts during a high-intensity conflict, (where counter-battery radar provides targetable data on enemy long-range artillery, satellites, and theater-level radars provide ballistic missile warning, and mission command depends on SATCOM) provides little benefit and fails miserably at conveying the true impacts space weather events have on a ground force. No single source is readily available in extant literature that adequately translates space weather events to impacts faced by a ground commander who has no background in astrophysics or electromagnetic wave propagation theory. This paper provides an overview of space weather that arises in the solar-terrestrial system and how space weather impacts can be incorporated into the planning process during heightened solar activity.

The Natural Space Environment

The natural space environment consists of the sun and the interplanetary space between the sun and near-Earth space environment referred to as the magnetosphere. The magnetosphere is a 1-million-mile magnetic shell surrounding the Earth consisting of radiation belts and associated radiation phenomena which can affect spacecraft components.

Additionally, the Earth’s atmosphere consists of several layers; the most important portion with respect to space weather effects is the ionosphere. The ionosphere is a region in Earth’s upper atmosphere from approximately 60 to 600 kilometers (km) and consists of the D, E and F layers. The D layer extends to approximately 60 to 90 km above the Earth. Radio waves traveling through this layer lose energy, resulting in some absorption in the frequency range up to 10 megahertz (MHz). The E layer extends from approximately 90 km to 140 km above the Earth and consists of ionized gasses which exist only during daylight hours. During periods of high-intensity solar activity, the E layer can contain regions of high ionization called sporadic E.

The F layer extends from approximately 140 to 600 km above the Earth and separates into two layers, F1 and F2, during the day. According to the Encyclopedia Britannica, the F layer has the greatest concentration of free electrons and is important for high frequency (HF) radio wave reflection and long distance propagation for frequencies from 10 to 35 MHz. Ultimately, all satellites must communicate their radio frequency signals through the ionosphere to reach terrestrial users. Depending upon the frequency of the radio signal, the ionosphere can significantly degrade associated systems’ performance.

Possible Mitigation Factors in the Space Segment

The strategies for dealing with space weather effects have different forms. In some cases this requires better equipment design, with increased reliability or economy. Appropriate electrical connection of electricity distribution subsystems, shielding vulnerable satellite components against electrical discharge or radiation, and controlling the electric potential of pipelines to avoid corrosion are some examples. In other cases, day-to-day or hour-to-hour space weather prediction and monitoring can be used to alter operational behavior. To protect a satellite’s electronics, a satellite might be placed into safe mode during severe solar activity. In this instance, the satellite will not be functional for the ground force. For SATCOM, the Regional Satellite Communications Support Center (RSSC) should notify the end users of pending safe mode operations. The geographic combatant commands will then re-prioritize the remaining SATCOM assets and the RSSC will move users, accordingly. Links not determined to have priority will have to communicate without SATCOM until the solar activity settles. If an intelligence, surveillance and reconnaissance (ISR) satellite is required to mitigate threats, the collection managers will need to request additional airborne ISR capability or wait until the solar activity lessens to collect information as long as the latest time of intelligence value is not exceeded.

Space Weather

Space weather effects can lead to disruption of not only satellites that operate GPS, but terrestrial power grids as well. Additionally, these effects can not only pose risk to astronauts operating beyond a low-earth orbit, but could potentially cause rerouting of flights over the polar regions of the Earth (Stormy, 2012).

Everyday life, however, is not as affected by space weather as it is by meteorological weather. But as technology has advanced, the consequences to a broad range of technologies have become more prominent. Current capabilities can continuously observe the sun in the range covering x-rays to ultraviolet (UV) rays and many missions have set out to study the sun-Earth connection. Consequently, these observations demonstrated the connection between events on the sun and the space weather in the near-Earth environment. Although many questions remain, space weather prediction has become a possibility (Glover et al, 2002). Space weather, much like terrestrial weather, is an everyday occurrence. The complex interaction of the sun and Earth lead to several daily occurrences that may impact operations for a ground force. Just as terrestrial weather occasionally has storms, space weather occasionally causes geomagnetic storms. This section will explain the basics of space weather without requiring a background in heliophysics or magnetohydrodynamics.

The sun is a blackbody radiator that emits radiation in all portions of the electromagnetic spectrum. Visible and infrared radiation output, however, is more predictable and constant (Jursa, 1985). The sun’s complex interactions lead to phenomenon such as solar wind, solar radio bursts, solar flares, and coronal mass ejections (CME). When the sun’s solar wind is especially strong, like during a CME, and lasts for a long period of time, it can lead to geomagnetic storms. These storms can last up to five days, but occur infrequently.

