HEAT-FLUX OBSERVATIONS IN THE MESOPAUSE REGION ABOVE HALEAKALA

Horizontal and vertical heat fluxes between 85 and 100 km were compute d using temperature and wind profiles observed on 21 October 1993 by t he Na Wind/Temperature lidar operated at Haleakala during the ALOHA-93 Campaign. On this night a warm layer developed between 85 and 90 km. The temperature increased by almost 40 K near 88 km, reaching a maximu m of approximately 235 K at 1030 UT before decreasing throughout the r emainder of the 5 h observation period. This substantial temperature i ncrease was associated with a large amplitude wave, possibly the diurn al tide, and with a sporadic Na layer. The meridional wind field exhib ited a strong vertical shear zone within the warm layer and sporadic N a layer which briefly exceeded the shear instability limit of approxim ate to 42 m/s/km at the time the temperature reached maximum. The vert ical heat flux was directed upward within the warm layer reaching maxi mum at 88 km and downward above resulting in strong flux convergence. The average heat fluxes between 85 and 100 km were 2.5 +/- 2.4 K m/s ( vertical), 77 +/- 25 K m/s (zonal), and -19 +/- 20 K m/s (meridional). The maximum heating rate associated with the convergence of vertical heat flux was 11 +/- 4.1 K/h at 91 km. The average heating rate betwee n 85 and 100 km was 1.9 +/- 0.8 K/h.