Solar Influences on Stratospheric Circulation Patterns

2020 ◽  
Author(s):  
Yonatan Givon ◽  
Chaim Garfinkel
Keyword(s):  
Zonal Wind ◽  
Wind Anomaly ◽  
Zonal Wind Anomaly ◽  
Circulation Patterns ◽  
Downward Propagation ◽  
P Flux ◽  
Stratospheric Circulation ◽  
The Tropics ◽  
The Impact ◽  
Transformed Eulerian Mean

<p>The impact of the solar cycle on the NH winter stratospheric circulation is analyzed using<br>simulations of a Model of an idealized Moist Atmosphere (MiMA). By comparing solar minimum<br>periods to solar maximum periods, the solar impact on the stratosphere is evaluated: Solar<br>maximum periods are accompanied by warming of the tropics that extends into the midlatitudes<br>due to an altered Brewer Dobson Circulation. This warming of the subtropics and the altered<br>Brewer Dobson Circulation leads to an increase in zonal wind in midlatitudes, which is then<br>followed by a decrease in E-P flux convergence near the winter pole which extends the enhanced<br>westerlies to subpolar latitudes.<br>We use the transformed Eulerian mean framework to reveal the processes that lead to the<br>formation of this sub-polar zonal wind anomaly and its downward propagation from the top of the<br>stratosphere to the tropopause.</p>

Mechanism for Southward Shift of Zonal Wind Anomalies During the Mature Phase of ENSO

2021 ◽  
pp. 1-45
Author(s):  
Yuhan Gong ◽  
Tim Li
Keyword(s):  
Zonal Wind ◽  
General Circulation ◽  
Boreal Summer ◽  
Positive Contribution ◽  
Antisymmetric Mode ◽  
Wind Anomaly ◽  
Zonal Wind Anomaly ◽  
Model Experiments ◽  
Southward Shift ◽  
Background State

AbstractThe cause of southward shift of anomalous zonal wind in the central equatorial Pacific (CEP) during ENSO mature winter was investigated through observational analyses and numerical model experiments. Based on an antisymmetric zonal momentum budget diagnosis using daily ERA-Interim data, a two-step physical mechanism is proposed. The first step involves advection of the zonal wind anomaly by the climatological mean meridional wind. The second step involves the development of an antisymmetric mode in the CEP, which promotes a positive contribution to the observed zonal wind tendency by the pressure gradient and Coriolis forces. Two positive feedbacks are responsible for the growth of the antisymmetric mode. The first involves the moisture–convection–circulation feedback, and the second involves the wind–evaporation–SST feedback. General circulation model experiments further demonstrated that the boreal winter background state is critical in generating the southward shift, and a northward shift of the zonal wind anomaly is found when the same SST anomaly is specified in boreal summer background state.

scholarly journals The Development of Upper-Tropospheric Wind over the Western Hemisphere in Association with MJO Convective Initiation

2015 ◽  
Vol 72 (8) ◽  
pp. 3138-3160 ◽  
Author(s):  
Naoko Sakaeda ◽  
Paul E. Roundy
Keyword(s):  
Zonal Wind ◽  
Western Hemisphere ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Kelvin Wave ◽  
Wind Anomaly ◽  
Convective Initiation ◽  
Zonal Wind Anomaly ◽  
Easterly Wind ◽  
Driving Mechanisms

Abstract This study examines the structure and driving mechanisms of upper-tropospheric intraseasonal zonal wind anomalies over the Western Hemisphere (WH) during the convective initiation of the Madden–Julian oscillation (MJO) over the Indian Ocean using composite and budget analyses. The initiating MJO convection is more often associated with WH upper-tropospheric intraseasonal easterly wind anomalies, and when it is, it tends to develop a stronger and zonally broader envelope of enhanced convection than events associated with westerly wind anomalies. The WH upper-tropospheric zonal wind anomaly associated with the MJO is often described as a dry Kelvin wave radiated from MJO convection, but the results show that both the structure and driving mechanisms are different from the ones of theoretical Kelvin waves. Unlike the theoretical Kelvin wave, the zonal wind anomaly is not driven mainly by the zonal pressure gradient force and it is strongly coupled with rotational wind associated with subtropical and equatorward-propagating midlatitude Rossby waves. The intraseasonal zonal wind anomaly amplifies over the eastern Pacific and Atlantic basins because of advection of the background wind by intraseasonal wind in the presence of background zonal wind convergence, which allows acceleration in the same sign of the present intraseasonal zonal wind anomaly. A part of the WH intraseasonal easterly wind initiates in the lower stratosphere and is advected downward as it merges with eastward-propagating easterly wind in the upper troposphere. The initial sources of the lower-stratospheric intraseasonal easterly wind include equatorward intrusion of midlatitude waves and an equatorial Rossby wave.

