Gravity wave drag estimation from global analyses using variational data assimilation principles. II: A case study.

PULIDO M AND J. THUBURN

QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY

Wiley

Lugar: Reading UK; Año: 2006 vol. 132 p. 1528 - 1543

0035-9009

An estimate of the three-dimensional gravity wave drag field derived from middle atmosphere analyses is presented. It is obtained using a novel technique based on variational data assimilation principles described in Part~I. The assimilation is performed for a one week period starting on 1/7/2002 using Met Office middle atmosphere analyses as the observations as well as the initial condition. The rotational component of the gravity wave drag is robustly estimated by the technique. The zonal mean drag estimates reach maximum amplitudes of $50 \,  m \, s^{-1} \, day^{-1}$ at 0.4 hPa near the winter hemisphere polar jet. In the middle stratosphere drag estimates are much weaker with zonal mean peak values of $5 m \, s^{-1} day^{-1}$ and show transient small-scale features not obviously correlated with the local background flow. Vertical variations in the sign and pattern of the estimated drag suggest filtering of the gravity wave spectrum by the background flow.