Space
Weather
OVERVIEW
• What is Space Weather ?
• Space Weather on Flight
Weather Briefing
• Space Weather Products,
Use and Impacts
What is Space Weather?
Space weather describes
the conditions in space that
affect Earth and its
technological systems.
Space Weather is a consequence of
the behavior of the sun, the nature
of Earth's magnetic field and
atmosphere, and our location in the
solar system.
What is Space Weather?
Solar Wind
Magnetosphere
Electromagnetic
Radiation
Energetic
Charged Particles
Ionosphere
The Earth is surrounded by its own magnetic field (Magnetosphere)
and upper atmosphere (Ionosphere)
Solar electromagnetic radiation and energetic particles impact the
Earth’s Magnetosphere and Ionosphere, causing space weather
disturbances which may degrade military systems
SUNSPOTS
Sunspots are the most
common indication of
solar activity
Larger and more
complex sunspot
groups have greater
potential for instability
SUNSPOTS
Huge sunspot group -- On 30 March 2001, the sunspots within the
group spanned an area more than 13 times the surface area of the
Earth! It was the source of numerous flares and coronal mass
ejections, including the largest flare recorded in 25 years on 2 April
2001.
THE SOLAR CYCLE
• Sunspots follows an 11-year
cycle, called the “Solar Cycle”.
Solar
Maximum • Generally, there is a 4-year rise
to a “Solar Maximum”
• Followed by a gradual 7-year
decline to a “Solar Minimum”.
• Last solar maximum occurred in
Solar Spring 2000
Minimum
THE SOLAR CYCLE
• Our next solar maximum is rapidly approaching
• Anticipated in approximately 2011
• We must prepare for the possible impacts
200
150
100
CYCLE CYCLE CYCLE CYCLE CYCLE
50
19 20 21 22 23
0
1954 1962 1970 1978 1986 1994 2002
SPACE WEATHER AWARENESS
ON DD FORM 175-1 AND MEF
WEATHER BRIEFINGS
FREQUENCY IMPACTS
• Identifies areas where
HF communication may
be degraded
• Severe, marginal or
no impact noted in
“FREQ” row of Block 15
• Boundaries of the
impact will be noted in
the blank space of
Block 15
Yellow area = marginal impact
Red area = severe impact
No color = no impact
RADIATION IMPACTS
• Quantifies global level
of radiation at high
altitude
• Primarily targets high
altitude flights over
polar regions
• Severe, marginal or
no impact noted in
“RAD” row of Block 15
• Boundaries of the
10.0 to 99.9 milirems per hour = marginal impact
impact will be noted in
≥ 100.0 milirems per hour = severe impact
50 meters = severe impact
10 db fade) UHF propagation highlighted in
red. Use in tandem with UHF SATCOM Scintillation Nowcast and Forecast.
Operational Impacts/Uses. Customers can use this product for situational awareness and to
develop planning guidance for operations using UHF and SATCOM systems. Areas specified as being
impacted represent the worst-case scenario for long-haul HF communications being attempted
through the contoured region.
6-Hour Forecast of Ionospheric
Conditions Impacting HF Propagation
Description. Graphical bulletin issued four times per day and valid for the following six hours;
contains information on high frequency (HF) radio propagation conditions and solar and terrestrial
conditions that relate to or have an impact on HF communications. Regions of forecasted marginal
HF operations highlighted in yellow, and regions forecast to experience severely degraded HF
propagation highlighted in red. The marginal HF implies impacts to frequencies up to 20 MHz,
while the severely degraded HF operations implies impacts to the entire HF spectrum (up to 30
MHz).
Operational Impacts/Uses. Customers can use this product for situational awareness and to
develop planning guidance for operations using HF systems. Areas specified as being impacted
represent the worst-case scenario for long-haul HF communications being attempted through the
contoured region. Amber represents areas where frequencies up to 20 MHz may suffer
degradation for upwards of 40 minutes. Red areas represent degradations of frequencies above
20 MHz for over 40 minutes.
UHF SATCOM Scintillation Nowcast and
Forecast
Description. This product is a graphic map depicting the estimated potential amount of
performance degradation (signal fading) of UHF SATCOM as a result of ionospheric
scintillation. Although DoD SATCOM uses the entire UHF radio band, these UHF
Scintillation maps apply only to UHF SATCOM between 225 MHZ and 400 MHZ (the lower
portion of the UHF spectrum is impacted more than the higher end). Regions of light or
weak degradation (1-4 dB) are in green, regions of moderate degradation (4-10 dB) are in
yellow and regions of severe degradation (greater that 10 decibels) are in red. Use in
tandem with 6-Hour Forecast of Ionospheric Conditions Impacting UHF SATCOM.
