Atmospheric gravity waves (GWs) play an important role in atmospheric dynamics but accurately representing them in general circulation models (GCMs) is challenging. This is especially true for ...orographic GWs generated by wind flow over small mountainous islands in the Southern Ocean. Currently, these islands lie in the “grey zone” of global model resolution, where they are neither fully resolved nor fully parameterised. It is expected that as GCMs approach the spatial resolution of current high-resolution local-area models, small-island GW sources may be resolved without the need for parameterisations. But how realistic are the resolved GWs in these high-resolution simulations compared to observations? Here, we test a high-resolution (1.5 km horizontal grid, 118 vertical levels) local-area configuration of the Met Office Unified Model over the mountainous island of South Georgia (54∘ S, 36∘ W), running without GW parameterisations. The island's orography is well resolved in the model, and real-time boundary conditions are used for two time periods during July 2013 and June–July 2015. We compare simulated GWs in the model to coincident 3-D satellite observations from the Atmospheric Infrared Sounder (AIRS) on board Aqua. By carefully sampling the model using the AIRS resolution and measurement footprints (denoted as model sampled as AIRS hereafter), we present the first like-for-like comparison of simulated and observed 3-D GW amplitudes, wavelengths and directional GW momentum flux (GWMF) over the island using a 3-D S-transform method. We find that the timing, magnitude and direction of simulated GWMF over South Georgia are in good general agreement with observations, once the AIRS sampling and resolution are applied to the model. Area-averaged zonal GWMF during these 2 months is westward at around 5.3 and 5.6 mPa in AIRS and model sampled as AIRS datasets respectively, but values directly over the island can exceed 50 mPa. However, up to 35 % of the total GWMF in AIRS is actually found upwind of the island compared to only 17 % in the model sampled as AIRS, suggesting that non-orographic GWs observed by AIRS may be underestimated in our model configuration. Meridional GWMF results show a small northward bias (∼20 %) in the model sampled as AIRS that may correspond to a southward wind bias compared to coincident radiosonde measurements. Finally, we present one example of large-amplitude (T′≈15–20 K at 45 km altitude) GWs at short horizontal wavelengths (λH≈30–40 km) directly over the island in AIRS measurements that show excellent agreement with the model sampled as AIRS. This suggests that orographic GWs in the full-resolution model with T′≈45 K and λH≈30–40 km can occur in reality. Our study demonstrates that not only can high-resolution local-area models simulate realistic stratospheric GWs over small mountainous islands but the application of satellite sampling and resolution to these models can also be a highly effective method for their validation.
The mesosphere and lower thermosphere (MLT) is a critical region that must be accurately reproduced in general circulation models (GCMs) that aim to
include the coupling between the lower and middle ...atmosphere and the thermosphere. An accurate representation of the MLT is thus important for
improved climate modelling and the development of a whole atmosphere model. This is because the atmospheric waves at these heights are particularly
large, and so the energy and momentum they carry is an important driver of climatological phenomena through the whole atmosphere, affecting
terrestrial and space weather. The Extended Unified Model (ExUM) is the recently developed version of the Met Office's Unified Model which has been
extended to model the MLT. The capability of the ExUM to model atmospheric winds and tides in the MLT is currently unknown. Here, we present the
first study of winds and tides from the ExUM. We make a comparison against meteor radar observations of winds and tides from 2006 between 80 and
100 km over two radar stations – Rothera (68∘ S, 68∘ W) and Ascension Island (8∘ S, 14∘ W). These
locations are chosen to study tides in two very different tidal regimes – the equatorial regime, where the diurnal (24 h) tide dominates, and the
polar regime, where the semi-diurnal (12 h) tide dominates. The results of this study illustrate that the ExUM is capable of reproducing
atmospheric winds and tides that capture many of the key characteristics seen in meteor radar observations, such as zonal and meridional wind
maxima and minima, the increase in tidal amplitude with increasing height, and the decrease in tidal phase with increasing height. In particular, in
the equatorial regime some essential characteristics of the background winds, tidal amplitudes and tidal phases are well captured but with
significant differences in detail. In the polar regime, the difference is more pronounced. The ExUM zonal background winds in austral winter are
primarily westward rather than eastward, and in austral summer they are larger than observed above 90 km. The ExUM tidal amplitudes here are in
general consistent with observed values, but they are also larger than observed values above 90 km in austral summer. The tidal phases are
generally well replicated in this regime. We propose that the bias in background winds in the polar regime is a consequence of the lack of in situ
gravity wave generation to generate eastward fluxes in the MLT. The results of this study indicate that the ExUM has a good natural capability for
modelling atmospheric winds and tides in the MLT but that there is room for improvement in the model physics in this region. This highlights the
need for modifications to the physical parameterization schemes used in the model in this region – such as the non-orographic spectral gravity wave
scheme – to improve aspects such as polar circulation. To this end, we make specific recommendations of changes that can be implemented to improve
the accuracy of the ExUM in the MLT.
