Enhanced internal gravity wave activity and breaking over the northeastern Pacific–eastern Asian region

Šácha, Petr; Kuchař, Aleš; Jacobi, Ch.; Pišoft, Petr

doi:10.5194/acp-15-13097-2015

Cited by 26 publications

(27 citation statements)

References 75 publications

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“…It is worth noting that Mongolia has a particularly large impact on the upper tropospheric flow in the North Pacific (White et al, 2017), a region thought to be particularly important for SSWs (e.g., Garfinkel et al, 2012). The region over Eastern Asia and the North Pacific has been previously highlighted regarding longitudinal asymmetries in the stratosphere (Kozubek et al, 2015;Sácha et al, 2015).…”

Section: Discussionmentioning

confidence: 99%

“…EP fluxes associated with SSWs also show anomalous poleward propagation in the upper troposphere from 22 days prior to an SSW, with anomalous vertical fluxes centered around 70 ∘ N (Limpasuvan et al, 2004), similar to the response we find to the Mongolian mountains. The region over Eastern Asia and the North Pacific has been previously highlighted regarding longitudinal asymmetries in the stratosphere (Kozubek et al, 2015;Sácha et al, 2015). Different mountain ranges have substantially different impacts on the stratospheric circulation, with orographic height clearly not the most important factor.…”

Section: Discussionmentioning

confidence: 99%

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Orography and the Boreal Winter Stratosphere: The Importance of the Mongolian Mountains

White

Battisti

Sheshadri

2018

Geophysical Research Letters

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The impact of mountains on stratospheric circulation is explored using the Whole Atmosphere Community Climate Model. The “Mongolian mountains” decrease the boreal winter stratospheric jet strength by ∼1/3 and increase the frequency of major sudden stratospheric warmings from 0.08 year−1 to the observed 0.60 year−1. These changes are twice the magnitude of the impacts of the Tibetan plateau and Himalayas. Consistent with the decrease in the zonal jet, there is enhanced Eliassen‐Palm flux convergence; this is predominantly from changes in wave propagation pathways through changes to the upper troposphere circulation, not from an increased amplitude of planetary waves reaching the stratosphere. The Mongolian mountains have the greater impact on upper tropospheric circulation due to their meridional location. The Rocky Mountains have no significant impact on the stratospheric jet. Changes in wave propagation in response to the Mongolian mountains are similar to those associated with major sudden stratospheric warming events in observations.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Orography and the Boreal Winter Stratosphere: The Importance of the Mongolian Mountains

White

Battisti

Sheshadri

2018

Geophysical Research Letters

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“…Figure 1 shows the OGWD climatology at 100, 50, 30 and 10 hPa levels. The 100 hPa level is traditionally below the level taken into account in the GW analyses from satellite observations (e.g., Šácha et al, 2015;Wright et al, 2016a). At this level, in the DJF season, the OGWD is dominated by a Himalayan hotspot, which has not received significant attention in observational analyses yet (probably due to its emergence at rather lower levels).…”

Section: Cmam-sd Gwd Climatologymentioning

confidence: 99%

Interannual variability in the gravity wave drag – vertical coupling and possible climate links

Šácha¹,

Mikšovský²,

Pišoft³

2018

Earth Syst. Dynam.

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Abstract. Gravity wave drag (GWD) is an important driver of the middle atmospheric dynamics. However, there are almost no observational constraints on its strength and distribution (especially horizontal). In this study we analyze orographic GWD (OGWD) output from Canadian Middle Atmosphere Model simulation with specified dynamics (CMAM-sd) to illustrate the interannual variability in the OGWD distribution at particular pressure levels in the stratosphere and its relation to major climate oscillations. We have found significant changes in the OGWD distribution and strength depending on the phase of the North Atlantic Oscillation (NAO), quasi-biennial oscillation (QBO) and El Niño-Southern Oscillation. The OGWD variability is shown to be induced by lowertropospheric wind variations to a large extent, and there is also significant variability detected in near-surface momentum fluxes. We argue that the orographic gravity waves (OGWs) and gravity waves (GWs) in general can be a quick mediator of the tropospheric variability into the stratosphere as the modifications of the OGWD distribution can result in different impacts on the stratospheric dynamics during different phases of the studied climate oscillations.

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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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Enhanced internal gravity wave activity and breaking over the northeastern Pacific–eastern Asian region

Cited by 26 publications

References 75 publications

Orography and the Boreal Winter Stratosphere: The Importance of the Mongolian Mountains

Orography and the Boreal Winter Stratosphere: The Importance of the Mongolian Mountains

Interannual variability in the gravity wave drag – vertical coupling and possible climate links

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

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