scholarly journals Impact of local gravity wave forcing in the lower stratosphere on the polar vortex stability: Effect of longitudinal displacement

2019 ◽  
Author(s):  
Nadja Samtleben ◽  
Aleš Kuchař ◽  
Petr Šácha ◽  
Petr Pišoft ◽  
Christoph Jacobi
Keyword(s):  
Refractive Index ◽  
North America ◽  
Gravity Wave ◽  
Rocky Mountains ◽  
Polar Region ◽  
Lower Stratosphere ◽  
Middle Atmosphere ◽  
Negative Refractive Index ◽  
Polar Vortex ◽  
Longitudinal Distribution

Abstract. The effects of gravity wave (GW) breaking hotspots in the lower stratosphere, especially the role of their longitudinal distribution, are evaluated through a sensitivity study by using a simplified middle atmosphere circulation model. For the position of the local GW hotspot, we first selected a fixed latitude range between 37.5 and 62.5° N and a longitude range from 112.5 to 168.75° E, as well as an altitude range between 18 and 30 km. This confined GW hotspot was then shifted in longitude by 45° steps, so that we created 8 artificial GW hotspots in total. Strongly depending on the location of the respective GW hotspot with regard to the phase of the stationary planetary wave of wavenumber 1 (SPW 1) generated in the model, the local GW forcing may interfere constructively or destructively with the modeled SPW 1. GW hotspots, which are located in North America near the Rocky Mountains lead to an increase of the SPW 1 amplitude and EP flux, while hotspots located near the Caucasus, the Himalayas or the Scandinavian region lead to a decrease of these parameters. Thus, the polar vortex is less (Caucasus and Himalayan hotspots) or more weakened (Rocky Mountains hotspot) by the prevailing SPW activity. Because the local GW forcing generally suppresses wave propagation at midlatitudes, the SPWs 1 are propagating into the polar region, where the refractive index turned to positive values for the majority of the artificial GW hotspots. An additional source of SPW 1 may be local instabilities indicated by the reversal in the meridional potential vorticity gradient in the polar region in connection with a positive EP divergence. In most cases, the SPWs 1 are breaking in the polar region and maintain the deceleration and thus, the weakening of the polar vortex. While the SPWs 1 that form when the GW hotspots are located above North America propagate through the polar region into the middle atmosphere, the SPWs 1 in the remaining GW hotspot simulations were not able to propagate further upwards because of a negative refractive index above the positive refractive index anomaly in the polar region. GW hotspots, which are located near the Himalayas influence the mesosphere/lower thermosphere region because of possible local instabilities in the lower mesosphere generating additional SPWs 1, which propagate upwards into the mesosphere.

scholarly journals Impact of local gravity wave forcing in the lower stratosphere on the polar vortex stability: effect of longitudinal displacement

2020 ◽  
Vol 38 (1) ◽  
pp. 95-108 ◽  
Author(s):  
Nadja Samtleben ◽  
Aleš Kuchař ◽  
Petr Šácha ◽  
Petr Pišoft ◽  
Christoph Jacobi
Keyword(s):  
Refractive Index ◽  
North America ◽  
Gravity Wave ◽  
Rocky Mountains ◽  
Polar Region ◽  
Lower Stratosphere ◽  
Middle Atmosphere ◽  
Negative Refractive Index ◽  
Polar Vortex ◽  
Longitudinal Distribution

