[1] The role of planetary waves in causing stratospheric sudden warmings (SSWs) is well understood and quantified. However, recent studies have indicated that secondary planetary waves are excited in the mesosphere and lower thermosphere following SSWs. We use a version of the Whole Atmosphere Community Climate Model constrained by reanalysis data below 50 km to simulate the SSW of January 2012, a minor warming followed by the formation of an elevated stratopause. We document the occurrence of enhanced Eliassen-Palm flux divergence in the mesosphere and lower thermosphere associated with faster, secondary westward-propagating planetary waves of wave number 1 and period <10 days. We confirm the presence of these secondary planetary waves using observations made by the Sounding of the Atmosphere using the Broadband Emission Radiometry instrument onboard NASA's Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics satellite. Citation: Chandran, A., R.R. Garcia, R. L. Collins, and L. C. Chang (2013), Secondary planetary waves in the middle and upper atmosphere following the stratospheric sudden warming event

Elevated stratopause (ES) events occurring during Northern Hemisphere winter are identified in four climate simulations of the period 1953–2005 made with the Whole Atmosphere Community Climate Model (WACCM). We find 68 ES events in 212 winters. These events are found in winters when the middle atmosphere is disturbed and there are zonal wind reversals in the stratosphere at high latitudes. These disturbances can be associated with both major and minor stratospheric sudden warming events (SSWs). The ES events occur under conditions where the stratospheric jet, the gravity wave forcing, and the residual circulation remain reversed longer than in those winters where an SSW occurs without an ES. We compare ES events with the type of SSW (vortex splitting and vortex displacement) and find that 68% of ES events form after vortex splitting events. We also present a climatology of ES events based on NASA's Modern‐Era Retrospective Analysis for Research and Applications reanalysis data from 1979 to 2012 and compare it to the model results. WACCM composites of major SSW and ES also show enhanced Eliassen‐Palm flux divergences in the upper mesosphere after the stratospheric warming, immediately before the formation of an ES. However, the formation of an ES in WACCM is due primarily to adiabatic heating from gravity wave‐driven downwelling, which follows the reestablishment of the eastward jet in the upper stratosphere. We find nine winters where an ES forms in the absence of any significant planetary wave activity in the upper mesosphere and illustrate one such event.

An unusually long data set was acquired at the sodium lidar facility at Colorado State University (41N, 105W), between Sep 18 and Oct 01, 2003, including a 9‐day continuous observation. This time is long enough to average out the perturbations of gravity waves and short‐period planetary waves. As such, it can be used to define tidal‐period perturbations in temperature and horizontal wind. Assuming the sodium mixing ratio is a constant of motion, the observed tidal‐period oscillation in sodium density follows that of vertical wind. Thus, the data set defines tidal‐period perturbations of temperature and wind vector. The observed amplitudes and phases were compared to Global Scale Wave Model predictions (both GSWM00 and GSWM02). We found excellent agreement in diurnal phases and reasonable agreement in semidiurnal phases. However, GSWM02 overestimates diurnal amplitudes and both model versions underestimate observed semidiurnal amplitudes. Since the data period is long enough for the study of planetary waves and of tidal variability, we perform spectral analysis of the data, revealing a strong quasi 3‐day wave in meridional wind, a 14 hour perturbation in zonal wind, and both 14‐hour and 10‐hour periods in meridional wind, likely the result of nonlinear interactions. The observed semidiurnal amplitudes are much larger than the corresponding diurnal amplitudes above 85 km, and over a few days the diurnal and semidiurnal amplitudes vary by factors of 2–3. Causes for the observed tidal variability in terms of planetary wave modulation and tide‐gravity wave interaction are explored qualitatively.

No abstract