The Hunga Tonga-Hunga Ha'apai volcano erupted on 15 January 2022, launching Lamb waves and gravity waves into the atmosphere. In this study, we present results using 13 globally distributed meteor ...radars and identify the volcanogenic gravity waves in the mesospheric/lower thermospheric winds. Leveraging the High-Altitude Mechanistic general Circulation Model (HIAMCM), we compare the global propagation of these gravity waves. We observed an eastward-propagating gravity wave packet with an observed phase speed of 240 ± 5.7 m s.sup.-1 and a westward-propagating gravity wave with an observed phase speed of 166.5 ± 6.4 m s.sup.-1 . We identified these waves in HIAMCM and obtained very good agreement of the observed phase speeds of 239.5 ± 4.3 and 162.2 ± 6.1 m s.sup.-1 for the eastward the westward waves, respectively. Considering that HIAMCM perturbations in the mesosphere/lower thermosphere were the result of the secondary waves generated by the dissipation of the primary gravity waves from the volcanic eruption, this affirms the importance of higher-order wave generation. Furthermore, based on meteor radar observations of the gravity wave propagation around the globe, we estimate the eruption time to be within 6 min of the nominal value of 15 January 2022 04:15 UTC, and we localized the volcanic eruption to be within 78 km relative to the World Geodetic System 84 coordinates of the volcano, confirming our estimates to be realistic.
Climatological structure of the quasi-2-day wave (Q2DW) at middle latitudes in temperature and horizontal winds in the mesosphere and lower thermosphere (MLT) was compared between the northern and ...southern hemispheres. Determination of the Q2DW in temperature was based on observation data by the Microwave Limb Sounder (MLS) onboard NASA's Earth Observing System (EOS) Aura satellite over 17 years from August 2004 to May 2021 and the Q2DW in horizontal winds was derived from Aura/MLS geopotential height data using balance equations. Amplitudes were maximized in summer in the southern hemisphere and in the meridional wind in the northern hemisphere, but in winter in the zonal wind in the northern hemisphere. Summer amplitudes were larger in the meridional wind than the zonal wind in the southern hemisphere, but zonal amplitudes in winter were larger than meridional amplitudes in summer in the northern hemisphere. Westward propagating zonal wavenumber 3 (W3) was largest in both hemispheres, but in addition to well-known W4, W3, W2 and eastward propagating zonal wavenumber 2 (E2), we also found W1, zonally symmetric standing (S0), and E1. Eliassen-Palm fluxes were derived for each mode. W3, W2, W1, and E2 fluxes were exhibited upward and poleward in January in the southern hemisphere while only W3 fluxes were exhibited clearly upward and poleward in July in the northern hemisphere. The balance winds and radar winds agreed in both amplitude and phase in the southern hemisphere and at lower latitudes in the northern hemisphere in January, and at lower latitudes in both hemispheres in July. Furthermore, the Q2DW is modulation in amplitude and phase from the W3 by accumulating other modes.
•The Q2DW winds derived from MLS/balance wind exhibited enhancements in summer and winter in both hemispheres.•W1, S0, and E1 modes were found in the Q2DW in January and July in both northern and southern hemispheres.•Q2DW EP fluxes exhibited unique structure for each mode.•Q2DW winds agreed between MLS/balance winds and meteor radar winds at lower middle latitudes in January and July.
A joint special issue explores the potential of collaboration to help understand atmospheric gravity waves in the Polar Regions and their effect on global circulation.
Meteorological and atmospheric models are being extended up to 80 km altitude but there are very few observing techniques that can measure stratospheric–mesospheric winds at altitudes between 20 and ...80 km to verify model datasets. Here we demonstrate the feasibility of horizontal wind profile measurements using ground-based passive millimetre-wave spectroradiometric observations of ozone lines centred at 231.28, 249.79, and 249.96 GHz. Vertical profiles of horizontal winds are retrieved from forward and inverse modelling simulations of the line-of-sight Doppler-shifted atmospheric emission lines above Halley station (75°37′ S, 26°14′ W), Antarctica. For a radiometer with a system temperature of 1400 K and 30 kHz spectral resolution observing the ozone 231.28 GHz line we estimate that 12 h zonal and meridional wind profiles could be determined over the altitude range 25–74 km in winter, and 28–66 km in summer. Height-dependent measurement uncertainties are in the range 3–8 m s−1 and vertical resolution ∼ 8–16 km. Under optimum observing conditions at Halley a temporal resolution of 1.5 h for measuring either zonal or meridional winds is possible, reducing to 0.5 h for a radiometer with a 700 K system temperature. Combining observations of the 231.28 GHz ozone line and the 230.54 GHz carbon monoxide line gives additional altitude coverage at 85 ± 12 km. The effects of clear-sky seasonal mean winter/summer conditions, zenith angle of the received atmospheric emission, and spectrometer frequency resolution on the altitude coverage, measurement uncertainty, and height and time resolution of the retrieved wind profiles have been determined.
Progress in the science of weather -- on Earth and in space -- depends on understanding the whole of the atmosphere, from the surface of the Earth into space. Tracy Moffat-Griffin reports on an RAS ...specialist discussion meeting that crossed traditional disciplinary boundaries. PUBLICATION ABSTRACT
1. Overview
The 3rd ANtarctic Gravity Wave Instrument Network （ANGWIN） science workshop was held on 12-14 April 2016 in Cambridge, UK. ANGWIN is a highly successful grassroots program that was ...started in 2011 （in the Cornish English dialect ANGWIN means ＂the white＂）. Although ini- tially focused on the Antarctic, we now aim to develop collaborations in both polar regions.
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