Observed and Modeled Mountain Waves from the Surface to the Mesosphere Near the Drake Passage

Four state-of-the-science numerical weather prediction (NWP) models were used to perform mountain wave- (MW) resolving hind-casts over the Drake Passage of a 10-day period in 2010 with numerous observed MW cases. The Integrated Forecast System (IFS) and the Icosahedral Nonhydrostatic (ICON) model were run at Δx ≈ 9 and 13 km globally. TheWeather Research and Forecasting (WRF) model and the Met Office Unified Model (UM) were both configured with a Δx = 3 km regional domain. All domains had tops near 1 Pa (z ≈ 80 km). These deep domains allowed quantitative validation against Atmospheric InfraRed Sounder (AIRS) observations, accounting for observation time, viewing geometry, and radiative transfer. All models reproduced observed middle-atmosphere MWs with remarkable skill. Increased horizontal resolution improved validations. Still, all models underrepresented observed MW amplitudes, even after accounting for model effective resolution and instrument noise, suggesting even at Δx ≈ 3 km resolution, small-scale MWs are under-resolved and/or over-diffused. MWdrag parameterizations are still necessary in NWP models at current operational resolutions of Δx ≈ 10 km. Upper GW sponge layers in the operationally configured models significantly, artificially reduced MW amplitudes in the upper stratosphere and mesosphere. In the IFS, parameterized GW drags partly compensated this deficiency, but still, total drags were ≈ 6 time smaller than that resolved at Δx ≈ 3 km. Meridionally propagating MWs significantly enhance zonal drag over the Drake Passage. Interestingly, drag associated with meridional fluxes of zonal momentum (i.e. ) were important; not accounting for these terms results in a drag in the wrong direction at and below the polar night jet.

Turbulent parameters in the middle atmosphere: Theoretical estimates deduced from a gravity-wave resolving general circulation model

We present a scaling analysis for the stratified turbulent and small-scale turbulent regimes of atmospheric flow with emphasis on the mesosphere. We distinguish rotating-stratified macroturbulence turbulence (SMT), stratified turbulence (ST), and small-scale isotropic Kolmogorov turbulence (KT), and we specify the length and time scales and the characteristic velocities for these regimes. It is shown that the buoyancy scale (Lb) and the Ozmidov scale (Lo) are the main parameters that describe the transition from SMT to KT. We employ the buoyancy Reynolds number and horizontal Froude number to characterize ST and KT in the mesosphere. This theory is applied to simulation results from a high-resolution general circulation model with a Smagorinsky-type turbulent diffusion scheme for the sub-grid scale parameterization. The model allows us to derive the turbulent root-mean-square (RMS) velocity in the KT regime. It is found that the turbulent RMS velocity has a single maximum in summer and a double maximum in winter months. The secondary maximum in the winter MLT we associate with a secondary gravity wave breaking phenomenon. The turbulent RMS velocity results from the model agree well with Full Correlation Analyses based on MF-radar measurements. A new scaling for the mesoscale horizontal velocity based on the idea of direct energy cascade in masoscales is proposed. The latter findings for mesoscale and small-scale characteristic velocities supports the idea proposed in this research that mesoscale and small-scale dynamics in the mesosphere are governed by SMT, ST, and KT in the statistical average.

ARISE - Atmospheric Dynamics Research InfraStructure in Europe

<p>The Atmospheric dynamics Research InfraStructure in Europe (ARISE) project has integrated different meteorological and geophysical station networks and technologies providing observations from the ground to the lower thermosphere. A particular emphasis is on improving observations in the middle atmosphere, as this is a crucial region affecting tropospheric weather and climate. Besides supporting innovative prototypes of mobile lidars and microwave radiometers, ARISE utilized the global infrasound network developed for the Comprehensive Nuclear-Test-Ban Treaty (CTBT) verification, the lidar Network for the Detection of Atmospheric Composition Change (NDACC), meteor radars, wind radiometers, ionospheric sounders and satellites.</p> <p>This presentation highlights the objectives and results as well as perspectives of the first two project phases – one within the European Union’s 7th Framework Programme and the second within the Horizon 2020 programme. ARISE has facilitated multi-instrument stations and collocated measurement campaigns at different latitudes in Europe, including the observatories ALOMAR in northern Norway, OHP in southern France and Maïdo on Reunion Island (France), as well as the infrasound station in southern Germany. One ARISE study, for instance, analyzed different ground-based and space-borne observation technologies, revealing systematic biases for temperature and wind in both analysis and reanalysis models. Such biases are critical to the CTBT verification when validating infrasound signal detections by propagation modelling. Also, the potential of infrasound to be assimilated in weather or climate models was proposed, as infrasound can be used to probe winds and cross-wind effects in the middle atmosphere. Meanwhile, offline assimilation tests relying on infrasound data from ground-truth explosion events and wind data of ECMWF’s ERA5 model have been conducted. Overall, the interest of ARISE is to provide atmospheric data products and services for both scientific and civilian-security applications, including the monitoring of extreme events that have an atmospheric signature, such as meteors, thunderstorms or volcanic eruptions. For early warnings on volcanic eruptions, the Volcano Information System (VIS) was proposed as an ARISE product in cooperation with the CTBT organization and the Toulouse Volcanic Ash Advisory Center (VAAC).</p>