Operational Impacts/Uses. Customers can use this product for situational awareness and
to develop planning guidance for operations using UHF and SATCOM systems.
Point-to Point HF Radio Usable
Frequency Forecasts
Description. Provides predictions of HF radio propagation conditions, including Maximum
Usable Frequency (MUF), Frequency of Optimum Transmission (FOT), and Lowest Useable
Frequency (LUF).
Operational Impacts/Uses. Customers can use this product to develop planning guidance as
well as relatively precise mission-support information for operations using long-haul HF
communications. The equipment and signal paths used can be specified, allowing the user to
customize this product for their particular needs.
HF Illumination Maps Nowcast and
Forecast
Description. This product is designed to help HF operators better understand the HF propagation
environment and to better react to ionospheric conditions to improve HF communications. It is also
designed to help HF communicators select an operating frequency that will provide the greatest
probability of successful communications. The map displays the signal strength, noise intensity, or
signal-to-noise ratio on the ground. The product is color-coded and visually displays zones of
possible communications frequencies.
Operational Impacts/Uses. Customers can use this product for situational awareness and to develop
planning guidance for operations using HF systems. The output is frequency specific, and can be
applied directly to long-haul HF communications being attempted from the transmitter location.
Estimated GPS Single Frequency Error
Maps: 1-Hour Nowcast and Forecast
Description. A graphical product that estimates near real-time positioning errors that result from
inaccurate ionospheric correction for single-frequency GPS users. The product displays errors in
total position (latitude, longitude, and height), horizontal position (latitude only), and altitude
position (height only). Product assumes a greater GPS error for hilly terrain than flat terrain.
Geometric data from 4 visible GPS satellites are used to create the product. GPS errors are color-
coded and are displayed in meters.
Operational Impacts/Uses. Customers can use this product for situational awareness and to
develop planning guidance for operations using single-frequency GPS systems. It is important to
note that the effects shown in this product do not apply to dual-frequency GPS systems.
Short Wave Fade Event Warning
(WOXX50 KGWC)
WOXX50_KGWC - SHORT WAVE FADE EVENT Description. Notifies customers of
WARNINGWOXX50 KGWC 110018SUBJECT: short-wave fades (affecting high-
AFWA EVENT WARNING REPORT ISSUED AT frequency (HF) communications).
0018Z 11 MAR 2002PART A. SHORT WAVE
FADE EVENT: THE SHORT WAVE FADE
EVENT, WHICH BEGAN AT 2254Z10 MAR Operational Impacts/Uses. Short wave
2002 IS STILL IN PROGRESS, AS SOLAR X- fades cause a loss of communications on
RAY LEVELS REMAIN HIGH. PART B. HIGH HF frequencies; instead of reflecting HF
FREQUENCY RADIO COMMUNICATIONS radio weaves, the ionosphere absorbs
AND INTERCEPT CAPABILITY IN DAYLIT them. Effects may last up to 30 minutes
AREAS OF THE GLOBE WILL EXPERIENCE in a smaller event, and several hours in a
SIGNAL FADES UP TO 12 MHZ FOR AN large event. Frequencies affected depend
ADDITIONAL 60 MINUTES OR MORE. on the size of an event; in large events,
EFFECTS MAY LAST SOMEWHAT LONGER AT the entire HF spectrum is affected. High
LOWER FREQUENCIES. NO FURTHER Frequency radio users may experience
UPDATES WILL FOLLOW UNLESS THIS degradation at certain frequencies or a
EVENT EXTENDS BEYOND THE EXPECTED complete HF communication blackout.
DURATION OR AN ADDITIONAL SHORT Length of time depends on location of
WAVE FADE OCCURS.PART C. transmitter/receiver, duration and
REMARKS:ISSUED BY THE AIR FORCE intensity of X-ray event. Also radar
WEATHER AGENCY, OFFUTT AFB, NE. IF systems that utilize HF to even lower
YOU HAVE QUESTIONS OR REQUIRE UHF band may experience anomalous
FURTHER INFORMATION, CALL THE DUTY returns (If the radar is pointed into the
FORECASTER AT DSN 272-8087, sun’s general direction during the time of
COMMERCIAL 402-232-8087. INFORMATION the X-ray event).
