UNDERSTANDING SOLAR TERRESTRIAL REPORTS PART II - INTERPRETING THE REPORTS REVISION 1.1 Cary Oler Solar Terrestrial Dispatch Box 357, Stirling, Alberta, Canada, T0K 2E0 ABSTRACT Part I of this document discussed the morphology of solar and geophysical phenomena. With this background now in hand, a discussion of the solar terrestrial reports themselves can begin. The purpose of this document is to explain the meaning of the various sections of the Solar Terrestrial Forecast and Review which are posted over the networks on a weekly basis. In addition, the purpose and application of the other reports, alerts and warnings will be discussed. After having digested the material in parts I and II of this document, the interested reader should have enough background and knowledge to begin actively applying the information in the reports. The reader is encouraged to digest part I of this document first (Part I - Morphological Analysis of Phenomena). It may be obtained upon request from "oler@hg.uleth.ca". May 7, 1991 UNDERSTANDING SOLAR TERRESTRIAL REPORTS PART II - INTERPRETING THE REPORTS REVISION 1.1 Cary Oler Solar Terrestrial Dispatch Box 357, Stirling, Alberta, Canada, T0K 2E0 1. Introduction The solar terrestrial reports posted over the networks presently consist of several reports, alerts and warnings. The Solar Terres- trial Forecast and Review is the only regular weekly publication. It contains a summary of conditions which occurred over the preceding week and includes forecasts for the next 10 to 20 days. This report is the one which will be concentrated on most heavily in part II of this document. It contains most of the data, forecasts and charts required and used in practical applications. The Major Solar Flare Warning is a brief message which is posted over the nets when a major flare (or flares) may be possible. These messages are only sent when regions on the solar surface are complex and threatening enough to produce potentially major energetic activity. They are therefore only intended to alert people to the increased potential for major flare activity. A Major Flare Alert is posted whenever a major energetic flare erupts on the sun (of class M5.0 or greater). Such an alert include a description of the event and any outstanding accompanying phenomena (ex. sweep frequency events, abnormally high radio bursts, etc.). If the flare could have a terrestrial impact, an impact assessment is given within the body of the alert message. The Major Geomagnetic Storm Alert is posted whenever geomagnetic conditions reach storm levels over middle latitudes. These alerts are not posted when storm conditions may exist for high latitudes, because high latitudes experience a significantly greater number of magnetic storms than do the lower latitudes and fewer numbers of people are affected by the high latitude storm periods than middle latitude storms. We begin our discussion of the solar terrestrial reports with an analysis of the solar terrestrial review section of the reports. We will attempt to cover the language used and discuss the format of this section of the reports. Following this, we will continue with a dis- cussion of the Monthly Solar Terrestrial Review followed by a discus- sion of the Geomagnetic Storm Alerts. The Major Solar Flare alerts May 7, 1991 - 2 - and warnings should be more easily understood after this document has been digested. The interested reader may need to re-read parts I and II of this document before aquiring a clearer understanding of these reports and their applications. A great deal of material is covered in this docu- ment and may not be fully understood the first time through. Applica- tion of these reports to the various inter-related fields may require practice and persistence in order to understand the impacts of certain events on specific terrestrial systems (such as radio communications). The interested reader is encouraged to do personal research on the subjects of solar activity, ionospheric properties, radio propagation and geophysical activity. Research in these areas will significantly enhance ones understanding and ability to interpret and apply the information contained in the publicized reports, alerts and warnings. 2. The Solar Terrestrial Forecast and Review This report is the primary report of solar and geophysical activity. It includes enough information and data to be of use to many people involved in radio communications, solar physics and geo- physics. It is issued once a week and contains summaries and fore- casts for the next 10 to 20 days. The report itself is compiled from raw data obtained from several sources. One of the major sources is the Space Environment Services Center (SESC), which serves as a major global data-collection center for space-related environmental data. The SESC is responsible for the solar terrestrial information which is posted on radio stations WWV and WWVH at 18 minutes past each hour. The data obtained from the various sources are all collected and analyzed by before being compiled into the reports which are publi- cally posted. Computer models, coronal maps and recurrent patterns are all examined and analyzed. The results are incorporated into the various forecasts in the reports. The actual prediction methods are beyond the scope of this paper. In this section, we will begin a systematic analysis of the vari- ous sections of the Solar Terrestrial Forecast and Review. Some of the terms contained herein may not be clearly defined. For those terms which are unclear, the interested reader is encouraged to con- sult the "Glossary of Solar Terrestrial Terms", available upon request from "oler@hg.uleth.ca". 