Long-term changes in mesospheric wind and wave estimates based on radar observations in both hemispheres

<p class="western">Several studies (Banerjee et al. (2020) and before that Sun et al. (2014)) found a trend reversal between winter and summer circulation in the southern hemisphere around 2000 in the middle atmosphere. One may argue that the negative trend after 2000 is due to the CO<sub>2</sub>-induced change in stratospheric dynamics. However, Ramesh et al. (2020), using the newest WACCM6 simulation and a multiple linear regression model, confirmed that the negative trend in the stratosphere after 2000 can be attributed to ozone recovery. Here we investigate how stratospheric trends relate to trends in the mesosphere and lower thermosphere (MLT) dynamics. Using the adaptive spectral filtering (ASF) method (Stober et al., 2021), we study long-term changes in mesospheric wind and planetary and gravity wave estimates<span lang="en-GB"> of meteor radar stations in the northern (NH: Collm, Kiruna, Sodankyla, CM</span><span lang="en-GB">OR</span><span lang="en-GB">) and southern (SH: Rio Grande, Davis, Rothera) hemisphere, respectively, for the altitude range of 80–100 km. </span>Linear trends have been estimated (from monthly means calculated from the preprocessed original data using ASF) by the Theil–Sen estimator (Theil, 1950; Sen, 1968). The robustness of our fitting method is assessed in terms of spurious trends due to, e.g., high autocorrelation of relatively short time series. The long-term changes are validated in two whole-atmosphere models, namely, GAIA and WACCMX-SD (both nudged in the stratosphere). While both models reveal issues reproducing basic climatology in the mesosphere, GAIA fairly reproduces the trends captured by the meteor radars. Finally, we conclude that the ozone recovery effects in the SH stratosphere influence the dynamics in MLT via gravity wave coupling.</p>

A deeper insight into the dynamics and effects of the Hiccup of the fall transition

<p>In autumn the prevailing wind in the middle atmosphere at mid and high latitudes changes from summer easterly to winter westerly.  This process is not smooth but interrupted by the Hiccup of the fall transition with characteristics similar to a mini sudden stratospheric warming (SSW) which occurs in fall even though the zonal mean zonal wind does not reverse to easterly again. Combining global reanalysis data and satellite observations we improve our knowledge and understanding of the dynamics of the Hiccup of the fall transition in the middle atmosphere. The introduction of a new definition for the onset of the Hiccup focusing now on its core region in the lower mesosphere allows us the automatic detection of a Hiccup in almost every year and thus a deeper insight into its dynamics. For example, we found a latitudinal and altitudinal shift in the zonal wind regime during the Hiccup. We also investigate its 3D-structure and compare the characteristics of the Hiccup in the Northern hemisphere with those in the Southern hemisphere. We found that the latitudinal and altitudinal shift of the zonal wind regime occurs in both hemispheres but is more pronounced in the Northern hemisphere and smoother in the Southern hemisphere.  Additionally, we discuss the possible impact of the Hiccup on the D-region.</p>

Analysis of interaction between parameterized orographic gravity wave drag and resolved dynamics in CMAM.

