Exploring the Unknown - NASA's History Office

178
OBSERVING THE EARTH FROM SPACE
figures accompanying the article are omitted here, but their captions are included, along with the
description of Figure 1. Note the British-style spellings, such as the word “centre.”
[269]
Introduction
Observing the Weather from
a Satellite Vehicle*
By Dr. Harry Wexler,
Chief Scientific Services Division, U.S. Department of Commerce,
Weather Bureau
To predict the future of the atmosphere, the meteorologist must know its present
state—as defined by the three-dimensional distribution of pressure, temperature, wind,
humidity, clouds, precipitation, etc. To do this, at hundreds of stations throughout the
Northern Hemisphere, the atmosphere is probed by balloon-borne instruments which
radio back to Earth values of pressure, temperature, humidity, and whose paths can be
translated into wind direction and speed of the various layers through which the balloon
ascends. These observations expressed as numbers or symbols, plus auxiliary information
of clouds, precipitation, etc., are plotted on weather charts and synthesized into an instantaneous
picture of the atmosphere which, however, is presently incomplete because of
lack of observations in large portions of the atmosphere, specially over oceans and
unpopulated areas. Knowing the present state of the atmosphere and past motions of the
storms enables a prediction to be made by extrapolation and other techniques.
A satellite vehicle traveling about the Earth outside the atmosphere would not assist
in portraying the pressure, temperature, humidity, and wind fields by direct measurement.
However, by a “bird’s-eye” view of a good portion of the Earth’s surface and the
cloud structure, it should be possible by inference to identify, locate, and track storm areas
and other meteorological features. The vehicle would then serve principally as a “storm
patrol.” There exists under normal conditions a characteristic cloud condition for a “typical”
extra-tropical storm.
A plan view of a typical mid-latitude storm shows cold and warm fronts, whose lowpressure
centre is at their vertex, and their accompanying cloud systems.
A major cyclonic storm-cloud system visible from above will be the warm front cloud
from which the major portion of the storm’s precipitation usually falls. In west-east vertical
sections, the cloud at the extreme right is composed of high-level (5–10 miles) tenuous
cirrus or cirrostratus clouds which change to denser altostratus and altocumulus and
finally to thick precipitating nimbostratus as one approaches the storm. If the ascending
warm air above the warm front is unstable enough, cumulonimbus or thunderstorm
clouds will penetrate above the top of the nimbostratus cloud.
In the warm sector, or the area between the warm front and cold front, there will be
stratus and fog, if the surface is colder than the air, or cumulus clouds, if it is warmer.
Approaching the cold front the higher altocumulus clouds will [text continued on page
271 after Figure 2]
* Presented at the Third Symposium on Space Travel, American Museum, Hayden Planetarium, New York,
May 4, 1954.