Abstract. The effects of gravity wave (GW) breaking hotspots in the lower stratosphere, especially the role of their longitudinal distribution, are evaluated through a sensitivity study by using a simplified middle atmosphere circulation model. For the position of the local GW hotspot, we first selected a fixed latitude range between 37.5 and 62.5∘ N and a longitude range from 112.5 to 168.75∘ E, as well as an altitude range between 18 and 30 km. This confined GW hotspot was then shifted in longitude by 45∘ steps, so that we created eight artificial GW hotspots in total. Strongly dependent on the location of the respective GW hotspot with regard to the phase of the stationary planetary wave of wavenumber 1 (SPW 1) generated in the model, the local GW forcing may interfere constructively or destructively with the modeled SPW 1. GW hotspots, which are located in North America near the Rocky Mountains, lead to an increase in the SPW 1 amplitude and EP flux, while hotspots located near the Caucasus, the Himalayas or the Scandinavian region lead to a decrease in these parameters. Thus, the polar vortex is less (Caucasus and Himalayan hotspots) or more weakened (Rocky Mountains hotspot) by the prevailing SPW activity. Because the local GW forcing generally suppresses wave propagation at midlatitudes, the SPWs 1 propagate into the polar region, where the refractive index turned to positive values for the majority of the artificial GW hotspots. An additional source of SPW 1 may be local instabilities indicated by the reversal in the meridional potential vorticity gradient in the polar region in connection with a positive EP divergence. In most cases, the SPWs 1 are breaking in the polar region and maintain the deceleration and, thus, the weakening of the polar vortex. While the SPWs 1 that form when the GW hotspots are located above North America propagate through the polar region into the middle atmosphere, the SPWs 1 in the remaining GW hotspot simulations were not able to propagate further upwards because of a negative refractive index above the positive refractive index anomaly in the polar region. GW hotspots, which are located near the Himalayas, influence the mesosphere–lower thermosphere region because of possible local instabilities in the lower mesosphere generating additional SPWs 1, which propagate upwards into the mesosphere.

scholarly journals Effect of latitudinally displaced gravity wave forcing in the lower stratosphere on the polar vortex stability

2019 ◽  
Author(s):  
Nadja Samtleben ◽  
Christoph Jacobi ◽  
Petr Pišoft ◽  
Petr Šácha ◽  
Aleš Kuchař
Keyword(s):  
Refractive Index ◽  
Gravity Wave ◽  
Zonal Wind ◽  
Polar Region ◽  
Middle Atmosphere ◽  
Negative Refractive Index ◽  
Baroclinic Instability ◽  
Polar Vortex ◽  
Circulation Model ◽  
The Impact

Abstract. In order to investigate the impact of a locally confined gravity wave (GW) hotspot, a sensitivity study based on simulations of the middle atmosphere circulation during northern winter was performed with a nonlinear, mechanistic, global circulation model. To this end, for the hotspot region we selected a fixed longitude range in the East Asian region (120° E–170° E) and a latitude range from 22.5° N–52.5° N between 18 km and 30 km, which was then shifted northward in steps of 5°. For the southernmost hotspots, we observe a decreased stationary planetary wave (SPW) 1 activity in the upper stratosphere/lower mesosphere, i.e. less SPWs 1 are propagating upwards. These GW hotspots are leading to a negative refractive index inhibiting SPW propagation at midlatitudes. The decreased SPW 1 activity is connected with an increased zonal mean zonal wind at lower latitudes. This in turn decreases the meridional potential vorticity gradient (qy) from midlatitudes towards the polar region. A reversed qy indicates local baroclinic instability which generates SPWs 1 in the polar region, where we observe a strong positive Eliassen-Palm (EP) divergence. Thus, the EP flux is increasing towards the polar stratosphere (corresponding to enhanced SPW 1 amplitudes) where the SPWs 1 are breaking and the zonal mean zonal wind is decreasing. Thus, the local GW forcing is leading to a displacement of the polar vortex towards lower latitudes. The effect of the local baroclinic instability indicated by the reversed qy also produces SPWs 1 in the lower mesosphere. The effect on the dynamics in the middle atmosphere by GW hotspots which are located northward of 50° N is negligible because the refractive index of the atmosphere is strongly negative in the polar region. Thus, any changes in the SPW activity due to the local GW forcing are quite ineffective.

scholarly journals Effect of latitudinally displaced gravity wave forcing in the lower stratosphere on the polar vortex stability

