Directional gravity wave momentum fluxes in the stratosphere derived from high‐resolution AIRS temperature data

Ern, Manfred; Hoffmann, Lars; Preusse, Peter

doi:10.1002/2016gl072007

Cited by 96 publications

(151 citation statements)

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“…However, global satellite observations are needed to determine dominant tropospheric source regions and processes as well as global propagation pathways and the resulting gravity wave drag imposed on the mean flow to constrain GW parameterizations for climate and weather prediction models (Alexander et al, 2010;Geller et al, 2013). Since the pioneering work by Fetzer and Gille (1994), Wu and Waters (1996), and Eckermann and Preusse (1999) there have been many attempts to characterize the global distribution of gravity wave activity using such different remote-sensing techniques as Limb (e.g., Ern et al, 2004Ern et al, , 2011Preusse et al, 2009;Zhang et al, 2012) and Nadir sounders (e.g., Hoffmann et al, 2016;Ern et al, 2017), as well as GPS-based radio occultation (RO) measurements (e.g., Tsuda et al, 2000;Hei et al, 2008;Schmidt et al, 2008Schmidt et al, , 2016Fröhlich et al, 2007;Hindley et al, 2015;Šácha et al, 2015;Khaykin et al, 2015;Khaykin, 2016). This paper focusses on the derivation of gravity wave potential energy densities (E P ) from GPS RO measurements on board the operational METOP-A and METOP-B satellites operated by EUMETSAT (European Organisation for the Exploitation of Meteorological Satellites) and the subsequent systematic comparison of E P fields with ECMWF (European Centre for Medium-Range Weather Forecasts) operational forecast and reanalysis data.…”

Section: Introductionmentioning

confidence: 99%

An intercomparison of stratospheric gravity wave potential energy densities from METOP GPS radio occultation measurements and ECMWF model data

2018

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Abstract. Temperature profiles based on radio occultation (RO) measurements with the operational European METOP satellites are used to derive monthly mean global distributions of stratospheric (20-40 km) gravity wave (GW) potential energy densities (E P ) for the period July 2014-December 2016. In order to test whether the sampling and data quality of this data set is sufficient for scientific analysis, we investigate to what degree the METOP observations agree quantitatively with ECMWF operational analysis (IFS data) and reanalysis (ERA-Interim) data. A systematic comparison between corresponding monthly mean temperature fields determined for a latitude-longitude-altitude grid of 5 • by 10 • by 1 km is carried out. This yields very low systematic differences between RO and model data below 30 km (i.e., median temperature differences is between −0.2 and +0.3 K), which increases with height to yield median differences of +1.0 K at 34 km and +2.2 K at 40 km. Comparing E P values for three selected locations at which also ground-based lidar measurements are available yields excellent agreement between RO and IFS data below 35 km. ERA-Interim underestimates E P under conditions of strong local mountain wave forcing over northern Scandinavia which is apparently not resolved by the model. Above 35 km, RO values are consistently much larger than model values, which is likely caused by the model sponge layer, which damps small-scale fluctuations above ∼ 32 km altitude. Another reason is the wellknown significant increase of noise in RO measurements above 35 km. The comparison between RO and lidar data reveals very good qualitative agreement in terms of the seasonal variation of E P , but RO values are consistently smaller than lidar values by about a factor of 2. This discrepancy is likely caused by the very different sampling characteristics of RO and lidar observations. Direct comparison of the global data set of RO and model E P fields shows large correlation coefficients (0.4-1.0) with a general degradation with increasing altitude. Concerning absolute differences between observed and modeled E P values, the median difference is relatively small at all altitudes (but increasing with altitude) with an exception between 20 and 25 km, where the median difference between RO and model data is increased and the corresponding variability is also found to be very large. The reason for this is identified as an artifact of the E P algorithm: this erroneously interprets the pronounced climatological feature of the tropical tropopause inversion layer (TTIL) as GW activity, hence yielding very large E P values in this area and also large differences between model and observations. This is because the RO data show a more pronounced TTIL than IFS and ERA-Interim. We suggest a correction for this effect based on an estimate of this "artificial" E P using monthly mean zonal mean temperature profiles. This correction may be recommended for application to data sets that can only be analyzed using a vertical background determination me...

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Section: Introductionmentioning

confidence: 99%

An intercomparison of stratospheric gravity wave potential energy densities from METOP GPS radio occultation measurements and ECMWF model data

2018

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“…For example, it is known that deep convection excites a broad spectrum of gravity wave phase speeds (e.g., Beres et al, 2004), as well as a broad range of gravity wave vertical and, in particular, horizontal wavelengths. There are indications that the horizontal scales range from several tens to several hundreds of kilometers (e.g., Choi et al, 2012;Trinh et al, 2016;Kalisch et al, 2016;Ern et al, 2017). Similarly, gravity waves emitted from jets and fronts cover horizontal wavelengths from less than 100 km to more than 500 km (e.g., Plougonven and Zhang, 2014, and references therein), and the horizontal scales of mountain waves cover a range of less than 10 km to several hundred kilometers (e.g., Fritts et al, 2016;Ehard et al, 2017, and references therein).…”

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confidence: 99%

“…Tsuchiya et al (2016) investigated interactions of gravity waves with the Madden-Julian Oscillation (MJO) using the same data set. Ern et al (2017) and Wright et al (2017) applied 3-D spectral analysis techniques to the AIRS high-resolution retrievals, thereby estimating directional gravity wave momentum flux.…”

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confidence: 99%

Intercomparison of AIRS and HIRDLS stratospheric gravity wave observations

Meyer¹,

Ern²,

Hoffmann³

et al. 2018

Atmos. Meas. Tech.

