Geos and LeosAdded : Monday at 10:30 Satellite meteorology is still a relative newcomer when it comes to observations. It all started in October 1946 when technicians in Nevada decided to fire a V2 rocket into the sky with a 35mm camera attached to the nose cone!
On descent, the camera started taking pictures every second and a half until it crash landed and the images recovered. The idea was simply to see what a human would see if they could survive the ascent of the rocket, instead though, they saw the curvature of the earth and clouds from above as well as a quarter of the USA with cloud streets visible. This gave them, or rather, meteorologists a rather good idea...
These days, we take charts such as the cloud forecast from above for granted :-
But all we are doing is mimicking what we see on satellite images and this is why they have become so important.
In meteorology, we have Geos and Leos. Geos are the Geostationary (or Geosynchronous) satellites which orbit at 36,000km above the equator and remain fixed at a certain spot. They aren't stationary at all and move at 3.07km per second! Which funnily enough is the same speed as the rotation of the earth.
These satellites are fantastic for looped images and seeing developments over a wide area, but there is a problem... The earth is a sphere. This means that taking accurate observations over the equator and nearby is easy, but at the poles the satellite has a distorted view and as a result the observations are somewhat unreliable.
Then we have Leos, these are Low Earth Orbiting satellites which fly low and fast at below 2000km and circle the planet from North to South on the descending track and then South to North on the ascending track. These are really important satellites for meteorologists as they can detect a whole multitude of weather variables at high resolution from overhead, but there is a problem... These satellites only take snapshots of areas as they fly over them and are limited to the passes they make each day.
Here is a picture of a Geo satellite image, this one from Meteosat courtesy of Eumetsat :-
You can see how the observations towards the north and south poles are distorted in comparison to regions across Africa, but here is a Leo image :-
This is the MODIS satellite which crisscrosses the Earth throughout the day at a height of 705km, travelling at 17,000mph it builds up a mosaic of the Earth. These satellites also monitor a huge amount of weather data as they pass over during daylight and this data is fed back into numerical weather models in what we call observational data.
Here is an example image of the cloud top pressure recorded by the MODIS satellite as it passes over Europe :-
This data is incredibly important to numerical weather models. Not only does it go into the starting conditions, but more importantly, it goes into the Data Assimilation which is one of the most important parts of numerical weather forecasting.
Tomorrow, we will look at Data Assimilation and why some of the best weather models in the world focus so heavily on this one area, and for good reason too...
METEOROLOGIST : MARSH |