2.1. Summary of Solar Terrestrial Activity This section of the report summarizes the highlights of solar and geomagnetic activity which took place over the preceeding week. Solar activity is given first, followed by a summary of geomagnetic and auroral activity. Following this, a summary of the HF and VHF propa- gation conditions for the preceeding week are given. Any particularly May 7, 1991 - 3 - severe solar or terrestrial activity will be given special treatment in this section. Basically, the summary of solar activity includes a discussion of those regions on the sun which exhibited abnormal signs of activity. This may include a description of major solar flares, noteworthy fila- ment disappearances, or unusually large coronal holes. It may also include a description of various unusual or impressive forms of limb- activity such as prominences, plage or faculae activity, or limb surges or flares. In all of the solar summaries, references will be made to specific regions postfixed with specific numbers (ie. Region 6354). These "region numbers" are simply sequential numbers assigned to active regions as they appear or are identified. The numbering of these regions was started by the SESC many years ago. The first region to be assigned was given a region number of 1. Consecutively identified regions were given numbers of 2, 3, 4 and so on. Each new region is given the next consecutive region number. In order for a region to be assigned a region number, it must qualify according to one of the following criteria: (1) If the region has a sunspot group which has a first-postion type-classification of C, D, E, F or H, it will be given a region number (see the "Glossary of Solar Terrestrial Terms for a description of the sunspot classifi- cation scheme). (2) If two or more reports confirm the presence of class A or B spots (again, see the above-referenced document), it will be given a region number. (3) If the region produces a solar flare, it will be given a region number. (4) If the region is "bright" in H-alpha light and exceeds 5 heliographic degrees in either latitude or longitude, it will be given a region number. These four criteria are used in determining what areas are assigned solar region numbers by the SESC and which areas are not. The vast majority of solar summaries include statements regarding the intensity (or class) of specific flare events. Flares are categorized using two types of classifications. The first method categorizes a flare with regards to its output energy at X-ray wavelengths measured by orbiting satellites. The second method categorizes flares according to their size and brightness at optical wavelengths (observed using monochromatic H-alpha light filters). Both of these flare classifications are described fully in the "Glos- sary of Solar Terrestrial Terms." Refer to it for more information. The positions of all solar regions and events are given according to the format: AxxByy, where xx represents a latitude (in degrees), "A" represents either the "N" (North) or "S" (South) solar hemisphere, "yy" represents the solar longitude given in degrees east or west of the central solar meridian, and "B" represents either "E" (East) or "W" (West) of this central meridian (ex. N26E72). The exact center of the visible sun represents the origin where the longitude is measured from. The extreme limbs of the solar disk represent longitudes of 90 degrees (either East or West, depending on which limb you look at), while the extreme poles of the sun represent 90 degrees latitude May 7, 1991 - 4 - (either North or South, again depending on which hemisphere is observed). It should be noted that the orbit of the earth carries us slightly above and below the suns rotational equator. During six months of the year, we are above the northern portion of the solar equator, while during the next six months, we fall below the southern portion of the solar equator. Near the equinoctial periods (spring and fall), our orbit places us at our maximum distance above or below the solar equator. If, at these times of the year, the earth were moved in a straight line toward the center of the sun, the earth would make contact with the suns surface at a latitude of about 7.3 degrees with respect to the solar equator. Although these periods do not exactly coincide with the each equinox (ie. maximum southerly extent is achieved on 07 March, while maximum northerly extent is reached on 09 September), they do coincide within a month of the equinox. These latitudinal changes are important, since it alters the way we must observe the sun. During the equinox periods, the center of the sun as we see it is actually about 7 degrees to the north or south of the actual solar equator. If this were not taken into account, the measured positions of sunspots and other surface features would be grossly in error. The important point to remember when studying the positions of sunspot groups is that the coordinates given represent the position of the sunspots relative to the rotation axis of the sun as viewed from earth. For example, a sunspot group located at a position of N21E62 represents a position 21 degrees north of the solar equator, and 62 degrees east of the solar central meridian (or 28 degrees away from the eastern limb [ 90 - 62 = 28 ]). Since the sun rotates from east to west, all sunspot groups and other observed features rotate in the same direction. More specifi- cally, the sunspots rotate at an average speed of about 13 degrees per day. So the sunspot group located at N21E62 would be located at N21E49 the following day, and N21E36 the day after that. They may also occasionally drift in latitude, although the drift in latitude is negligable most of the time. Following the solar summary, the summary for geophysical and auroral activity is presented. These summaries should be mostly self-explanatory with the exception of possible notes regarding mag- netic fluctuations. In summaries of particularly intense magnetic activity, state- ments may be made regarding the maximum intensity of some of the mag- netic fluctuations observed during the period being reviewed. These summaries will generally involve the terms nanotesla and/or gamma, which are synonymous. The intensity of magnetic fluctuations are latitude-dependent. Higher latitudes naturally experience more intense magnetic fluctuations than the lower latitudes. Southerly middle latitude regions consider magnetic fluctuations of 500 nanotesla (nT) to be very severe, while high latitudes may consider May 7, 1991 - 5 - fluctuations of 2500 nT to be very severe. The magnetic A and K indices have been developed to aid in equating the intensity of mag- netic fluctuations over wide latitudes. For example, a magnetic fluc- tuation at Anchorage Alaska may be considered to be as "equally intense" as a similar fluctuation in California if the A or K-indices for both locations are equal, even though the actual magnitude of the fluctuations at Anchorage are much higher than the corresponding fluc- tuations in California. A K-index of 4 at Yellowknife in northern Canada may correspond to a magnetic fluctuation of 160 nT, while a K- index value of 4 at Boulder Colorado may correspond to an actual mag- netic fluctuation of only 50 nT. Both fluctuations may be considered equally severe based on how often fluctuations of