Dynamical Processes of Equatorial Atmospheric Angular Momentum

Feldstein, Steven B.

doi:10.1175/jas3586.1

Cited by 8 publications

(24 citation statements)

References 22 publications

(38 reference statements)

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“…7 from Garreaud (2000), which shows the meridional and vertical extension In past studies about the equatorial AAM budget, it has been shown that the evolution of the EAAM is largely dominated by the equivalent barotropic planetary waves with zonal wavenumber s 5 1, and that the mountain torque has a rather small impact on these waves. On the contrary, the evolution of the mass term plays an important role in the EAAM evolution associated with planetary barotropic waves (Egger and Hoinka 2002;Feldstein 2006). In the present study, the focus is on regional scales, so we do not try to address this problem.…”

Section: Results With a Modified Lower Boundary Conditionmentioning

confidence: 95%

“…The two components of the global subseasonal EMT acting on the atmosphere are computed following Feldstein (2006):…”

Section: A Spectral Analysis Of the Equatorial Mountain Torquesmentioning

confidence: 99%

“…If we adopt a planetary-scale approach, which is mandatory for large-scale mountains, the atmospheric angular momentum (AAM) budget (Feldstein 2006) provides a more satisfactory formalism to analyze these forces, with the mountain forces translating into torques along the three planetary axes. For example, Mailler and Lott (2009) have shown that before convective events associated with the East Asian winter monsoon, there are strong signals on the equatorial mountain torque (EMT) components T M1 and T M2 due to the Tibetan Plateau (TP).…”

Section: Introductionmentioning

confidence: 99%

“…The two studies cited above are representative of the fact that many authors focused on T M3 , whereas T M1 and T M2 have received less attention. Quite recently, however, Feldstein (2006) has analyzed their relation with changes in the equatorial components of the atmospheric angular momentum, and Egger and Hoinka (2008) have described the regional circulation patterns associated with the equatorial torques produced by the TP.…”

Section: Introductionmentioning

confidence: 99%

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Equatorial Mountain Torques and Cold Surge Preconditioning

Mailler

Lott

2010

Journal of the Atmospheric Sciences

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The evolution of the two components of the equatorial mountain torque (EMT) applied by mountains on the atmosphere is analyzed in the NCEP reanalysis. A strong lagged relationship between the EMT component along the Greenwich axis T M1 and the EMT component along the 908E axis T M2 is found, with a pronounced signal on T M1 followed by a signal of opposite sign on T M2 . It is shown that this result holds for the major massifs (Antarctica, the Tibetan Plateau, the Rockies, and the Andes) if a suitable axis system is used for each of them. For the midlatitude mountains, this relationship is in part associated with the development of cold surges.Following these results, two hypotheses are made: (i) the mountain forcing on the atmosphere is well measured by the regional EMTs and (ii) this forcing partly drives the cold surges. To support these, a purely dynamical linear model is proposed: it is written on the sphere, uses an f-plane quasigeostrophic approximation, and includes the mountain forcings. In this model, a positive (negative) peak in T M1 produced by a mountain massif in the Northern (Southern) Hemisphere is due to a large-scale high surface pressure anomaly poleward of the massif. At a later stage, high pressure and low temperature anomalies develop in the lower troposphere east of the mountain, explaining the signal on T M2 and providing the favorable conditions for the cold surge development.It is concluded that the EMT is a good measure of the dynamical forcing of the atmospheric flow by the mountains and that the poleward forces exerted by mountains on the atmosphere are substantial drivers of the cold surges, at least in their early stage. Therefore, the EMT time series can be an important diagnostic to assess the representation of mountains in general circulation models.

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Section: Results With a Modified Lower Boundary Conditionmentioning

confidence: 95%

“…The two components of the global subseasonal EMT acting on the atmosphere are computed following Feldstein (2006):…”

Section: A Spectral Analysis Of the Equatorial Mountain Torquesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Equatorial Mountain Torques and Cold Surge Preconditioning

Mailler

Lott

2010

Journal of the Atmospheric Sciences

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“…The observational results in Mailler and Lott (2010) have been obtained with the NCEP reanalysis, which does not provide an accurate closure of the atmospheric angular momentum (AAM) budget, neither in its axial component nor in its equatorial components (Feldstein 2006). On the contrary, we know that the Laboratoire de Météorologie Dynamique model with zoom (the LMDz) GCM closes well the axial AAM budget Lebonnois et al 2010), and also has a good closure of the EAAM budget at subdiurnal periodicities (De Viron et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Impact of Subgrid-Scale Orography on Equatorial Angular Momentum Budget and the Cold Surges in a General Circulation Model

Mailler

Lott

2015

Monthly Weather Review

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The dynamical relations between equatorial atmospheric angular momentum (EAAM), equatorial mountain torques, and cold surges are analyzed in a general circulation model (GCM). First, the authors show that the global EAAM budget is well closed in the GCM, much better than in the NCEP-NCAR reanalysis. They then confirm that the equatorial torques due to the Tibetan Plateau, the Rockies, and the Andes are well related to the cold surges developing over East Asia, North America, and South America, respectively. For all these mountains, a peak in the equatorial mountain torque components precedes by few days the development of a cold surge, confirming that the cold surge's ''preconditioning'' is dynamically driven by large-scale mountains.The authors also analyze the contribution of the subgrid-scale orography (SSO) parameterizations and find that they contribute substantially to the torques. In experiments where these parameterizations are almost entirely reduced over a given massif, the authors find that the explicit pressure torques produced by that massif largely compensate the reduction in the parameterized torques. On the one hand, this proves that the explicitly resolved equatorial mountain torques are effective dynamical drivers of the flow dynamics, since they are enhanced when a parameterized torque is reduced. On the other hand, this shows that the cold surges can be captured in GCMs, provided that the synoptic conditions prior to their onset are realistic. The compensation between torques is nevertheless not complete and some weakening of the cold surges is found when the parameterized mountain torques are reduced.

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Earth Rotation Variations – Long Period

Gross

2015

Treatise on Geophysics

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Dynamical Processes of Equatorial Atmospheric Angular Momentum

Cited by 8 publications

References 22 publications

Equatorial Mountain Torques and Cold Surge Preconditioning

Equatorial Mountain Torques and Cold Surge Preconditioning

Impact of Subgrid-Scale Orography on Equatorial Angular Momentum Budget and the Cold Surges in a General Circulation Model

Earth Rotation Variations – Long Period

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