Solar radio bursts and solar flares are unpredictable and the effects reach Earth in approximately 8 minutes. Therefore, their effects cannot be mitigated, but an awareness of their possibility can lead to mitigating factors to lessen their impact. CMEs are interrelated with sunspots. CMEs occur from sunspots, but sunspots do not predict CMEs. Solar radio bursts and solar flares accompany CMEs, but CMEs also result in a mass of energized particles that can take between 1 and 2 days to reach Earth. The energized particles cause additional interaction with Earth and increased ionization. Depending on the strength of the CME, the resulting geomagnetic storm can lead to effects lasting from tens of minutes to several days; the stronger the storm and wind, the greater the ionization, resulting in longer duration for the outages.

A Description of Possible Effects

In order to assist the Space Support Element in translating space weather into observable effects for a ground force, we created tables 1 through 3. The tables describe probable affects based on the National Oceanic and Atmospheric Administration (NOAA) space weather scales for space events. They describe specific exemplary equipment found in the current inventory and describe the affects as a ground commander would better understand them in order to better add information to the composite risk management process.

 

Table 1. Effects of Space Weather in Mid-Latitude Regions

(Effects on THE sunlight side of THE Earth only)

Definitions

 

Normal

Normal space weather

Moderate

NOAA Solar Radiation Storm levels S1 and S2, NOAA Radio Blackout levels R1 and R2, NOAA Geomagnetic Storm levels G1 and G2

Severe

NOAA Solar Radiation Storm levels S3–S5, NOAA Radio Blackout levels R3–R5, NOAA Geomagnetic Storm levels G3–G5

 

Normal

Moderate

Severe

Reason

Frequency effected

Example system

Firefinder radar

No effect

Non-phased array radar: track volume decrease, increased minimum range to track, reduced probability of detection at high angle.

Phased array: more porous track volume, increased track time needed

Non-phased array radar: track volume decrease, increased minimum range to track, reduced probability of detection at high angle. Phased array: more porous track volume, increased track time needed

Type IV solar radio burst if the sun is in the main or side lobe of the radar during an event

2–4 GHz

Q53, Q36, Q37

Tactical missile/air warning radar

No effect

Low probability of degraded range and elevation angle accuracy for minutes to hours after solar event

Degraded range and elevation angle accuracy for hours after solar event

Models do not replicate increased ionization levels in ionosphere. Look angle of radar intersects ionosphere at approximately 1/3 of the range.

4–6 GHz

Patriot

Theater ballistic missile defense capability

No effect

Low probability of degraded range and elevation angle accuracy for minutes to hours after a solar event

Degraded range and elevation angle accuracy for hours after solar event

Models do not replicate increased ionization levels in ionosphere

8–12 GHz

THAAD

Air traffic control radar

No effect

No effect

Non-phased array radar: track volume decrease, increased minimum range to track, reduced probability of detection at high angle. Phased array: more porous track volume, increased track time needed

Type IV solar radio burst if the sun is in the main or side lobe of the radar during an event. Radar operates below the ionosphere (highest recorded aircraft 37.6 km < 60km ionosphere)

1–2 GHz

AN/ARN-153

Static ballistic missile warning radar

No effect

Low probability of degraded range and elevation angle accuracy for minutes to hours after a solar event

Degraded range and elevation angle accuracy for hours after solar event

Models do not replicate increased ionization levels in the ionosphere. Scintillation in auroral zones lower in latitude than normal

300 MHz–3 GHz

BMEWS at Thule or Fylingdales

Space situational awareness radar

No effect

Low probability of degraded range and elevation angle accuracy for minutes to hours after solar event

Degraded range and elevation angle accuracy for hours after solar event

Models do not replicate increased ionization levels in ionosphere. Scintillation in auroral zones lower in latitude than normal

300 MHz–1 GHz

AN/FPS-85

HF radio

No effect

Increased LUF, limited blackout of frequencies in 3 MHz–20 MHz range for up to 10 minutes, short wave fade, change in area coverage

Increase LUF, decreased MUF, limited blackout of frequencies in 3 MHz–30 MHz range for several hours, short wave fade, change in area coverage