that magnitude are usually encountered for that latitude. Yellowknife may encounter fluctuations of 50 nT on a daily basis whereas Boulder may not encounter magnetic fluctuations of that magnitude for weeks. Hence the need for indices which can equalize the latitudinal dependencies. Notes of auroral activity in the review section of the report are generally limited to descriptions as described in the Glossary of Solar Terrestrial Terms. However, for extraordinary events such as occur during auroral storms, a more detailed examination of auroral activity may be given. Such descriptions may include auroral types, color fluctuations, pulsations or movement patterns of auroral forms. All of these descriptions are contained in the Glossary mentioned above and part I of this document. Notes regarding HF and VHF propagation are usually confined to brief accounts of overall global conditions. These conditions are generally rated as either above normal, normal, below normal or very poor. Above normal propagation indicates strong signals which are abnormally stable. Above normal propagation is most often associated with good to very good DX potentials. Normal propagation denotes nor- mal conditions after considering the season and the position within the sunspot cycle. It is compared with the average conditions experi- enced over previous seasons and solar cycles. Below normal propaga- tion is usually associated with increased geomagnetic activity and is more consistent with signals of lower quality, less stability, and weaker strengths. Chances for DX drop noticably during periods of below normal propagation, except for the VHF bands where an increase in DX may actually occur. Very poor propagation is most often associ- ated with magnetic storms or PCA events where signal absorption, fad- ing and instability dramatically affect the quality of signals. Dur- ing intense storms, localized blackout conditions may occur. This term may be used in these instances to denote exceedingly high signal absorption levels. Again, the exception is VHF frequencies, where long-distance communications often improves during periods of high HF absorption or blackout periods. However, the quality of the VHF sig- nals may be quite poor despite the enhanced communication range. 2.2. Short Term Solar Terrestrial Forecast This section of the report follows the same basic structure as the review described in the last section, except that predictions are given instead of reviews. The predictions are made using the same May 7, 1991 - 6 - methods described in the preceding sections, but are translated from tables and charts into sentence form. This short-term prediction section is intended to point out the highlights which can be expected over the coming week. Overall global conditions are given in this section of the report. Therefore, the person interested in radio communications or auroral activity should keep in mind the nature of this section. It is not intended to list the possible localized phenomena which might occur. Just the general overall global conditions are stated. The short term forecasts should be used as a guide only. The art of predicting geomagnetic storms and major flares is by no means an easy process. There are many variables which are unknown and processes which are not fully understood yet. Although we have made great advancements in the fields of solar physics and geophysics, we have a long way to go in the area of predictions. The forecasts presented in these reports may therefore be in error at times. They are, however, based on the most current models and the most recent data. 2.3. Solar Region Summary The summary of solar regions is the section of the report which is in tabular form and includes the region numbers, sunspot sizes, sunspot classes, angular extents, magnetic configuration, etc. This section is of great value to those who are tracking sunspot groups or watching for signs of growth or increased magnetic complexity and/or flaring. Although each of the aspects of this table are described in the Glossary of Solar Terrestrial Terms, we will elaborate on some of the more vague terms of in this section. Each solar region is given a number and its position on the solar disk is measured (as was described above). This identifies and defines the exact position of a solar region on the sun. The posi- tional description (ie. the latitude/longitude description) is rela- tive to the hemisphere of the sun which is in view. That is, the longitude of a solar region is relative to the center of rotation as seen from the earth. This places the 00 degree longitude (ie. the central meridian) continuously at the center of the sun (in a line stretching from the north solar pole through the center of the disk as observed from the earth, to the south solar pole). All of the solar regions rotate while the longitudinal lines remain stationary. This method of marking positions of sunspots and other phenomena is very adequate, but fails to describe the position of sunspots on a solar global basis with respect to a fixed 360 degree longitudinal system (as is employed for the Earth). In order to solve this problem, a system was developed to begin mapping active regions on a fixed solar geographical basis. The actual longitudinal position of sunspots are therefore recorded in two different ways. The first way (described in the preceding sections) May 7, 1991 - 7 - enables us to determine how far away a solar region is from the cen- tral meridian. It effectively separates the observable solar disk into an east and a west hemisphere with the dividing line coinciding with the central solar meridian. The second method is analagous to the way we have mapped the Earth, with fixed lines of longitude divid- ing up the entire sphere. The figures in the region summary under the heading "LO" represent this second mapping method. This second method is useful in determining the movement of a sunspot region compared to the flow of gases around the sunspot region. Sometimes, sunspots will move slightly slower than the gases around the spot, which will gradually cause the longitudinal location of the sunspot to change. Sometimes, they move faster than the gases normally do at that location. So by observing these longitudinal values, you can determine whether a sun- spot is moving faster or slower than usual. This method of referencing sunspots is also useful in identifying regions of the sun which are abnormally active. During the years of maximum solar