scholarly journals A Simple Kinematic Source of Skewness in Atmospheric Flow Fields

2012 ◽  
Vol 69 (2) ◽  
pp. 578-590 ◽  
Author(s):  
Fay Luxford ◽  
Tim Woollings
Keyword(s):  
Geopotential Height ◽  
General Circulation ◽  
Dynamical Behavior ◽  
Kinematic Model ◽  
Circulation Model ◽  
Jet Stream ◽  
Jet Streams ◽  
Close Link ◽  
Nonlinear Dynamical ◽  
Kinematic Effect

Abstract Geopotential height fields exhibit a well-known pattern of skewness, with distributions that are positively skewed on the poleward side of the midlatitude jets/storm tracks and negatively skewed on the equatorward side. This pattern has often been interpreted as a signature of nonlinear dynamical features, such as blocking highs and cutoff lows, and there is renewed interest in the higher moments of flow variables as indicators of the nature of the underlying dynamics. However, this paper suggests that skewness can arise as a simple kinematic consequence of the presence of jet streams and so may not be a reliable indicator of nonlinear dynamical behavior. In support of this, reanalysis data are analyzed to demonstrate a close link between the jet streams and the skewness patterns. Further evidence is provided by a simple stochastic kinematic model of a jet stream as a Gaussian wind profile. The parameters of this model are fitted to data from the reanalysis and also from an aquaplanet general circulation model. The skewness of the model’s geopotential height and zonal wind fields are then compared to those of the original data. This shows that a fluctuating jet stream can produce patterns of skewness that are qualitatively similar to those observed, although the magnitude of the skewness is significantly overestimated by the kinematic model. These results suggest that this simple kinematic effect does contribute to the observed patterns of skewness but that other processes (such as nonlinear dynamics) likely also play a role.

scholarly journals Interannual Variations of Wind Regimes off the Subtropical Western Australia Coast during Austral Winter and Spring

2012 ◽  
Vol 25 (16) ◽  
pp. 5587-5599 ◽  
Author(s):  
Evan Weller ◽  
Ming Feng ◽  
Harry Hendon ◽  
Jian Ma ◽  
Shang-Ping Xie ◽  
...  
Keyword(s):  
Western Australia ◽  
Geopotential Height ◽  
General Circulation ◽  
Circulation Model ◽  
Interannual Variations ◽  
Storm Events ◽  
Austral Winter ◽  
Easterly Wind ◽  
Upper Troposphere ◽  
Australian Continent

Abstract Off the Western Australia coast, interannual variations of wind regime during the austral winter and spring are significantly correlated with the Indian Ocean dipole (IOD) and the southern annular mode (SAM) variability. Atmospheric general circulation model experiments forced by an idealized IOD sea surface temperature anomaly field suggest that the IOD-generated deep atmospheric convection anomalies trigger a Rossby wave train in the upper troposphere that propagates into the southern extratropics and induces positive geopotential height anomalies over southern Australia, independent of the SAM. The positive geopotential height anomalies extended from the upper troposphere to the surface, south of the Australian continent, resulting in easterly wind anomalies off the Western Australia coast and a reduction of the high-frequency synoptic storm events that deliver the majority of southwest Australia rainfall during austral winter and spring. In the marine environment, the wind anomalies and reduction of storm events may hamper the western rock lobster recruitment process.

Tropical Connections to Climatic Change in the Extratropical Southern Hemisphere: The Role of Atlantic SST Trends

2014 ◽  
Vol 27 (13) ◽  
pp. 4923-4936 ◽  
Author(s):  
Graham R. Simpkins ◽  
Shayne McGregor ◽  
Andréa S. Taschetto ◽  
Laura M. Ciasto ◽  
Matthew H. England
Keyword(s):  
Climatic Change ◽  
Atmospheric Circulation ◽  
Southern Hemisphere ◽  
Geopotential Height ◽  
General Circulation ◽  
Rossby Waves ◽  
Circulation Model ◽  
Hadley Cell ◽  
Austral Spring ◽  
The Impact

The austral spring relationships between sea surface temperature (SST) trends and the Southern Hemisphere (SH) extratropical atmospheric circulation are investigated using an atmospheric general circulation model (AGCM). A suite of simulations are analyzed wherein the AGCM is forced by underlying SST conditions in which recent trends are constrained to individual ocean basins (Pacific, Indian, and Atlantic), allowing the impact of each region to be assessed in isolation. When forced with observed global SST, the model broadly replicates the spatial pattern of extratropical SH geopotential height trends seen in reanalyses. However, when forcing by each ocean basin separately, similar structures arise only when Atlantic SST trends are included. It is further shown that teleconnections from the Atlantic are associated with perturbations to the zonal Walker circulation and the corresponding intensification of the local Hadley cell, the impact of which results in the development of atmospheric Rossby waves. Thus, increased Rossby waves, forced by positive Atlantic SST trends, may have played a role in driving geopotential height trends in the SH extratropics. Furthermore, these atmospheric circulation changes promote warming throughout the Antarctic Peninsula and much of West Antarctica, with a pattern that closely matches recent observational records. This suggests that Atlantic SST trends, via a teleconnection to the SH extratropics, may have contributed to springtime climatic change in the SH extratropics over the past three decades.

