PACKET RADIO: SESCH
Steve Wolf, W8IZ@W8IZ
(This text from the W8IZ packet radio bulletin
board. It's formatted to fit a 80 character screen.)
The Space Environment Laboratory (SEL) is unique within the US Department of Commerce, National Oceanic and Atmospheric Administration (NOAA), Environmental Research Laboratories in providing both real time services to meet national needs, and research and support activities to improve these services. SEL , through the Space Environment Service Center (SESC) is a national center for providing around-the-clock forecasts and warnings of solar and space disturbances, an activity which requires a substantial fraction of its resources. The rest of its efforts are devoted to studying and analyzing solar and terrestrial disturbances, and to developing systems to improve monitoring, understanding, forecasting, and analysis of disturbances.
The genesis of the mission of SEL is traceable to activities of the U.S. Government during the Second World War, when the Interservice Radio Propagation Laboratory (IRPL) was formed in the National Bureau of Standards (NBS). At that time there was a strong requirement to support ionospherically propagated communications to the European Theatre, which could be severely disrupted during times of solar and geomagnetic disturbances. In 1946, the Central Radio Propagation Laboratory (CRPL) was formed in NBS to place the work of IRPL on a permanent basis. In the early 1950's, CRPL moved to the new NBS facilities in Boulder. From these beginnings, the radio propagation work moved to the Environmental Science and Services Administration, and still later the space environment services and research activities moved to NOAA when it was established.
The modern era of providing space environment services dates from 1965, when SEL (then the Space Disturbances Laboratory) established a real-time forecast and warnings center. The needs for these services have grown and diversified, extending well beyond ionospheric communications to include such problems as radiation hazards to astronauts, increased drag on navigation satellites during magnetic disturbances, upsets of geostationary satellite electronics and other systems, induced currents in long lines, and the impact of geomagnetic activity on geophysical exploration by air-borne magnetometers.
Major terrestrial space disturbances are traceable to three different types of solar activity: large solar flares, coronal mass ejections (some of which are associated with eruptive filaments), and high speed solar wind streams emanating from coronal holes. The time required for disturbances to reach the earth ranges from the immediate effects of X-rays associated with flares, to 10's of minutes to hours for energetic solar protons from major flares, to 1 to 5 days for shock waves and plasma clouds from solar flares and the solar wind disturbances which are a result of coronal mass ejections. Disturbances associated with a given high speed solar wind stream tend to affect the earth every 27 days, as the stream overtakes the earth due to solar rotation. Only the flare X-rays reach the earth unperturbed by the intervening medium. The propagation of both the energetic particles, and the shock waves and mass ejections can be profoundly influenced by the solar wind and its magnetic fields.
The terrestrial impacts of solar activity of concern to users include
. radiation hazards to astronauts and high flying aircraft (energetic solar protons)
. surface charging and deep charging of satellites (enhanced plasma environment and energetic solar protons)
. disturbed ionospheric communications (solar X-rays, solar protons, magnetospheric particle precipitation)
. disturbances of the external geomagnetic field (ionospheric currents associated with particle precipitation, ring current in the inner magnetosphere)
. induced currents in long lines (temporal variations of the magnetic fields from ionospheric currents)
. upper atmosphere heating (joule heating by ionospheric currents).
(The sources of the problems are given parenthetically.)
The forecasts, warnings, real-time data, and summary information provided by SEL's Space Environment Services Center are generic products designed to serve the entire set of users concerned with these problems. Several methods of distributing these products are used, including commerical satellite broadcasts. This bulletin board is on experiment to see if this method of distribution can make the products available conveniently to a wider audience.
The thrust of research activities within SEL is to increase man's understanding of solar activity and consequent disturbances at the earth, and to develop techniques for improving man's capablities to monitor, forecast, and analyze solar-terrestrial disturbances.
Report of Solar and Geophysical Activity
Part IA This first part contains a general description of sig- nificant solar features and activity observed during the 24 hours ending at 2100Z. This discussion includes character- istics of sunspots, plages, magnetic fields, active filaments, limb and flare activity and other phenomena (such as x-ray and radio bursts) associated with significant solar activity.
Part IB A discussion of the potential for solar activity during the next 3 days. Solar regions expected to rotate onto the visible solar disk during this period are noted. The Sun rotates aproximately once every 27 days.
Part IIA This part contains a brief description of significant geophysical activity observed during the 24 hours ending at 2100Z. This includes polar cap absorption (PCA) events, satellite level particle (protons and alpha particles) enhancements and a general description of the planetary geomagnetic activity.
Part IIB This is a forecast of significant geophysical activity for the next 3 days.
