Intercomparison of Middle Atmospheric Meteorological Analyses for the Northern Hemisphere Winter 2009–2010

Abstract

Abstract. Detailed meteorological analyses based on observations extending through the middle atmosphere (~15–100 km altitude) can provide key information to whole atmosphere modelling systems regarding the physical mechanisms linking day-to-day changes in ionospheric electron density to meteorological variability near the Earth’s surface. It is currently unclear how middle atmosphere analyses produced by various research groups consistently represent the wide range of proposed linking mechanisms involving migrating and non-migrating tides, planetary waves, gravity waves, and their impact on the zonal mean state in the mesosphere and lower thermosphere (MLT) region. To begin to address this issue, we present the first intercomparison among four such analyses, JAGUAR-DAS, MERRA-2, NAVGEM-HA, and WACCMX+DART, focusing on the Northern Hemisphere (NH) 2009–2010 winter that includes a major stratospheric sudden warming (SSW) in late January. This intercomparison examines the altitude, latitude, and time dependences of zonal mean zonal winds and temperatures among these four analyses over the 1 December 2009–31 March 2010 period, as well as latitude and altitude dependences of monthly mean amplitudes of the diurnal and semidiurnal migrating solar tides, the eastward propagating diurnal zonal wave number 3 nonmigrating tide, and traveling planetary waves associated with the quasi-5 day and quasi-2-day Rossby modes. Our results show generally good agreement among the four analyses up to the stratopause (~50 km altitude). Large discrepancies begin to emerge in the MLT owing to (1) differences in the types of satellite data assimilated by each system and (2) differences in the details of the global atmospheric models used by each analysis system. The results of this intercomparison provide initial estimates of uncertainty in analyses commonly used to constrain middle atmospheric meteorological variability in whole atmosphere model simulations.

Intercomparison of middle atmospheric meteorological analyses for the Northern Hemisphere winter 2009–2010

“…Based on the results of this intercomparison among four analysis systems that assimilate middle atmospheric satellite observations, we find that there is overall good agreement in the latitude, altitude, and time behavior of the zonal mean temperature and zonal winds up to approximately 50 km altitude during the December 2009 to March 2010 period. This finding is consistent with the results presented in Harvey et al (2021), which examined 10 reanalysis data sets but only 1 (MERRA-2) that extended above the stratopause and assimilated middle atmospheric temperature observations (from MLS). Also consistent with Harvey et al (2021), we find that significant differences among the four analyses begin to emerge above 50 km altitude at low latitudes.…”

“…We begin with an examination of the Q5DW, which consists of a westward-propagating zonal wave number 1 disturbance related to the first hemispherically symmetric normal (Rossby) mode. As shown in Harvey et al (2021), the middle atmospheric Q5DW can manifest in two forms: first, as a hemispherically symmetric feature related to latent heat release in the tropical upper troposphere (Salby, 1981;Miyoshi and Hirooka, 2003) peaking between 30 and 50 • latitude in the summer hemisphere; and second, as a high latitude wintertime feature related to growth through baroclinic/barotropic instability, leading to what is commonly referred to as the 6.5 d wave in the mesosphere and lower thermosphere (Talaat et al, 2001;Lieberman et al, 2003;Forbes and Zhang, 2017). Given the complex dynamical interactions that give rise to the Q5DW, capturing this feature is a good test for middle atmospheric meteorological analyses.…”

“…In the remainder of this section, we present results from space-time analysis of the four analyses related to the Q5DW, Q2DW, DW1, SW2, and DE3 features. Recognizing that many other planetary wave and tidal features (e.g., Forbes et al, 2008;Sassi et al, 2012) are also important for producing T-I variability related to meteorological forcing from the middle atmosphere (McDonald et al, 2018), the present study is not meant to be an all-inclusive assessment of every feature but rather is meant to provide an initial extension of the intercomparison study by Harvey et al (2021) to include the mesosphere and lower thermosphere.…”

“…A recent intercomparison of several reanalyses was performed as part of the Stratospheric Reanalysis Intercomparison Project (S-RIP; Fujiwara et al, 2017), with a chapter focusing specifically on the ability of reanalyses to capture key processes in the upper stratosphere and lower mesosphere (Harvey et al, 2021). A key finding of Harvey et al (2021) is that the most commonly used reanalyses (e.g., MERRA-2, ERA-I, JRA55) show good agreement in their representation of the zonal mean atmospheric state and in their representation of planetary waves (PWs) and tides up to ∼ 50 km altitude, but the representations diverge quite substantially above 50 km altitude, particularly in the equatorial region. This is not surprising since these systems were originally developed with a focus on tropospheric and stratospheric applications, with top levels extending into the lower mesosphere (∼ 60 km altitude) in most cases.…”

“…The initial plan for this intercomparison was conceived as a follow-on study of Harvey et al (2021) by the SPARC (Stratosphere-troposphere Processes and their Role in Climate) Data Assimilation Working Group (https:// www.sparc-climate.org/activities/data-assimilation/, last access: 16 November 2021) to examine high-altitude meteorological analyses extending throughout the middle atmosphere. Due to the large computational resources needed to generate these types of meteorological analyses, a detailed multi-year intercomparison is not currently within the scope of the present study.…”