D, E and F layer density

3 MHz–30 MHz

AN/PRC-150

Tactical FM/SINCGARS

No effect

No effect

No effect

Operates LOS

30 MHz–87.975 MHz

AN/PRC 119

VHF radio

No effect

No effect

Signal degradation, signal polarization if using linear polarization

Scintillation, Faraday Rotation

30 MHz–300 MHz

AN/PRC-117G, AN-PRC 52

UHF radio

No effect

No effect

Signal degradation

Scintillation

300 MHz–3 GHz

AN/PRC-117G, Iridium, INMARSAT

SHF radio

No effect

No effect

Signal degradation between 3 GHz and 4 GHz only

Radio frequencies not effected by ionosphere density, scintillation or TEC

3 GHz–30 GHz

 

EHF radio

No effect

No effect

No effect

Radio frequencies not effected by ionosphere density, scintillation or TEC

30 GHz–300 GHz

SMART-T

GPS receiver*

No effect

No effect

Outages of single frequency GPS receivers for hours, position errors up to 100 Meters horizontal and 200m vertical

Scintillation from auroral zones lower in latitude than normal, TEC

L Band

Civilian GPS receiver

Electrical transformers

No effect

Low probability that high-latitude power systems may experience voltage alarms, long-duration storms may cause transformer damage

Power systems may experience voltage alarms, protective system problems or grid outages, long-duration storms may cause transformer damage

Geomagnetic induced currents trip SCADA sensors overloading power grid zones and transformers

N/A

 

*Dual frequency GPS receivers have a better algorithm for factoring the effects of atmospheric scintillation. GPS studies have shown receivers in a scintillation environment have a low probability of losing lock with multiple satellites simultaneously (Knight, 2000).

Legend:

BMEWS—ballistic missile early warning system

EHF—extremely high frequency

FM—frequency modulation

GHz—gigahertz

GPS—Global Positioning System

HF—high frequency

INMARSAT—-international maritime satellite

km—kilometer

LOS—line of sight

LUF—lowest usable frequency

MHz—megahertz

MUF—maximum usable frequency

N/A—not applicable

NOAA—National oceanic and Atmospheric Administration

 

SCADA—supervisory control and data acquisition

SHF—super high frequency

SINCGARS—single-channel ground and airborne radio system

SMART-T—Secure Mobile Anti-Jam Reliable Tactical Terminal

TEC—total electron content

THAAD—terminal high altitude area defense

UHF—ultrahigh frequency

VHF—very high frequency

 

 

 

 

 

Table 2. Effects of Space Weather in Polar Regions

(Effects on THE sunlight side of THE Earth only)

Definitions

 

Normal

Normal space weather

Moderate

NOAA Solar Radation Storm levels S1 and S2, NOAA Radio Blackout levels R1 and R2, NOAA Geomagnetic Storm levels G1 and G2

Severe

NOAA Solar Radation Storm levels S3–S5, NOAA Radio Blackout levels R3–R5, NOAA Geomagnetic Storm levels G3–G5

                 

Normal

Moderate

Severe

Reason

Frequency effected

Example system

Firefinder radar

No effect

Non-phased array radar: track volume decrease, increased minimum range to track, reduced probability of detection at high angle.

Phased array: more porous track volume, increased track time needed

Non-phased array radar: track volume decrease, increased minimum range to track, reduced probability of detection at high angle.

Phased array: more porous track volume, increased track time needed

Type IV solar radio burst if the sun is in the main or side lobe of the radar during an event

2–4 GHz

Q53, Q36, Q37

Tactical missile/air warning radar

No effect

Low probability of degraded range and elevation angle accuracy for minutes to hours after solar event

Degraded range and elevation angle accuracy for hours after solar event

Models do not replicate increased ionization levels in ionosphere. Look angle of radar intersects ionosphere at approximately 1/3 of range.

4–6 GHz

Patriot

Theater ballistic missile defense capability

No effect

Low probability of degraded range and elevation angle accuracy for minutes to hours after solar event

Degraded range and elevation angle accuracy for hours after solar event

Models do not replicate increased ionization levels in ionosphere

8–12 GHz

THAAD

Air traffic control radar

No effect

No effect

Non-phased array radar: track volume decrease, increased minimum range to track, reduced probability of detection at high angle.