activity, the sun often exhibits longitudinal regions which are more active than other longitudes. During solar maximum years, there are often two areas of abnormal activity separated by about 180 degrees. By observing the positions of sunspots using this method of mapping, the active solar longitudes can be discovered. This is valuable for those who want to forecast solar activity. Like- wise, some solar longitudes are often regions of enhanced corpuscular emissions (ie. regions where matter is ejected from the sun), which can significantly affect radio communications and geomagnetic activity. Plotting the positions of these active longitudes can also be of tremendous aid in predicting recurrent storms or periods of increased geophysical activity. The column in the table labelled "Z" represents an optical clas- sification scheme for sunspots and sunspot groups. The details of this classification method are given in the Glossary of Solar Terres- trial Terms. The interested reader is directed to consult this docu- ment for more information. It categorizes the optical shape and com- plexity of sunspot groups. The column labelled "LL" represents the angular extent of the sunspot group. Angular extent is given in solar degrees. Comparing this value with the number of spots within the region (denoted by the "NN" column of the table) yields the density of the group. The den- sity is important because it is an indirect measure of the gradients of magnetic fields within the region. High gradients produce more frequent and more severe solar flares, while weak gradients are usu- ally associated with less-compact spot groups which produce less severe and less frequent flares. The "MAG TYPE" or magnetic-type of sunspot groups as noted in the last column of the table can also be used to determine the magnetic complexity and magnetic gradients within active regions. Consult the Glossary mentioned above for more information regarding these classif- ications. May 7, 1991 - 8 - In addition to details on spot groups, this region of the report also enumerates those areas which are not associated with sunspots, but contain areas of enhanced H-alpha plages. These regions are assigned region numbers according to the rules noted above. These regions are often the sites for sunspot formation. They may also be associated with old regions which are decaying. 2.4. Geomagnetic Activity Summary Following the solar region summary, a graphical analysis of recent geomagnetic activity is presented. This graphical table charts planetary geomagnetic activity as it is recorded for many magnetic observatories around the world. It includes recent data for the last 96 hours up to the time the report was compiled. The use of planetary geomagnetic activity gives a good indication of global activity from the high latitudes to the low latitudes. This chart has been constructed from each of the 3-hourly K-index values reported by all of the participating magnetic observatories. Each graph line, therefore, represents a 3-hour period of time. The time on this graph is in Universal Time (relative from Greenwhich, England). Therefore, the first graph line of this chart represents the activity occurring from 00 UT to 03 UT (actually, from 00 UT to 02:59:59 UT). The second line represents activity occurring from 03 UT to 06 UT, and so on. The left-hand side of the chart relates the levels of geomagnetic activity to the approximate corresponding severity of activity. This activity is defined from "Very Quiet" levels, which corresponds to magnetic K-indices of zero, to "Extremely Severe" levels which corresponds to magnetic K-indices of about nine. The right-hand side of this chart serves as a very rough guide to the potential severity of magnetic-induction that might be experienced during corresponding levels of magnetic activity. By "magnetic induc- tion," we mean the severity of magnetic fluctuations necessary to begin influencing ground-based systems such as electrical powerline systems, telecommunications systems, pipeline networks, etc. This end of the chart is not intended to be a definitive classification, but rather is only meant to serve as a potential indicator to possible magnetic-induction. There are a great many variables that must be taken into account before magnetic fluctuations can be qualitatively classified as capable of inducing electrical currents into ground- based systems. These variables are not considered in this chart. Only the general level of magnetic fluctuations are considered and are related to possible magnetic induction. Such localized parameters as air-earth conductivity, ionospheric current system parameters, electr- ical field configuration, ground resistivity, and ground-based system network configurations must be considered (among other things) before true hazards regarding magnetic induction can be determined. There- fore, this area of the chart should be used only as a very rough guide. Nothing more and nothing less. It should be noted, however, that magnetic fluctuations rated as K-indices greater than 6 generally become capable of wide-spread electrical current induction. Storms May 7, 1991 - 9 - with fluctuations this high are usually capable of influencing ground-based systems over wide areas. The geomagnetic activity graphed in this chart represents the peak global magnetic activity observed during the respective periods. It does not represent average magnetic activity. This is important to realize. These K-index values are not the same values reported on radio stations WWV and WWVH. The values reported by these stations represent the magnetic activity occurring at Boulder, Colorado. Since this chart is derived from measurements of geomagnetic activity around the world (not at one specific location), the planetary values are more valuable and applicable on a global scale. 2.5. 10-Day Geomagnetic Activity Forecast This chart graphs the expected levels of planetary geomagnetic activity over a 10-day period. Each day is separated into three 8- hour segments. Each line of the chart therefore represents one eight hour interval of time. This chart graphs expected conditions relative to Universal Time. That is, the first line after each date dividing line represents expected conditions between 00 UT and 08 UT for that day. The middle graph line represents conditions expected between 08 UT and 16 UT. The last graph line for each day in the chart represents the magnetic activity that is expected from 16 UT to 24 UT. This chart should be more easily interpreted than the previous geomag- netic activity summary chart. It is certainly more valuable. The predictions are based primarily on data regarding coronal holes, potential recurrent activity, diurnal trends and potential solar activity influences. The transient solar component (ex. major flares) are not included as part of this prediction, since flaring is extremely unpredictable and forecasts of potential major flaring in excess of a day or two is very unreliable. 