Subj: AstroAlert: Auroral Activity Watch for Middle Latitudes Date: 7/30/99 8:07:57 PM Pacific Daylight Time From: oler@dns.uleth.ca (Cary Oler) Sender: owner-sun-earth@skypub.com To: sun-earth@skypub.com ------------------------------------ | | Auroral Activity | A s t r o A l e r t | 31 July 1999 WATCH | | 03:00 UTC ---------------- Sun-Earth Alert ---------------- The arrival of a fairly vigorous solar disturbance at 19:48 UTC on 30 July has resulted in considerable intensification of auroral activity, particularly during the last six hours. There is a fair to good possibility many middle latitude regions may spot periods of auroral activity over the next 12 to 18 hours. Recent data from the NOAA TIROS satellites suggests that moderate to strong auroral activity may be taking place at the present time. Unfortunately, there has not been any POLAR spacecraft imagery to compare with this since about 18:47 UTC. The network of Canadian magnetometers indicates that periods of moderate auroral oval activity is indeed probably in progress. The near-full phase of the moon will hamper attempts to view activity, particularly for those where activity is typically close to the horizon. We don't expect this to become a severe auroral storm, but there is a good possibility that substorming over the higher latitudes could become intense enough to become visible from many middle latitude regions despite the full phase of the moon. Expansion of the auroral oval equatorward will also help bring periods of activity to the middle latitudes. For North American observers, the best chances of observing activity may be just prior to and shortly after moonrise. Statistically, the most intense phases of auroral activity occur during the hours around local midnight. This also corresponds to the most equatorward position of the auroral oval. At the present time, the main area of auroral activity should be spanning from western Europe to just off the U.S./Canada east coast. Over the next few hours, activity should become increasingly visible from North American middle and high latitude regions. Overall, we expect auroral activity to be frequently fairly quiescent with periods of moderate to strong bursts of substorm activity. During the quiescent periods, activity may appear as nothing more than a diffuse arc of light or a twilight-style glow to the north (or south if you're in Australia or New Zealand). During substorm periods, curtains, rays, pulsations of activity and color variations may be commonly observed. We do not expect auroral activity to become visible over widespread low latitude regions. For North America, most observations will probably be confined to the northern tier of the U.S. states and all of the Canadian provinces. The effects of this activity have already been manifested to those involved in ionospheric radio propagation. For a good example of the effects that can occur, tune your shortwave radio to radio stations WWV (Colorado) or WWVH (Hawaii) at 2.5, 5, 10, 15 or 20 MHz. During the evening hours, the ionosphere typically only supports propagation on the lower frequencies. Periods of stronger auroral activity are often audible in these signals as a rapid flutter (rapid fading that resembles a flutter). Similar signal effects may be observed with Radio Station CHU, in Ottawa (another time clock service) on frequencies 3.330, 7.335 and 14.670 MHz. There is a chance this activity may (at times) become intense enough to support VHF auroral backscattered signal propagation. For those without VHF radios, try tuning tuning your TV to the lower channels. For brief periods, it may be possible to pick up distant TV stations caused by their signals being reflected and refracted by the turbulent ionospheric conditions in and near the auroral zone. We would appreciate receiving reports of observed odd radio signal propagation. Observers who witness activity may report their observations to us using the web page: http://solar.uleth.ca/www/subcaros.html. Within 5 minutes, all reported observations are made available for others to read at the site: http://solar.uleht.ca/www/caros.html. If you spot auroral activity (regardless of your latitude), please make the observation available for others to see by posting to our main aurora submission site at: http://solar.uleth.ca/www/subaurora.html. All reported observations will be made available (within 5 minutes) on our auroral activity observers network page at: http://solar.uleth.ca/www/auroras.html. All observations are archived in our database of auroral activity sightings, which is made available to those performing research in this field. The locations of all ground-based reports that are submitted to us are also automatically plotted on our DMSP spacecraft-derived auroral oval map (as supplied from data from the USAF). This map, as well as near-realtime POLAR spacecraft imagery and derived statistical NOAA TIROS maps of near-realtime auroral oval activity (from SEC) can be found at: http://solar.uleth.ca/www/aurora.html. The University of Alberta, cooperating with the Canadian Space Agency and the CANOPUS project, also make available a near-realtime web resource that plots the estimated position of the auroral oval and associated activity based on the CANOPUS network of magnetometer data at: http://www.space.ualberta.ca/canopus.html. We appreciate those who participate in reporting auroral activity. This disturbance should begin subsiding later in the UTC day of 31 July. Generally quiet conditions are expected to return on 01 August. ** End of AstroAlert **