2019 ◽  
Vol 37 (4) ◽  
pp. 507-523 ◽  
Author(s):  
Nadja Samtleben ◽  
Christoph Jacobi ◽  
Petr Pišoft ◽  
Petr Šácha ◽  
Aleš Kuchař
Keyword(s):  
Refractive Index ◽  
Gravity Wave ◽  
Zonal Wind ◽  
Polar Region ◽  
Middle Atmosphere ◽  
Negative Refractive Index ◽  
Baroclinic Instability ◽  
Polar Vortex ◽  
Wave Number ◽  
The Impact

Abstract. In order to investigate the impact of a locally confined gravity wave (GW) hotspot, a sensitivity study based on simulations of the middle atmosphere circulation during northern winter was performed with a nonlinear, mechanistic, general circulation model. To this end, we selected a fixed longitude range in the East Asian region (120–170∘ E) and a latitude range from 22.5 to 52.5∘ N between 18 and 30 km for the hotspot region, which was then shifted northward in steps of 5∘. For the southernmost hotspots, we observe a decreased stationary planetary wave (SPW) with wave number 1 (SPW 1) activity in the upper stratosphere and lower mesosphere, i.e., fewer SPWs 1 are propagating upwards. These GW hotspots lead to a negative refractive index, inhibiting SPW propagation at midlatitudes. The decreased SPW 1 activity is connected to an increased zonal mean zonal wind at lower latitudes. This, in turn, decreases the meridional potential vorticity gradient (qy) from midlatitudes towards the polar region. A reversed qy indicates local baroclinic instability, which generates SPWs with wave number 1 in the polar region, where we observe a strong positive Eliassen–Palm (EP) divergence. As a result, the EP flux increases towards the polar stratosphere (corresponding to enhanced SPW 1 amplitudes), where the SPWs with wave number 1 break, and the zonal mean zonal wind decreases. Thus, the local GW forcing leads to a displacement of the polar vortex towards lower latitudes. The effect of the local baroclinic instability indicated by the reversed qy also produces SPWs with wave number 1 in the lower mesosphere. The effect on the dynamics in the middle atmosphere due to GW hotspots that are located northward of 50∘ N is negligible, as the refractive index of the atmosphere is strongly negative in the polar region. Thus, any changes in the SPW activity due to the local GW forcing are quite ineffective.

scholarly journals Mutual Interference of Local Gravity Wave Forcings in the Stratosphere

Atmosphere ◽  
2020 ◽  
Vol 11 (11) ◽  
pp. 1249
Author(s):  
Nadja Samtleben ◽  
Aleš Kuchař ◽  
Petr Šácha ◽  
Petr Pišoft ◽  
Christoph Jacobi
Keyword(s):  
Gravity Wave ◽  
Rocky Mountains ◽  
Middle Atmosphere ◽  
East Asian ◽  
Polar Vortex ◽  
Circulation Model ◽  
Global Circulation Model ◽  
Mean Flow ◽  
Destructive Effect ◽  
The Impact