2.6. Graphical Analysis of Solar Activity The graphical chart summarizing solar activity is produced each week for a 60-day period. This period covers two complete solar rota- tions and is sufficient to show the cyclic behavior of solar activity from one cycle to another. The solar flux (the intensity of solar radio noise observed at 10.7 cm wavelengths) is plotted in this graphical analysis. The solar flux represents the slowly varying component of the sun (see part I) and is strongly correlated with the number and intensity of sunspot groups on the solar surface. The higher the number of sun- spots visible, the higher the solar flux. As sunspots disappear behind the western solar limb, the solar flux decreases. The 10.7 cm solar radio flux is therefore a good indicator of the overall state of the observed solar environment. Under normal conditions, the plot lines for the solar flux are plotted using asterisks (*). However, on days when major flares erupt, these plot lines are changed from asterisks to "F"'s. This May 7, 1991 - 10 - enables readers to determine the period during the rotational cycle of the sun when major flares occurred. In most cases, it will be observed that most of the major flare activity occurs during the rota- tional peak of each cycle. There are, however, exceptions to this, as will occasionally be noted. Plot lines are only changed from asterisks to F's when major flares erupt which meet or exceed an X-ray intensity of class M5.0. A flare of class M4.9 may be a fairly major event, but is not considered a major class flare since it never reached M5.0 class intensities. Most flares, however, are either above or notably below this limit. There are many more flares of class M3.0 intensity than there are flares of class M4.0 intensity. Most major flares, therefore, are observed to occur above this M5.0 transition level. Very few are borderline cases. 2.7. 20-Day Solar Activity Forecast The 20-day solar activity forecast chart is constructed based on the activity which was observed over previous solar rotations, in addition to the status of the regions which are currently visible on the sun. The intensity, size and number of sunspots in each region are all analyzed (among other things) before this prediction chart is produced. The plot lines of this chart represent the solar flux levels which are expected to occur throughout the 20-day period covered by the chart. The actual flux values will frequently differ from the actual flux values observed, since predicting the activity of solar regions is still very difficult to do beyond approximately one week. Regions behind the sun may be developing which could significantly alter the shape of the prediction charts. These regions cannot be seen or detected in any way until they approach the eastern limb of the sun. Hence, these solar activity predictions should be used only as a guide. The predictions are generally good at forecasting the times when the solar flux will peak or reach its minimum during a rotational cycle, and this can be of tremendous value to people interested in the level of ionospheric ionization which is propor- tional to the solar flux. Flares are not included in this prediction of solar activity. Flares are extremely difficult to predict, even in the short-term. Our knowledge of flares has grown rapidly since the early part of this century. However, our knowledge is still not sufficient to reliably predict the occurrence of major flares over periods in excess of several days. Therefore, this graphical solar activity forecast is limited to a treatment of the solar flux only. As far as flares go, an increasing solar flux generally increases the risk for major flares. The higher the solar flux values, the greater the risk for major flares, since the solar flux is directly related to the number and intensity of active regions on the sun. May 7, 1991 - 11 - 2.8. HF Radio Signal Propagation Predictions This section of the Solar Terrestrial Forecast and Review involves the propagation of high-frequency (HF) radio waves over long-distances. It is a forecast of the expected quality of HF radio signals travelling over long-distances. The quality of radio signals is divided into several areas. Radio signals which have outstanding strength and stability over long-distances are categorized as excellent. These conditions are rarely observed and occur more frequently over the lower latitudes than the high latitudes. Signals which are abnormally strong and stable over long-distances are classified as very good. These are above-normal conditions when considering the time of year and the state of the solar cycle. Signals which are normal for the current season and state of the solar cycle are given a good classification. These signals are generally stable and relatively strong considering the time of year, but may suffer some minor fading or distortion. Noise may also be somewhat of a factor, but is generally tolerable. When signals fall below the normal quality, they may be categorized as poor. Poor radio signals over long distances are those which experi- ence moderate to strong fading or flutter, abnormally high levels of absorption, or increased levels of noise (or any combination of the above). Long-distance propagation is still usually possible in these cases, but suffer significantly increased levels of distortion which may hamper attempts at long-distance voice contacts. Very poor radio signal propagation occurs when signals experience severe fading and flutter, high levels of absorption, high levels of noise and high lev- els of distortion (or any combination of the above). Long-distance communication usually becomes very difficult during these periods and may not be possible at all over some regions. When radio signals are unable to be propagated at all over long distances, or are very poor over short to moderate distances, communication is rated as being extremely poor. This category will only usually be encountered at higher latitudes and during