Measuring Initial Conditions

Margules's and Bjerknes's ideas depended very heavily on one thing: timely, accurate data collected from all atmospheric levels. This was a very complicated problem for a number of reasons.

Scholars had observed the atmosphere in a systematic way since at least the time of Aristotle, but these observations were qualitative until the time of the Scientific Revolution (ca. 1550 to 1700). Qualitative observations gave relative information about temperature (hot or cold), wind (very windy or calm), clouds (overcast or clear), and precipitation (rain, hail, or drizzle). During the Scientific Revolution, craftsmen and scholars working together had developed thermometers, barometers, and hygrometers. Anemometers and wind vanes were perfected later. Once these instruments were standardized and affordable and produced consistently reliable information, weather observers could collect quantitative data that attached numerical values to the weather element. For example, instead of recording cool, the observer would note 39.2°F (4°C).

What Margules, Bjerknes, and a new generation of meteorologists needed for theory development and accurate forecasts were quantitative observations taken with accurate instruments using standard methodologies. In the early 20th century, mercurial barometers were extremely accurate. Those used by weather stations could measure the pressure to 0.001 inch (0.025 mm) of mercury. Rooftop thermometers usually gave higher values in winter than those closer to the ground. Anemometers were reasonably accurate at low speeds, but not at high speeds. Hair hygrometers reacted too slowly to changing moisture content. Meteorologists needed to address instrumentation problems. They would need time and money to do so.

Setting aside the problem of equipment accuracy, there was also a problem with the timing and reporting of observations. Both Margules and Bjerknes needed observations taken simultaneously everywhere. If o o

BAROMETER

Movable scale

Movable scale

Aneroid barometer

— Mercury reservoir o_o

— Mercury reservoir

Mass-marketed aneroid barometers, complete with weather descriptions to accompany pressure measurements, were much less accurate than mercury barometers used by weather observatories.

Mercury barometer

© Infobase Publishing

Aneroid barometer stations took observations on a schedule of their own devising, it would be impossible to analyze the atmospheric situation at a specific time. Bjerknes needed to convince scientists across Europe and in England to coordinate their observations.

In addition, not everyone used the same units to report his findings. Some stations reported air pressure in inches of mercury and some reported in millimeters of mercury (the height of the mercury in the tube). Similarly, wind speeds were reported in miles per hour, nautical miles per hour (knots), and kilometers per hour. Some stations reported temperatures using the Fahrenheit scale (freezing at 32°) and some used the Celsius scale (freezing at 0°). In order to solve the physical equations defining atmospheric processes, Bjerknes argued, all stations would need to report in absolute units. An absolute unit is based on fundamental units of length (meter or foot), mass (kilogram or slug), and time (seconds). Air pressure reported as "millimeters of mercury" did not equate to the units used for pressure (pounds/square inch or newtons/square meter). A conversion would need to be made. In addition, all stations would need to report their pressure readings as if they were at sea level. If they did not do so, higher-altitude stations would always show a lower pressure reading than lower-altitude stations even when they were experiencing exactly the same weather. If all stations reported as if they were at sea level, then it would be possible for Bjerknes and his colleagues to draw a map of the atmospheric conditions at Earth's surface—a necessary condition for making a forecast for the next day.

Surface observations were just part of the story. Bjerknes realized that in order to solve the equations, he needed upper air data. Most upper air observations were taken with instruments carried aloft by balloons and kites at aerological observatories, which supported manned-balloon flights. Because the observations were taken just in advance of the flights—not at regularly scheduled times—they were of limited use to meteorologists, who needed to consider observations that were taken at the same time. They also tended to be qualitative. The balloon pilots were not concerned with exact measurements. They often wanted to know the height of the cloud ceiling and the direction of winds aloft. Bjerknes was terribly frustrated. As the historian of science Robert Marc Friedman noted in his 1993 book Appropriating the Weather, Bjerknes wrote a letter of complaint to the president of the Carnegie Institution in Washington, D.C., which was providing funds for his project. Bjerknes grumbled, "In as much as my work is dependent upon such observations it cannot bring more out of them than their quality admits."

To overcome data problems, Bjerknes turned to the International Commission for Scientific Aeronautics during its 1909 meeting. He pointed out that the study of weather conditions in the upper atmosphere could make a tremendous contribution to aeronautics. As flight became more common, such studies could provide accurate predictions to pilots and keep them safe during takeoff, flight, and landing. To be useful, Bjerknes told those attending, upper air data had to be collected at the same time and in the same way each day. The audience finally started to accept his message. Within a short period, other prominent scientists joined Bjerknes in his quest for absolute units and simultaneous observation times. The German climatologist Wladimir Koppen (1846-1940) of the Deutsche Seewarte (German Naval Observatory) in Hamburg and William Napier Shaw (1854-1945), head of the British Meteorological Office, both supported Bjerknes. Despite their efforts, absolute units were not widely accepted until the next decade, and they were not universally adopted until 1929. It would take even longer for meteorological stations to agree on standard observation times.

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