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Special Sensor Microwave Imager/Sounder (SSMIS) on operational Defense Meteorological Satellite Program (DMSP) platforms. Additional details are provided in section 2b in Eckermann et al. (2016) . For estimating the planetary wave activity in the stratosphere and mesosphere, temperature and geopotential height from the MLS are analyzed ( Waters et al. 2006 ; Livesey et al. 2017 ). MLS covers Earth’s atmosphere from 82°S to 82°N on each sun-ynchronous sorbit and the data are analyzed between
Special Sensor Microwave Imager/Sounder (SSMIS) on operational Defense Meteorological Satellite Program (DMSP) platforms. Additional details are provided in section 2b in Eckermann et al. (2016) . For estimating the planetary wave activity in the stratosphere and mesosphere, temperature and geopotential height from the MLS are analyzed ( Waters et al. 2006 ; Livesey et al. 2017 ). MLS covers Earth’s atmosphere from 82°S to 82°N on each sun-ynchronous sorbit and the data are analyzed between
driving. While the changes of the stratospheric wind from west to east imply changes in the propagation conditions for GWs, leading to a breakdown of dynamic heating in the mesosphere within a few days, the return to winter with stratospheric westerlies leads to enhanced dynamic heating through downwelling during a more extended time. This depends not only on the strength of the perturbation during the peak of the SSW but also on the seasonal and planetary-scale state of the atmosphere. Hence
driving. While the changes of the stratospheric wind from west to east imply changes in the propagation conditions for GWs, leading to a breakdown of dynamic heating in the mesosphere within a few days, the return to winter with stratospheric westerlies leads to enhanced dynamic heating through downwelling during a more extended time. This depends not only on the strength of the perturbation during the peak of the SSW but also on the seasonal and planetary-scale state of the atmosphere. Hence
turbulence due to large GW amplitudes and superpositions; 6) energy, momentum, and tracer transports; 7) parameterizations of GW effects in large-scale (LS) models; and 8) GW influences on other processes such as convection, cloud microphysics, chemical reactions, and plasma dynamics and instabilities in the ionosphere. Many other papers have addressed important GW roles in oceans, lakes, other planetary atmospheres, and stellar interiors. PREVIOUS RESEARCH. The scope of GW dynamics and roles is
turbulence due to large GW amplitudes and superpositions; 6) energy, momentum, and tracer transports; 7) parameterizations of GW effects in large-scale (LS) models; and 8) GW influences on other processes such as convection, cloud microphysics, chemical reactions, and plasma dynamics and instabilities in the ionosphere. Many other papers have addressed important GW roles in oceans, lakes, other planetary atmospheres, and stellar interiors. PREVIOUS RESEARCH. The scope of GW dynamics and roles is
;2 . Holton , J. , and M. Alexander , 2000 : The role of waves in the transport circulation of the middle atmosphere . Atmospheric Science across the Stratopause , Geophys. Monogr. , Vol. 123, Amer. Geophys. Union, 21–35 . Hong , S.-Y. , and J.-O. Lim , 2006 : The WRF single-moment 6-class microphysics scheme (WSM6) . J. Korean Meteor. Soc. , 42 , 129 – 151 . Hu , X.-M. , J. Nielsen-Gammon , and F. Zhang , 2010 : Evaluation of three planetary boundary layer schemes in
;2 . Holton , J. , and M. Alexander , 2000 : The role of waves in the transport circulation of the middle atmosphere . Atmospheric Science across the Stratopause , Geophys. Monogr. , Vol. 123, Amer. Geophys. Union, 21–35 . Hong , S.-Y. , and J.-O. Lim , 2006 : The WRF single-moment 6-class microphysics scheme (WSM6) . J. Korean Meteor. Soc. , 42 , 129 – 151 . Hu , X.-M. , J. Nielsen-Gammon , and F. Zhang , 2010 : Evaluation of three planetary boundary layer schemes in
1. Introduction As one of the most fundamental physical modes in meteorology, gravity waves (GWs) are ubiquitous buoyancy oscillations in the atmosphere. The sources of excited gravity waves include, among others, topographic forcing ( Smith 1980 ; Menchaca and Durran 2017 ), convection ( Alexander et al. 1995 ; Lane et al. 2001 ), the jets ( Zhang 2004 ; Plougonven and Zhang 2014 ; Hien et al. 2018 ), frontal systems ( Snyder et al. 1993 ; Griffiths and Reeder 1996 ), and shear
1. Introduction As one of the most fundamental physical modes in meteorology, gravity waves (GWs) are ubiquitous buoyancy oscillations in the atmosphere. The sources of excited gravity waves include, among others, topographic forcing ( Smith 1980 ; Menchaca and Durran 2017 ), convection ( Alexander et al. 1995 ; Lane et al. 2001 ), the jets ( Zhang 2004 ; Plougonven and Zhang 2014 ; Hien et al. 2018 ), frontal systems ( Snyder et al. 1993 ; Griffiths and Reeder 1996 ), and shear
