Aliasing Effects in the Diagnosis of Tides and Planetary Waves in Satellite Data

Abstract:

The identification of waves from satellite data typically requires a data window such that the phase space of the wave of interest is appropriately sampled. As satellites precess slowly, a few weeks of data is generally required for the diagnosis of migrating tides to completely sample the phase space. As has been noted in earlier studies this results in aliasing of zonal mean into migrating tides when the zonal mean varies over time. Similarly stationary planetary wave amplitudes varying over time alias into non-migrating tides and vice versa. Data gaps also can affect the authentic diagnosis of wave amplitudes and phases. In this paper, we report on a study of aliasing effects on various temperature wave components in a few satellite data sets (SABER and COSMIC). The effects of sampling are studied using a run of CMAM30 and sampling the model data in the same manner as the satellites. It is found that the derived amplitudes of the non-migrating tides and planetary waves depend on the sampling and method of analysis. Further, the aliasing also depends on latitude for measurements taken by the same satellite due to yaw maneuvers, if any, and care must be taken in interpreting results from any particular satellite.