Observations of planetary waves in the mesosphere-lower thermosphere during stratospheric warming events

Stray, Nora H.; Orsolini, Yvan; Espy, P. J.; Limpasuvan, Varavut; Hibbins, R. E.

doi:10.5194/acp-15-4997-2015

Cited by 58 publications

(83 citation statements)

References 25 publications

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“…Here we separate Arctic winters that exhibit a substantial mesospheric response to SSWs from years without such a response. We employ the conventions originally outlined by Tweedy et al () and later applied by Stray et al (), Limpasuvan et al (), and Harvey et al () to define SSW winters with an elevated stratopause (ES) event (see Manney et al (, ) and Tomikawa et al () for a detailed description of the observed meteorology during these events). Specifically, Arctic winters are considered to have an ES if they satisfy the following three criteria: (1) easterlies at the stratopause from 70°–90°N for five or more days, (2) 70°–90°N temperature is below 185 K, and (3) the polar stratopause “jumps” 10 km or more in altitude from its climatological altitude.…”

Section: Resultsmentioning

confidence: 99%

“…In addition, there is a significant mesospheric response during 22% of major SSW days (e.g., Zülicke et al, ) and this response is well reproduced by WACCM (Limpasuvan et al, , ). In particular, the model captures observed mesospheric cooling and wind reversals (e.g., Eswaraiah et al, ), enhanced PW activity in the MLT (Chandran, Collins, et al, , Chandran, Garcia, et al, ; Stray et al, ), and observed enhancements in nighttime ozone at the secondary ozone maximum (Tweedy et al, ). However, to date there has not been a comprehensive evaluation of mesospheric polar vortex characteristics in WACCM, nor the response of the mesospheric polar vortex to SSWs.…”

Section: Introductionmentioning

confidence: 93%

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Evaluation of the Mesospheric Polar Vortices in WACCM

et al. 2019

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This work evaluates the wintertime mesospheric polar vortices in the Whole Atmosphere Community Climate Model. Mesospheric altitudes are where high‐top models underestimate the concentration of nitrogen oxides produced by energetic particle precipitation. For this reason, we seek to determine the extent to which the observed mesospheric vortex size and frequency of occurrence is reproduced by the model. We compare 13 years (2005–2017) of “specified dynamics” Whole Atmosphere Community Climate Model (where meteorology in the troposphere and stratosphere is constrained by observations) to Sounding of the Atmosphere using Broadband Emission Radiometry and Mesospheric Limb Sounder observations. Near 75 km, the model reproduces observed winter mesospheric vortex frequency of occurrence rates and size reasonably well. The simulated Antarctic mesospheric vortex is displaced toward the Pacific longitude sector, and the Arctic mesospheric vortex is present 10–20% less often over the pole but ~5% more often in midlatitudes, particularly over the continents. These differences are attributed to larger planetary waves in the model. There are significant differences between the modeled and observed mean polar winter circulation near 90 km. Model‐measurement differences suggest that the simulated Antarctic mesospheric vortex does not extend to high enough altitudes, and the Arctic mesospheric vortex is too displaced from the pole. Despite these differences, the model accurately captures the evolution of structural changes to the mesospheric vortex following prolonged sudden stratospheric warmings. Thus, we conclude that model underestimates of nitrogen oxides produced by energetic particle precipitation after these warmings are not due to a misrepresentation of the mesospheric vortex strength and size below 80 km.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 93%

Evaluation of the Mesospheric Polar Vortices in WACCM

et al. 2019

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“…Model fields are output every 3 h. For each run, ES‐SSW events are identified following the three criteria used by Stray et al . []. Based on the polar cap averaged (70°N to 90°N) zonal‐mean zonal wind and zonal‐mean temperature between October and May of each winter, we require that (1) the temperature between 80–100 km falls below 190 K, (2) the reversal of the zonal‐mean zonal wind from eastward to westward direction at the 1 hPa level (~50 km) persists for longer than 5 days, and (3) the stratopause altitude, based on the zonal‐mean temperature maximum between 20 km and 100 km, as discussed by Tweedy et al .…”