scholarly journals Winter North Atlantic Oscillation Hindcast Skill: 1900–2001

2006 ◽  
Vol 19 (22) ◽  
pp. 5762-5776 ◽  
Author(s):  
Christopher G. Fletcher ◽  
Mark A. Saunders
Keyword(s):  
North Atlantic Oscillation ◽  
Snow Cover ◽  
North Atlantic ◽  
Warm Season ◽  
Skill Score ◽  
Sea Surface ◽  
Skill Assessment ◽  
Wind Anomaly ◽  
Zonal Wind Anomaly ◽  
The Tropics

Abstract Recent proposed seasonal hindcast skill estimates for the winter North Atlantic Oscillation (NAO) are derived from different lagged predictors, NAO indices, skill assessment periods, and skill validation methodologies. This creates confusion concerning what is the best-lagged predictor of the winter NAO. To rectify this situation, a standardized comparison of NAO cross-validated hindcast skill is performed against three NAO indices over three extended periods (1900–2001, 1950–2001, and 1972–2001). The lagged predictors comprise four previously published predictors involving anomalies in North Atlantic sea surface temperature (SST), Northern Hemisphere (NH) snow cover, and an additional predictor, an index of NH subpolar summer air temperature (TSP). Significant (p < 0.05) NAO hindcast skill is found with May SST 1900–2001, summer/autumn SST 1950–2001, and warm season snow cover 1972–2001. However, the highest and most significant hindcast skill for all periods and all NAO indices is achieved with TSP. Hindcast skill is nonstationary using all predictors and is highest during 1972–2001 with a TSP correlation skill of 0.59 and a mean-squared skill score of 35%. Observational evidence is presented to support a dynamical link between summer TSP and the winter NAO. Summer TSP is associated with a contemporaneous midlatitude zonal wind anomaly. This leads a pattern of North Atlantic SST that persists through autumn. Autumn SSTs may force a direct thermal NAO response or initiate a response via a third variable. These findings suggest that the NH subpolar regions may provide additional winter NAO lagged predictability alongside the midlatitudes and the Tropics.

Local time variation of equatorial temperature and zonal wind anomaly (ETWA)

1998 ◽  
Vol 60 (6) ◽  
pp. 631-642 ◽  
Author(s):  
R. Raghavarao ◽  
R. Suhasini ◽  
W.R. Hoegy ◽  
H.G. Mayr ◽  
L. Wharton
Keyword(s):  
Local Time ◽  
Zonal Wind ◽  
Time Variation ◽  
Wind Anomaly ◽  
Zonal Wind Anomaly

scholarly journals How can we understand the global distribution of the solar cycle signal on the Earth's surface?

2016 ◽  
Vol 16 (20) ◽  
pp. 12925-12944 ◽  
Author(s):  
Kunihiko Kodera ◽  
Rémi Thiéblemont ◽  
Seiji Yukimoto ◽  
Katja Matthes
Keyword(s):  
Solar Cycle ◽  
Surface Temperature ◽  
Zonal Wind ◽  
High Solar Activity ◽  
Mean Flow ◽  
Central Pacific ◽  
Solar Signal ◽  
The Tropics ◽  
Solar Influence ◽  
The Impact