Gravity wave (GW) breaking and associated GW drag is not uniformly distributed among latitudes and longitudes. In particular, regions of enhanced GW breaking, so-called GW hotspots, have been identified, major Northern Hemisphere examples being located above the Rocky Mountains, the Himalayas and the East Asian region. These hotspots influence the middle atmosphere circulation both individually and in combination. Their interference is here examined by performing simulations including (i) the respective single GW hotspots, (ii) two GW hotspots, and (iii) all three GW hotspots with a simplified global circulation model. The combined GW hotspots lead to a modification of the polar vortex in connection with a zonal mean flow decrease and an increase of the temperature at higher latitudes. The different combinations of GW hotspots mainly prevent the stationary planetary wave (SPW) 1 from propagating upward at midlatitudes leading to a decrease in energy and momentum transfer in the middle atmosphere caused by breaking SPW 1, and in turn to an acceleration of the zonal mean flow at lower latitudes. In contrast, the GW hotspot above the Rocky Mountains alone causes an increase in SPW 1 amplitude and Eliassen–Palm flux (EP flux), inducing enhanced negative EP divergence, decelerating the zonal mean flow at higher latitudes. Consequently, none of the combinations of different GW hotspots is comparable to the impact of the Rocky Mountains GW hotspot alone. The reason is that the GW hotspots mostly interfere nonlinearly. Depending on the longitudinal distance between two GW hotspots, the interference between the combined Rocky Mountains and East Asian GW hotspots is more additive than the interference between the combined Rocky Mountains and Himalaya GW hotspots. While the Rocky Mountains and the East Asian GW hotspots are longitudinally displaced by 105°, the Rocky Mountains are shifted by 170° to the Himalayas. Moreover, while the East Asian and the Himalayas are located side by side, the interference between these GW hotspots is the most nonlinear because they are latitudinally displaced by 20°. In general, the SPW activity, e.g., represented in SPW amplitudes, EP flux or Plumb flux, is strongly reduced, when the GW hotspots are interacting with each other. Thus, the interfering GW hotspots mostly have a destructive effect on SPW propagation and generation.

scholarly journals Technical note: LIMS observations of lower stratospheric ozone in the southern polar springtime of 1978

2020 ◽  
Vol 20 (6) ◽  
pp. 3663-3668
Author(s):  
Ellis Remsberg ◽  
V. Lynn Harvey ◽  
Arlin Krueger ◽  
Larry Gordley ◽  
John C. Gille ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Nitrogen Dioxide ◽  
Southern Hemisphere ◽  
Polar Region ◽  
Lower Stratosphere ◽  
Stratospheric Ozone ◽  
Polar Vortex ◽  
Technical Note ◽  
Stratospheric Ozone Layer ◽  
Antarctic Ozone

Abstract. The Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) instrument operated from 25 October 1978 through 28 May 1979. This note focuses on its Version 6 (V6) data and indications of ozone loss in the lower stratosphere of the Southern Hemisphere subpolar region during the last week of October 1978. We provide profiles and maps that show V6 ozone values of only 2 to 3 ppmv at 46 hPa within the edge of the polar vortex near 60∘ S from late October through mid-November 1978. There are also low values of V6 nitric acid (∼3 to 6 ppbv) and nitrogen dioxide (< 1 ppbv) at the same locations, indicating that conditions were suitable for a chemical loss of Antarctic ozone some weeks earlier. These “first light” LIMS observations provide the earliest space-based view of conditions within the lower stratospheric ozone layer of the southern polar region in springtime.

scholarly journals Global analysis for periodic variations of gravity wave squared amplitudes and momentum fluxes in the middle atmosphere

2019 ◽  
Author(s):  
Dan Chen ◽  
Cornelia Strube ◽  
Manfred Ern ◽  
Peter Preusse ◽  
Martin Riese
Keyword(s):  
Gravity Wave ◽  
Annual Variation ◽  
Middle Atmosphere ◽  
Global Analysis ◽  
Lower Thermosphere ◽  
Polar Vortex ◽  
Absolute Gravity ◽  
Coupling Mechanism ◽  
Quasi Biennial Oscillation ◽  
Oblique Propagation

