Solar Help Page

By clicking on the icons or the sub-section headings you will find explanations of the data and information presented in the Solar Section. For general terms and definitions please refer to our Glossary of Solar Terrestrial Terms.

Note: The indices and icons below are SAMPLES ONLY.

Day-Night Location

Clicking on Day-Night Location gives a world map showing the portions of the globe presently in daylight or darkness. This is of interest especially for HF Communications as the daylit and night-time ionosphere is dramatically different. In particular it is important to know the location on the globe of local dawn and dusk (grey regions) since communication circuits which pass from daylight to darkness, traversing one of the grey regions, can be particularly poor. This is the case when the Absorption Limiting Frequency (ALF) at the transmitter (daylit ionosphere) approaches or exceeds the Maximum Usable Frequency (MUF) at the receiver (night- time ionosphere). See also Introduction to HF Radio or the PDF file.

Solar Region Data

Solar Region Data lists the sunspot regions presently visible on the solar disk. A sunspot region contains one or more sunspots. Sunspots are transient, highly active dark spots on the solar surface resulting from very intense, frustrated magnetic fields. As the sun rotates, with a period of about 27 days, sunspot regions move from left to right across the earth-ward face of the sun, appearing under Current region status, before moving around to the farside. After a further 13 to 14 days the sunspot region may emerge once again on the eastern limb (left hand edge of the solar disk) if it has not dissipated. Returning region last day status refers to the state of a possible returning sunspot region just before it disappeared from view around the western limb (right hand edge of the solar disk) and gives its expected date of return. Sunspot regions are numbered sequentially as they appear with regions which return from the far- side being re-numbered. With each region is given:

• flares - major x-ray flares associated with the region
• level - see activity level
• lat long - the location on the visible solar disk with 0 latitiude being the solar "equator" and -90 and +90 the eastern and western limbs (left and right hand edges of the solar disk) respectively
• area - a measure of the size of the region
• mag. - the magnetic classification of the region
• state - whether the area is STABLE, GROWING or DECLINING.

Sunspots

Sunspots are the source of solar flares and are closely associated with strongly ionising radiation. Ionisation of the ionosphere by solar radiation makes HF communication possible. Click Here for related entries in the Education section.

Level of Solar Activity

The observed or predicted activity level of a sunspot region or of the sun as a whole is based on the number and strength of x-ray flares within a 24 hour period. Classifications are as follows:

• Very Low - x-ray events less than C-class
• Low - C-class x-ray events
• Moderate - isolated (one to 4) M-class x- ray events
• High - several (5 or more) M-class x-ray events, or isolated (one to 4) M5 or greater x-ray events
• Very High - several (5 or more) M5 or greater x-ray events

See Also:

• solar X-ray Flare Classes
• X-ray radiation intensity, provided by the US GOES18 satellite
• entries on x-ray flares in the Education section

Magnetic Classification

The Magnetic Classification of a sunspot region describes the distribution and complexity of its magnetic field structure. Possible classifications are:

• ALPHA - unipolar
• BETA - bipolar, possessing well- defined positive and negative magnetic poles within the region
• BETA-GAMMA - a bipolar region of increased complexity
• GAMMA - an even more complex region with positive and negative poles scattered throughout the region
• DELTA - indicates the presence of a very closely separated pair of spots which have opposite polarity

Increasing magnetic complexity corresponds to an increased chance of flare activity.

Solar Activity Plot

This shows the observed solar activity each day over the past month.

Solar Wind Speed

Clicking on the Solar Wind Speed icon on the main Solar page or on the Solar menu list gives information on the state of the solar wind. There are 3 sections:

1. Solar wind parameters gives the current wind velocity, Bz (the north/south component of the IMF) and the wind density. Parameters are updated every 10 minutes.
2. The green-yellow-red diagram gives a quick visual indication of the likelihood of the current solar wind parameters causing a geomagnetic distubance. High solar wind speeds and strong south pointing (negative) Bz are associated with geomagnetic storms on earth. The red area indicates an approximate region in which disturbed conditions would be expected.
3. The curves at the bottom of the page give the variation in wind velocity and Bz component over the last 2 hours.