<div class="page" title="Page 1"> <div class="layoutArea"> <div class="column"> <p>In the extratropical atmosphere, Rossby waves (RWs) and internal gravity waves (GWs) propagating from the troposphere mediate a coupling with the middle atmosphere by influencing the dynamics herein. In current generation chemistry-climate models (CCMs), GWs are usually smaller than the model resolution and the majority of their spectrum therefore must be parameterized. From observations, we know that GWs are intermittent and asymmetrically distributed around the globe, which holds to some extent also for the parameterized GW drag (GWD) (in particular for orographic GWD (oGWD)). The GW parameterizations in CCMs are usually tuned to mitigate biases in the zonal mean climatology of particular quantities, but the complex interaction of parameterized GWs with the large- scale circulation and resolved waves in the models remains to date poorly understood.</p> <p>This presentation will combine observational evidence, idealized modeling and dynamical analysis of a CCM output to study both the short-term and long-term model response to the oGWD. Our results demonstrate that the oGW-resolved dynamics interaction is a complex two-way process, with the most prominent oGWD impact being the alteration of propagation of planetary-scale Rossby waves on a time-scale of a few days. The conclusions give a novel perspective on the importance of oGWD for the stratospheric polar vortex and atmospheric transport studies outlining potential foci of future research.</p> </div> </div> </div>

Stratosphere-Mesosphere exchange: Long term changes and drivers

<p>The meridional overturning mass circulation in the middle atmosphere, i.e. the Brewer-Dobson circulation (BDC), was first discovered before decades based on the distribution of trace gases and a basic analytical concept of BDC has been derived using the transformed Eulerian mean equations. Since then, BDC is usually defined as consisting of a diffusive part, and an advective, residual mean circulation. In the vertical, BDC is separated into two branches – a shallow branch in the lower stratosphere and a deep branch higher in the middle atmosphere.<br />Climate model simulations robustly show that the advective BDC part accelerates in connection to the greenhouse gas-induced climate change and this acceleration dominates the middle atmospheric changes in climate model projections. A prominent quantity that is being studied as a proxy for advective BDC changes is the net tropical upwelling across the tropopause, which measures the amount of mass advected by residual circulation from the troposphere to the stratosphere per unit of time. The upper BDC branch received considerably less research attention than its shallow part, but features some striking phenomenon in the terrestrial atmosphere. It couples the stratosphere and mesosphere and is also responsible for a large portion of interhemispheric transport and coupling in the middle atmosphere.<br />In our research, for the first time, we produce a conceptual study of the advective stratosphere-mesosphere exchange. The analysis of advective exchange of mass between the stratosphere and mesosphere, i.e. the advective mass transport across the stratopause represents another step towards a better understanding of the structure of the upper BDC part and at the same time provides valuable insights into the relatively little-explored stratopause region. We investigate the variability and trends in mass fluxes from the stratosphere to the mesosphere and vice versa based on data from the EMAC-L90 model CCMI-1 simulation for the period 1960-2100. We develop an analytical method that allows us to attribute the changes of transport to causative factors such as acceleration of residual circulation, variable height of the stratopause, change of a geometric shape of the stratopause and changes in width of the upwelling and downwelling regions. The main driver of the increasing mass exchange between the stratosphere and the mesosphere is the faster circulation, however, the other terms are not negligible. The derived methodology offers the possibility of using an analogous procedure also for the tropopause in the future.</p>

Climatology and Long-Term Trends in the Stratospheric Temperature and Wind Using ERA5

This study analyses long-term trends in temperature and wind climatology based on ERA5 data. We study climatology and trends separately for every decade from 1980 to 2020 and their changes during this period. This study is focused on the pressure levels between 100–1 hPa, which essentially covers the whole stratosphere. We also analyze the impact of the sudden stratospheric warmings (SSW), North Atlantic Oscillation (NAO), El Nino Southern Oscillation (ENSO) and Quasi-biennial oscillation (QBO). This helps us to find details of climatology and trend behavior in the stratosphere in connection to these phenomena. ERA5 is one of the newest reanalysis, which is widely used for the middle atmosphere. We identify the largest differences which occur between 1990–2000 and 2000–2010 in both temperature climatology and trends. We suggest that these differences could relate to the different occurrence frequency of SSWs in 1990–2000 versus 2000–2010.

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

Detailed meteorological analyses based on observations extending through the middle atmosphere (∼ 15 to 100 km altitude) can provide key information to whole atmosphere modeling systems regarding the physical mechanisms linking day-to-day changes in ionospheric electron density to meteorological variability near the Earth's surface. However, the extent to which independent middle atmosphere analyses differ in their representation of wave-induced coupling to the ionosphere is unclear. 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, which includes a major sudden stratospheric warming (SSW). 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 to 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 d and quasi-2 d 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 mesosphere and lower thermosphere 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.