CAN ALSO BE OBTAINED AT
https://weather.afwa.af.mil UNDER THE SPACE
WEATHER LINK.
Solar X-ray Event Warning
(WOXX55 KGWC)
WOXX55_KGWC - SOLAR X-RAY EVENT
WARNING
WOXX55 KGWC 110817SUBJECT: Description. Messages sent when an X-
AFWA EVENT WARNING REPORT ray event occurs.
ISSUED AT 0817Z 11 DEC 2001PART A.
SOLAR X-RAY EVENT:THE X-RAY
EVENT WHICH BEGAN AT 0804Z 11 DEC Operational Impacts/Uses. Short-wave
2001 REACHED A MAXIMUM OF X3 AT fades for high frequency (HF) radio
0808Z 11 DEC 2001, AND FELL BELOWX1 communications, where radio operators in
LEVEL AT 0815Z 11 DEC 2001.PART B. most cases, will find HF unusable. Very
THIS EVENT AFFECTED HIGH large X-ray events can also damage
FREQUENCY RADIO satellite components, though this is rare.
COMMUNICATIONS AND INTERCEPT
CAPABILITY IN DAYLIT AREAS OF THE
GLOBE. PART C. REMARKS:ISSUED BY
THE AIR FORCE WEATHER AGENCY,
OFFUTT AFB, NE. IF YOU HAVE
QUESTIONS OR REQUIRE FURTHER
INFORMATION, CALL THE DUTY
FORECASTER AT DSN 272-8087,
COMMERCIAL 402-232-8087.
INFORMATION CAN ALSO BE
OBTAINED AT
https://weather.afwa.af.mil UNDER THE
SPACE WEATHER LINK.
Major Solar Flare Event Warning
(WOXX51 KGWC)
WOXX51_KGWC - MAJOR SOLAR FLARE Description. Notifies customers of
EVENT WARNING significant solar flares. Reports are issued
when a USAF SOON site reports a flare of
WOXX51 KGWC 131445 importance 3B or greater. If there is no
optical patrol (unable to observe the sun
SUBJECT: AFWA EVENT WARNING optically), a report is issued if the X-ray flux
REPORT ISSUED AT 1445Z 13 DEC 2001 equals or exceeds X5.
PART A. MAJOR SOLAR FLARE EVENT:
AT 1430Z 13 DEC 2001 A SOLAR FLARE
EQUALED OR EXCEEDED SIZE AND Operational Impacts/Uses.
IMPORTANCE OF 3B. Major solar flare, enhanced X-ray emission:
PART B. THIS EVENT WILL AFFECT HF systems operating in the sunlit hemi-
HIGH FREQUENCY RADIO sphere may experience short wave fades
COMMUNICATIONS IN SUNLIT AREAS up to 30 MHz. Fades generally persist for
OF THE GLOBE. THE FLARE WILL less than one hour, but may persist much
DECLINE TO PRE-EVENT LEVELS longer.
DURING THE NEXT ONE TO TWO LF and VLF systems operating through the
HOURS. sunlit hemisphere may experience sudden
PART C. REMARKS: phase advances during the event.
ISSUED BY THE AIR FORCE WEATHER Major solar flare, enhanced radio frequency
AGENCY, OFFUTT AFB, NE. IF YOU emission:
HAVE QUESTIONS OR REQUIRE VHF, UHF, and SHF systems operating in
FURTHER INFORMATION, CALL THE the sunlit hemisphere may experience
DUTY FORECASTER AT DSN 272-8087, radio frequency interference (RFI) during
COMMERCIAL 402-232-8087. event. Systems pointing sunward are
INFORMATION CAN ALSO BE especially susceptible to RFI.
OBTAINED AT
https://weather.afwa.af.mil UNDER THE
SPACE WEATHER LINK.
Geomagnetic Event Warning (WOXX54
KGWC)
Description. Notifies customers of forecasted or
observed geomagnetic disturbances.
Operational Impacts/Uses.
HF systems operating in middle and auroral zones will
WOXX54_KGWC - GEOMAGNETIC EVENT experience Maximum Usable Frequency (MUF) depressions
WARNINGWOXX54 KGWC 222010SUBJECT: AFWA during the disturbance. Long east-west paths (over 3000
EVENT WARNING REPORT ISSUED AT 2010Z 22 km) extending poleward of ~55o may experience non-great
OCT 2001PART A. GEOMAGNETIC EVENT IN circle propagation, multipathing, and auroral zone
PROGRESS (UPDATE): THE GEOMAGNETIC FIELD IS absorption.
