Global distribution and variability of quasi 2 day waves based on the NOGAPS-ALPHA reanalysis model

This study presents the analysis of 14 months (January 2009 to February 2010) of continuous hourly Navy Operational Global Atmospheric Prediction System-Advanced Level Physics High Altitude reanalysis data used for examining the quasi 2 day wave (QTDW). The global structure and seasonal variability of the eastward and westward traveling QTDWs in all meteorological fields (geopotential height, zonal and meridional wind, and temperature) have been studied. The use of hourly reanalysis data allows a comprehensive understanding of the global spatial-temporal QTDW distribution by simultaneous separations of all tides and planetary waves. The wave characteristics (amplitudes and phases) are presented in latitude range +/-80 degrees and altitudes from 15 to 95 km. Two different types of eastward traveling waves are identified: (i) waves at middle and high latitudes with zonal wave numbers 2 and 3, which are observed in the local winters, and (ii) waves observed predominantly over the equator with zonal wave number 2, which do not have a well-defined seasonal variability but show some enhancement between June and August. While the first type waves are seen in all meteorological fields, the second ones are not seen in the meridional wind and belong to the ultrafast Kelvin waves. Two different types of westward traveling waves have been identified as well: (i) waves at middle and high latitudes with zonal wave numbers 2, 3, and 4, which are observed mainly in summer hemisphere, and (ii) waves observed predominantly over the equator with zonal wave numbers 1, 2, and 3, enhanced predominantly at both solstices but are seen in other seasons as well. While the first type waves are seen in all meteorological fields, the second ones are observed in the meridional wind and are Rossby-gravity normal modes.