periods of intense geomagnetic storming. In these forecasts, each day is composed of three 8-hour inter- vals. Since these forecasts are also UT-correlated, the first plot line of each day represents the interval between 00 UT and 08 UT. There is one very important note which should be understood by all those who use these forecasts as guides. The local time of attempted communications is a very important factor in long-distance communications. This factor is not considered in these forecasts, nor could it be easily incorporated into these charts. The charts are intended to be globally valid. Hence, the obvious diurnal enhancements which occur cannot be included in this global forecast. The person interested in radio communications is already expected to have a knowledge of the diurnal enhancements for his or her region. These charts, therefore, are only intended to aid the interested communica- tions operator in determining the potential times when enhanced radio communications may be possible. It is not intended to reflect the diurnal enhancements which occur, unless the enhancements are signifi- cant. May 7, 1991 - 12 - The forecasts are based heavily on recurrent geomagnetic and auroral activity, which are primary factors in determining the quality of radio signal propagation conditions. The intensity of ionization of the appropriate ionospheric layers are also examined when preparing these charts. This section is separated into three charts for the high latitude regions, middle latitudes and the low latitude regions. Global separation of areas into latitudinal zones is required since the characteristics and quality of radio propagation differ from zone to zone. To make the best use of these charts, the interested reader is encouraged to follow this procedure. Determine the path endpoint of your signal. That is, determine the location where you want your transmitted signal to be received. This is the path endpoint or des- tination. Your transmitter location is the startpoint or source. Now draw a great-circle between the startpoint and the endpoint. Next, determine the most northerly geographical coordinates of the great- circle connecting the startpoint and the endpoint (we will call this point the northpoint) and note the UT time of your transmission. After calculating this information, determine what latitudinal zone the path northpoint lies in. Finally, consult the HF propagation prediction charts and select the latitudinal zone chart that corresponds to the latitude of the path northpoint. Using the UT time of the transmission, select the appropriate day in the chart and exam- ine the plot line which corresponds to the UT time of the transmis- sion. This is the propagation quality that can be expected for that path at that time. Note, however, that you must also consider the local time of day of your transmission, and the local time of day at the path endpoint in order to determine the diurnal characteristics that should be expected. This information is not given in these charts, but should already be known by the radio operator who is fami- liar with the diurnal conditions which occur at his or her site. In order to be most accurate, this diurnal component must be considered together with the propagation predictions. Therefore, if your transmission were conducted during a period of time when you know your signal is enhanced, a truer representation of the propagation quality may be obtained by examining the prediction charts (using the method above) and increasing the quality of propagation up by no more than one level (ie. from "fair" to "good"). For example, suppose you wanted to communicate between Florida and Great Britain. Florida is a low latitude zone and Great Britain is a middle-latitude zone. Next, we draw a great circle between Florida and Great Britain. If you have no numerical method of doing this, you can approximate the great circle path by stretching a narrow piece of paper on a globe of the world such that the ends of the piece of paper intersect the path startpoint and endpoint (the paper should be bent so that one of its edges lays flat on the surface of the globe). The path that this paper makes on the globe will be curved and represents the great-circle path between Florida and Great Bri- tain. By examining the great circle path, we are able to see that the most northerly geographical position on the path is at Great Britain. May 7, 1991 - 13 - Since Great Britain is a middle-latitude region, we consult the middle latitude prediction chart. If you were to transmit to Great Britain at 10:00 UT on Thursday, you would examine the middle plot line of the middle-latitude prediction chart for Thursday. Since 10:00 UT in Florida is near the time the sun rises, you might expect propagation conditions to be enhanced somewhat (depending on your location, time of year, etc.). If this were the case, the prediction charts may underestimate the quality of propagation you might expect during that period. On the other hand, if the time were about 05:00 UT Florida time, conditions might be worse than those suggested by the charts. So local time at the startpoint and endpoint are both important when determining possible diurnal influences and might need to be con- sidered. In many cases, the great-circle path of the signal may travel over more northerly latitudes than the startpoint and endpoint. For example, a transmission between central Canada and Great Britain may result in a great-circle path that passes through the high-latitude regions before reaching Great Britain, even though both the startpoint and endpoint are middle-latitude stations. In these cases, the most northerly position of the great-circle path should be used. If the signal path (or the two path endpoints) are near the boun- daries of two latitudinal zones, a mix of the propagation predictions for the two latitudinal zones may be required to yield a more accurate representation of propagation conditions. For example, if a transmis- sion were conducted between Denver and Atlantic City, which both border as low and middle latitude locations, both of the charts for the low and middle latitude zones should be analyzed and mixed in order to determine the conditions which might be expected over that path. Since the distances in this latter example are relatively small (compared to the latter examples), the northpoint of the signal path will not significantly affect propagation conditions. This is why we only examined the latitude of the startpoint and endpoint. For greater distances, the northpoint must be considered. 