Exploiting close zonal-sampling of HIRDLS profiles near turnaround
latitude to investigate missing drag in chemistry-climate models near 60
S
Abstract
This study exploits the high-density zonal sampling at the turnaround
latitude of the High Resolution Dynamics Limb Sounder (HIRDLS) in the
Southern Hemisphere to investigate the missing drag in chemistry-climate
models near 60 S. Gravity wave (GW) properties including amplitude,
zonal wavenumber, vertical wavelength, and momentum flux are estimated
with a wavelet analysis method based on the S-transform. Monthly means
of GW properties compare well with estimates from previous studies. We
further investigate the contribution to GW momentum flux above
orographic and nonorographic regions and find that while fluxes are much
larger locally over orographic regions, the contribution to the zonal
mean is roughly 3 times smaller than the contribution over nonorographic
regions. We also investigate the relationship with the zonal wind and
find that GW momentum flux is highly correlated with the near surface
winds over orographic regions. In addition to momentum flux, we also
provide estimates of the zonal drag and use these estimates to evaluate
the current GW parameterizations and resolved wave forcing in models
participating in phase 1 of the Chemistry-Climate Model Initiative
(CCMI-1). The HIRDLS zonal drag estimates suggest that the CCMI-1 models
have insufficient zonal drag, especially in June, July, and August, and
that the majority of the missing drag is over nonorographic regions. Our
discussion includes implications for the Brewer-Dobson Circulation and
ozone hole.