Phased array: more porous track volume, increased track time needed

Type IV solar radio burst if the sun is in the main or side lobe of the radar during an event, Radar operates below the Ionosphere (highest recorded aircraft 37.6 km < 60km ionosphere)

1–2 GHz

AN/ARN-153

Static ballistic missile warning radar

Low probability of degraded range and elevation angle accuracy for minutes to hours during daily scintillation windows

Low probability of degraded range and elevation angle accuracy for minutes to hours after solar event

Degraded range and elevation angle accuracy for hours after solar event

Models do not replicate increased ionization levels in ionosphere. Scintillation in auroral zones lower in latitude than normal

300 MHz–3 GHz

BMEWS at Thule or Fylingdales

Space Situational Awareness radar

N/A

N/A

N/A

N/A

N/A

N/A

HF radio

No effect

Increased LUF, limited blackout of frequencies in 3 MHz–20 MHz range for up to 10 minutes, short wave fade, change in area coverage

Increase LUF, limited blackout of frequencies in 3 MHz–30 MHz range for several hours, short wave fade, change in area coverage

D, E and F layer density

3 MHz–30 MHz

AN/PRC-150

Tactical FM/SINCGARS

No effect

No effect

No effect

Operates LOS

30 MHz–87.975 MHz

AN/PRC 119

VHF radio

Degraded signal during daily scintillation periods, possible shift in signal polarization

Degraded signal during daily scintillation periods, possible shift in signal polarization

Degraded signal during daily scintillation periods, degraded signal for minutes to hours after a solar event; possible shift in signal polarization

Scintillation, Faraday Rotation

30 MHz–300 MHz

AN/PRC-117G, AN-PRC 52

UHF Radio

Degraded signal during daily scintillation periods

Degraded signal during daily scintillation periods

Degraded signal during daily scintillation periods, degraded signal for minutes to hours after a solar event

Scintillation

300 MHz–3 GHz

AN/PRC-117G, Iridium, INMARSAT

SHF radio

Degraded signal during daily scintillation periods between 3 GHz and 4 GHz only

Degraded signal during daily scintillation periods between 3 GHz and 4 GHz only

Degraded signal during daily scintillation periods between 3 GHz and 4 GHz only, degraded signal for minutes to hours after solar event in frequencies between 3 GHZ and 4 GHz

The majority of radio frequencies are not effected by ionosphere density, scintillation or total electron content

3 GHz–30 GHz

 

EHF radio

No effect

No effect

No effect

Radio frequencies not effected by ionosphere density, scintillation or total electron content

30 GHz–300 GHz

SMART-T

GPS receiver*

No effect

Outages of single frequency GPS receivers for minutes, position errors up to 100 meters (m) horizontal and 200m vertical

Outages of single frequency GPS receivers for hours, position errors up to 100m horizontal and 200m vertical

Scintillation from auororal zones, TEC

L Band

Civilian GPS receiver

Electrical transformers

No effect

High-latitude power systems may experience voltage alarms, long-duration storms may cause transformer damage

Power systems may experience voltage alarms, protective system problems or grid outages, long-duration storms may cause transformer damage

Geomagnetically induced currents trip SCADA sensors overloading power grid zones and transformers

N/A

 

*Dual frequency GPS receivers have a better algorithm for factoring out the effects of atmospheric scintillation. GPS studies have shown receivers in a scintillation environment have a low probability of losing lock with multiple satellites simultaneously (Knight, 2000).

Legend:

BMEWS—ballistic missile early warning system

EHF—extremely high frequency

FM—frequency modulation

GHz—gigahertz

GPS—Global Positioning System

HF—high frequency

INMARSAT—-international maritime satellite

km—kilometer

LOS—line of sight

LUF—lowest usable frequency

MHz—megahertz

N/A—not applicable

NOAA—National oceanic and Atmospheric Administration

 

SCADA— supervisory control and data acquisition

SHF—super high frequency

SINCGARS—single-channel ground and airborne radio system

SMART-T—Secure Mobile Anti-Jam Reliable Tactical Terminal

TEC—total electron content

THAAD—terminal high altitude area defense

UHF—ultrahigh frequency

VHF—very high frequency

 

 

Table 3. Effects of Space Weather in Equatorial Regions

(Effects on THE sunlight side of THE Earth only)

Definitions

 

Normal

Normal space weather

Moderate

NOAA Solar Radation Storm levels S1 and S2, NOAA Radio Blackout levels R1 and R2, NOAA Geomagnetic Storm levels G1 and G2

Severe

NOAA Solar Radation Storm levels S3–S5, NOAA Radio Blackout levels R3–R5, NOAA Geomagnetic Storm levels G3–G5

 

 

Normal

 

Moderate

 

Severe

 

Reason

Frequency effected

 

Example system

Firefinder radar

No effect

Non-phased array radar: track volume decrease, increased minimum range to track, reduced probability of detection at high angle.