2.9. VHF Propagation Prediction Charts The prediction of potential VHF DX is not as simple as it is for HF. VHF signals have properties which are not usually affected by the ionospheric layers. In our context, "VHF" will be considered those frequencies ranging from about 50 MHz to 300 MHz. For information regarding the major types of VHF propagation which are possible, con- sult part I of this document. A great deal of information can be extracted from the VHF predic- tion charts. Information pertaining to HF communications is also imbedded in these charts. As was done for the HF prediction charts, the VHF predictions are separated into three charts; one for each of the major latitude zones. The upper part of the chart forecasts the quality of potential distant VHF signals. It does not depict the quality of locally transmitted VHF signals. This is an important point to remember. May 7, 1991 - 14 - Locally transmitted "line of sight" signals can not be affected and are not affected by geomagnetic activity, auroral activity, or SIDs. Therefore, only the distant signals which can be affected by these phenomena are considered in these charts. As was the case with the other propagation prediction charts, the VHF prediction charts are separated into groups of three 8-hour daily intervals. However, the reference of time used in these charts is LOCAL time, not UT time. That is, the first line of each day in these charts represents the period between local midnight and 8 am local time. This is the only major difference between these charts and the HF prediction charts. It is also a very important diference. To use these charts, simply determine what time it is locally and examine the appropriate day in the charts and the appropriate plot line within that day. The top portion of the prediction charts define the quality of VHF signals which can be expected over larger dis- tances. The bottom chart describes the probability of experiencing conditions capable of supporting VHF DX. Both charts use the same reference of time (local time). The SID ENHANCEMENT chart at the upper right-hand corner describes the probability of a SID (sudden ionospheric disturbance) temporarily enhancing VHF communications. The probability of SID enhancements increases with solar activity, but decreases with increasing latitude. This data is also of value to the HF radio operator, since SIDs almost always produce short-wave fades (SWFs) which can disrupt HF communications. Since SIDs are sporadic and very unpredictable (due to the unpredictable nature of solar flares), they are predicted as percentages in these charts. SID-related VHF enhancements do not occur on the dark-side of the earth. Neither do SWFs. Therefore, these SID prediction charts only apply to those locations which are still well illuminated by the sun. The AURORAL BACKSCATTER prediction charts are of value to the VHF radio operator. Auroral backscattering (as was described in part I of this document) is possible at VHF frequencies during times of increased geomagnetic and auroral activity. These prediction charts define the approximate probabilities of VHF propagation via auroral backscattering over the various latitudes. VHF signals which are pro- pagated via aurorae can travel fairly large distances. Propagation via aurorae is therefore considered a potential method of DXing on VHF frequencies. It is, however, a fairly local and sporadic phenomena and is usually not a widely-encountered form of propagation until auroral and geomagnetic activity reaches significant storm levels. To make use of these VHF charts, simply consult the appropriate plot lines according to what day it is and the local time. The HF operator may be able to determine what days will prove less reliable as far as day-time propagation goes by examining the probability for SID related SWFs. Most SWFs, however, are only temporary and do not pose a significant threat to most HF operators, unless the flares which produce them are particularly intense. May 7, 1991 - 15 - 2.10. Auroral Activity Predictions Auroral activity is predicted for the three major latitude zones identified earlier. Since the auroral oval itself is situated within the high-latitude zone, the high latitudes will naturally experience significantly more auroral activity than the middle and low latitudes. The prediction charts for auroral activity are most useful to those people interested in either observing auroral activity, pro- pagating radio signals using aurorae, or for people interested in determining the extent of magnetic fluctuations occurring near areas of auroral activity. Since auroral activity migrates equatorward during geomagnetic storms, locations which may usually be outside of the auroral zone itself may occasionally find themselves inside the auroral zone during periods of increased geomagnetic activity. Likewise, as auroral activity shifts equatorward, low latitudes may be able to begin spot- ting the activity. These prediction charts can be used to determine whether or not potential auroral activity may be intense enough to be seen at low latitudes, or whether auroral activity will be dull and inactive or bright and very active. To use the charts, simply examine the appropriate chart (ex. if you're a middle latitude location, examine the middle-latitude chart) and select the column on the day you are most interested. The first plot line of each day represents the evening twilight period. This is the period between when the sun sets and before the sky gets com- pletely dark. The second plot line represents the midnight sector where the sky remains completely dark (excluding effects of lunar phase). The last plot line is the morning twilight period and represents the time when the sky just barely begins to brighten until the sun rises. The phase of the moon is not taken into consideration in these charts. The moon can have a profound effect on the visibility of auroral activity, but does not affect auroral activity itself. That is, just because the moon may be blocking out light of auroral activity does not mean that auroral activity is not in progress. Indeed, intense auroral storms can occur during a full moon as easily as they can during new moons. Therefore, these charts represent the occurrence of auroral activity regardless of lunar phase. The intensity of auroral activity is measured according to several parameters. Each of these parameters