Abstract. Atmospheric gravity waves (GWs) are an important coupling mechanism in the middle atmosphere. For instance, they provide a large part of the driving of long-period atmospheric oscillations such as the quasi-biennial oscillation (QBO) and the semiannual oscillation (SAO) and are in turn modulated. They also induce the wind reversal in the mesosphere – lower thermosphere region (MLT) and the residual mean circulation at these altitudes. In this study, the variations of monthly zonal mean gravity wave square temperature amplitudes (GWSTA) and, for a first time, absolute gravity wave momentum flux (GWMF) on different time scales such as the annual, semiannual, terannual and quasi-biennial variations are investigated by spectrally analyzing SABER observations from 2002 to 2015. Latitude-altitude cross sections of spectral amplitudes and phases of GWSTA and absolute GWMF in stratosphere and mesosphere are presented and physically interpreted. It is shown that the time series of GWSTA/GWMF at a certain altitude and latitude results from the complex interplay of GW sources, propagation through and filtering in lower altitudes, oblique propagation superposing GWs from different source locations and, finally, the modulation of the GW spectrum by the winds at a considered altitude and latitude. The strongest component is the annual variation, dominated on the summer hemisphere by subtropical convective sources, and on the winter hemisphere by polar vortex dynamics. At heights of the wind reversal also a 180° phase shift occurs, which is at different altitudes for GWSTA and GWMF. In the intermediate latitudes a semi-annual variation (SAV) is found. Dedicated GW modeling is used to investigate the nature of this SAV, which is a different phenomenon from the tropical SAO also seen in the data. In the tropics a stratospheric and a mesospheric QBO are found, which are, as expected, in anti-phase. Indication for a QBO influence is also found at higher latitudes. In previous studies a terannual variation (TAV) was identified. In the current study we explain its origin. In particular the observed patterns for the shorter periods, SAV and TAV, can only be explained by poleward propagation of GWs from the lower stratosphere subtropics into the mid and high latitude mesosphere. In this way, critical wind filtering in the lowermost stratosphere is avoided and this oblique propagation hence is likely an important factor for MLT dynamics.

scholarly journals Atmospheric tracers during the 2003–2004 stratospheric warming event and impact of ozone intrusions in the troposphere

2009 ◽  
Vol 9 (6) ◽  
pp. 2157-2170 ◽  
Author(s):  
Y. Liu ◽  
C. X. Liu ◽  
H. P. Wang ◽  
X. X. Tie ◽  
S. T. Gao ◽  
...  
Keyword(s):  
Polar Region ◽  
Lower Stratosphere ◽  
Transport Model ◽  
Stratospheric Ozone ◽  
Polar Vortex ◽  
Planetary Waves ◽  
Chemical Transport Model ◽  
Ozone Concentrations ◽  
Ozone Flux ◽  
Atmospheric Tracers

Abstract. We use the stratospheric/tropospheric chemical transport model MOZART-3 to study the distribution and transport of stratospheric O3 during the remarkable stratospheric sudden warming event observed in January 2004 in the northern polar region. A comparison between observations by the MIPAS instrument on board the ENVISAT spacecraft and model simulations shows that the evolution of the polar vortex and of planetary waves during the warming event plays an important role in controlling the spatial distribution of stratospheric ozone and the downward ozone flux in the lower stratosphere and upper troposphere (UTLS) region. Compared to the situation during the winter of 2002–2003, lower ozone concentrations were transported from the polar region to mid-latitudes, leading to exceptional large areas of low ozone concentrations outside the polar vortex and "low-ozone pockets" in the middle stratosphere. The unusually long-lasting stratospheric westward winds (easterlies) during the 2003–2004 event greatly restricted the upward propagation of planetary waves, causing the weak transport of ozone-rich air originated from low latitudes to the middle polar stratosphere (30 km). The restricted wave activities led to a reduced extratropical downward ozone flux from the lower stratosphere to the lowermost stratosphere (or from the "overworld" into the "middleworld"), especially over East Asia. Consequently, during wintertime (15 December~15 February), the total downward ozone transport on 100 hPa surface by the descending branches of Brewer-Dobson circulation over this region was about 10% lower during the 2003–2004 event. Meanwhile, the extratropical total cross-tropopause ozone flux (CTOF) was also reduced by ~25%. Compared to the cold 1999–2000 winter, the vertical CTOF in high latitudes (60°~90° N) increased more than 10 times during the two warming winters, while the vertical CTOF in mid-latitudes (30°~60° N) decreased by 20~40%. Moreover, during the two warming winters, the meridional CTOF caused by the isentropic transport associating with the enhanced wave activity also increased and played an important role in the total extratropical CTOF budget.