Phased array: more porous track volume, increased track time needed

Non-phased array radar: track volume decrease, increased minimum range to track, reduced probability of detection at high angle.

Phased array: more porous track volume, increased track time needed

Type IV solar radio burst if the sun is in the main or side lobe of the radar during an event

2–4 GHz

Q53, Q36, Q37

Tactical missile/air warning radar

No effect

Low probability of degraded range and elevation angle accuracy for minutes to hours after solar event

Degraded range and elevation angle accuracy for hours after solar event

Models do not replicate increased ionization levels in ionosphere. Look angle of radar intersects ionosphere at approximately 1/3 of range.

4–6 GHz

Patriot

Theater ballistic missile defense capability

No effect

Low probability of degraded range and elevation angle accuracy for minutes to hours after solar event

Degraded range and elevation angle accuracy for hours after solar event

Models do not replicate increased ionization levels in ionosphere

8–12 GHz

THAAD

Air traffic control radar

No effect

No effect

Non-phased array radar: track volume decrease, increased minimum range to track, reduced probability of detection at high angle.

Phased array: more porous track volume, increased track time needed

Type IV solar radio burst if the sun is in the main or side lobe of the radar during an event. Radar operates below the Ionosphere (highest recorded aircraft 37.6 km < 60km ionosphere).

1–2 GHz

AN/ARN-153

Static ballistic missile warning radar

Low probability of degraded range and elevation angle accuracy for minutes to hours during daily scintillation windows

Low probability of degraded range and elevation angle accuracy for minutes to hours after solar event

Degraded range and elevation angle accuracy for hours after solar event

Models do not replicate increased ionization levels in ionosphere. Scintillation in equatorial zones

300 MHz–3 GHz

BMEWS at Thule or Fylingdales

Space Situational Awareness radar

Low probability of degraded range and elevation angle accuracy for minutes to hours during daily scintillation windows

Low probability of degraded range and elevation angle accuracy to minutes to hours after solar event

Degraded range and elevation angle accuracy for hours after solar event

Models do not replicate increased ionization levels in ionosphere. Scintillation in equatorial zones

300 MHz–1 GHz

AN/FPS-85

HF radio

No effect

Increased LUF, limited blackout of frequencies in 3 MHz–20 MHz range for up to 10 minutes, short wave fade, change in area coverage

Increase LUF, limited blackout of frequencies in 3 MHz–30 MHz range for several hours, short wave fade, change in area coverage

D, E and F layer density

3 MHz–30 MHz

AN/PRC-150

Tactical FM/ SINCGARS

No effect

No effect

No effect

Operates LOS

30 MHz–87.975 MHz

AN/PRC 119

VHF radio

Degraded signal during daily scintillation periods, possible shift in signal polarization

Degraded signal during daily scintillation periods, possible shift in signal polarization

Degraded signal during daily scintillation periods, degraded signal for minutes to hours after solar event, possible shift in signal polarization

Scintillation, Faraday Rotation

30 MHz–300 MHz

AN/PRC-117G, AN-PRC 52

UHF radio

Degraded signal during daily scintillation periods

Degraded signal during daily scintillation periods

Degraded signal during daily scintillation periods, degraded signal for minutes to hours after solar event

Scintillation

300 MHz–3 GHz

AN/PRC-117G, Iridium, INMARSAT

SHF radio

Degraded signal during daily scintillation periods between 3 GHz and 4 GHz only

Degraded signal during daily scintillation periods between 3 GHz and 4 GHz only

Degraded signal during daily scintillation periods between 3 GHz and 4 GHz only, degraded signal for minutes to hours after solar event in frequencies between 3 GHZ and 4 GHz

Majority of radio frequencies not effected by ionosphere density, scintillation or total electron content

3 GHz–30 GHz

 

EHF radio

No effect

No effect

No effect

Radio frequencies not effected by ionosphere density, scintillation or TEC

30 GHz–300 GHz

SMART-T

GPS receiver*

No effect

Outages of single frequency GPS receivers for minutes, position errors up to 100m horizontal and 200m vertical

Outages of single frequency GPS receivers for hours, position errors up to 100 Meters horizontal and 200m vertical

Scintillation in equatorial region, TEC

L Band

Civilian GPS receiver

Electrical transformers

No effect

No Effect

No Effect

N/A

N/A

 

* Dual frequency GPS receivers have a better algorithm for factoring out the effects of atmospheric scintillation. GPS studies have shown receivers in a scintillation environment have a low probability of losing lock with multiple satellites simultaneously (Knight, 2000).

