scholarly journals Dynamics of the Stationary Anomalies Associated with the Interannual Variability of the Midwinter Pacific Storm Track—The Roles of Tropical Heating and Remote Eddy Forcing

2007 ◽  
Vol 64 (7) ◽  
pp. 2442-2461 ◽  
Author(s):  
Edmund K. M. Chang ◽  
Yanjuan Guo
Keyword(s):  
Interannual Variability ◽  
Storm Track ◽  
Circulation Model ◽  
Wave Model ◽  
Stationary Wave ◽  
Global Circulation Model ◽  
Global Circulation ◽  
The Pacific ◽  
Eddy Fluxes ◽  
Tropical Heating

Abstract The leading mode of interannual variability of the midwinter Pacific storm track is such that the storm track is weaker during the winters when the Pacific jet is strong, and stronger when the jet is weak. In this paper, experiments are conducted using a stationary wave model as well as an idealized global circulation model to explore the roles of anomalous tropical heating and eddy fluxes in forcing the observed Pacific jet anomalies. It is found that enhanced tropical heating over the region 60°E to the date line, 25°S to 25°N, acts to force a stronger and narrower Pacific jet. On average, tropical heating may account for about one-third of the strong jet anomaly, but there is significant year-to-year variability. Moreover, tropical heating does not appear to contribute to the weak jet anomaly. Much of the Pacific jet anomalies are forced by anomalous eddy fluxes. By examining the regional contributions from the Pacific, the Atlantic, and Asia, it is found that local eddy feedback over the Pacific only acts to force part of the stationary anomaly, while much of the signal is forced by remote eddy forcings from the Atlantic and Asia. Since significant parts of the jet anomalies are forced by anomalous tropical heating and remote eddy fluxes, it is concluded that the observed Pacific jet/storm-track variability is not a pure local wave–mean flow interaction mode internal to the Pacific basin. Both stationary wave model diagnostics and idealized global circulation model experiments suggest that stronger eddy activity over the Atlantic may force a weaker Pacific jet and stronger Pacific eddies. On the other hand, changes in eddy activity over the Pacific may also act to force changes in the Atlantic storm track. There are also indications that tropical heating anomalies may force a simultaneous weakening of both storm tracks. These possibilities may be some of the factors behind the observed significant correlation between the Pacific and Atlantic storm tracks and should be further explored in more realistic GCM experiments.

scholarly journals Diabatic and Orographic Forcing of Northern Winter Stationary Waves and Storm Tracks

2009 ◽  
Vol 22 (3) ◽  
pp. 670-688 ◽  
Author(s):  
Edmund K. M. Chang
Keyword(s):  
Storm Track ◽  
Lower Troposphere ◽  
Circulation Model ◽  
Storm Tracks ◽  
Minor Role ◽  
Stationary Waves ◽  
Global Circulation Model ◽  
Mean Flow ◽  
The Pacific ◽  
Eddy Fluxes

Abstract In this study, a dry global circulation model is used to examine the contributions made by orographic and diabatic forcings in shaping the zonal asymmetries in the earth’s Northern Hemisphere (NH) winter climate. By design, the model mean flow is forced to bear a close resemblance to the observed zonal mean and stationary waves. The model also provides a decent simulation of the storm tracks. In particular, the maxima over the Pacific and Atlantic, and minima over Asia and North America, are fairly well simulated. The model also successfully simulates the observation that the Atlantic storm track is stronger than the Pacific storm track, despite stronger baroclinicity over the Pacific. Sensitivity experiments are performed by imposing and removing various parts of the total forcings. In terms of the NH winter stationary waves in the upper troposphere, results of this study are largely consistent with previous studies. Diabatic forcings explain most of the modeled stationary waves, with orographic forcings playing only a secondary role, and feedbacks due to eddy fluxes probably play only minor roles in most cases. Nevertheless, results of this study suggest that eddy fluxes may be important in modifying the response to orographic forcings in the absence of zonal asymmetries in diabatic heating. On the other hand, unlike the conclusion reached by previous studies, it is argued that the convergence of eddy momentum fluxes is important in forcing the oceanic lows in the lower troposphere, in agreement with one’s synoptic intuition. Regarding the NH winter storm-track distribution, results of this study suggest that NH extratropical heating is the most important forcing. Zonal asymmetries in NH extratropical heating act to force the Pacific storm track to shift equatorward and the Atlantic storm track to shift poleward, attain a southwest–northeast tilt, and intensify. It appears to be the main forcing responsible for explaining why the Atlantic storm track is stronger than the Pacific storm track. Tibet and the Rockies are also important, mainly in suppressing the storm tracks over the continents, forcing a clearer separation between the two storm tracks. In contrast, asymmetries in tropical heating appear to play only a minor role in forcing the model storm-track distribution.