Solar Wind

The Solar Wind is the outward flow of solar particles (electrons, protons and alpha particles) and magnetic fields from the sun towards the earth. The solar wind is a result of the magnetic field lines around the sun (similar to but less regular than those around the earth) distending greatly at the solar equator. The solar "magnetosphere" close to the ecliptic of the earth stretches out far into the solar system impacting the earth and other planets. This is known as the Interplanetary Magnetic Field (IMF). The solar particles which are carried along by the IMF exert a dynamic pressure on the magnetopause of the earth which can lead to fluctuations of the earth's magnetic field (a geomagnetic disturbance). The component of the IMF parallel to the geomagnetic axis of the earth (north/south) is called Bz and is particularly important. When Bz is negative or southward, the chance of the IMF interacting with and upsetting the earth's magnetic field is greatly increased. Click Here for the ASWFC Magnetopause model which simulates the response of the magnetopause to the solar wind. Note, that if the magnetopause is distorted so much as to move inside the radius of geostationary satellite orbits (about 40,000 km) then satellites become exposed to the full interplanetary force of the solar environment.

Summary and Forecast

The Solar Summary and Forecast is extracted from the ASWFC Daily Solar and Geophysical Report and is divided into 2 sections; Solar Summary and Solar Forecast.

The Solar Summary section summarises the last 24 hours of solar activity. The level of solar activity is classified from Very Low to Very High and any x-ray flares of C8 or greater are recorded. The 10.7 cm flux is the intensity in solar flux units (sfu) of a particular wavelength of solar radiation (10.7 cm) associated with the presence on the solar disk of "plage". Plage forms in the chromosphere, particularly in regions overlying sunspots in the photosphere, and is the source of Extreme Ultra-Violet (EUV) radiation from the sun. EUV causes ionisation in the upper regions of the earth's ionosphere (F-region) making HF communications possible. Thus the 10.7 cm flux level is a measure of solar activity with direct relevance to HF communications. The equivalent sunspot number given in the report is the sunspot number inferred from the measured 10.7 cm flux (rather than from direct observation). This is made possible by the empirical relationship established from many years of historical data between R (see Monthly Sunspot Numbers) and measured 10.7cm flux.

In the Solar Forecast section a 3-day forecast of expected solar activity is given, based on detailed observations of the current state and recent history of the solar disk and of active sunspot regions. A comment is often included containing further details of observed and forecast solar activity as concerning the behaviour of the solar wind.

Monthly Sunspot Numbers

Presented here are the observed and predicted monthly sunspot numbers reflecting long term solar activity. The Smoothed Sunspot Number (top of page) and the Observed Monthly Sunspot Numbers (further down the page) are the monthly sunspot numbers as observed from daily white-light images of the solar disk. The sunspot number (sometimes called R) is a count of the number of spot and spot groups (regions) present on the sun. It is defined as R = k(f + 10g) where: f is the number of spots visible, g is the number of sunspot regions visible and k is a constant related to the sensitivity of the observations from a particular station. A simple smoothing algorithm is applied in the case of the Smoothed Sunspot Number to pick up the longer timescale (year to year) variation. Presented at the bottom of the page is a plot of the observed (smoothed and raw data) sunspot numbers and numbers forecast using solar activity models. Also given at the top of page is an equivalent measure of solar activity, the equivalent sunspot number, inferred from the 10.7 cm flux (see Summary and Forecast).

X-ray Flux

Clicking on the X-ray Flux icon on the main solar page or selecting X-ray Flux from the menu gives the current x-ray solar flux level measured by the US GOES18 satellite. The X-ray flux is near to real-time being updated every 5 minutes. During an x-ray flare the x-ray flux increases rapidly over 10 - 20 minutes to a maximum, before returning to background levels over another 1 to 2 hours. When the x-ray flux exceeds C8 (8 x 10⁶ Watts/m²) the x-ray flux icon turns red and flashes to indicate that a solar flare is in progress (very exciting!). See Also Solar X-ray Flare Classes and Solar X-rays.

X-ray Flares

This gives a listing of the last 6 major X-ray Flare events. During a major X-ray flare (greater than C8) the lower regions of the ionosphere in the daylit hemisphere become highly ionisided. This sudden ionisation of the D-region leads to much greater absorption of HF waves and if a very large flare occurs (greater than M5), a complete HF "blackout" is likely for 1 to 2 hours. This is known as a short-wave or daylight fadeout. See Also Solar X-ray Flare Classes.

Solar Flare Forecast

The Solar Flare Forecast page provides probabilistic forecasts of X-ray solar flare activity for the 24 hour period following the forecast issue time. Forecast probabilities are provided for both the full visible solar disk as well as discrete active regions on the Sun. The probabilities relate to flaring at each of two peak flux levels:

1. M-class or greater flares (peak flux in 1-8Å band exceeding 10-5 W/m2). This is equivalent to the R1 level on the NOAA R-scale (see NOAA Scales).
2. X-class or greater flares (peak flux in 1-8Å band exceeding 10-4 W/m2). This is equivalent to the R3 level on the NOAA R-scale (see NOAA Scales).