-state wave field and background flow, (ii) the neglect of the impact of horizontal large-scale flow gradients on the GWs, and (iii) one-dimensional vertical propagation. Under these conditions, the wave-dissipation or nonacceleration theorem states that GWs can deposit their momentum only where they break. In theoretical analyses of this problem in a rotating atmosphere, Bühler and McIntyre (1999 , 2003 , 2005 ) point out that the steady-state assumption can lead to the neglect of important aspects of
-state wave field and background flow, (ii) the neglect of the impact of horizontal large-scale flow gradients on the GWs, and (iii) one-dimensional vertical propagation. Under these conditions, the wave-dissipation or nonacceleration theorem states that GWs can deposit their momentum only where they break. In theoretical analyses of this problem in a rotating atmosphere, Bühler and McIntyre (1999 , 2003 , 2005 ) point out that the steady-state assumption can lead to the neglect of important aspects of
the Arctic stratospheric vortex were unusually cold ( Fig. 3 ). In November–December 2015, the Arctic vortex was minimally disturbed by upward-propagating planetary waves ( Matthias et al. 2016 ) and the polar cap minimum temperature T MIN between 65° and 90°N dropped well below the climatological mean. The red T MIN line in Fig. 3 reveals that the threshold of T NAT at 50 hPa was already reached at the beginning of December 2015, and T MIN dropped below T FROST at the end of 2015
the Arctic stratospheric vortex were unusually cold ( Fig. 3 ). In November–December 2015, the Arctic vortex was minimally disturbed by upward-propagating planetary waves ( Matthias et al. 2016 ) and the polar cap minimum temperature T MIN between 65° and 90°N dropped well below the climatological mean. The red T MIN line in Fig. 3 reveals that the threshold of T NAT at 50 hPa was already reached at the beginning of December 2015, and T MIN dropped below T FROST at the end of 2015
1. Introduction Internal gravity waves (GWs) play a significant role in atmospheric dynamics on various spatial scales ( Fritts and Alexander 2003 ; Kim et al. 2003 ; Alexander et al. 2010 ; Plougonven and Zhang 2014 ). Already in the lower atmosphere GW effects are manifold. Examples include the triggering of high-impact weather (e.g., Zhang et al. 2001 , 2003 ) and clear-air turbulence ( Koch et al. 2005 ), as well as the effect of small-scale GWs of orographic origin on the predicted
1. Introduction Internal gravity waves (GWs) play a significant role in atmospheric dynamics on various spatial scales ( Fritts and Alexander 2003 ; Kim et al. 2003 ; Alexander et al. 2010 ; Plougonven and Zhang 2014 ). Already in the lower atmosphere GW effects are manifold. Examples include the triggering of high-impact weather (e.g., Zhang et al. 2001 , 2003 ) and clear-air turbulence ( Koch et al. 2005 ), as well as the effect of small-scale GWs of orographic origin on the predicted
1. Introduction Atmospheric gravity waves (GWs) play a key role in defining the large-scale global circulation and thermal structure of the middle and upper atmosphere, and they are important drivers of global atmospheric variability on various time scales. They are the main driver of the mesospheric summer to winter pole-to-pole circulation ( Holton 1982 , 1983 ) and the reason for the cold summer mesopause ( Björn 1984 ). In the stratosphere, GWs affect the timing of the springtime
1. Introduction Atmospheric gravity waves (GWs) play a key role in defining the large-scale global circulation and thermal structure of the middle and upper atmosphere, and they are important drivers of global atmospheric variability on various time scales. They are the main driver of the mesospheric summer to winter pole-to-pole circulation ( Holton 1982 , 1983 ) and the reason for the cold summer mesopause ( Björn 1984 ). In the stratosphere, GWs affect the timing of the springtime
-based lidar observations in the lee of New Zealand’s Alps during DEEPWAVE revealed enhanced gravity wave activity in the stratosphere and mesosphere, which lasted about 1–3 days and alternated with quiescent periods ( Kaifler et al. 2015 ). The gravity wave forcing due to passing weather systems, the appearance of tropopause jets, and the middle atmosphere wave response were all observed with a similar frequency and duration of 2–4 days ( Fritts et al. 2016 ; Gisinger et al. 2017 ). The episodic nature
-based lidar observations in the lee of New Zealand’s Alps during DEEPWAVE revealed enhanced gravity wave activity in the stratosphere and mesosphere, which lasted about 1–3 days and alternated with quiescent periods ( Kaifler et al. 2015 ). The gravity wave forcing due to passing weather systems, the appearance of tropopause jets, and the middle atmosphere wave response were all observed with a similar frequency and duration of 2–4 days ( Fritts et al. 2016 ; Gisinger et al. 2017 ). The episodic nature