scholarly journals First outcomes from the CNR-ISAC monthly forecasting system

2012 ◽  
Vol 8 (1) ◽  
pp. 77-82 ◽  
Author(s):  
D. Mastrangelo ◽  
P. Malguzzi ◽  
C. Rendina ◽  
O. Drofa ◽  
A. Buzzi
Keyword(s):  
Geopotential Height ◽  
General Circulation ◽  
Circulation Model ◽  
Forecast Errors ◽  
Preliminary Evaluation ◽  
National Council ◽  
Probabilistic Forecasting ◽  
Monthly Basis ◽  
Standard Pressure ◽  
Forecasting System

Abstract. A monthly probabilistic forecasting system is experimentally operated at the ISAC institute of the National Council of Research of Italy. The forecasting system is based on GLOBO, an atmospheric general circulation model developed at the same institute. The model is presently run on a monthly basis to produce an ensemble of 32 forecasts initialized with GFS-NCEP perturbed analyses. Reforecasts, initialized with ECMWF ERA-Interim reanalyses of the 1989–2009 period, are also produced to determine modelled climatology of the month to forecast. The modelled monthly climatology is then used to calibrate the ensemble forecast of daily precipitation, geopotential height and temperature on standard pressure levels. In this work, we present the forecasting system and a preliminary evaluation of the model systematic and forecast errors in terms of non-probabilistic scores of the 500-hPa geopotential height. Results show that the proposed forecasting system outperforms the climatology in the first two weeks of integrations. The adopted calibration based on weighted bias correction is found to reduce the systematic and the forecast errors.

The Effect of a Strong Zonal Jet Stream on the Temporal Evolution of Baroclinic Eddies

2020 ◽  
Author(s):  
Or Hadas ◽  
Yohai Kaspi
Keyword(s):  
General Circulation ◽  
Baroclinic Instability ◽  
Storm Track ◽  
Storm Tracks ◽  
Jet Stream ◽  
Similar Response ◽  
Jet Streams ◽  
Eddy Activity ◽  
Zonal Jets ◽  
The Pacific

<p>The midlatitude storm tracks are one of the most prominent features of the extratropical climate. Much of our understanding of what controls the storm tracks comes from linear theory of baroclinic instability, which explains generally most of the observed response of storms to the general circulation. One example to where this approach is lacking is the Pacific midwinter minimum, a decrease in the eddy activity over the Pacific storm track during midwinter when baroclinicity is at its peak due to extremely strong zonal jets. A similar response was found recently for the Atlantic storm track<strong>,</strong> in correlation to periods of strong zonal jets. Following on these findings we study the effect of strong zonal jet streams on eddy activity in the midlatitudes. In order to isolate the effect of the jet strength we used several idealized GCM experiments with different jet strengths, and analyze the formed storm track from a Lagrangian perspective by using a storm tracking algorithm. In both the Eulerian analysis and analysis of the tracks a strong reduction of high level eddy activity is prominent, as well as a modest weakening of the low-level activity. The observed response is then further analyzed by studying the connection between the upper and lower wave and how it changes with jet-stream intensity. </p><p> </p>

Composite Life Cycle of West Pacific Jet-Superposition Events and the Large-Scale Environmental Response over Western North America

2021 ◽  
Author(s):  
Zachary J. Handlos ◽  
Jonathan E. Martiny
Keyword(s):  
Geopotential Height ◽  
General Circulation ◽  
Large Scale ◽  
Cold Season ◽  
Height Anomaly ◽  
Lower Latitude ◽  
Environmental Response ◽  
Jet Streams ◽  
West Pacific ◽  
Asian Winter Monsoon

AbstractVertical alignment of the polar and subtropical jet streams in the west Pacific basin occurs most often during the boreal cold season. Recent work has revealed that the large-scale environment conducive to producing such superpositions involves interaction between East Asian Winter Monsoon cold surge events, lower latitude convection and internal jet dynamics. The evolution of the large-scale environments associated with these events post-superposition as well as the significance of that evolution on aspects of the wintertime Northern Hemisphere general circulation is examined through construction of a 44-case composite. The post-superposition west Pacific jet extends eastward associated with an anomalous positive/negative geopotential height couplet straddling the jet’s exit region. This jet extension results in ridge building over Alaska and northwestern Canada. The large-scale evolutions associated with the composite post-superposition environment occurs consistently amongst the majority of cases considered within this analysis. The positive/negative geopotential height anomaly couplet, enhanced jet entrance circulation, low latitude convection and internal jet dynamics present in the pre-superposition environment weaken post-superposition. As a result, the characteristic vertical PV “wall” associated with the composite vertically superposed jet weakens. Lastly, investigation of the value of using the two most dominant modes of west Pacific jet variability in observing the evolution of the superposed west Pacific jet post-superposition reveals that, while the extension of the jet is exhibited, significant variability exists when analyzing each of the 44 cases of interest individually.

scholarly journals Determined Seasonal Variation of Polar Jet Streams over Baghdad City for period 2012-2014