Section: Model and Methodologymentioning

confidence: 99%

On the composite response of the MLT to major sudden stratospheric warming events with elevated stratopause

et al. 2016

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Based on a climate-chemistry model (constrained by reanalyses below~50 km), the zonal-mean composite response of the mesosphere and lower thermosphere (MLT) to major sudden stratospheric warming events with elevated stratopauses demonstrates the role of planetary waves (PWs) in driving the mean circulation in the presence of gravity waves (GWs), helping the polar vortex recover and communicating the sudden stratospheric warming (SSW) impact across the equator. With the SSW onset, strong westward PW drag appears above 80 km primarily from the dissipation of wave number 1 perturbations with westward period of 5-12 days, generated from below by the unstable westward polar stratospheric jet that develops as a result of the SSW. The filtering effect of this jet also allows eastward propagating GWs to saturate in the winter MLT, providing eastward drag that promotes winter polar mesospheric cooling. The dominant PW forcing translates to a net westward drag above the eastward mesospheric jet, which initiates downwelling over the winter pole. As the eastward polar stratospheric jet returns, this westward PW drag persists above 80 km and acts synergistically with the return of westward GW drag to drive a stronger polar downwelling that warms the pole adiabatically and helps reform the stratopause at an elevated altitude. With the polar wind reversal during the SSW onset, the westward drag by the quasi-stationary PW in the winter stratosphere drives an anomalous equatorial upwelling and cooling that enhance tropical stratospheric ozone. Along with equatorial wind anomalies, this ozone enhancement subsequently amplifies the migrating semidiurnal tide amplitude in the winter midlatitudes.

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“…Apart from direct enhancements of stratospheric temperatures, SSWs have been demonstrated to affect planetary wave activity even extending into the opposite hemisphere (e.g. Stray et al, 2015). If such effects were capable of, for example, triggering the springtime breakdown of the polar vortex, associated horizontal transport of stratospheric ozone would contribute to determination of the tropopause altitude (e.g.…”

Section: Discussionmentioning

confidence: 99%

Change in turbopause altitude at 52 and 70° N

Hall¹,

Holmen

Meek

et al. 2016

Atmos. Chem. Phys.

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Abstract. The turbopause is the demarcation between atmospheric mixing by turbulence (below) and molecular diffusion (above). When studying concentrations of trace species in the atmosphere, and particularly long-term change, it may be important to understand processes present, together with their temporal evolution that may be responsible for redistribution of atmospheric constituents. The general region of transition between turbulent and molecular mixing coincides with the base of the ionosphere, the lower region in which molecular oxygen is dissociated, and, at high latitude in summer, the coldest part of the whole atmosphere.This study updates previous reports of turbopause altitude, extending the time series by half a decade, and thus shedding new light on the nature of change over solar-cycle timescales. Assuming there is no trend in temperature, at 70 • N there is evidence for a summer trend of ∼ 1.6 km decade −1 , but for winter and at 52 • N there is no significant evidence for change at all. If the temperature at 90 km is estimated using meteor trail data, it is possible to estimate a cooling rate, which, if applied to the turbopause altitude estimation, fails to alter the trend significantly irrespective of season.The observed increase in turbopause height supports a hypothesis of corresponding negative trends in atomic oxygen density, [O]. This supports independent studies of atomic oxygen density, [O], using mid-latitude time series dating from 1975, which show negative trends since 2002.

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Observations of planetary waves in the mesosphere-lower thermosphere during stratospheric warming events

Cited by 58 publications

References 25 publications

Evaluation of the Mesospheric Polar Vortices in WACCM

Evaluation of the Mesospheric Polar Vortices in WACCM

On the composite response of the MLT to major sudden stratospheric warming events with elevated stratopause

Change in turbopause altitude at 52 and 70° N

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