Anomalous temperature and zonal wind in the tropical upper stratosphere, 1982/1983


  • Timothy J. Dunkerton,

  • Donald P. Delisi


Aerosol from the eruption of El Chichón (April 1982, 17°N) warmed the tropical lower stratosphere in 1982. Temperature data from the Nimbus 7 stratospheric and mesospheric sounder (SAMS) indicate that in mid-1982, cooling occurred in the upper and middle tropical stratosphere, starting shortly after the eruption. Radiative (IR) cooling above the aerosol cloud was a predicted, but unverified, response to El Chichón. In this paper an attempt was made to determine whether the cooling could be attributed to El Chichón Rocketsonde data from Kwajalein gave additional evidence of cooling and revealed that zonal winds in the upper and middle stratosphere were anomalous in 1982 and also in 1983. Where comparison can be made, rocketsonde observations were consistent with balance winds derived from SAMS. Upper level cooling was linked to anomalous easterlies near the equator and therefore could not be interpreted as a radiative (nondynamical) response to El Chichón. The structure of an expected two-dimensional dynamical response to aerosol heating is examined with a numerical model and compared to the data. This response is partly consistent with observations but is inadequate to explain the magnitude of cooling and associated easterlies in the tropical upper stratosphere in mid-1982. It is suggested that internal sources of atmospheric variability (e.g., extratropical forcing and quasi-biennial oscillation) contributed to equatorial cooling observed in 1982.