Part III Numerical predictions of significant solar and geophys- ical phenomena for the next 3 days:
(a) CLASS M: Daily forecast of the probability of occurrence of one or more Class M x-ray events. (b) CLASS X: Daily forecast of the probability of occurrence of one or more Class X x-ray events. (c) PROTON: Daily forecast of the probability of occurrence of a flare that will cause a signifi- cant proton event (at least 10 protons/sqcm/sec/ ster at energies greater than 10 MeV). (d) PCAF: A 24-hour forecast of a significant polar cap absorption (PCA) event (at least 2.0 dB absorption in sunlight or at least 0.5 dB absorp- tion in darkness, on a riometer located in the polar cap). These forecasters are issued as a "color-coded" Polar Cap Absorption Forecast (PCAF) as follows: 1. PCAF GREEN - No active region exists on the Sun likely to produce a PCA event in the next 24 hours. 2. PCAF YELLOW - A region which possess char- acteristics favorable for producing a PCA event is present on the Sun. If an ener- getic flare event occurs in this region, the probability of a significant PCA event resulting is very high. 3. PCAF RED - An energetic solar event has occurred or a proton event has been ob- served at satellite altitudes and there is a high probability that a significant PCA event will result within the next 24 hours.
NOTE: If a significant PCA event is in prog- ress, at forecast time, the statement, "IN PROGRESS" will be used.
Part IV A part containing observed and forecast values of the 10.7cm solar radio flux.
(a) OBSERVED: Previous day's 10.7cm solar radio flux observed at 1700Z at the Algonquin Radio Observa- tory near Ottawa, Canada. (b) PREDICTED: Daily forecasts of the 10.7cm flux for the next 3 days. (c) 90-DAY MEAN: The 90-day mean of the observed 10.7cm flux.
Part V This part contains the observed, estimated and predicted values of daily geomagnetic indices.
(a) OBSERVED AFR/AP: The observed daily geomagnetic A-index for Fredericksburg, Virginia (AFR) and the observed daily planetary geomagnetic index (AP) for the day indicated. (b) ESTIMATED AFR/AP: For the day indicated, an esti- mate of the daily geomagnetic A-index (AFR) for Fredericksburg, Virginia and an estimate of the planetary geomagnetic index (AP). (c) PREDICTED AFR/AP: Predictions of the daily geomag- netic A-index for Fredericksburg and the plane- tary geomagnetic index for the next 3 days.
When implemented, an Abbreviated Solar-Geophysical Glossary will be available on this bulletin board to help those who are unfamiliar with the terms used above. In the interim, users are directed to the references mentioned in Help File 2.
HF Propagation Report Description
Part I The Report provides observed and forecast HF propagation conditions in 20 areas of the Northern Hemisphere. That hemisphere is divided into 4 longitude sectors and 5 latitude zones as follows:
Sectors Zones I 0 to 90 deg. West Polar more than 70 deg. II 90 to 180 deg. West Auroral 55 to 70 deg. III 180 to 90 deg. East Middle 30 to 55 deg. IV 90 to 0 deg. East Low 10 to 30 deg. Equatorial 0 to 10 deg.
Observed conditions (over the previous 6 hours) are specified on a relative scale. One of three letters (N=normal, U=fair, W=poor) identifies overall propagation conditions in comparison to normal conditions for that latitude, local time, season and phase of the sunspot cycle. Consequently, an N at auroral latitudes in the sunrise sector does not have the same absolute meaning as an N in the after- noon sector at low latitudes. Conditions are normally much better in the latter block than the former, but N may apply to both blocks. Numbers from 1 through 9 represent forecast conditions for the next 6 hours:
1 - Useless 4 - Poor to Fair 7 - Good 2 - Very Poor 5 - Fair 8 - Very Good 3 - Poor 6 - Fair to Good 9 - Excellent
Forecast conditions are described on an absolute scale ranging from 1 to 9. A given number has the same absolute meaning regardless of the block in which it is placed. Referring to the previous example, it would be extremely unusual for all blocks to have the same number forecast. The number forecast refers to overall propagation conditions, taking into account MUF or LUF values, and such phenomena as spread-F and blanketing sporadic-E.
Also included in this part is a 6 hour prediction of maximum usable frequency (MUF) deviations of 20% or more from seasonal means. Communicators may use these figures in conjunction with monthly mean predictions to plan which frequencies to use during the forecast period. Forecast deviations apply to oblique, single hop 4000km paths with mid-points located in the relevant grid block. Deviations are represented by P (Plus) for enhancements and M (Minus) for depressions.
Part II This part of the 0600Z bulletin contains a plain lang- uage discussion of geomagnetic and ionospheric conditions and their effects on propagation. It covers conditions observed on the previous Zulu day and a forecast for the remainder of the current Zulu day.
Part III This is a summary of possible and confirmed solar flare induced ionospheric disturbances, specifically short wave fades (SWFs), during the previous Zulu day. These include: (1) reported SWFs, (2) X-ray events larger than C5 and show- ing a flux enhancement of more than 10 times background, and (3) solar optical flares greater than 0B if X-ray data is not available. This part also includes a plain language forecast of the probability of a solar flare induced SWF during the remainder of the current Zulu day:
Probability Descriptive Word less than or equal to 1% Nil equal to or greater than 2%, Slight but less than 20% equal to or greater than 20%, Moderate but less than 50% equal to or greater than 50% Strong
Part IV This part contains information that can be used to plan operations during the 3 day forecast period. It includes the previous Zulu day's observed F10 (10.7cm solar radio flux reported at 1700Z), Ap (24 hourly value reported at 2400Z) and corresponding geomagnetic K value. It also includes a three day forecast for F10, Ap and K. The 10.7cm radio flux may be used as an indicator of the general level of solar activity. Variations of 10 units or more above the 90 day mean indicate a reasonable chance of solar related disrup- tions occurring. Conversely, values significantly below the 90 day mean can be interpreted as an expectation of low solar activity.
