SOARING METEOROLOGY

ATC Observer, Volume 3, Issue 8, 2 March 1945, Page 12

SOARING METEOROLOGY

PT. V. (concluded). W. Craven.

Upcurrent of over 30 m.p.h. in cumulonimbus clouds are prevalent. Pilots keep out of these clouds at all costs and remain just ahead of them. An interesting point worth noting about rapidly developed cumulus and cumulonimbus, is their billowy edges. This i epresents visible turbulence eddies formed through friction of the updraft in the cloud with the ambient air.

As the air mass front and its storms pass over, we now find ourselves under the rule of the cold mass and fine, but cold, weather is the order. The cold front sweeps* the air clean of all inversions in the temperature lapse rate, and the air takes on a general lapse rate of 3° per 1,000 feet. This does not last long however, for the ground now heats up, evapora-

GRAPH A. Shows the rates of cooling of moist and dry thermal bubbles as they pass through the atmosphere. GRAPH B. Shows how various lapse rates may exist in the atmosphere at the same time in different layers. These are measured with the aid of the radio-meteorgraph balloon and should not be confused with those for thermals, shown in Graph A. CURVE. (1) Shows a ground inversion, a condition found in the mornings and usually accompanied by

ting the excess moisture which fell as rain with the “front.” Soon the lapse rate will be superadiabatic. Convection begins, the bubbles rise fast in the superadiabatic condition, and with the low condensation level and high humidity, cloud development becomes very rapid, and extensive, great towering cumulus decorating the skies; some developing into cumulonimbus and providing showers and even local thunder storms. Visibility is excellent because of the unstable air and lack of inversions. Visibility takes on a haze when most hygroscopic particles of dust are held aloft in the inversion layer and deter vision considerably over a distance. And so, if a pilot misses the approach of a cold front, he can well use the strong convection which follows.

ground mist, and sometimes fog. CURVE. (2) Could occur later in

the day. (a) A ground inversion, (b) Super adiabatic lapse rates (caused by extreme heating of the ground. It seldom exists other than near the ground and is of short duration.) (c) An isothermal layer which may check vertical development. (There is a constant isothermal condition in the stratosphere.) (d) An inversion layer that will choke thermal activity.