Abstract. To understand solar cycle signals on the Earth's surface and identify the physical mechanisms responsible, surface temperature variations from observations as well as climate model data are analysed to characterize their spatial structure. The solar signal in the annual mean surface temperature is characterized by (i) mid-latitude warming and (ii) no overall tropical warming. The mid-latitude warming during solar maxima in both hemispheres is associated with a downward penetration of zonal mean zonal wind anomalies from the upper stratosphere during late winter. During the Northern Hemisphere winter this is manifested by a modulation of the polar-night jet, whereas in the Southern Hemisphere, the upper stratospheric subtropical jet plays the major role. Warming signals are particularly apparent over the Eurasian continent and ocean frontal zones, including a previously reported lagged response over the North Atlantic. In the tropics, local warming occurs over the Indian and central Pacific oceans during high solar activity. However, this warming is counterbalanced by cooling over the cold tongue sectors in the southeastern Pacific and the South Atlantic, and results in a very weak zonally averaged tropical mean signal. The cooling in the ocean basins is associated with stronger cross-equatorial winds resulting from a northward shift of the ascending branch of the Hadley circulation during solar maxima. To understand the complex processes involved in the solar signal transfer, results of an idealized middle atmosphere–ocean coupled model experiment on the impact of stratospheric zonal wind changes are compared with solar signals in observations. Model integration of 100 years of strong or weak stratospheric westerly jet condition in winter may exaggerate long-term ocean feedback. However, the role of ocean in the solar influence on the Earth's surface can be better seen. Although the momentum forcing differs from that of solar radiative forcing, the model results suggest that stratospheric changes can influence the troposphere, not only in the extratropics but also in the tropics through (i) a downward migration of wave–zonal mean flow interactions and (ii) changes in the stratospheric mean meridional circulation. These experiments support earlier evidence of an indirect solar influence from the stratosphere.

Zonal displacement of western Pacific warm pool and zonal wind anomaly over the Pacific Ocean

2007 ◽  
Vol 25 (3) ◽  
pp. 277-285 ◽  
Author(s):  
Qilong Zhang ◽  
Qinghua Zhang ◽  
Yijun Hou ◽  
Jianping Xu ◽  
Xuechuan Weng ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Zonal Wind ◽  
Warm Pool ◽  
Western Pacific ◽  
Western Pacific Warm Pool ◽  
Wind Anomaly ◽  
Zonal Wind Anomaly ◽  
The Pacific ◽  
Pacific Warm Pool ◽  
The Pacific Ocean

scholarly journals How can we understand the solar cycle signal on the Earth's surface?

2016 ◽  
Author(s):  
Kunihiko Kodera ◽  
Rémi Thiéblemont ◽  
Seiji Yukimoto ◽  
Katja Matthes
Keyword(s):  
Solar Cycle ◽  
Surface Temperature ◽  
Zonal Wind ◽  
High Solar Activity ◽  
Late Winter ◽  
Mean Flow ◽  
Central Pacific ◽  
Solar Signal ◽  
The Tropics ◽  
The Impact

Abstract. To understand solar cycle signals on the Earth's surface and identify the physical mechanisms responsible, surface temperature variations from observations as well as climate model data are analyzed to characterize their spatial structure. The solar signal in the annual mean surface temperature is characterized by (i) mid-latitude warming and (ii) no warming in the tropics. The mid-latitude warming during solar maxima in both hemispheres is associated with a downward penetration of zonal mean zonal wind anomalies from the upper stratosphere during late winter. During Northern Hemisphere winter this is manifested in a modulation of the polar-night jet whereas in the Southern Hemisphere the subtropical jet plays the major role. Warming signals are particularly apparent over the Eurasian continent and ocean frontal zones, including a previously reported lagged response over the North Atlantic. In the tropics, local warming occurs over the Indian and central Pacific oceans during high solar activity. However, this warming is counter balanced by cooling over the cold tongue sectors in the southeastern Pacific and the South Atlantic, and results in a very weak zonally averaged tropical mean signal. The cooling in the ocean basins is associated with stronger cross-equatorial winds resulting from a northward shift of the ascending branch of the Hadley circulation during solar maxima. To understand the complex processes involved in the solar signal transfer, results of an idealized middle atmosphere–ocean coupled model experiment on the impact of stratospheric zonal wind changes are compared with solar signals in observations. The model results suggest that both tropical and extra-tropical solar surface signals can result from circulation changes in the upper stratosphere through (i) a downward migration of wave–zonal mean flow interactions and (ii) changes in the stratospheric mean meridional circulation. These experiments support earlier evidence of an indirect solar influence from the stratosphere.

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