The HF Propagation Report is issued at 0600Z (Greenwich Mean Time) daily. This corresponds to 0100 EST. Secondary reports (6-hourly updates) are issued at 1200Z (0700 EST), 1800Z (1300 EST) and 2400Z (1900 EST).
The meaning of some of the phrases in this help file, such as "maximum usable frequency" and "short wave fade" may not be familiar to some people accessing this bulletin board. For a thorough discussion of these terms, as well as suggest- ions on making use of the solar radio flux and geomagnetic data please refer to The ARRL Handbook for the Radio Amateur or the Radio Handbook (by William Orr). Amateur radio and SWL magazines frequently contain helpful material regarding HF propagation, as well. A more detailed technical discussion of this material is found in the book Ionospheric Radio Propagation by Kenneth Davies. This is out of Print but may be available through libraries.
Part I This first part summarizes white light sunspot observa- tions received by the SESC during the previous 24-hour UT day. The terms used are defined as follows:
NMBR - Region number assigned to each sunspot group or plage region during each visible disk rotation. LOCATION - Sunspot group or plage region location in degrees heliographic latitude and degrees East or West from meridian. LO - Carrington longitude of the group. AREA - Total area of the group in millionths of the solar hemisphere. Z - Modified Zurich classification of the group. LL - Longitudinal extent of the group in heliographic degrees. NN - Total number of visible sunspots in the group. MAG TYPE - Magnetic classification of the group. Mount Wilson magnetogram data will be used when available.
Part IA This part keeps track of regions, still on the visible disk, which have become spotless.
Part II Part II lists those old regions which are due to return to the visible solar disk during the 3-day period covered by the Summary. The terms used are defined as follows:
LAT - Latitude at which region is due to return. LO - Last Carrington longitude of group.
Solar and Geophysical Activity Summary
Part A This first part contains significant solar flare data including start, maximum and end times; region number and location (if known); x-ray and optical classification of flare (if available); significant radio emission at 245 MHz, 10 cm (2695 MHz), and sweep frequency; and significant short wave fades. Flares are included in this section if one or more of the following thresholds are reached:
(a) Class M or greater x-ray burst. (b) Optical flare of importance 2B or greater. (c) Radio burst at 245 MHz 5 times background. (d) Radio burst at 2695 MHz 100% above background. (e) Type II or Type IV sweep frequency burst. (f) Short wave fade of importance 2 or greater.
Part B This part contains proton event data whenever the flux of greater than 10 MeV particles reaches or exceeds 10 particles/sq cm/sec/steradian.
Part C Data is listed covering geomagnetic disturbances (Ap greater than or equal to 25, Kp greater than or equal to 6, or sudden storm commencement (SSC)).
Part D Data on stratospheric warmings.
Part E This part contains the following indices for the previous UT day:
(a) Observed Ottawa 10.7 cm flux. (b) Zurich sunspot number based on latest spot drawing. (c) Estimated daily geomagnetic A-index for Fredericks- burg, Virginia (AFR) and observed planetary geomagnetic index (Ap). (d) Average x-ray background in ergs/sq cm/second. (e) Daily proton fluences (flux accumulation over 24 hours) greater than 1 MeV and greater than 10 MeV protons at geosynchronous altitudes. (f) 3-hourly K-indices (Boulder and planetary).
Part F Reserved for additional comments (as required).
SESC Sunspot Numbers -
On a daily basis, reports of solar observations are gathered from observatories around the World. The main contributing observatories are five U.S. Air Force-operated observatories (located in New Mexico, Hawaii, Australia, Italy and Puerto Rico) and a NOAA observatory in Boulder, CO. These reports are used at the end of each Universal Time day to compile lists of sunspot groups currently visible on the Sun.
The SESC Daily Sunspot Number is formulated in the following way: (1) The number of separate groups of sunspots (g) is determined. (2) The total number of individual spots (n) seen on the Sun that day is tallyed. (3) The SESC number is calculated using the relation (n + 10g). This is the method developed by Wolf in the mid-19th century. This number is reported under "SSN" in Data File 1.
Experience shows that recently the SESC Daily Sunspot Number differs from the International Daily Sunspot Number (RI) by a factor of 0.88. This has been computed using the most recent 18 monthly average values. Therefore, the number shown under "RI(est.)" in Data File 1, is our best guess at the end of each UT day for the daily RI value which will be reported, by Brussels, some weeks after the end of the current month.
Details about the groups of sunspots (SESC Regions) are avail- able in the SESC weekly publication Preliminary Report and Fore- cast of SOLAR GEOPHYSICAL DATA. This is published by the Space Environment Services Center, R/E/SE2, 325 Broadway, Boulder, CO 80303. This publication also lists comparisons between the SESC Sunspot Numbers and the RI Sunspot Numbers.
