Vertical motion during the 1957 stratospheric warming

Abstract

Vertical motion has been computed by the adiabatic method for (a) each of ninety locations on a grid covering most of the United States, Canada, and the adjacent North Atlantic region; (b) each of the 100‐mb, 50‐mb, and 25‐mb levels; (c) each twice‐daily observing time during the period January 16, 1957, to February 15, 1957. Until the occurrence of rapid warming, the vertical‐motion patterns typically showed downward motion west of troughs and upward motion east of troughs. After the beginning of rapid warming (after January 23 at 25 mb and after February 2 at the lower levels), the vertical‐motion pattern was characterized by a very large area of uniformly downward motion. Extreme magnitudes of vertical motion were about 8 cm sec−1 at 25 mb, 6 cm sec−1 at 50 mb, and 4 cm sec−1 at 100 mb. These and other results are illustrated by maps showing the distribution of height, temperature, and vertical motion at the three pressure surfaces for four selected map times.

The Kinetic-Energy Budget of the Stratosphere Over North America During the Warming of 1957

“…The significance of the changes in the vertical motion patterns that occurred at 25 mb by about 25 January and at the lower levels after about 2 February, has been discussed by Craig and Lateef (1962). They have pointed out that the important difference between vertical motions prior to and after about 23 January at 25 mb and before and after 2 February at the lower levels lay in the scale of downward motion at these levels, rather than in any large changes in their magnitude.…”

“…The accuracy of computed vertical motions in the stratosphere, on the assumption of adiabatic temperature variations, has been discussed by Craig and Lateef (1962).…”

The energy budget of the stratosphere over North America during the warming of 1957

“…Within the region, the conversion term always represented a change from kinetic to potential energy. The rapidity of the warming at the 25-mb level from January 23 to about February 3 [Craig and Lateef, 1962a] corresponded to consistently large magnitudes of the conversion term, but the occurrence, later on, of large-scale descent and rapid temperature increases at the lower levels corresponded to the maximum mag• nitudes from about February 4 to February 9. The extremely large values for the conversion rates over the analysis region as compared with similar rates computed on a hemispheric scale [Reed, 1962] indicate that the rapid conversion to potential energy in the region of the stratospheric warming was a major sink for the hemispheric kinetic energy.…”

Vertical Motion at 100 Mb. In the Tropics

“…where R is the gas constant for dry air. The finite difference approximations used for the computation of terms in the numerator of (1) are as follows: In view of the observed slow changes in the wind and temperature fields at stratospheric levels, the 24-hr. centered difference used for computing b T / b t term usually yields the correct sign and approximate magnitude of the time change of temperature over a shorter period centered at map time.…”