are discussed in the Glossary of Solar Terrestrial Terms. In their most basic form, the parameters (low, moderate, high, etc.) may be considered the bright- ness of auroral activity during dark-sky conditions (ie. periods of new moon). However, actual visual movements, color changes and aerial extent are also considered when classifying auroral activity in these prediction charts. May 7, 1991 - 16 - 3. Monthly Solar Terrestrial Review Every month, statistics and information regarding solar and ter- restrial activity for the preceding month are gathered and compiled into a document called the Monthly Solar Terrestrial Review. This document contains not only information regarding the nature of activity of solar and geophysical phenomena during the preceding month, but also includes a six month solar cycle outlook. This can be of great value to the radio operator who is interested in determining what conditions might be like six months down the road. It can also be of interest to the astronomer who may enjoy searching for auroral activity or solar flares. In addition to the written summary, a statistical summary of the previous month is given in tabular form, summarizing all of the major solar parameters (ie. solar flux, sunspot numbers, active region sizes, numbers and types of flares, etc.). This report is intended to serve as a general summary regarding activity and phenomena encountered during the previous month. It can provide some interesting results if data from the report is charted or graphed or statistically analyzed. 4. Geomagnetic Storm Alert This alert is posted over the nets whenever magnetic storm condi- tions reach or exceed minor storm levels over middle latitudes. This alert may be preceded by a warning if a magnetic storm is expected to occur but hasn't yet begun. These alerts always summarize the current level of activity and may also include descriptions of outstanding geomagnetic activity occurring prior to the time the alert was issued. A brief textual forecast of the expected geomagnetic activity is also included with these reports. This effectively serves as an intermediate forecast which can be of value during geomagnetic storm periods when conditions change rapidly. Full HF and VHF summaries are included with the storm alerts and all following storm information updates. This information is of value to those who rely on ionospheric and/or auroral-related communica- tions. 5. Availability of Additional Services Solar Terrestrial Dispatch also supplies other services not men- tioned in this document, which may be of interest or value to certain individuals or organizations. One of the additional services provided are GIC forecast and warning services for individuals or organizations May 7, 1991 - 17 - requiring predictions of possible Geomagnetically Induced Currents caused by magnetic storming over the high and/or middle latitudes. Forecasts are produced on a weekly basis, and warnings are issued whenever conditions (or expected conditions) warrant. For more information on this or other services not mentioned in this document, feel free to contact Solar Terrestrial Dispatch by writing to: Solar Terrestrial Dispatch, Box 357, Stirling, Alberta Canada, T0K 2E0. Alternatively, for those of you with access to one of the large electronic networks, you may contact: oler@hg.uleth.ca for more information (this is an Internet address). Significant enhanced services will soon be available from Solar Terrestrial Dispatch for individuals and researchers interested in obtaining up-to-the-minute solar terrestrial data (ex. x-ray data, proton data, geomagnetic data, flare-related data, ionospheric data, etc). For more information or questions regarding the availability of these or other services, consult Solar Terrestrial Dispatch as given above. 6. Concluding Remarks The solar terrestrial reports which are posted over the networks contain a great deal of information. Understanding them may take some time. Applying the information contained in them may take even longer. This document (part I and II) was developed to help explain the nature and format of these reports. It was also developed to help those who are interested in interpreting and applying the information contained in the reports. It is hoped that this document will help those who are interested in better understanding the solar terrestrial reports. Questions and/or comments are welcome. If any further explanations are required which have not been adequately covered in this document, feel free to send an inquiry to "oler@hg.uleth.ca". We have learned a great deal over the years regarding the impacts of solar activity on our terrestrial sphere. But there is still a great deal more we need to learn before we can expect to master the art of predicting the impacts of solar activity on the earth. Our curiosity drives us further and our lust for knowledge quickens our pace of learning. With developements of new devices and technologies, we are steadily edging closer to understanding both our terrestrial environment and the vast environment of space. The educational insti- tutions and research organizations are the backbones of our knowledge and growth. We must therefore respect these institutions, support them, and encourage them so that our body of knowledge is able to con- tinue expanding into the limitless realm of science. May 7, 1991 - i - Table of Contents Introduction .................................................... 1 The Solar Terrestrial Forecast and Review ....................... 2 Summary of Solar Terrestrial Activity ........................... 2 Short Term Solar Terrestrial Forecast ........................... 5 Solar Region Summary ............................................ 6 Geomagnetic Activity Summary .................................... 8 10-Day Geomagnetic Activity Forecast ............................ 9 Graphical Analysis of Solar Activity ............................ 9 20-Day Solar Activity Forecast .................................. 10 HF Radio Signal Propagation Predictions ......................... 11 VHF Propagation Prediction Charts ............................... 13 Auroral Activity Predictions .................................... 15 Monthly Solar Terrestrial Review ................................ 16 Geomagnetic Storm Alert ......................................... 16 Availability of Additional Services ............................. 16 Concluding Remarks .............................................. 17 May 7, 1991