Gravity wave momentum fluxes in the MLT-Part II: Meteor radar investigations at high and midlatitudes in comparison with modeling studies

摘要

For the analysis of gravity waves the method presented by Hocking (2005) is used, which enables us to derive wind variances and gravity wave momentum fluxes in the mesosphere and lower thermosphere from all-sky interferometric meteor radar wind measurements considering waves and variances with periods less than 2. h. A sensitivity study for the applicability of this method has been performed for the first time using a mechanistic general circulation model with high spatial resolution and explicit description of gravity waves. Wind variances and momentum fluxes have been determined from the model directly and by Hocking's method. Results of both methods are in good agreement except for vertical wind variances in case of weak vertical winds, which in the model are of the order of 1. m/s, whereas short period gravity waves estimated by meteor radar lead to larger vertical winds with a smaller ratio between horizontal and vertical wind fluctuations. A latitudinal comparison of mean annual variations of wind variances and momentum fluxes has been performed using meteor radar measurements at the high latitude site Andenes (69.3°N, 16.0°E) and the midlatitude site Juliusruh (54.6°N, 13.4°E). A semi-annual variation of the activity of short period gravity waves has been found having stronger magnitudes at high latitudes. The mean zonal winds show the typical summer wind reversal that shifts to higher altitudes from middle to high latitudes. Finally, the coupling between gravity waves and the mean background circulation is investigated based on long-term measurements at Andenes and the midlatitude site Collm (51.3°N, 13.0°E) during a period from 2004 to 2009.