Aliasing problems in variability of migrating and nonmigrating tides in the middle atmosphere obtained from satellites, models and reanalyses datasets.

Abstract:

Satellite observations provide an important source of data for analyzing for tides and their variability. However, owing to the specific sampling patterns they have, the various data analysis methods to extract wave and tidal information suffer severe aliasing problems. To elaborate on this problem, we resampled existing model and reanalysis datasets in Fourier space to create ‘satellite sampled’ model and reanalysis data which were analyzed with regular methods for extraction of tidal characteristics and variability. Specifically, we sampled the ECMWF (European Centre for Medium-Range Weather Forecasts) Re-Analysis Interim (ERA-Interim) and the Canadian Middle Atmosphere Model (CMAM30) datasets using the sampling patterns of Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite and Formosa Satellite-3/Constellation Observing System for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC) during the period from 2007 to 2010. This period is chosen as it is the common epoch of data availability among these four datasets. It is found that there is significant aliasing in migrating as well as non-migrating tidal variability due to changing stationary planetary wave amplitudes and mean temperatures, particularly over mid- and high-latitude middle atmosphere of the winter hemisphere. Particularly, these exercises provide evidence that non-linear interactions might not be a strong source for generation of non-migrating tides in these regions. Various numerical experiments are also performed to further investigate these problems. The results show that our understanding of non-migrating tidal variabilities from SABER/TIMED have to be relooked carefully after taking these aliasing issues into account.