Final International (RI) Sunspot Number data and additional information about sunspot numbers are published monthly in the SOLAR-GEOPHYSICAL DATA Prompt Reports by the National Geophysical Data Center, NOAA/NESDIS, E/GC2, 325 Broadway, Boulder, CO 80303.
Since 1947, the daily noontime (1700Z) solar radio flux at 2800 MHz (10.7 cm wavelength) has been measured at the National Research Council of Canada's Algonquin Radio Observatory near Ottawa. These flux readings are highly correlated with the sunspot number index, and preferred by some as a 'more physi- cally meaningful' measurement of solar activity.
These solar radio flux readings are reported each day to the Space Environment Services Center in Boulder, CO and are listed here for your use. Some HF propagation prediction tech- niques require this value as input.
The weekly publication Preliminary Report and Forecast of SOLAR GEOPHYSICAL DATA contains additional information about solar radio emissions at a variety of frequencies. This is published by the Space Environment Services Center, R/E/SE2, 325 Broadway, Boulder, CO 80303.
Each month the Ottawa 10.7 cm flux values, as well as solar radio fluxes over a range of other wavelengths, are published in the SOLAR-GEOPHYSICAL DATA Prompt Reports by the National Geophysical Data Center, NOAA/NESDIS, E/GC2, 325 Broadway, Boulder, CO 80303.
GLOSSARY OF SOLAR-TERRESTRIAL TERMS
a INDEX. A 3-hourly "equivalent amplitude" index of local geomagnetic activity; "a" is related to the 3-hourly K INDEX according to the following scale:
K 0 1 2 3 4 5 6 7 8 9 a 0 3 7 15 27 48 80 140 240 400
A INDEX. A daily index of geomagnetic activity derived as the average of the eight 3-hourly a indices.
ACTIVE. Geomagnetic levels such that 15 <= Ap < 30.
ACTIVE DARK FILAMENT (ADF). An ACTIVE PROMINENCE seen on the DISK.
ACTIVE LONGITUDE. The approximate center of a range of heliographic longitudes in which ACTIVE REGIONS are more numerous and more FLARE-active than the average.
ACTIVE PROMINENCE. A PROMINENCE displaying material motion and changes in appearance over a few minutes of time.
ACTIVE PROMINENCE REGION (APR). A portion of the solar LIMB displaying ACTIVE PROMINENCEs.
ACTIVE REGION (AR). A localized, transient volume of the solar atmosphere in which PLAGEs, SUNSPOTS, FACULAe, FLAREs, etc. may be observed.
ACTIVE SURGE REGION (ASR). An ACTIVE REGION that exhibits a group or series of spike-like surges that rise above the limb.
AFRED. Abbreviation for the A INDEX for Fredericksburg.
ANGSTROM. A unit of length = 1.0E-08cm.
Ap INDEX. An averaged planetary A INDEX based on data from a set of specific stations.
ARCH FILAMENT SYSTEM (AFS). A bright, compact PLAGE crossed by a system of small, arched FILAMENTS, which is often a sign of rapid or contin- ued growth in an ACTIVE REGION.
ASTRONOMICAL UNIT (AU). The mean earth-sun distance, equal to 1.496E+13cm or 214.94 solar radii.
AURORA. A faint visual phenomenon associated with geomagnetic activity, which occurs mainly in the high-latitude night sky; typical auroras are 100 to 250 km above the ground.
AURORAL OVAL. An oval band around each geomagnetic pole which is the locus of structured AURORAe.
AUTUMNAL EQUINOX. The EQUINOX that occurs in September.
BARTEL'S ROTATION NUMBER. The serial number assigned to 27-day rotation periods of solar and geophysical parameters. Rotation 1 in this sequence was assigned arbitrarily by Bartel to begin in January 1833.
BRIGHT SURGE ON THE DISK (BSD). A bright gaseous stream (SURGE) emanating from the CHROMOSPHERE.
BRIGHT SURGE ON THE LIMB (BSL). A large gaseous stream (SURGE) that moves outward more than 0.15 solar radius above the LIMB.
BURST. A transient enhancement of the solar RADIO EMISSION, usually associated with an ACTIVE REGION or FLARE.
CARRINGTON LONGITUDE. A system of fixed longitudes rotating with the sun.
CENTIMETER BURST. A solar radio burst in the centimeter wavelength range.
CENTRAL MERIDIAN PASSAGE (CMP). The passage of an ACTIVE REGION or other feature across the longitude meridian that passes through the apparent center of the solar DISK.
CHROMOSPHERE. The layer of the solar atmosphere above the PHOTOSPHERE and beneath the TRANSITION REGION and the CORONA.
CONJUGATE POINTS. Two points on the earth's surface, at opposite ends of a geomagnetic field line.
CONTINUUM STORM (CTM). General term for solar noise lasting for hours and sometimes days.
COORDINATED UNIVERSAL TIME. By international agreement, the local time at the prime meridian, which passes through Greenwich, England. Therefore, it is also known as GREENWICH MEAN TIME, or sometimes simply UNIVERSAL TIME.
CORONA. The outermost layer of the solar atmosphere, characterized by low densities (<1.0E+09/cc) and high temperatures (>1,0E+06deg.K).