Legend:

BMEWS—ballistic missile early warning system

EHF—extremely high frequency

FM—frequency modulation

GHz—gigahertz

GPS—Global Positioning System

HF—high frequency

INMARSAT—-international maritime satellite

km—kilometer

LOS—line of sight

LUF—lowest usable frequency

m—meter

MHz—megahertz

N/A—not applicable

NOAA—National oceanic and Atmospheric Administration

 

SCADA— supervisory control and data acquisition

SHF—super high frequency

SINCGARS—single-channel ground and airborne radio system

SMART-T—Secure Mobile Anti-Jam Reliable Tactical Terminal

TEC—total electron content

THAAD—terminal high altitude area defense

UHF—ultrahigh frequency

VHF—very high frequency

 

Clutter Due to Solar Radio Bursts

Solar emissions come in many types and each is distinctive with regard to its characteristics and impacts. Moreover, low energy particle streams composed of electrons and protons arrive at Earth within 2 to 4 days and cause ionospheric and geomagnetic storms lasting from hours to a few days. These particles interact with the magnetosphere and are most frequently experienced on the night side of the Earth (Gehred, 2008).

Solar radio bursts are radio transmissions from the sun and are subdivided into five classifications. If a radar’s look angle is directed at the sun (main or side lobes) when a solar radio burst occurs, and the burst is in the frequency range of the radar, the additional clutter may be more than the constant false alarm rate mechanism normally accounts for and may cause effects similar to jamming. For non-phased array radars, the clutter will result in a decrease in track volume. For phased array radars the clutter will result in a more porous track volume. Therefore, solar radio bursts can affect the probability of detection of counter fire radars such as the AN/TPQ-53 or the air traffic control Sentinel radar.

Scintillation

Ionospheric scintillations are amplitude and phase changes in radio signals caused by density irregularities in the ionosphere resulting in degraded received signals if the scintillation is greater than the receiver fade margin (Knight, 2000). Due to the inverse power law, the effects are only significant up to a frequency of 2 Gigahertz (GHz), but can create some effects up to 4 GHz under the right conditions (Tanskanen et al., 2001). Two peak times, near noon and near midnight, exist for scintillation in the polar (50º and 90º latitudes) and equatorial (0º to 20º latitude) regions (Aarons, 1997). Scintillation may affect mid-latitude systems if the look angle to the satellite crosses the ionosphere within the scintillation belt. Dual frequency radars can use an algorithm to better correct for ionospheric disturbances, such as scintillation. Severe scintillation will cause UHF radios, such as the AN/PRC-117G, to experience difficulty receiving and transmitting clearly. Additionally, single channel, civilian or military GPS receivers (without the cryptological key loaded) may experience errors up to 100 meters horizontally and 200 meters vertically. Similarly, static space surveillance or ballistic missile radars may experience range and elevation errors.

Faraday Rotation

A Faraday rotation is a phenomenon that rotates the polarization of light as it passes through the ionospheric plasma (Kishore, n.d.). It can affect space based synthetic aperture radar (SAR) imagery if the ionosphere density differential is more than the algorithms can account for. Single frequency, linearly polarized radio waves may also be affected by this phenomenon.

Space Environment Events and the Impact to a Ground Force

Our greatest space environment concern is the effect it has on ground systems we rely upon. To determine the impact to the warfighter, the source of the environmental effect must be linked to the associated system being affected. Communications-on-the-move capability, for example, is provided by SATCOM. If the user has adequate warning that space weather will disrupt SATCOM at certain times, the ability to mitigate the effect by planning for alternate methods (such as terrestrial communication or other SATCOM capabilities) is available. By being able to determine the source is environmental not only mitigates down time, but can help the user distinguish environmental factors from a hostile attack (Hand et al., 2006).