Storm-track organization and variability in a simplified atmospheric global circulation model

1998 ◽  
Vol 124 (548) ◽  
pp. 1019-1043 ◽  
Author(s):  
Thomas Frisius ◽  
Frank Lunkeit ◽  
Klaus Fraedrich ◽  
Ian N. James
Keyword(s):  
Storm Track ◽  
Circulation Model ◽  
Global Circulation Model ◽  
Global Circulation

scholarly journals A Comparative Evaluation of a Mesoscale Model and Atmospheric Global Circulation Model for Air Quality Simulation: A Multiscale, Multisite Evaluation

2012 ◽  
Vol 2012 ◽  
pp. 1-15 ◽  
Author(s):  
P. Goswami ◽  
J. Baruah
Keyword(s):  
High Resolution ◽  
Mesoscale Model ◽  
Large City ◽  
Circulation Model ◽  
Urban Pollution ◽  
Atmospheric Pollutants ◽  
Scale Model ◽  
Global Circulation Model ◽  
Global Circulation ◽  
Meso Scale

Concentrations of atmospheric pollutants are strongly influenced by meteorological parameters like rainfall, relative humidity and wind advection. Thus accurate specifications of the meteorological fields, and their effects on pollutants, are critical requirements for successful modelling of air pollution. In terms of their applications, pollutant concentration models can be used in different ways; in one, short term high resolution forecasts are generated to predict and manage urban pollution. Another application of dynamical pollution models is to generate outlook for a given airbasin, such as over a large city. An important question is application-specific model configuration for the meteorological simulations. While a meso-scale model provides a high-resolution configuration, a global model allows better simulation of large-sale fields through its global environment. Our objective is to comparatively evaluate a meso-scale atmospheric model (MM5) and atmospheric global circulation model (AGCM) in simulating different species of pollutants over different airbasins. In this study we consider four locations: ITO (Central Delhi), Sirifort (South Delhi), Bandra (Mumbai) and Karve Road (Pune). The results show that both the model configurations provide comparable skills in simulation of monthly and annual loads, although the skill of the meso-scale model is somewhat higher, especially at shorter time scales.

scholarly journals The Annular Response to Tropical Pacific SST Forcing

2006 ◽  
Vol 19 (9) ◽  
pp. 1802-1819 ◽  
Author(s):  
Shuanglin Li ◽  
Martin P. Hoerling ◽  
Shiling Peng ◽  
Klaus M. Weickmann
Keyword(s):  
General Circulation ◽  
Storm Track ◽  
Circulation Model ◽  
Tropical Pacific ◽  
Transient Eddy ◽  
West Pacific ◽  
Core Energy ◽  
The Pacific ◽  
Sst Forcing ◽  
Sst Anomaly

Abstract The leading pattern of Northern Hemisphere winter height variability exhibits an annular structure, one related to tropical west Pacific heating. To explore whether this pattern can be excited by tropical Pacific SST variations, an atmospheric general circulation model coupled to a slab mixed layer ocean is employed. Ensemble experiments with an idealized SST anomaly centered at different longitudes on the equator are conducted. The results reveal two different response patterns—a hemispheric pattern projecting on the annular mode and a meridionally arched pattern confined to the Pacific–North American sector, induced by the SST anomaly in the west and the east Pacific, respectively. Extratropical air–sea coupling enhances the annular component of response to the tropical west Pacific SST anomalies. A diagnosis based on linear dynamical models suggests that the two responses are primarily maintained by transient eddy forcing. In both cases, the model transient eddy forcing response has a maximum near the exit of the Pacific jet, but with a different meridional position relative to the upper-level jet. The emergence of an annular response is found to be very sensitive to whether transient eddy forcing anomalies occur within the axis of the jet core. For forcing within the jet core, energy propagates poleward and downstream, inducing an annular response. For forcing away from the jet core, energy propagates equatorward and downstream, inducing a trapped regional response. The selection of an annular versus a regionally confined tropospheric response is thus postulated to depend on how the storm tracks respond. Tropical west Pacific SST forcing is particularly effective in exciting the required storm-track response from which a hemisphere-wide teleconnection structure emerges.

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