Transient eddies in the MACDA Mars reanalysis

Abstract

We present a survey of the transient eddy activity in the Mars Analysis Correction Data Assimilation (MACDA) reanalysis. The spatial structure and propagation characteristics of the eddies are emphasized. Band-pass-filtered variance and covariance fields are found to be zonally modulated, indicating a longitude dependence of the typical amplitudes of Martian transient eddies. Considerable repeatability of the eddy field spatial structures is found across Mars years, including a roughly wave number 3 pattern of low-level eddy meridional temperature transport (v′T′¯) in the northern hemisphere that is evident before and after winter solstice and a possible tendency for northern hemisphere eddy kinetic energy maxima to be located above low-lying areas. Southern hemisphere eddy fields tend to feature two local maxima, one roughly south of Tharsis and the other associated with Hellas. Eddies are weakened near winter solstice in both hemispheres and were generally weakened in the northern hemisphere during the 2001 (Mars year 25) global dust storm, albeit with little change in spatial patterns. Because the transient eddies propagate in space, we also used a teleconnection map-based technique to estimate their phase velocities. Eddy propagation at the surface is found to follow topography, a phenomenon less evident at higher altitude. Possible physical mechanisms underlying the documented eddy phenomena are discussed.