On the Existence of Storm-Tracks

Hoskins, Brian J.; Valdes, Paul J.

doi:10.1175/1520-0469(1990)047<1854:oteost>2.0.co;2

Cited by 746 publications

(565 citation statements)

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“…In both the runs, lowlevel baroclinicity is a very good indicator of the growth of baroclinic eddies, their subsequent downstream development and the formation of storm tracks. These results support the linear model study of Hoskins and Valdes (1990). Our AGCM experiments demonstrate that variations in low-level baroclinicity can be caused by the teleconnection from the tropics or alternatively by changes in local SST gradient.…”

Section: Resultssupporting

confidence: 88%

Tropical and Extratropical SST Effects on the Midlatitude Storm Track.

Inatsu

Mukougawa

Xie

2002

Journal of the Meteorological Society of Japan

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Effects of zonal variations in sea surface temperature (SST) on synoptic eddy activity are examined using an atmospheric general circulation model under the perpetual January and the aqua-planet conditions. In the presence of zonal variations in tropical SST, upper tropospheric zonal wind displays large zonal asymmetry and the storm track is located downstream of the maximum westerly speed. When only extratropical SST varies in the east-west direction, a storm track develops along the sharp meridional SST gradient despite a nearly zonally uniform westerly jet in the upper troposphere. The latter result suggests that zonal variations in upper tropospheric westerlies contribute to but are not necessary for zonally confined storm tracks.

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Section: Resultssupporting

confidence: 88%

Tropical and Extratropical SST Effects on the Midlatitude Storm Track.

Inatsu

Mukougawa

Xie

2002

Journal of the Meteorological Society of Japan

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“…Previous studies have linked the diabatic heating of the lower troposphere to the storm track over the midlatitude (Hoskins and Valdes 1990). The changes of the storm tracks are, therefore, analyzed in the following.…”

Section: Heating Anomaliesmentioning

confidence: 99%

“…The baroclinicity of the atmosphere is evaluated using the maximum Eady growth rate (Hoskins and Valdes 1990), defined at 850 hPa as 0:31f j›U/›zjN 21 with f the Coriolis parameter, ›U/›z the horizontal wind shear, and N the Brunt-Väisälä frequency. The storm track activity is measured by the bandpass-(2-6 days) filtered geopotential height variance at 500 hPa (Blackmon et al 1977).…”

Section: E Storm Track and Eddy Feedbackmentioning

confidence: 99%

Mechanisms Determining the Winter Atmospheric Response to the Atlantic Overturning Circulation

et al. 2016

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In climate models, an intensification of the Atlantic meridional overturning circulation (AMOC) precedes a warming in the North Atlantic subpolar basin by a few years. In the IPSL-CM5A-LR model, this warming may explain the atmospheric response to the AMOC observed in winter, which resembles a negative phase of the North Atlantic Oscillation (NAO). To firmly establish the causality links between the ocean and the atmosphere and illustrate the underlying mechanisms in this model, ensembles of atmosphere-only simulations are conducted, prescribing the SST and sea ice anomalies that follow an AMOC intensification. In late winter, the North Atlantic SST and sea ice anomalies drive atmospheric circulation anomalies similar to those found in the coupled model. Simulations only driven by the SST anomalies related to the AMOC show that the largest oceanic influence is due to the warm subpolar SST anomaly, which enhances the oceanic heat release and decreases the lower-tropospheric baroclinicity in the region of maximum eddy growth, resulting in a weaker meridional eddy heat flux in the atmosphere. The transient eddy feedback leads to a negative NAO-like response. An AMOC intensification is also followed by less sea ice over the Labrador Sea and more sea ice over the Nordic seas. The simulations with full boundary forcing suggest that such anomalies act to strengthen both the poleward momentum flux and the upward heat flux into the polar stratosphere and lead to a stratospheric warming, which then reinforces the negative NAO signal in late winter.

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“…This affects the baroclinicity of the lower troposphere and thus the synoptic perturbation growth. The maximum Eady growth rate defined by 0:31f j›u/›zjN 21 , where f is the Coriolis parameter, ›u/›z is the zonal wind shear, and N is the Brunt-V€ ais€ al€ a frequency, governs the amplitude of the atmospheric perturbations (Hoskins and Valdes 1990). Its climatology (Fig.…”

Section: Oceanic Influence On the Atmospheric Circulation In The Red mentioning

confidence: 99%

The Influence of the AMOC Variability on the Atmosphere in CCSM3

2013

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The influence of the Atlantic meridional overturning circulation (AMOC) variability on the atmospheric circulation is investigated in a control simulation of the NCAR Community Climate System Model, version 3 (CCSM3), where the AMOC evolves from an oscillatory regime into a red noise regime. In the latter, an AMOC intensification is followed during winter by a positive North Atlantic Oscillation (NAO). The atmospheric response is robust and controlled by AMOC-driven SST anomalies, which shift the heat release to the atmosphere northward near the Gulf Stream/North Atlantic Current. This alters the low-level atmospheric baroclinicity and shifts the maximum eddy growth northward, affecting the storm track and favoring a positive NAO. The AMOC influence is detected in the relation between seasonal upper-ocean heat content or SST anomalies and winter sea level pressure. In the oscillatory regime, no direct AMOC influence is detected in winter. However, an upper-ocean heat content anomaly resembling the AMOC footprint precedes a negative NAO. This opposite NAO polarity seems due to the southward shift of the Gulf Stream during AMOC intensification, displacing the maximum baroclinicity southward near the jet exit. As the mode has somewhat different patterns when using SST, the wintertime impact of the AMOC lacks robustness in this regime. However, none of the signals compares well with the observed influence of North Atlantic SST anomalies on the NAO because SST is dominated in CCSM3 by the meridional shifts of the Gulf Stream/ North Atlantic Current that covary with the AMOC. Hence, although there is some potential climate predictability in CCSM3, it is not realistic.

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On the Existence of Storm-Tracks

Cited by 746 publications

References 0 publications

Tropical and Extratropical SST Effects on the Midlatitude Storm Track.

Tropical and Extratropical SST Effects on the Midlatitude Storm Track.

Mechanisms Determining the Winter Atmospheric Response to the Atlantic Overturning Circulation

The Influence of the AMOC Variability on the Atmosphere in CCSM3

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