AT SEVERE STORM LEVELS. THE 3-HOUR AP WAS Poleward pointing HF/VHF/UHF radars, equatorward of
122 AND THE 24-HOUR AP WAS 72 AT 22/1915Z the auroral zone, may observe enhanced clutter,
THE DISTURBANCE IS FORECAST TO CONTINUE interference, and false targeting.
AT SEVERE STORM LEVELS THROUGH THE NEXT 10 VHF and UHF space track radars operating through the
HOURS (BASED ON 24-HOUR AP) WHEN VALUES auroral zone may experience unusual signal retardation
WILL DECREASE TO ACTIVE LEVELS. THIS and refraction, causing ranging and pointing errors.
PRODUCT WILL BE UPDATED EVERY 6 HOURS VHF, UHF and SHF satellite communication systems
UNTIL THIS EVENT ENDS.PART B.POSSIBLE operating through the auroral zone may experience
EFFECTS ARE SATELLITE DRAG ON LOW EARTH enhanced phase/amplitude scintillation.
ORBIT SATELLITES, SATCOM SCINTILLATION, HF
RADIO COMMUNICATION INTERFERENCE LF and VLF systems operating across the Auroral and
ORLAUNCH TRAJECTORY ERRORS.PART C. Polar Regions may experience phase advances during the
REMARKS: ISSUED BY THE AIR FORCE WEATHER event.
AGENCY, OFFUTT AFB, NE. IF YOU HAVE Geosynchronous and other high-altitude satellites may
QUESTIONS OR REQUIRE FURTHER experience spacecraft charging, especially when in the
INFORMATION, CALL THEDUTY FORECASTER AT midnight to sunrise sector. Subsequent discharges may
DSN 272-8087, COMMERCIAL 402-232-8087. cause electrical upsets. Similar charging problems may
INFORMATION CAN ALSO BE OBTAINED AT occur on low altitude satellites with inclinations transiting
https://weather.afwa.af.mil UNDER THE SPACE auroral latitudes.
WEATHER LINK. Low altitude polar orbiting satellites may experience
increased atmospheric drag due to enhanced atmospheric
density. This effect will begin approximately 6 hours
after the storm starts, and last until approximately 12
hours after the storm ends.
Energetic Particle Event Warning
(WOXX53 KGWC)
WOXX53_KGWC - ENERGETIC PARTICLE
Description. Notifies customers of forecast or
EVENT WARNING observed enhancements of energetic particles in
the near-earth environment.
WOXX53 KGWC 021125 Operational Impacts/Uses.
SUBJECT: AFWA EVENT WARNING REPORT Satellite-borne sensors may be contaminated,
ISSUED AT 1125Z 02 OCT 2001 damaged or destroyed by direct collision with
PART A. ENERGETIC PARTICLE EVENT END: high-energy particles.
THE SATELLITE-ALTITUDE ENERGETIC Geosynchronous and other high-altitude
PARTICLE EVENT THAT BEGAN NEAR 0510Z satellites (or satellites in lower orbits, but with
02 OCT 2001 HAS ENDED. paths through the Auroral zones) may
THE PEAK 5-MIN AVERAGED FLUX OBSERVED experience problems associated with 2 different
DURING THE EVENT WAS: GREATER THAN anomaly sources:
50 MEV 25 P/CM2/SEC/STER AT 02/0845Z. Internal charging and discharging associated
GREATER THAN 10 MEV 2360 with the energetic particle environment.
P/CM2/SEC/STER AT 02/0810Z. NO FURTHER Single event upsets (SEU) associated with
MESSAGES WILL BE SENT FOR THIS EVENT. the cosmic ray environment.
PART B. High altitude aircraft, such as the Supersonic
THIS EVENT MAY HAVE PRODUCED Transport, traversing polar latitudes may be
SPACECRAFT CHARGING AND SENSOR exposed to enhanced radiation levels.
CONTAMINATION OR DAMAGE, ESPECIALLY High latitude HF communication (generally
FOR GEOSYNCRONOUS OR poleward of 55 degrees of latitude) will
HIGH INCLINATION ORBITS. experience degraded or a complete blackout due
PART C. REMARKS: ISSUED BY AIR FORCE to the increased ionization from the charged
WEATHER AGENCY, OFFUTT AFB, NE. IF YOU particles entering the auroral zone, termed as a
HAVE QUESTIONS OR REQUIRE FURTHER PCA, Polar Cap Absorption event. Details outlined
INFORMATION, CALL THE in 2.9.