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Abstract. We investigate stratospheric gravity wave observations by the Atmospheric InfraRed Sounder (AIRS) aboard NASA's Aqua satellite and the High Resolution Dynamics Limb Sounder (HIRDLS) aboard NASA's Aura satellite. AIRS operational temperature retrievals are typically not used for studies of gravity waves, because their vertical and horizontal resolution is rather limited. This study uses data of a high-resolution retrieval which provides stratospheric temperature profiles for each individual satellite footprint. Therefore the horizontal sampling of the high-resolution retrieval is 9 times better than that of the operational retrieval. HIRDLS provides 2-D spectral information of observed gravity waves in terms of along-track and vertical wavelengths. AIRS as a nadir sounder is more sensitive to short-horizontal-wavelength gravity waves, and HIRDLS as a limb sounder is more sensitive to short-vertical-wavelength gravity waves. Therefore HIRDLS is ideally suited to complement AIRS observations. A calculated momentum flux factor indicates that the waves seen by AIRS contribute significantly to momentum flux, even if the AIRS temperature variance may be small compared to HIRDLS. The stratospheric wave structures observed by AIRS and HIRDLS often agree very well. Case studies of a mountain wave event and a non-orographic wave event demonstrate that the observed phase structures of AIRS and HIRDLS are also similar. AIRS has a coarser vertical resolution, which results in an attenuation of the amplitude and coarser vertical wavelengths than for HIRDLS. However, AIRS has a much higher horizontal resolution, and the propagation direction of the waves can be clearly identified in geographical maps. The horizontal orientation of the phase fronts can be deduced from AIRS 3-D temperature fields. This is a restricting factor for gravity wave analyses of limb measurements. Additionally, temperature variances with respect to stratospheric gravity wave activity are compared on a statistical basis. The complete HIRDLS measurement period from January 2005 to March 2008 is covered. The seasonal and latitudinal distributions of gravity wave activity as observed by AIRS and HIRDLS agree well. A strong annual cycle at mid-and high latitudes is found in time series of gravity wave variances at 42 km, which has its maxima during wintertime and its minima during summertime. The variability is largest during austral wintertime at 60 • S. Variations in the zonal winds at 2.5 hPa are associated with large variability in gravity wave variances. Altogether, gravity wave variances of AIRS and HIRDLS are complementary to each other. Large parts of the gravity wave spectrum are covered by joint observations. This opens up fascinating vistas for future gravity wave research.

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“…Fritts and Alexander, 2003). Therefore, amplitudes, wavelengths, and phases of a GW can be determined from its temperature structure (Fritts et al, 2014;Ern et al, 2004Ern et al, , 2017.…”

Section: Introductionmentioning

confidence: 99%

“…Utilizing limb soundings, these data sets include temperature or density data acquired by the Limb Infrared Monitor of the Stratosphere (LIMS) Gille, 1994, 1996), the Global Positioning System (GPS) radio occultation (RO) (Tsuda et al, 2000), Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) (Eckermann and Preusse, 1999), Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) (Ern et al, 2011;Preusse et al, 2009a), High Resolution Dynamics Limb Sounder (HIRDLS) (Alexander et al, 2008), and Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) aircraft (Riese et al, 2014;Kaufmann et al, 2015;Ungermann et al, 2010bUngermann et al, , 2011. GWs can be also characterized by nadir-viewing instruments, such as the Atmospheric Infrared Sounder (AIRS) (Alexander and Barnet, 2007;Hoffmann and Alexander, 2009;Gong et al, 2012;Hoffmann et al, 2016;Ern et al, 2017), and the Advanced Microwave Sounding Unit (AMSU) (Wu, 2004).…”

Section: Introductionmentioning

confidence: 99%

Tomographic reconstruction of atmospheric gravity wave parameters from airglow observations

et al. 2017

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Abstract. Gravity waves (GWs) play an important role in the dynamics of the mesosphere and lower thermosphere (MLT). Therefore, global observations of GWs in the MLT region are of particular interest. The small scales of GWs, however, pose a major problem for the observation of GWs from space. We propose a new observation strategy for GWs in the mesopause region by combining limb and sub-limb satellite-borne remote sensing measurements for improving the spatial resolution of temperatures that are retrieved from atmospheric soundings. In our study, we simulate satellite observations of the rotational structure of the O 2 A-band nightglow. A key element of the new method is the ability of the instrument or the satellite to operate in so-called "target mode", i.e. to point at a particular point in the atmosphere and collect radiances at different viewing angles. These multi-angle measurements of a selected region allow for tomographic 2-D reconstruction of the atmospheric state, in particular of GW structures. The feasibility of this tomographic retrieval approach is assessed using simulated measurements. It shows that one major advantage of this observation strategy is that GWs can be observed on a much smaller scale than conventional observations. We derive a GW sensitivity function, and it is shown that "target mode" observations are able to capture GWs with horizontal wavelengths as short as ∼ 50 km for a large range of vertical wavelengths. This is far better than the horizontal wavelength limit of 100-200 km obtained from conventional limb sounding.

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Directional gravity wave momentum fluxes in the stratosphere derived from high‐resolution AIRS temperature data

Cited by 96 publications

References 60 publications

An intercomparison of stratospheric gravity wave potential energy densities from METOP GPS radio occultation measurements and ECMWF model data

An intercomparison of stratospheric gravity wave potential energy densities from METOP GPS radio occultation measurements and ECMWF model data

Intercomparison of AIRS and HIRDLS stratospheric gravity wave observations

Tomographic reconstruction of atmospheric gravity wave parameters from airglow observations

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