CORONAL HOLE. An extended region of the CORONA, exceptionally low in density and associated with unipolar photospheric regions.
CORONAL RAIN (CRN). Material condensing in the CORONA and appearing to rain down into the CHROMOSPHERE as observed in H-ALPHA at the solar LIMB above strong SUNSPOTS.
CORONAL TRANSIENTS. A general term for short-time-scale changes in the CORONA, but principally used to describe outward-moving PLASMA clouds.
COSMIC RAY. An extremely energetic (relativistic) charged particle.
CROCHET. A sudden deviation in the sunlit geomagnetic field (H component; see GEOMAGNETIC ELEMENTS) associated with large solar FLARE X-ray emission.
D REGION. A daytime layer of the earth's IONOSPHERE approximately 50 to 90 km in altitude.
DARK SURGE ON DISK (DSD). Dark gaseous ejections visible in H-ALPHA.
DIFFERENTIAL ROTATION. The change in SOLAR ROTATION RATE with latitude. Low latitudes rotate at a faster angular rate (approx. 14 degrees per day) than do high latitudes (approx. 12 degrees per day).
DISAPPEARING SOLAR FILAMENT (DSF). The sudden (timescale of minutes to hours) disappearance of a solar FILAMENT (PROMINENCE).
DISK. The visible surface of the sun (or any heavenly body) projected against the sky.
Dst INDEX. A geomagnetic index describing variations in the equatorial RING CURRENT.
E REGION. A daytime layer of the earth's ionosphere roughly between the altitudes of 85 and 140 km.
EMERGING FLUX REGION (EFR). An area on the sun where new magnetic flux is erupting.
ERUPTIVE PROMINENCE ON LIMB (EPL). A solar PROMINENCE that becomes activa- ted and is seen to ascend from the sun.
EXTREMELY LOW FREQUENCY (ELF). That portion of the radio frequency spectrum from 30 to 3000 hertz.
EXTREME ULTRAVIOLET (EUV). A portion of the electromagnetic spectrum from approximately 100 to 1000 angstroms.
F CORONA. Of the white-light CORONA (that is, the corona seen by the eye at a total solar ECLIPSE), that portion which is caused by sunlight scattered or reflected by solid particles (dust) in inter- planetary space.
F REGION. The upper layer of the IONOSPHERE, approximately 120 to 1500 km in altitude. The F region is subdivided into the F1 and F2 regions. The F2 region is the most dense and peaks at altitudes between 200 and 600 km. The F1 region is a smaller peak in electron density, which forms at lower altitudes in the daytime.
FACULA. A bright region of the PHOTOSPHERE seen in white light, seldom visible except near the solar LIMB.
FIBRIL. A linear pattern in the H-ALPHA CHROMOSPHERE of the sun, as seen through an H-alpha filter, occurring near strong SUNSPOTS and PLAGE or in FILAMENT channels.
FILAMENT. A mass of gas suspended over the PHOTOSPHERE by magnetic fields and seen as dark lines threaded over the solar DISK. A filament on the LIMB of the sun seen in emission against the dark sky is called a PROMINENCE.
FILAMENT CHANNEL. A broad pattern of FIBRILS in the CHROMOSPHERE, marking where a FILAMENT may soon form or where a filament recently disappeared.
FLARE. A sudden eruption of energy on the solar DISK lasting minutes to hours, from which radiation and particles are emitted.
fMIN. The lowest radiowave frequency that can be reflected from the IONOSPHERE.
foEs. The maximum ORDINARY MODE radiowave frequency capable of reflec- tion from the SPORADIC E REGION of the IONOSPHERE.
foF2. The maximum ORDINARY MODE radiowave frequency capable of reflec- tion from the F2 REGION of the IONOSPHERE.
FORBUSH DECREASE. An abrupt decrease, of at least 10%, of the background galactic COSMIC RAY intensity as observed by neutron monitors.
GAMMA. A unit of magnetic field intensity equal to 1 x 10.0E-05 GAUSS, also equal to 1 NANOTESLA.
GAMMA RAYS. High energy radiation (energies in excess of 100 keV) observed during large, extremely energetic solar FLARES.
GAUSS. The unit of magnetic induction in the cgs (centimeter-gram- second) system.
GEOMAGNETIC ELEMENTS. The components of the geomagnetic field at the sur- face of the earth. In SESC use, the northward and eastward components are often called the H and D components, where the D component is expressed in gammas and is derived from D (the declination angle) using the small angle approximation.
GEOMAGNETIC FIELD. The magnetic field observed in and around the earth. The intensity of the magnetic field at the earth's surface is approximately 0.32 gauss at the equator and 0.62 gauss at the north pole.
GEOMAGNETIC STORM. A worldwide disturbance of the earth's magnetic field, distinct from regular diurnal variations.
Minor Geomagnetic Storm: A storm for which the Ap index was greater than 29 and less than 50.
Major Geomagnetic Storm: A storm for which the Ap index was greater than 49 and less than 100.
Severe Geomagnetic Storm: A storm for which the Ap index was 100 or more.
Initial Phase: Of a geomagnetic storm, that period when there may be an increase of the MIDDLE-LATITUDE horizontal intensity (H).
