Last Thursday I found myself on Pennsylvania Avenue, Washington DC. You will assume immediately, of course, that I was there to visit Bill and Hillary at No 1600 - but no, not this time. Instead, I went next door to the US Department of Commerce, which, until they built the Pentagon, was the largest building in the world and which is home to the National Oceanic and Atmospheric Administration, more commonly known by the acronym NOAA. I was there to witness the signing of an historic agreement between the United States and Europe.
Ever since weather satellites began, in the 1960s, the United States, through NOAA, has operated "polar-orbiting" weather satellites. These spacecraft, as their name implies, travel around the globe from pole to pole, following, as it were, the lines of longitude, and are only 500 miles or so above the surface. They photograph the whole globe, bit by bit, from directly overhead as the Earth revolves on its axis underneath.
Now it is convenient if polar-orbiting satellites are deployed so that each time a satellite appears it crosses the equator on one side of the Earth at the same time, local time, each day. This can be arranged if the orbital plane of the spacecraft is allowed to "precess" - to rotate, as it were, almost with the Earth, so that its orbital plane is always on the same position relative to the sun. The result of the Initial Joint Polar System Agreement, signed last week between NOAA and its European counterpart, EUMETSAT, is that EUMETSAT will operate such a spacecraft in a "morning" orbit, and NOAA will be on duty each afternoon.
The IJPS agreement between the two organisations has taken more than five years to negotiate and will culminate in the launch of EUMETSAT's first polar orbiting spacecraft, Metop-1, in 2003. Central to the arrangement is that both spacecraft will have many meteorological instruments in common, thus ensuring that their readings of temperature, humidity, and a wide variety of other atmospheric elements, are directly comparable with each other, and can be used directly and without unnecessary complication in the numerical weather prediction models of the atmosphere used for producing weather forecasts by computer.
The signatories of the agreement were Dr Tillmann Mohr, director of EUMETSAT, and his American counterpart, Dr James Baker of NOAA. Meteorologists on both sides of the Atlantic are excited by this example of international co-operation and are confident the new generation of satellite instruments will improve our weather forecasts and assist in our capability to monitor the global climate.