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

Abstract

<p><strong>Abstract.</strong> 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 reanalyses is found for diurnal migrating tides in the upper stratosphere and the lower mesosphere, specifically that the amplitude of trapped modes in reanalyses is significantly smaller than that in SABER, although such difference is less clear between MLS and reanalyses. The interannual variability and the possibility of long-term changes of 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) which 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 free running model has no QBO in equatorial stratospheric mean circulation and our results show that it displays no quasibiennial variability in the tides.</p>

The Stratospheric Diurnal Cycle in COSMIC GPS Radio Occultation Data: Scientific Applications

“…The midlatitude nonpropagating feature in the upper stratosphere has been diagnosed previously in TIMED/SABER data (Mukhtarov et al., 2009; Sakazaki et al., 2012, 2018) but with some question. The previous work identified it as a predominantly diurnal feature with maximum at 16:00 solar time but cast some doubt on the diagnosis because the TIMED/SABER data coverage was obtained by nodal regression.…”

“…For thorough descriptions of previous research on thermal tides in the upper atmosphere, stratosphere through thermosphere and ionosphere, see a recent review (Pancheva & Mukhtarov, 2011) or some of the most recent papers on the topic (Mukhtarov et al., 2009; Sakazaki et al., 2012, 2018). As discussed in the Introduction, most observational work on atmospheric tides uses the observations of the SABER instrument on the TIMED satellite (Russell et al., 1999), but the analyses are focused on the mesosphere and thermosphere with little analysis in the stratosphere and without coverage poleward of 50° latitude in both hemispheres.…”

“…Propagating modes are dissipated by propagation, but a trapped mode such as this can be dissipated only by eddy dissipation or long‐wave radiative relaxation. Atmospheric models in the form of reanalyses do reproduce this mode (Sakazaki et al., 2018), but this analysis shows that at least one of them, ERA‐Interim, overestimates its amplitude and produces a maximum in phase too early in the day. Both the increased amplitude and the phase lead of this mode produced by the model can be explained by mis‐modeling of eddy diffusivity in the upper stratosphere.…”

Equatorial Waves, Diurnal Tides and Small‐Scale Thermal Variability in the Tropical Lower Stratosphere From COSMIC‐2 Radio Occultation

“…The C2 sampling does not allow characterization of this behavior at higher latitudes, but that might be achieved in the future by combining RO measurements from additional satellites. As a note, there are numerous other studies of tides in the stratosphere and higher altitudes based on satellite observations (e.g., Mukhtarov et al., 2009; Pancheva et al., 2010; Sakazaki et al., 2015, 2018; Wu et al., 1998; Zhang et al., 2010), but these typically highlight behavior above the middle stratosphere (∼30 km). The radio occultation measurements provide a complementary data source at lower altitudes, as used by Sakazaki et al., 2015.…”

Observations of Gravity Wave Refraction and Its Causes and Consequences

“…There is also evidence that in this region different sources coalesce. Given that above 40 km the reliability of model data is known to decrease (see Ern et al., 2021; Sakazaki et al., 2018), we have insufficient information to disentangle this completely.…”