Main Phase: Of a geomagnetic storm, that period when the hori- zontal magnetic field at middle latitudes is generally decreasing.
Recovery Phase: Of a geomagnetic storm, that period when the depressed northward field component returns to normal levels.
GEOSYNCHRONOUS. Term applied to any equatorial satellite with an orbital velocity equal to the rotational velocity of the earth. The net effect is that the satellite is virtually motionless with respect to an observer on the ground.
GMT. Greenwich Mean Time. (See COORDINATED UNIVERSAL TIME.)
GRADUAL COMMENCEMENT. The commencement of a geomagnetic storm that has no well-defined onset.
GRANULATION. Cellular structure of the PHOTOSPHERE visible at high spatial resolution.
GREEN LINE. The green line is one of the strongest (and first-recognized) visible coronal lines. It identifies moderate temperature regions of the CORONA.
Greenwich Mean Time. See COORDINATED UNIVERSAL TIME.
GROUND-LEVEL EVENT (GLE). A sharp increase in ground-level COSMIC RAY count to at least 10% above background, associated with solar protons of energies greater than 500 MeV. GLEs are relatively rare, occur- ring only a few times each SOLAR CYCLE.
H-ALPHA. This ABSORPTION LINE of neutral hydrogen falls in the red part of the visible spectrum and is convenient for solar observations. The H-alpha line is universally used for patrol observations of solar flares.
H-component of the Geomagnetic Field. See GEOMAGNETIC ELEMENTS.
HIGH LATITUDES. With specific reference to zones of geomagnetic activity, "high latitudes" refers to 50o to 80o geomagnetic.
HIGH-SPEED STREAM. A feature of the SOLAR WIND having velocities that are about double average solar wind values.
HOMOLOGOUS FLARES. Solar flares that occur repetitively in the same ACTIVE REGION, with essentially the same position and with a common pattern of development.
HYDER FLARE. A FILAMENT-associated TWO-RIBBON FLARE, often occurring in spotless regions. The flare presumably results from the impact on the CHROMOSPHERE of infalling FILAMENT material.
INTERPLANETARY MAGNETIC FIELD (IMF). The magnetic field carried with the SOLAR WIND.
IONOSPHERE. The region of the earth's upper atmosphere containing a small percentage of free electrons and ions produced by photoioniza- tion of the constituents of the atmosphere by solar ultraviolet radiation at very short wavelengths (<1000 angstroms). The ionosphere significantly influences radiowave propagation of fre- quencies less than about 30 MHz.
IONOSPHERIC STORM. A disturbance in the F REGION of the IONOSPHERE, which occurs in connection with geomagnetic activity.
K CORONA. Of the white-light CORONA (that is, the corona seen by the eye at a total solar eclipse), that portion which is caused by sunlight scattered by electrons in the hot outer atmosphere of the sun.
K INDEX. A 3-hourly quasi-logarithmic local index of geomagnetic activity relative to an assumed quiet-day curve for the recording site. Range is from 0 to 9. The K index measures the deviation of the most disturbed horizontal component.
KELVIN. A unit of absolute temperature.
Kp INDEX. A 3-hourly planetary geomagnetic index of activity generated in Gottingen, Germany, based on the K INDEX from 12 or 13 stations distributed around the world.
LEADER SPOT. In a magnetically bipolar or multipolar SUNSPOT group, the western part precedes and the main spot in that part is called the leader.
LIGHT BRIDGE. Observed in white light, a bright tongue or streaks penetra- ting or crossing SUNSPOT UMBRAe. The appearance of a light bridge is frequently a sign of impending region division or dissolution.
LIMB. The edge of the solar DISK.
LIMB FLARE. A solar FLARE seen at the edge (LIMB) of the sun.
LOOP PROMINENCE SYSTEM (LPS). A system of loop prominences associated with major FLARES.
LOW FREQUENCY (LF). That portion of the radio frequency spectrum from 30 to 300 kHz.
M 3000. The optimum HIGH FREQUENCY radio wave with a 3000 km range, which reflects only once from the IONOSPHERE (single hop transmission).
MAGNETIC BAY. A relatively smooth excursion of the H (horizontal) component (see GEOMAGNETIC ELEMENTS) of the geomagnetic field away from and returning to quiet levels.
MAGNETOGRAM. Solar magnetograms are a graphic representation of solar mag- netic field strengths and polarity.
MAGNETOPAUSE. The boundary layer between the SOLAR WIND and the MAGNETO- SPHERE.
MAGNETOSPHERE. The magnetic cavity surrounding the earth, carved out of the passing SOLAR WIND by virtue of the GEOMAGNETIC FIELD, which pre- vents, or at least impedes, the direct entry of the solar wind PLASMA into the cavity.
MeV. Mega (million) electronvolt. A unit of energy used to describe the total energy carried by a particle or photon.
MEDIUM FREQUENCY (MF). That portion of the radio frequency spectrum from 0.3 to 3 MHz.
MICROWAVE BURST. A radiowave signal associated with optical and/or X-ray FLAREs.
MIDDLE LATITUDES. With specific reference to zones of geomagnetic activity, "middle latitudes" refers to 20 deg. to 50 deg. geomagnetic.
