Abstract
Abstract. Recent studies have shown that day-to-day variability of the migrating semidiurnal solar (SW2) tide within the mesosphere and lower thermosphere (MLT) is a key driver of anomalies in the thermosphere–ionosphere system. Here, we study the variability in both the amplitude and phase of SW2 using meteor radar wind and lidar temperature observations at altitudes of 75–110 km as well as wind and temperature output from the Navy Global Environmental Model – High Altitude (NAVGEM-HA), a high-altitude meteorological analysis system. Application of a new adaptive spectral filter technique to both local radar wind observations and global NAVGEM-HA analyses offers an important cross-validation of both data sets and makes it possible to distinguish between migrating and non-migrating tidal components, which is difficult using local measurements alone. Comparisons of NAVGEM-HA, meteor radar and lidar observations over a 12-month period show that the meteorological analyses consistently reproduce the seasonal as well as day-to-day variability in mean winds, mean temperatures and SW2 features from the ground-based observations. This study also examines in detail the day-to-day variability in SW2 during two sudden stratospheric warming, events that have been implicated in producing ionospheric anomalies. During this period, both meteor radar and NAVGEM-HA winds show a significant phase shift and amplitude modulation, but no signs of coupling to the lunar tide as previous studies have suggested. Overall, these findings demonstrate the benefit of combining global high-altitude meteorological analyses with ground-based observations of the MLT region to better understand the tidal variability in the atmosphere.
Highlights
There is a growing need to understand the global wind field from the surface up to the lower thermosphere (0–100 km) and beyond as well as its day-to-day variability due to meteorological processes
The analysis is done for two examples of sudden stratospheric warming in the winters of 2009/10 and 2012/13 to determine how well the observed variations in the mesosphere and lower thermosphere (MLT) winds correspond to the NAVGEM-HA analysis data as well as to determine the day-to-day variability of the semidiurnal tide
We performed a detailed analysis of mean winds and temperatures and atmospheric tides using a recently developed tool called adaptive spectral filter (ASF), which is designed to capture the intermittent tidal behavior and provide vector information for mean winds and tides for climatologies
Summary
There is a growing need to understand the global wind field from the surface up to the lower thermosphere (0–100 km) and beyond as well as its day-to-day variability due to meteorological processes. The upward propagation of these drivers from their source regions near the surface into the MLT region is determined in large part by the global wind field. Accurate assessments of both daily and seasonal variability in winds and tidal modes has become necessary for better understanding lower atmospheric forcing of the thermosphere–ionosphere system. Manney et al (2008, 2009) characterized the SSW in 2006 as a vortex displacement and the SSW in 2009 as a vortex splitting event making use of global satellite observations (Microwave Limb Sounder; MLS) and data-assimilated reanalysis mostly at the stratosphere and lower mesosphere. Matthias et al (2013) investigated the role of planetary waves in the evolution of vortex splitting and displacement events combining satellite data and ground-based observations
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