DUTY FORECASTER AT DSN 272-8087, Spacecraft personnel, especially those engaged
COMMERCIAL 402-232-8087.INFORMATION in extra-vehicular activity (EVA) in polar orbit,
CAN ALSO BE OBTAINED AT may be exposed to enhanced radiation levels.
https://weather.afwa.af.mil UNDER THE SPACE
WEATHER LINK.
Radio Event Warning
(WOXX52 KGWC)
WOXX52_KGWC - RADIO EVENT WARNING
WOXX52 KGWC 250908
SUBJECT: AFWA EVENT WARNING REPORT Description. Notifies customers of significant
ISSUED AT 0908Z 25 SEP 2001 solar radio bursts. A preliminary report is issued
PART A. when a solar radio burst above 5,000 SFU is
detected. This report provides the start time of
THE SOLAR RADIO EVENT WHICH BEGAN AT the event. A final report is issued when the
0848Z 25 SEP 2001 CAUSED BURSTS OF: event ends. This report provides a list of
FREQUENCY (MHZ): 610 frequencies on which bursts exceeding 5,000
PEAK FLUX (SFU): 5800 SFU were observed, the peak flux, and the time
TIME OBSERVED: 0852 of the peak.
PART B. Operational Impacts/Uses.
THIS EVENT COULD HAVE AFFECTED Radars may experience interference, increased
SPACECRAFT COMMAND AND CONTROL, noise levels, and false targeting.
CAUSED RADIO FREQUENCY INTERFERENCE, Satellite communications may experience
AND/OR INTERCEPT CAPABILITY. increased noise levels or loss of communications.
PART C. REMARKS:
ISSUED BY THE AIR FORCE WEATHER
AGENCY, OFFUTT AFB, NE. IF YOU HAVE
QUESTIONS OR REQUIRE FURTHER
INFORMATION, CALL THE DUTY
FORECASTER AT DSN 272-8087,
COMMERCIAL 402-232-8087. INFORMATION
CAN ALSO BE OBTAINED AT
https://weather.afwa.af.mil UNDER THE SPACE
WEATHER LINK.
Solar Radio Burst Advisory (NWXX50
KGWC)
NWXX50 KGWC - SOLAR RADIO BURST
ADVISORY
NWXX50 KGWC 191527 Description. Notifies customers of solar radio
bursts that could cause radio frequency
SUBJECT: AFWA ADVISORY REPORT ISSUED interference (RFI) on radar/telemetry
AT 1527Z 19 JAN 2002 equipment at selected locations.
PART A. A SIGNIFICANT RADIO BURST IS Operational Impacts/Uses.
IN PROGRESS
Radar system may experience increased noise
THE FOLLOWING SITES MAY EXPERIENCE levels and false targets.
INTERFERENCE: ANTIGUA, ASCENSION,
BUCKLEY, CAPE COD, EGLIN, FYLINGDALE, Radar system may experience increased noise
KAPAUN, AND MILLSTONE. levels and false targets.
PART B. RADAR SYSTEMS MAY EXPERIENCE Satellite communications may experience
INCREASED NOISE LEVELS AND FALSE increased noise levels or loss of communications
TARGETS. SATELLITE COMMUNICATIONS due to interference.
MAY EXPERIENCE INCREASED NOISE LEVELS
OR LOSS OF COMMUNICATIONS DUE TO
INTERFERENCE.
PART C. REMARKS:
ISSUED BY THE AIR FORCE WEATHER
AGENCY, OFFUTT AFB, NE. IF YOU HAVE
QUESTIONS OR REQUIRE FURTHER
INFORMATION, CALL THE DUTY
FORECASTER AT DSN 272-8087,
COMMERCIAL 402-232-8087. INFORMATION
CAN ALSO BE OBTAINED AT
https://weather.afwa.af.mil UNDER THE SPACE
WEATHER LINK.
IMAGES
Sun Images
N
E W
S
This is a full disk H-alpha This is an X-ray image of the sun
image of the sun. taken with the Soft X-Ray Telescope
(SXT) on the orbiting Yohkoh satellite.
THE SUN APPROACHING SOLAR
MAXIMUM
A comparison of three EIT images almost three years apart illustrates
how the level of solar activity has increased significantly. The Sun
attains its expected sunspot maximum of its 11-years solar cycle in the
year 2000. These images are captured using Fe XII 195 Šemissions
showing the solar corona at a temperature of about 1 million K. Many
more sunspots, solar flares, and coronal mass ejections occur during the
solar maximum. The progression towards more active regions and the
number/size of magnetic loops is unmistakable.