MOUNT WILSON MAGNETIC CLASSIFICATIONS.
Alpha. Denotes a unipolar SUNSPOT group.
Beta. A sunspot group having both positive and negative mag- netic polarities, with a simple and distinct division between the polarities.
Beta-Gamma. A sunspot group that is bipolar but in which no continuous line can be drawn separating spots of opposite polarities.
Delta. A complex magnetic configuration of a solar sunspot group consisting of opposite polarity UMBRAe within the same PENUMBRA.
Gamma. A complex ACTIVE REGION in which the positive and nega- tive polarities are so irregularly distributed as to prevent classification as a bipolar group.
NANOTESLA (nT). A unit of magnetism 10.0E-09 tesla, equivalent to a gamma (10.0E-05 gauss).
NEUTRAL LINE. The line that separates longitudinal magnetic fields of oppo- site polarity.
PENUMBRA. The SUNSPOT area that may surround the darker UMBRA or umbrae. It consists of linear bright and dark elements radial from the sunspot umbra.
PERSISTENCE. Continuation of existing conditions. When a physical parameter varies slowly, the best prediction is often persistence.
PHOTOSPHERE. The lowest layer of the solar atmosphere; corresponds to the solar surface viewed in WHITE LIGHT. SUNSPOTs and FACULAe are observed in the photosphere.
PLAGE. An extended emission feature of an ACTIVE REGION that exists from the emergence of the first magnetic flux until the widely scattered remnant magnetic fields merge with the background.
PLAGE CORRIDOR. A space in chromospheric (see CHROMOSPHERE) PLAGE lacking plage intensity, coinciding with polarity inversion line.
PLASMA. Any ionized gas, that is, any gas containing ions and electrons.
POLAR CAP ABSORPTION (PCA). An anomalous condition of the polar IONOSPHERE whereby HF and VHF (3 - 300 MHz) radiowaves are absorbed, and LF and VLF (3 - 300 kHz) radiowaves are reflected at lower altitudes than normal. In practice, the absorption is inferred from the proton flux at energies greater than 10 MeV, so that PCAs and PROTON EVENTs are simultaneous. Transpolar radio paths may still be disturbed for days, up to weeks, following the end of a proton event.
POST-FLARE LOOPS. A LOOP PROMINENCE SYSTEM often seen after a major TWO- RIBBON FLARE, which bridges the ribbons.
PROMINENCE. A term identifying cloud-like features in the solar atmosphere. The features appear as bright structures in the CORONA above the solar LIMB and as dark FILAMENTs when seen projected against the solar DISK.
PROTON EVENT. By definition, the measurement of at least 10 protons/sq.cm/sec/steradian at energies greater than 10 MeV.
PROTON FLARE. Any FLARE producing significant FLUXes of greater-than-10 MeV protons in the vicinity of the earth.
QUIESCENT PROMINENCE (FILAMENT). Long, sheet-like prominences nearly vertical to the solar surface.
QUIET. A descriptive word specifically meaning geomagnetic levels such that Ap < 8 (see Ap INDEX).
RADIO EMISSION. Emissions of the sun in radio wavelengths from centimeters to dekameters, under both quiet and disturbed conditions.
Type I. A noise storm composed of many short, narrow-band bursts in the metric range (300 - 50 MHz).
Type II. Narrow-band emission that begins in the meter range (300 MHz) and sweeps slowly (tens of minutes) toward deka- meter wavelengths (10 MHz). Type II emissions occur in loose association with major FLAREs and are indicative of a SHOCK wave moving through the solar atmosphere.
Type III. Narrow-band bursts that sweep rapidly (seconds) from decimeter to dekameter wavelengths (500 - 0.5 MHz). They often occur in groups and are an occasional feature of complex solar ACTIVE REGIONs.
Type IV. A smooth continuum of broad-band bursts primarily in the meter range (300 - 30 MHz). These bursts are associated with some major flare events beginning 10 to 20 minutes after the flare maximum, and can last for hours.
RECURRENCE. Used especially in reference to the recurrence of physical parameters every 27 days (the rotation period of the sun).
RIOMETER (Relative Ionospheric Opacity meter). A specially designed radio receiver for continuous monitoring of COSMIC NOISE. The absorption of cosmic noise in the polar regions is very sensitive to the solar low-energy cosmic ray flux.
SECTOR BOUNDARY. In the SOLAR WIND, the area of demarcation between sec- tors, which are large-scale features distinguished by the predominant direction of the interplanetary magnetic field, toward or away from the sun.
SHORT WAVE FADE (SWF). A particular ionospheric solar flare effect under the broad category of sudden ionospheric disturbances (SIDs) whereby short-wavelength radio transmissions, VLF, through HF, are absorbed for a period of minutes to hours.
SMOOTHED SUNSPOT NUMBER. An average of 13 monthly RI numbers, centered on the month of concern.
Central Meridian Distance (CMD). The angular distance in solar longitude measured from the central meridian.
SOLAR CYCLE. The approximately 11-year quasi-periodic variation in frequency or number of solar active events.
