Interhemispheric Coupling Mechanisms in the Middle Atmosphere of WACCM6

Smith, Anne K.; Pedatella, Nicholas; Mullen, Zachary

doi:10.1175/jas-d-19-0253.1

Cited by 32 publications

(55 citation statements)

References 39 publications

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“…There is, however, an earlier formation of the westward winds in the MLT in the early transition years compared to the late transition years. The earlier transition in the Northern Hemisphere MLT is considered to be due to the interhemispheric coupling that is known to occur between the high latitude wintertime stratosphere and summer mesosphere (Körnich & Becker, 2010; Smith et al., 2020).…”

Section: Resultsmentioning

confidence: 99%

“…Although the seasonal transition of the middle atmosphere winds does not always occur during March or September, throughout the following we will use the terminology of September equinox to refer to the seasonal transition between summer and winter in the Northern Hemisphere (winter and summer in the Southern Hemisphere) despite the fact that this transition does not always occur during September. Variability in the winter stratosphere is also known to be a source of variability in the summer mesosphere (Körnich & Becker, 2010; Smith et al., 2020).…”

Section: Introductionmentioning

confidence: 99%

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Migrating Semidiurnal Tide During the September Equinox Transition in the Northern Hemisphere

et al. 2021

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Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension simulations are used to investigate the solar migrating semidiurnal tide (SW2) around September equinox at middle to high latitudes in the Northern Hemisphere. A pronounced minimum in SW2 occurs around September equinox, and is characterized by a ∼50% reduction in tidal amplitudes for 20–30 days. Analysis of the simulation results indicates that the SW2 minimum occurs due to the seasonal transition of the zonal mean zonal winds, which alter the generation and propagation of different symmetric and antisymmetric modes of SW2. In particular, the antisymmetric modes notably decrease due to the more hemispherically symmetric zonal winds around equinox. It is further demonstrated that interannual variability in the timing of the SW2 minimum is related to the timing of the seasonal transition of the zonal mean zonal winds in the middle atmosphere. This leads to an earlier occurrence of the SW2 minimum during years when the seasonal transition occurs earlier, such as the recent 2019 September equinox which saw an earlier transition of the Southern Hemisphere zonal mean zonal winds following the occurrence of a sudden stratosphere warming. The connection between the timing of the SW2 minimum in the Northern Hemisphere and the timing of the seasonal transition in the middle atmosphere winds is confirmed by seasonal variability of 12‐h tides deduced from specular meteor radar observations at middle to high latitudes in the Northern Hemisphere.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Migrating Semidiurnal Tide During the September Equinox Transition in the Northern Hemisphere

et al. 2021

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“…Though Körnich and Becker (2010) originally explained the coupling between wintertime SSWs and mesospheric warmings in the summer hemisphere as due to altered wave forcing in the summer hemisphere, Smith et al (2020) recently proposed that the interhemispheric coupling is due to changes in the stratosphere‐mesosphere circulation, and not due to modified wave forcing in the summer hemisphere mesosphere. The mesosphere‐lower thermosphere changes that occur during SSWs are only weakly correlated with the changes that occur in the stratosphere (e.g., Smith et al, 2020), and there is significant event‐to‐event variability (Zülicke & Becker, 2013; Zülicke et al, 2018). The lack of a direct linear correspondence between the stratosphere and mesosphere‐lower thermosphere illustrates the complexity of the coupling processes.…”

Section: Effects On the Atmosphere Above The Stratospherementioning

confidence: 99%

Sudden Stratospheric Warmings

Baldwin

Ayarzagüena

Birner

et al. 2021

Reviews of Geophysics

313

226

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Sudden stratospheric warmings (SSWs) are impressive fluid dynamical events in which large and rapid temperature increases in the winter polar stratosphere (∼10–50 km) are associated with a complete reversal of the climatological wintertime westerly winds. SSWs are caused by the breaking of planetary‐scale waves that propagate upwards from the troposphere. During an SSW, the polar vortex breaks down, accompanied by rapid descent and warming of air in polar latitudes, mirrored by ascent and cooling above the warming. The rapid warming and descent of the polar air column affect tropospheric weather, shifting jet streams, storm tracks, and the Northern Annular Mode, making cold air outbreaks over North America and Eurasia more likely. SSWs affect the atmosphere above the stratosphere, producing widespread effects on atmospheric chemistry, temperatures, winds, neutral (nonionized) particles and electron densities, and electric fields. These effects span both hemispheres. Given their crucial role in the whole atmosphere, SSWs are also seen as a key process to analyze in climate change studies and subseasonal to seasonal prediction. This work reviews the current knowledge on the most important aspects of SSWs, from the historical background to dynamical processes, modeling, chemistry, and impact on other atmospheric layers.

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“…Alternatively, several case studies based on high-altitude meteorological analyses suggest that changes in mesospheric Q2DW activity may play a role in interhemispheric coupling (e.g., Siskind and McCormack,430 2014; France et al, 2018;Lieberman et al, 2021). An additional mechanism was discussed in Smith et al (2020),…”

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confidence: 99%

Intercomparison of Middle Atmospheric Meteorological Analyses for the Northern Hemisphere Winter 2009–2010

McCormack

Harvey

Pedatella

et al. 2021

Preprint

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Abstract. Detailed meteorological analyses based on observations extending through the middle atmosphere (~15–100 km altitude) can provide key information to whole atmosphere modelling systems regarding the physical mechanisms linking day-to-day changes in ionospheric electron density to meteorological variability near the Earth’s surface. It is currently unclear how middle atmosphere analyses produced by various research groups consistently represent the wide range of proposed linking mechanisms involving migrating and non-migrating tides, planetary waves, gravity waves, and their impact on the zonal mean state in the mesosphere and lower thermosphere (MLT) region. To begin to address this issue, we present the first intercomparison among four such analyses, JAGUAR-DAS, MERRA-2, NAVGEM-HA, and WACCMX+DART, focusing on the Northern Hemisphere (NH) 2009–2010 winter that includes a major stratospheric sudden warming (SSW) in late January. This intercomparison examines the altitude, latitude, and time dependences of zonal mean zonal winds and temperatures among these four analyses over the 1 December 2009–31 March 2010 period, as well as latitude and altitude dependences of monthly mean amplitudes of the diurnal and semidiurnal migrating solar tides, the eastward propagating diurnal zonal wave number 3 nonmigrating tide, and traveling planetary waves associated with the quasi-5 day and quasi-2-day Rossby modes. Our results show generally good agreement among the four analyses up to the stratopause (~50 km altitude). Large discrepancies begin to emerge in the MLT owing to (1) differences in the types of satellite data assimilated by each system and (2) differences in the details of the global atmospheric models used by each analysis system. The results of this intercomparison provide initial estimates of uncertainty in analyses commonly used to constrain middle atmospheric meteorological variability in whole atmosphere model simulations.

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Interhemispheric Coupling Mechanisms in the Middle Atmosphere of WACCM6

Cited by 32 publications

References 39 publications

Migrating Semidiurnal Tide During the September Equinox Transition in the Northern Hemisphere

Migrating Semidiurnal Tide During the September Equinox Transition in the Northern Hemisphere

Sudden Stratospheric Warmings

Intercomparison of Middle Atmospheric Meteorological Analyses for the Northern Hemisphere Winter 2009–2010

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