Increased ionosphere ionization is the largest contributor to space weather issues. This includes thickening layers, increasing ionized plasma flow, and lowering normal heights of the layers that cause reflection, refraction, and absorption not normally experienced. Some effects are instantaneous, but others can be predicted. After the sun ejects magnetic streams and charged particles, it could take up to four days to cause magnetic storms on Earth. Therefore, planners would have an opportunity to develop solutions to problems based on more accurate forecasts of the impact timing (Wagner, 2012). The possible effects listed in the tables are all related to the increased ionization of the ionosphere caused by increased x-rays and UV rays from solar wind or an injection of energized particles by CMEs. Additionally, space weather reports are available from the Air Force and NOAA at http://www.afweather.af.mil/spaceweather.asp and http://www.swpc.noaa.gov/SWN/index.html, respectively. The times for CMEs can be used to predict actual times and make recommendations to ground force commanders using the tables.

Regions

Figure 1. Map of the world showing the approximate locations of the polar, mid-latitude and equatorial regions (Knight, 2000).

The tables we created provide the military space professional a description of probable effects on common equipment associated with an Army ground unit. To create the tables, we conducted research into the general effects of space weather. We started with military sources, such as the United States Air Force Space Environment Standard (MIL-STD-1809) and the Handbook of Geophysics and the Space Environment to obtain a general description of space weather and its possible effects. From there, we searched for more specific information. Russell wrote about how solar wind interacts with the magnetosphere and how these interactions create geomagnetic storms. Additionally, understanding the currents lead us to conclude the effects will be greater on ground equipment on the dayside, while satellite based effects would be greater at night (Russell, 2000). Iyer, et al. (2006) expanded our knowledge of CMEs and their possible effects on the F-layer and TEC. Marusek’s (2007) analysis of the Carrington event and its possible effects on a ground force commander’s operation was integral to framing the table descriptions. We learned more about different types of scintillation from Ho, et al (2002) and how the ionospheric scintillation effects radio wave propagation from Bourdillon (2008). Tanskanen et al (2001), in their Space Weather Effects catalogue, helped narrow the effects to specific frequencies and; therefore, specific systems. NOAA’s website was useful in describing radio wave propagation and how they are affected by geomagnetic storms. Our understanding of the history of scintillation and its effects was expanded by Aarons (1997).

Conclusion

Several authors provided insight into specific phenomena and effects that directly refer to military technology. As members of the Army, with little practical background in physics, the Faraday Rotation was completely new to us and Kishore’s (n.d.) unpublished work was crucial in understanding the phenomenon. When describing effects of Faraday Rotation that a ground commander would care about, Gilman’s work (Gilman et al., 2013) describing its effect on SAR images was informative. Lanzerotti (2004) wrote about the impact of solar radio effects on wireless communication systems, radar, and GPS. Knight (2000) added to our understanding of scintillation’s effects on GPS receivers in his very informative piece on the effects of space weather on GPS.

After doing the research, the next step was to determine how various pieces of military equipment operate and in what frequency range. We determined what portions of the electromagnetic spectrum the military uses referring to the Department of Defense strategic spectrum plan for 2007. Various field and technical manuals yielded equipment specification and spectrum usage. Skolnik (1970) educated us on how radar works in his seminal Radar Handbook. Other military writers, such as Hand and France (2006), further identified possible effects.

The last step was determining what severe space weather is and how often it occurs. We used the NOAA space weather scales and the Air Force Space Weather Agency website as bases for the discussion of severity. Additionally, Baker’s, et al. (2012) discussion of severe space weather storms further stratified severe space weather and catastrophically severe space weather. Riley (2014) helped us determine how rarely severe space weather events occur.

The literature about how space weather effects the ionosphere, magnetic fields, and the electromagnetic spectrum informed us on the possible effects. Reading technical manuals on Army equipment gave us a background enabling us to describe effects. Comparing Army equipment to effects from literature allowed us to posit specific impacts for types of equipment. We then used staff officer experience, at various levels of Army staff, to shape a table to help space professionals describe potential space weather related effects to their commander.

Author biographies

Lieutenant Colonel (retired) Gregory Sharpe served as an assistant professor in the Department of Joint, Interagency, and Multinational Operations, Command and General Staff School, Army University, Fort Leavenworth, Kansas. He holds a MA in Organizational Psychology and Leadership from Columbia Teacher’s College at Columbia University and served as the Chief, Space Division.

Major Kenneth Rich was an assistant professor in the Department of Joint, Interagency, and Multinational Operations, Command and General Staff School, Army University, Fort Leavenworth, Kansas.

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