SOLAR MAXIMUM. The month(s) during the SOLAR CYCLE when the 12-month mean of monthly average SUNSPOT NUMBERS reaches a maximum. The most recent solar maximum occurred in December 1979.
SOLAR MINIMUM. The month(s) during the SOLAR CYCLE when the 12-month mean of monthly average SUNSPOT NUMBERS reaches a minimum.
SOLAR SECTOR BOUNDARY (SSB). The apparent solar origin, or base, of the interplanetary SECTOR BOUNDARY marked by the larger-scale polarity inversion lines.
SOLAR WIND. The outward flux of solar particles and magnetic fields from the sun. Typically, solar wind velocities are near 350 km/s.
SPORADIC E. A phenomenon occurring in the E REGION of the IONOSPHERE, which significantly affects HF radiowave propagation. Sporadic E can occur during daytime or nighttime and it varies markedly with latitude.
SUDDEN COMMENCEMENT(SC, or SSC for Storm Sudden Commencement). An abrupt increase or decrease in the northward component of the geomagnetic field, which marks the beginning of a GEOMAGNETIC STORM.
SUDDEN IMPULSE (SI+ or SI-). A sudden perturbation of several gammas in the northward component of the low-latitude geomagnetic field, not associated with a following GEOMAGNETIC STORM. (An SI becomes an SC if a storm follows.)
SUDDEN IONOSPHERIC DISTURBANCE (SID). HF propagation anomalies due to ionospheric changes resulting from solar FLAREs, PROTON EVENTs and GEOMAGNETIC STORMs.
SUNSPOT. An area seen as a dark spot on the PHOTOSPHERE of the sun. Sunspots are concentrations of magnetic flux, typically occurring in bipolar clusters or groups. They appear dark because they are cooler than the surrounding photosphere.
SUNSPOT GROUP CLASSIFICATION (Modified Zurich Sunspot Classification).
A - A small single unipolar SUNSPOT or very small group of spots without PENUMBRA.
B - Bipolar sunspot group with no penumbra.
C - An elongated bipolar sunspot group. One sunspot must have penumbra.
D - An elongated bipolar sunspot group with penumbra on both ends of the group.
E - An elongated bipolar sunspot group with penumbra on both ends. Longitudinal extent of penumbra exceeds 10 deg. but not 15 deg.
F - An elongated bipolar sunspot group with penumbra on both ends. Longitudinal extent of penumbra exceeds 15 deg.
H - A unipolar sunspot group with penumbra.
SUNSPOT NUMBER. A daily index of SUNSPOT activity (R), defined as R = k (10 g + s) where S = number of individual spots, g = number of sunspot groups, and k is an observatory factor.
SURGE. A jet of material from ACTIVE REGIONs that reaches coronal heights and then either fades or returns into the CHROMOSPHERE along the trajectory of ascent.
TWO-RIBBON FLARE. A FLARE that has developed as a pair of bright strands (ribbons) on both sides of the main inversion ("neutral") line of the magnetic field of the ACTIVE REGION.
TYPE I, II, III, IV. See RADIO EMISSION
U BURST. A fast radio burst spectrum of a FLARE. It has a U-shaped appear- ance in an intensity-vs.-frequency plot.
ULTRA HIGH FREQUENCY (UHF). Those radio frequencies exceeding 300 MHz.
UMBRA. The dark core or cores (umbrae) in a SUNSPOT with PENUMBRA, or a sunspot lacking penumbra.
UNIVERSAL TIME (UT). See COORDINATED UNIVERSAL TIME.
UNSETTLED. With regard to geomagnetic levels, a descriptive word speci- fically meaning that 7 < the Ap INDEX < 15.
VERY HIGH FREQUENCY (VHF). That portion of the radio frequency spectrum from 30 to 300 MHz.
VERY LOW FREQUENCY (VLF). That portion of the radio frequency spectrum from 3 to 30 kHz.
WHITE LIGHT (WL). Sunlight integrated over the visible portion of the spec- trum (4000 - 7000 angstroms) so that all colors are blended to appear white to the eye.
WHITE LIGHT FLARE. A major FLARE in which small parts become visible in white light. Such flares are usually strong X-ray, radio, and particle emitters.
WOLF NUMBER. An historic term for SUNSPOT NUMBER. In 1849, R. Wolf of Zurich originated the general procedure for computing the sunspot number.
X-RAY BACKGROUND. A daily average background X-ray FLUX in the 1 to 8 angstrom range. It is a midday minimum designed to reduce the effects of FLAREs.
X-RAY BURST. A temporary enhancement of the X-ray emission of the sun. The time-intensity profile of soft X-ray bursts is similar to that of the H-ALPHA profile of an associated FLARE.
X-RAY FLARE CLASS. Rank of a FLARE based on its X-ray energy output. Flares are classified by the order of magnitude of the peak burst inten- sity (I) measured at the earth in the 1 to 8 angstrom band as follows:
Class (in Watt/sq. Meter)
B I < 10.0E-06
C 10.0E-06 <= I <= 10.0E-05
M 10.0E-05 <= I <= 10.0E-04
X I >= 10.0E-04
ZURICH SUNSPOT CLASSIFICATION. A sunspot classification system that has been modified for SESC use.
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