The forecasts are generated hourly by the Australian Bureau of Meteorology, based on statistical models of solar flare activity. The statistical models rely on observations of the structure, complexity, evolution and recent flaring history of visible sunspot groups to generate forecasts of future flaring probability.

Culgoora Overview

This provides a brief introduction to the ASWFC Culgoora Solar Observatory.

Culgoora Real-time, Hourly and Cumulative Spectrographs

A number of radio receivers situated at Culgoora Observatory continuously monitor radio emissions in the range 18 - 1800 MHz. A spectrograph displays the variation in radio emissions over time, across the entire frequency range. Emissions appear yellow/white in color while background levels appear blue. While a certain amount of interference comes from man-made sources the majority of radio emissions originate from the sun. In particular, intense radio emissions are often detected during solar flares (radio bursts) and with the presence of large sunspot groups (radio noise storms). Thus the spectrograph is one of the key indicators of solar activity. For example, Coronal Mass Ejections (CMEs) are generally associated with a Type II radio sweep resulting from ejected solar matter moving through the plasma of the corona. From the gradient of the sweep the velocity of the CME can be determined and hence the time to impact with the earth estimated. The Culgoora Real-time Spectrograph is monitored closely by ASWFC staff as the first sign of a solar flare. See Also the Culgoora Type II Tool.

Culgoora Real-time Spectrograph

The real-time spectrograph is the first indicator of the occurrence of major solar activity, such as a solar flare. The frequency range 18 - 1800 MHz is continuously swept every 3 seconds with the data arriving at near real-time in the ASWFC Space Weather Forecast Centre. Spectrographs are only available in daylight hours. See Also Culgoora Real-time, Hourly and Cumulative Spectrographs.

Last Type II Event

A type II event is a radio emission observed on a spectrograph which begins at a high frequency and steadily reduces in frequency over 10 to 20 minutes tracing out a rough downward sloping line. For example, a large solar flare was observed on December 13, with an associated Type II Radio Sweep. The type II sweep was evidence of a Coronal Mass Ejection (CME). As the ejected solar matter passes through the corona the plasma frequency of the corona is excited. Since the plasma frequency in the corona decreases with increasing distance from the sun the frequency of the radio emission decreases with time as the CME moves. From the slope of the type II sweep and estimate is made of the velocity of the CME and its expected time of impact with the earth. See Also the Culgoora Type II Tool.

Culgoora H-Alpha Image

At the Culgoora Observatory a telescope tracks the sun throughout daylight hours providing a continuous feed of images of the solar disk. Typical of solar observing telescopes, the Culgoora telescope is fitted with an H- Alpha filter which views the solar disk at a wavelength of 656.3nm, falling in the red part of the visible spectrum. This wavelength corresponds to the first atomic transition in the Balmer Series of Hydrogen (H-alpha). The H-alpha line is universally used for patrol observations of solar flares, filaments, prominences and the structure of active solar regions. H-Alpha images correspond to the chromosphere of the sun.

Solar X-ray Flare Classes

The levels of solar x-rays emitted by the sun are measured by space-weather satellites in geo-stationary orbit such as the US GOES11 and GOES18 satellites. The X-ray flare classes increasing in severity are A, B, C, M and X, corresponding to increasing levels of the measured Solar X-ray flux. The levels are:

• A: more than 10^-8 W/m²
• B: more than 10^-7 W/m²
• C: more than 10^-6 W/m²
• M: more than 10^-5 W/m²
• X: more than 10^-4 W/m²

Levels of < A are not uncommon around solar minimum when no active regions are present on the solar disk.

Solar X-rays

Solar X-rays are generated mostly in the corona where temperatures are extremely high, around 2 x 10^6 K. The corona is best viewed at X-ray wavelengths where coronal phenomena such as coronal holes are clearly visible. X-ray emissions are most intense from dense, very hot regions of the corona where the solar plasma is constrained by very high magnetic fields. Such areas overly active regions of the chromosphere and photosphere. During a solar flare massive amounts of magnetic energy are released into the corona as magnetic loops with their ends bound to the underlying shifting and twisting sunspot region in the photosphere are sheared and broken. The resultant intense heating in the vicinity of the flare site initiates a massive release of X-rays from the corona.

