Geostationary Wx Satellite Eclipse Period Beginning

[senorpepr]

Near the Vernal (Spring) and Autumnal (Fall) Equinoxes [of vcnty 21 March and 21 September respectively], the Earth disk will periodically block out the sun when directly opposite it at that satellite's local midnight timezone. This is because the satellites' orbits are over the equator, and near the equinoxes the sun is also "overhead" the equator. The spacecraft use direct solar energy for power and at these times of years the sunlight is blocked (eclipsed) and the satellite will briefly be without solar power.

Essentially, each eclipse season spans a 48-day period (about three and a half weeks either side of the equinoxes). There is typically a 0-3 hour outage of imagery each day as each geostationary satellite progresses through its local midnight timeframe each eclipse season. The maximum outage of 3 hours will occur at or near the equinox with the minimum about 3 weeks either side of the equinox.

Hence, IR images from GOES, METEOSAT, and GMS satellites will be unavailable when the longitude that satellite is parked over in orbit is experiencing local midnight to include an hour either side of it from mid August to late October and again from mid February to late April.

[Air Force Met]

I HATE this time of year for that reason.

[Guest]

That was interesting. Thanks for the post.

[Aslkahuna]

There is another effect that occurs during this same time period only this one occurs during the daytime. When the Sun is near the equinox, it will transit the Line of Sight between an antenna on Earth and the satellite. This will result in in noise interference with the satellite signal due to the natural radio noise form the Sun. During periods of high Solar activity, this radio flux from the Sun can severely degrade the signal and if a major flare occurs when the Sun is in the antenna field, then it can totally blot out the satellite signal. Because of parallax, this Solar Interference period occurs during different time periods at different latitudes but generally is strongest before the March and after the September equinoxes. The side lobe pattern of the dish antenna is also important since the Sun's noise during a Flare can be strong enough to degrade the signal even if the Sun is only in a side lobe of the antenna pattern.

One thing, you might want to look for during the eclipse season and that's the Full Moon near the Earth's Limb on images where the terminator is just on the limb to the east in afternoon images and to the west in morning images. It will usually show up best on the IR images as a black orb near the limb.

Steve

[ChaserUK]

That is interesting - never even knew that could happen! Thanks for the information Mike.

[senorpepr]

^BUMP^

...just a friendly reminder...

[WeatherEmperor]

Had no clue that could even happen. Interesting....

<RICKY>

[Brent]

Oh joy...

You'd think with 2004 technology we could solve the problem.