Jan 29, 2010

LIS science: rainfall estimates


Rainfall estimates from geostationary orbit

Because it will be in low Earth orbit, LIS can only be used as a research tool. It sees too little of the Earth, and its data system is not designed for real time warnings.

Still, it will benefit plans to put a Lightning Mapping Sensor on weather satellites in geostationary orbit. At that altitude, 35,680 km (22,300) miles, a satellite's orbit takes 24 hours and the satellite appears to stand over one spot on the equator. This gives TV weathermen the images they turn into movies of the weather. (It's also why a backyard TV dish does not have to track a satellite: it appears to stand still in the sky.)

Two U.S. satellites watch North and South America and the western Atlantic and Eastern Pacific Oceans. Satellites built by Japan, Europe, and Russia cover the rest of the world (only far ends of the polar caps are missed.)

From this vantage point, a lightning sensor could watch storms for hours and capture what forecasters think they are missing now. Satellite infrared and visible cameras can only see the tops of clouds. In infrared, this corresponds to temperature: the colder the cloud, the higher in the atmosphere it has been pushed.

This also implies that more energy is present to push the clouds that high.

We are more concerned with what happens under those towering clouds when the engine can't push the rain and hail any higher and it all collapses. Scientists have evidence that the cloud tops continue to grow even after the rain has fallen out. This gives a false impression that the storm is still building when, in fact, it's collapsed down below.

A lightning mapping sensor, though, could track the lightning in a storm as it built. When the lightning stops, forecasters would know that the system was collapsing and that conditions on the ground will be severe in a matter of minutes.

Thus, a Lightning Mapping Sensor would complement infrared imagers in understanding what a storm is doing now, and what it is likely to do in the next few minutes.

Back to the Lighting Imaging Sensor story.