Culgoora Historical Data

Links are provided to the ASWFC ftp server where key Culgoora data services are archived. The historical data available is Type II Event Reports dating back several years, daily spectrographs for the last 3 months and daily H-Alpha images for the last 4 months with images every 3 mintues for the last 3 days.

Culgoora White Light Image

White light refers to the sum of all visible wavelengths (400 - 700 nm). At the Culgoora Observatory a telescope continuously tracks the sun during daylight hours providing white light and H-Alpha images of the solar disk. White light observations of the solar disk are of the photosphere which radiates at predominantly infra-red, visible and ultra-violet wavelengths. Sunspots, which are darkened regions of the photosphere where radiation release is inhibited by intense magnetic fields, are best observed in white light images of the solar disk.

Learmonth Overview

This provides a brief introduction to the Learmonth Solar Observatory.

Learmonth Real-time, Hourly and Cumulative Spectrographs

A number of fixed and solar tracking radio receivers situated at Learmonth Observatory continuously monitor radio emissions in the range 25 - 180 MHz. A spectrograph displays the variation in radio emissions over time, across the entire frequency range. Emissions appear yellow/white in color while background levels appear blue. While a certain amount of interference comes from man-made sources the majority of radio emissions originate from the sun. In particular, intense radio emissions are often detected during solar flares (radio bursts) and with the presence of large sunspot groups (radio noise storms). Thus the spectrograph is one of the key indicators of solar activity. For example, Coronal Mass Ejections (CMEs) are generally associated with a Type II radio sweep resulting from ejected solar matter moving through the plasma of the corona. This type II sweep was the result of a CME associated with an X9 solar flare on 5 December 2006. From the gradient of the sweep the velocity of the CME can be determined and hence the time to impact with the earth estimated. Impact time to earth is typically between 24 and 48 hours. The Learmonth Real-time Spectrograph is monitored closely by ASWFC staff as the first sign of a solar flare.

Learmonth Real-time Spectrograph

The real-time spectrograph is the first indicator of the occurrence of major solar activity, such as a solar flare. The frequency range 25 - 180 MHz is continuously swept every 3 seconds with the data arriving at near real-time in the ASWFC Space-Weather Forecast Centre. Spectrographs are only available in day light hours. See Also Learmonth Real-time, Hourly and Cumulative Spectrographs.

Learmonth H-Alpha, White Light and Magnetogram Images

At the Learmonth Observatory a solar telescope tracks the sun throughout daylight hours providing a continuous feed of images of the solar disk. White Light (400 - 700 nm) images provide observations of the photosphere of the solar disk while H-alpha (656.3 nm) images are observations of the chromosphere. In addition, Learmonth is a member of GONG, the Global Oscillation Network Group, which provides detailed magnetic flux images of the solar disk. Such images show the intense and complex distribution of magnetic flux throughout an active sunspot region providing a detailed indication of the likelihood of a region flaring. In addition, the polarity of sunspot groups can be seen. The polarity of the leader and trailer spots of a sunspot group are reversed with a change in solar cycle.

Learmonth H-Alpha Images

Typical of solar observing telescopes, the Learmonth telescope is fitted with an H-Alpha filter which views the solar disk at a wavelength of 656.3nm, falling in the red part of the visible spectrum. This wavelength corresponds to the first atomic transition in the Balmer Series of Hydrogen (H-alpha). The H-alpha line is universally used for patrol observations of solar flares, filaments, prominences and the structure of active solar regions.

