Representation of solar tides in the stratosphere and lower mesosphere in state-of-the-art reanalyses and in satellite observations

Abstract

Abstract. Atmospheric solar tides in the stratosphere and the lower mesosphere are investigated using temperature data from five state-of-the-art reanalysis data sets (MERRA-2, MERRA, JRA-55, ERA-Interim, and CFSR) as well as TIMED SABER and Aura MLS satellite measurements. The main focus is on the period 2006-2012 during which the satellite observations are available for direct comparison with the reanalyses. Diurnal migrating tides, semidiurnal migrating tides, and nonmigrating tides are diagnosed. Overall the reanalyses agree reasonably well with each other and with the satellite observations for both migrating and nonmigrating components, including their vertical structure and the seasonality. However, the agreement among reanalyses is more pronounced in the lower stratosphere and relatively weaker in the upper stratosphere and mesosphere. A systematic difference between SABER and the reanalyses is found for diurnal migrating tides in the upper stratosphere and the lower mesosphere; specifically, the amplitude of trapped modes in reanalyses is significantly smaller than that in SABER, although such difference is less clear between MLS and the reanalyses. The interannual variability and the possibility of long-term changes in migrating tides are also examined using the reanalyses during 1980-2012. All the reanalyses agree in exhibiting a clear quasi-biennial oscillation (QBO) in the tides, but the most significant indications of long-term changes in the tides represented in the reanalyses are most plausibly explained by the evolution of the satellite observing systems during this period. The tides are also compared in the full reanalyses produced by the Japan Meteorological Agency (i.e., JRA-55) and in two parallel data sets from this agency: one (JRA-55C) that repeats the reanalysis procedure but without any satellite data assimilated and one (JRA-55AMIP) that is a free-running integration of the model constrained only by observed sea surface temperatures. Many aspects of the tides are closer in JRA-55C and JRA-55AMIP than these are to the full reanalysis JRA-55, demonstrating the importance of the assimilation of satellite data in representing the diurnal variability of the middle atmosphere. In contrast to the assimilated data sets, the freerunning model has no QBO in equatorial stratospheric mean circulation and our results show that it displays no quasibiennial variability in the tides.

On the evaluation of the phase relation between temperature and wind tides based on ground-based measurements and reanalysis data in the middle atmosphere

“…The dynamic fields of temperature and wind fluctuations induced by tides are similarly related to the polarization relation of gravity waves. Such a polarization relation for tides was theoretically derived from the primitive equations for fluctuations of an atmosphere without dissipation by She et al (2016). They showed that there is a fixed relation between both wind components and the temperature fluctuations induced by tides from the investigation of Na lidar measurements and model predictions from the Climatological Tidal Model of the Thermosphere (CTMT) based on the Hough mode extension (HME) technique in the MLT region.…”

“…A derivation and affirmation of a tidal polarization relation would lead to a possibility of deducing an unknown tidal field from another observed tidal field and are therefore also highly recommended for the altitude range below the mesopause region. For a westward-propagating monochromatic wave with a single zonal wave number s, the polarization relation between the temperature tide T and the zonal wind tide u derived by She et al (2016) is…”

Intercomparison of middle-atmospheric wind in observations and models

“…In parallel to the development of new measurement techniques most important general circulation models for numerical weather prediction and reanalysis have extended their lids further into the middle atmosphere due to the broad evidence for the influence of middle-atmospheric dynamics on tropospheric weather and climate (e.g. Baldwin and Dunkerton, 2001;Scaife et al, 2008;Kidston et al, 2015;Garfinkel et al, 2017). The most recent example of this trend towards increased model tops is the European Centre for Medium-Range Weather Forecast (ECMWF) ERA5 reanalysis released in July 2017, which extends up to 0.1 hPa, one pressure decade higher than its predecessor ERA-Interim.…”

Migrating and non-migrating tides observed in the stratosphere from FORMOSAT-3/COSMIC temperature retrievals

“…Data are considered at 1 km intervals from 15 to 50 km. It is known that the vertical resolution of RO-derived temperature profiles is 0.5 km in the troposphere and 2 km in the stratosphere (Kursinski et al, 1997;Scherllin-Pirscher et al, 2017). COS-MIC temperatures are smaller by 2 to 3 K than SABER temperatures across all latitudes below 0.3 hPa and larger above this altitude.…”