2020 ◽  
Vol 31 (1) ◽  
pp. 1
Author(s):  
Ramia M. Mahmood ◽  
Ahmed Sami Hassan
Keyword(s):  
Seasonal Variation ◽  
Geopotential Height ◽  
Climatic Conditions ◽  
Radiosonde Data ◽  
Jet Stream ◽  
Maximum Frequency ◽  
Jet Streams ◽  
Weather Forecasts

Analysis of the jet stream is diagnostic over Baghdad for period studies 2012 to 2014 using Radiosonde data and synoptic charts. The source of data is Iraq Meteorological Organization and Seismology (IMOS). Similar way for weather forecasts to identify areas, forecasters show that area has good predictability under jet stream case. The jet stream is happening clearly realized under the climatic conditions like temperature, humidity and geopotential height for upper layer. Two levels 300hPa and 500hPa is the best way to determine the current jet. Maximum frequency of jet stream happened in April and July in 500hPa that equal 13 times and in 300hPa happened 14 times in May. This study showed that the occurrence of cases of the jet stream is becoming increasingly volatile and decreasingly during 2012 and gradually increased in 2014 where that recorded in 2014.

The Structure and Evolution of Extratropical Cyclones, Fronts, Jet Streams, and the Tropopause in the GEOS General Circulation Model

2001 ◽  
Vol 82 (9) ◽  
pp. 1853-1868 ◽  
Author(s):  
A. L. Conaty ◽  
J. C. Jusem ◽  
L. Takacs ◽  
D. Keyser ◽  
R. Atlas
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Large Scale ◽  
North Atlantic Ocean ◽  
Potential Temperature ◽  
Circulation Model ◽  
Structural Features ◽  
Extratropical Cyclones ◽  
Jet Streams ◽  
The North

The realism of extratropical cyclones, fronts, jet streams, and the tropopause in the Goddard Earth Observing System (GEOS) general circulation model (GCM), implemented in assimilation and simulation modes, is evaluated from climatological and case-study perspectives using the GEOS-1 reanalysis climatology and applicable conceptual models as benchmarks for comparison. The latitude-longitude grid spacing of the datasets derived from the GEOS GCM ranges from 2° × 2.5° to 0.5° × 0.5°. Frontal systems in the higher-resolution datasets are characterized by horizontal potential temperature gradients that are narrower in scale and larger in magnitude than their lower-resolution counterparts, and various structural features in the Shapiro–Keyser cyclone model are replicated with reasonable fidelity at 1° × 1° resolution. The remainder of the evaluation focuses on a 3-month Northern Hemisphere winter simulation of the GEOS GCM at 1° × 1° resolution. The simulation realistically reproduces various large-scale circulation features related to the North Pacific and Atlantic jet streams when compared with the GEOS-1 reanalysis climatology, and conforms closely to a conceptualization of the zonally averaged troposphere and stratosphere proposed originally by Napier Shaw and revised by Hoskins. An extratropical cyclone that developed over the North Atlantic Ocean in the simulation features surface and tropopause evolutions corresponding to the Norwegian cyclone model and to the LC2 life cycle proposed by Thorncroft et al., respectively. These evolutions are related to the position of the developing cyclone with respect to upper-level jets identified in the time-mean and instantaneous flow fields. This article concludes with the enumeration of several research opportunities that may be addressed through the use of state-of-the-art GCMs possessing sufficient resolution to represent mesoscale phenomena and processes explicitly.

Can the Increase in the Eddy Length Scale under Global Warming Cause the Poleward Shift of the Jet Streams?

2011 ◽  
Vol 24 (14) ◽  
pp. 3764-3780 ◽  
Author(s):  
Joseph Kidston ◽  
G. K. Vallis ◽  
S. M. Dean ◽  
J. A. Renwick
Keyword(s):  
Global Warming ◽  
General Circulation ◽  
Phase Speed ◽  
Zonal Flow ◽  
General Circulation Models ◽  
Length Scale ◽  
Jet Stream ◽  
Jet Streams ◽  
Barotropic Model ◽  
Poleward Shift

Abstract The question of whether an increase in the atmospheric eddy length scale may cause a poleward shift of the midlatitude jet streams is addressed. An increase in the length scale of the eddy reduces its zonal phase speed and so causes eddies to dissipate farther from the jet core. If the eddy dissipation region on the poleward flank of the jet overlaps with the eddy source latitudes, shifting this dissipation to higher latitudes will alter which latitudes are a net source of baroclinic eddies, and hence the eddy-driven jet stream may shift poleward. This behavior does not affect the equatorward flank of the jet in the same way because the dissipation region on the equatorward flank is well separated from the source latitudes. An experiment with a barotropic model is presented in which an increase in the length scale of a midlatitude perturbation results in a poleward shift in the acceleration of the zonal flow. Initial investigations indicate that this behavior is also important in both observational data and the output of comprehensive general circulation models (GCMs). A simplified GCM is used to show that the latitude of the eddy-driven jet is well correlated with the eddy length scale. It is argued that the increase in the eddy length scale causes the poleward shift of the jet in these experiments, rather than vice versa.

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