Learmonth Radio Flux

In addition to the radio spectrograph data which monitors emissions in the range 25 - 180 MHz, the actual flux density is measured for a number of higher discrete frequencies using a series of dish antennas which track the sun throughout the day. The flux density at 8 discrete frequencies is measured in solar flux units (sfu); 245 MHz, 410 MHz and 610 MHz with an 8 metre dish, 1415 MHz, 2695 MHz, 4995 MHz and 8800 MHz with a 3 metre dish, and 15400 MHz with a 1 metre dish. The Sun is what we call a broadband emitter, that is, it gives off radiation over a very wide frequency range. The Learmonth solar radio telescopes monitor both the quiet and active Sun, at these frequencies. The background solar radio emission (the quiet Sun) can be used as a source to calibrate other electronic equipment. ASWFC makes available the Learmonth Quiet Solar Flux or IFLUX for this purpose. Solar radio bursts (the active Sun) can exceed the background solar radio emissions by several orders of magnitude. Solar radio emissions can cause interference to man made electromagnetic systems (eg radio, radar, and GPS). It is also useful to know that the source of the interference comes from the Sun, rather than another man made source, or an equipment fault. These solar radio emissions also indicate the strength of the solar activity, and help predict the arrival of high energy solar protons at the Earth, which can degrade solar panels of spacecraft, and cause transpolar HF circuits to become disrupted (PCA event). A strong burst on the 1415MHz frequency may indicate that some GPS satellite signals could be lost, if the satellites are near the position of the Sun in the sky. Two displays of the radio flux data are provided. "Plot Diagram" displays a time-series display for each frequency of the flux throughout the day while "Hour Plot Diagram" presents more detailed flux plots over the last hour. "Quiet Solar (IFLUX)" gives the background, baseline flux levels at each frequency. These values reflect the current stable (background) state of the solar disk in relation to physical processes which emit radiation at those frequencies. An example is the 10.7cm flux (corresponding to a frequency of 2800MHz, which is near the Learmonth 2695 MHz frequency) appearing in the Daily Solar Summary which reflects the background levels of plage on the solar disk, and the level of solar activity.

Learmonth SEON Messages

SEON is the US Air Force acronym for Solar Electro-Optical Network of which Learmonth is a member. The SEON messages presented here are the Spots Summaries from two other SEON observatories; Holloman (New Mexico) and San Vito (Italy) as well as the Learmonth Plain Message which describes the observing conditions and equipment status at Learmonth. The Quiet Solar (ILFUX) levels also appear each day as SEON messages.

Learmonth Historical Data

Links to the Learmonth Observatory ftp archives can be found here. Available for download are H-alpha images of the solar disk, daily for the last 4 months and every few minutes over the last month. Daily solar radio spectrographs are available for the last 3 months.

Solar Activity Rotation

The Solar Activity Rotation tool presents recent observations of solar activity occuring on a 27-day recurring pattern. Both sunspot groups and coronal holes can persist on the solar surface for a number of rotations of the sun. The sun has a rotation period of around 27 days which means that the effects to the earth of a persistent sunspot group or coronal hole will exhibit a 27- day cycle. See Also Solar Region Data. Coronal holes tend to be "geo-effective" (effect the earth) only when they are located near the solar equator and at a longitude of around 30 degrees West (right) of the central meridian. An active sunspot group can be geo-effective only when it is on the earthward hemisphere of the sun. The color of the dates on the recurrence board refer to the level of geomagnetic activity observed on that day. Either by clicking on the dates on the recurrence board or by using the Prev/Next buttons a wide range of information can be viewed about each day's activity. To the left is shown any flare activity. In the middle under the recurrence board is shown the days K-indices. The yellow solar disk diagram to the right shows coronal holes in blue, and any flaring regions. CME's associated with flares appear as either a red (geo-effective) or green (not geo-effective) circle about the solar disk with the CME shock speed estimated from radio spectrographs also given. ASWFC Daily Reports for each day can also be displayed.

Culgoora Type II Tool

The Culgoora Type II Tool displays the currently observed solar radio spectrographs and a tool for analysing Type II radio sweeps. A number of historical Type II sweeps are also included in the pull down menu. By clicking on the beginning and end of a Type II sweep and hitting the "Compute Speed" button the shock speed of the associated CME is estimated. The "Threshold" appearing to the top right of the spectrograph refers to the minimum flux density for data to be shown on the spectrograph. By changing the threshold and hitting the "Apply" button it may be possible to display the Type II sweep more clearly with a little experimentation. Click Here to see an example. Often a Type II sweep consists of a Fundamental and a Harmonic; two parallel sweeps related to the fundamental and first harmonic plasma frequencies excited by the CME shock front. In the Example the Harmonic is actually the clearer image of the sweep, with either mode giving the same gradient.

Learmonth Type II Tool

The Learmonth Type II Tool displays the currently observed Learmonth solar radio spectrographs and a tool for analysing Type II radio sweeps. The tool works in the same way as the Culgoora Type II Tool described above.

Solar Links

Clicking on Solar Links displays a number of links to data streams from other organisations who monitor solar flares and the solar wind.

Solar Help Page

The Solar Help Page gives a short explanation of the data and information provided under each sub-section of the Solar Section.

Latest News

Latest News consists of recent ASWFC news items of particular relevance to those interested in solar phenomenom and solar physics. News items include predictions and reports of significant space weather occurences and udpates or additions to the ASWFC website and services.