Solar Cycle
The number of sunspots seen on the "surface" of
the Sun changes from year to year. This rise and
fall in sunspot counts is a cycle. The length of the
cycle is about eleven years on average. The
Sunspot Cycle was discovered in 1843 by the
amateur German astronomer Samuel Heinrich
Schwabe.
A peak in the sunspot count is called "solar
maximum" (or "solar max"). The time when few
sunspots appear is called a "solar minimum" (or
"solar min"). An example of a recent sunspot cycle
spans the years from the solar min in 1986, when
13 sunspots were seen, through the solar max in
1989 when more than 157 sunspots appeared, on to
the next solar min in 1996 (ten years after the
1986 solar min) when the sunspot count had fallen
back down to fewer than 9.
The length of the sunspot cycle is, on average,
around eleven years. But the length of the cycle
does vary. Between 1700 and today, the sunspot
cycle (from one solar min to the next solar min)
has varied in length from as short as nine years to
as long as fourteen years.
The Sun is usually very active when sunspot counts
are high. Sunspots show us where the Sun's
magnetic field might be "twisted up" enough to
cause solar flares and coronal mass ejections. The
Sun gives off more radiation than usual during solar
max, and this extra energy changes the uppermost
layers of Earth's atmosphere.
Solar Atmosphere
The visible solar atmosphere consists of three
regions: the photosphere, the chromosphere,
and the solar corona. Most of the visible (white)
light comes from the photosphere, this is the
part of the Sun we actually see. The
chromosphere and corona also emit white light,
and can be seen when the light from the
photosphere is blocked out, as occurs in a solar
eclipse. The sun emits electromagnetic radiation
at many other wavelengths as well. Different
types of radiation (such as radio, ultraviolet, X-
rays, and gamma rays) originate from different
parts of the sun. Scientists use special
instruments to detect this radiation and study
different parts of the solar atmosphere.
The solar atmosphere is so hot that the gas is
primarily in a plasma state: electrons are no
Image of the solar corona in white light longer bound to atomic nuclei, and the gas is
made up of charged particles (mostly protons
(outer circle, blue and white) and X-Rays and electrons). In this charged state, the solar
(inner circle, red, yellow, and black) on atmosphere is greatly influenced by the strong
April 22, 1994, courtesy of the High solar magnetic fields that thread through it.
These magnetic fields, and the outer solar
Altitude Observatory and the Yohkoh atmosphere (the corona) extend out into
Science team. The dashed circle is the interplanetary space as part of the solar wind.
solar radius.
Photosphere
Most of the energy we receive from the Sun
is the visible (white) light emitted from the
photosphere. The photosphere is one of the
coolest regions of the Sun (6000 K), so only a
small fraction (0.1% ) of the gas is ionized (in
the plasma state). The photosphere is the
densest part of the solar atmosphere, but is
still tenuous compared to Earth's atmosphere
(0.01% of the mass density of air at sea
level). The photosphere looks somewhat
boring at first glance: a disk with some dark
spots. However, these sunspots are the site
of strong magnetic fields. The solar magnetic
field is believed to drive the complex activity
seen on the Sun. Magnetographs measure the
solar magnetic field at the photosphere.
Because of the tremendous heat coming from
the solar core, the solar interior below the
photosphere (the convection zone) bubbles
like a pot of boiling water. The bubbles of hot
material welling up from below are seen at
the photosphere, as slightly brighter regions.
Darker regions occur where cooler plasma is
sinking to the interior. This constantly
churning pattern of convection is called the
solar granulation pattern.
Chromosphere
Above the photosphere is the
chromosphere, a region about 2500
kilometers thick. Just prior to and just
after the peak of a total solar eclipse ,
the chromosphere appears as a thin
reddish ring. The conspicuous color of the
chromosphere (compared to the mostly
white corona) led to its name (meaning
``color sphere.'') The chromosphere is
most easily viewed in emission lines such
as Hydrogen alpha, where bright regions
known as plages, and dark features called
filaments are visible. Filaments are the
name given to prominences when they are
seen on the solar disk. Spicules are visible
in the chromosphere on the limb of the
sun. They are jets of plasma shooting up
from supergranule boundaries.