scholarly journals Stratospheric background aerosol and polar cloud observations by laser backscattersonde within the framework of the European project "Stratospheric Regular Sounding"

1999 ◽  
Vol 17 (10) ◽  
pp. 1352-1360 ◽  
Author(s):  
A. Adriani ◽  
F. Cairo ◽  
L. Pulvirenti ◽  
F. Cardillo ◽  
M. Viterbini ◽  
...  
Keyword(s):  
Lower Stratosphere ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
Atmospheric Composition ◽  
The Arctic ◽  
Tropical Regions ◽  
Convective Systems ◽  
Composition And Structure ◽  
Different Seasons ◽  
Stratospheric Clouds

Abstract. The Stratospheric Regular Sounding project was planned to measure regularly the vertical profiles of several tracers like ozone, water vapor, NOx, ClOx and BrOx radicals, aerosol, pressure and temperature, at three latitudes, to discriminate between the transport and photochemical terms which control their distribution. As part of this project, the "Istituto di Fisica dell'Atmosfera" launched nine laser backscattersondes (LABS) on board stratospheric balloons to make observations of background aerosol and PSCs. LABS was launched with an optical particle counter operated by the University of Wyoming. Observations have been performed in the arctic, mid-latitudes and tropical regions in different seasons. Polar stratospheric clouds have been observed in areas inside and outside the polar vortex edge. A background aerosol was observed both in mid-latitudes and in arctic regions with a backscattering ratio of 1.2 at 692 nm. Very stratified aerosol layers, possibly transported into the lower stratosphere by deep convective systems, have been observed in the lower stratosphere between 20 and 29 km in the tropics in the Southern Hemisphere. Key words. Atmospheric composition and structure (aerosols and particles; middle atmosphere – composition and chemistry; instruments and techniques)

scholarly journals Simulation of the climate impact of Mt. Pinatubo eruption using ECHAM5 – Part 2: Sensitivity to the phase of the QBO and ENSO

2009 ◽  
Vol 9 (9) ◽  
pp. 3001-3009 ◽  
Author(s):  
M. A. Thomas ◽  
M. A. Giorgetta ◽  
C. Timmreck ◽  
H.-F. Graf ◽  
G. Stenchikov
Keyword(s):  
General Circulation ◽  
Lower Stratosphere ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
Circulation Model ◽  
Climate Impact ◽  
High Latitudes ◽  
Stratospheric Temperature ◽  
Pinatubo Eruption ◽  
The Tropics

Abstract. The sensitivity of the climate impact of Mt. Pinatubo eruption in the tropics and extratropics to different QBO phases is investigated. Mt. Pinatubo erupted in June 1991 during the easterly phase of the QBO at 30 hPa and the phase change to westerly took place in August 1992. Here, the consequences are analyzed if the QBO phase had been in the opposite phase during the eruption of Mt. Pinatubo. Hence, in this study, simulations are carried out using the middle atmosphere configuration of ECHAM5 general circulation model for two cases – one with the observed QBO phase and the other with the opposite QBO phase. The response of temperature and geopotential height in the lower stratosphere is evaluated for the following cases – (1) when only the effects of the QBO are included and (2) when the effects of aerosols, QBO and SSTs (combined response) are included. The tropical QBO signature in the lower stratospheric temperature is well captured in the pure QBO responses and in the combined (aerosol + ocean + QBO) responses. The response of the extratropical atmosphere to the QBO during the second winter after the eruption is captured realistically in the case of the combined forcing showing a strengthening of the polar vortex when the QBO is in its westerly phase and a warm, weak polar vortex in the easterly QBO phase. The vortex is disturbed during the first winter irrespective of the QBO phases in the combined responses and this may be due to the strong influences of El Niño during the first winters after eruption. However, the pure QBO experiments do not realistically reproduce a strengthening of the polar vortex in the westerly QBO phase, even though below normal temperatures in the high latitudes are seen in October-November-December months when the opposite QBO phase is prescribed instead of the December-January-February winter months used here for averaging.

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