Solar Corona
Rising above the Sun's chromosphere , the
temperature jumps sharply from a few tens of
thousands degrees Kelvin to as much as a few
million degrees in the Sun's outer atmosphere,
the solar corona. Understanding the reason the
Sun's corona is so hot is one of the many
challenges facing solar physicists today.
Because of the very high temperatures, the
corona emits high energy radiation and can be
observed in X-rays. The Earth's atmosphere
absorbs X-rays, but satellites above the
atmosphere, such as the Yohkoh spacecraft,
can observe the Sun in these wavelengths.
Shown on the left is a blending of a Yohkoh X-
ray image (reddish colors) with an eclipse
image taken by the High Altitude Observatory
(gray-white colors) on November 3, 1994. Near
the poles of the Sun, the corona is dark for
both X-rays and white light. These regions are
coronal holes and are the source of the solar
wind that extends out into interplanetary
space. The scattered white light shows the
density of plasma in the corona. The large
white regions extending out far from the Sun
are helmet streamers, where the solar plasma
has been trapped by the Sun's magnetic field.
Sunspots
Sunspots are dark, planet-sized regions that
appear on the "surface" of the Sun. Sunspots are
"dark" because they are colder than the areas
around them. A large sunspot might have a
temperature of about 4,000 K (about 3,700° C or
6,700° F). This is much lower than the 5,800 K
(about 5,500° C or 10,000° F) temperature of the
bright photosphere that surrounds the sunspots.
Sunspots are only dark in contrast to the bright
face of the Sun. If you could cut an average
sunspot out of the Sun and place it in the night
sky, it would be about as bright as a full moon.
Sunspots have a lighter outer section called the
penumbra, and a darker middle region named the
umbra.
Sunspots are caused by the Sun's magnetic field
welling up to the photosphere, the Sun's visible
"surface". The powerful magnetic fields around
sunspots produce active regions on the Sun, which
often lead to solar flares and Coronal Mass
Ejections (CMEs). The solar activity of flares and
CMEs are called "solar storms".
Sunspots form over periods lasting from days to
weeks, and can last for weeks or even months. The
average number of spots that can be seen on the
face of the Sun is not always the same, but goes up
and down in a cycle.
Sunspots
Sunspots are caused by very strong magnetic
fields on the Sun. The best way to think about
the very complicated process of sunspot
formation is to think of magnetic "ropes"
breaking through the visible surface
(photosphere) of the Sun. Where the rope comes
up from the solar surface is one sunspot and
where the rope plunges into photosphere is
another sunspot.
As you can see in the picture to the left, one
sunspot has North magnetic polarity and one
sunspot has South magnetic polarity.
Scientists believe the differential rotation of
the Sun is the underlying cause of the magnetic
ropes on the Sun. Since the gaseous sphere of
the Sun rotates more quickly at its equator than
at its poles, the Sun's overall magnetic field
becomes distorted and twisted over time. The
twisted field lines eventually come through the
photosphere, showing their presence as sunspots.
When the tangled fields reach a "breaking point",
like a rubber band that snaps when wound too
tight, huge bursts of energy are released as the
field lines reconnect. This can lead to solar flares
and Coronal Mass Ejections (CMEs).
Prominences & Filaments
Large impressive loop-like structures on
the edge of the solar disk sometimes
stand out brightly against the dark
background of space. Though these
structures, called "prominences", appear
to be very bright and hot, they are
actually hundreds of times cooler and
denser than the surrounding gases in the
Sun's corona or outermost atmosphere.
Filaments are dark string-like features
that snake across regions of the solar
disk. They are actually prominences that
are silhouetted against the much brighter
solar surface.
Filaments and prominences can remain
stable for weeks or even months. Then,
without warning, these structures can
erupt and blow large amounts of gas and
plasma out into space. Erupting
prominences are closely associated with
an important space weather event called a
Coronal Mass Ejection (CME).
Coronal Loops
A feature in the Sun’s corona visible at X-ray,
ultraviolet, and white-light wavelengths,
consisting of an arch, extending upward from
the photosphere for tens or hundreds of
thousands of kilometers. Bright coronal loops, in
the form of coronal condensations and bright
spots, are common around the time of solar
maximum. Larger faint ones, lasting days or
weeks, are more typical of the quiet corona,
when solar activity is low. The two ends of a
loop, known as footprints, lie in regions of the
photosphere of opposite magnetic polarity to
each other.
Until recently, researchers had suspected that
coronal loops were essentially static, plasma-
filled structures. However, movies made from
observations by the TRACE (Transition Region
This picture shows a part of the Sun's and Coronal Explorer) spacecraft have shown
bright blobs of plasma racing up and down the
atmosphere called the corona. The corona is coronal loops. SOHO data confirmed that these
very, very hot - about 1 million degrees! Glowing plasma blobs were moving at tremendous speeds,
leading to the new view that coronal loops are
plasma, which is like magnetized gas, sometimes hypervelocity currents of plasma blasted from
forms loops in the corona. Magnetic fields the solar surface and squirted between the
magnetic structures in the corona. Rather than
around sunspots make these loops. They are being tubes of plasma enclosed within a magnetic
called coronal loops. The loops are huge - about container, the loops are jets of hot plasma
30 Earths would fit across them flowing along in the alleys between the strong
coronal magnetic fields.
Coronal Mass Ejections (CME)
Coronal mass ejections are explosions in
the Sun's corona that spew out solar
particles. A lot of material is thrown out
into the solar wind. Coronal mass
ejections can be dangerous when they hit
the Earth.
CME's can seriously disrupt the Earth's
environment. Intense radiation from the
Sun, which arrives only 8 minutes after
being released, can alter the Earth's
outer atmosphere, disrupting long-
distance radio communications. Very
energetic particles pushed along by the
shock wave of the CME can endanger
astronauts or fry satellite electronics.
These energetic particles arrive at the
Earth (or Moon) about an hour later. The
actual coronal mass ejection arrives at
the Earth one to four days after the
initial eruption, resulting in strong
geomagnetic storms, aurorae and
electrical power blackouts.
Coronal Mass Ejections
"Without warning, the relatively
calm solar atmosphere can be
torn asunder by sudden
outbursts of a scale unknown on
Earth. Catastrophic events of
incredible energy...stretch up to
halfway across the visible solar
surface, suddenly and
unpredictably open up and expel
their contents, defying the
Sun's enormous gravity."
A coronal mass ejection and prominence
eruption observed in white light from the
SMM (Solar Maximum Mission)
spacecraft. The time of each panel
increases from left to right. The dashed
inner circle in each panel is the solar
radius, the occulting radius is at 1.6 solar
radii.
Solar Wind
The Sun is flinging 1 million tons of
matter out into space every second! We
call this material solar wind. Once the
solar wind is blown into space, the
particles travel at supersonic speeds of
200-800 km/sec! These particles travel
all the way past Pluto and do not slow
down until they reach the termination
shock within the heliosphere. The
Heliosphere is the entire region of space
influenced by the Sun.
The solar wind plasma is very thin. Near
the Earth, the plasma is only about 6
particles per cubic centimeter. So, even
though the wind travels SUPER fast, it
wouldn't even ruffle your hair if you were
to stand in it because it's so thin! But, it
is responsible for such unusual things as:
auroral lights
fueling magnetospheric storms
forming a planet's magnetosphere
The particles of the solar wind, and the
Sun's magnetic field (IMF) are stuck
together, therefore the solar wind
carries the IMF (interplanetary magnetic
field) with it into space.
Solar Flares
Solar flares are essentially huge
explosions on the Sun. Flares occur when
intense magnetic fields on the Sun
become too tangled. Like a rubber band
This ultraviolet image of the Sun shows one of
that snaps when it is twisted too far, the
the largest solar flares ever seen. The flare, tangled magnetic fields release energy
which erupted in November 2003, is the bright when they "snap". Solar flares emit huge
region along the Sun's right limb. The horizontal bursts of electromagnetic radiation,
"spikes" extending to the right and left of the including X-rays, ultraviolet radiation,
flare are not real; they are an artifact produced visible light, and radio waves. The energy
by the imaging instrument, which was overloaded emitted by a solar flare is more than a
by the intense brightness of this flare.
million times greater than the energy
from a volcanic explosion on Earth!
Although solar flares can be visible in
white light, they are often more readily
noticed via their bright X-ray and
ultraviolet emissions. Coronal mass
ejections often accompany solar flares,
though scientists are still trying to
determine exactly how the two
This ultraviolet image of the Sun shows one of the phenomena are related. Solar flares burst
largest solar flares ever seen. The flare, which forth from the intense magnetic fields in
erupted in November 2003, is the bright region the vicinity of active regions on the Sun.
Solar flares are most common during
along the Sun's right limb. The horizontal "spikes" times of peak solar activity, the "solar
extending to the right and left of the flare are max" years of the sunspot cycle.
not real; they are an artifact produced by the
imaging instrument, which was overloaded by the
intense brightness of this flare.