scholarly journals Midwinter Suppression of Northern Hemisphere Storm Track Activity in the Real Atmosphere and in GCM Experiments

1997 ◽  
Vol 54 (12) ◽  
pp. 1589-1599 ◽  
Author(s):  
M. Christoph ◽  
U. Ulbrich ◽  
P. Speth
Keyword(s):  
Northern Hemisphere ◽  
Storm Track ◽  
The Real ◽  
Storm Track Activity ◽  
Real Atmosphere ◽  
Midwinter Suppression

scholarly journals Eddy-Induced Growth Rate of Low-Frequency Variability and Its Mid- to Late Winter Suppression in the Northern Hemisphere

2014 ◽  
Vol 71 (7) ◽  
pp. 2281-2298 ◽  
Author(s):  
Hong-Li Ren ◽  
Fei-Fei Jin ◽  
Jong-Seong Kug
Keyword(s):  
Northern Hemisphere ◽  
Storm Track ◽  
Low Frequency ◽  
Lower Troposphere ◽  
Surface Friction ◽  
Late Winter ◽  
Wind Maximum ◽  
Low Frequency Variability ◽  
Storm Track Activity ◽  
Effect Of Surface

Abstract Synoptic eddy and low-frequency flow (SELF) feedback plays an important role in reinforcing low-frequency variability (LFV). Recent studies showed that an eddy-induced growth (EIG) or instability makes a fundamental contribution to the maintenance of LFV. To quantify the efficiency of the SELF feedback, this study examines the spatiotemporal features of the empirical diagnostics of EIG and its associations with LFV. The results show that, in terms of eddy vorticity forcing, the EIG rate of LFV is generally larger (smaller) in the upper (lower) troposphere, whereas, in terms of eddy potential vorticity forcing, it is larger in the lower troposphere to partly balance the damping effect of surface friction. The local EIG rate shows a horizontal spatial distribution that corresponds to storm-track activity, which tends to be responsible for maintaining LFV amplitudes and patterns as well as sustaining eddy-driven jets. In fact, the EIG rate has a well-defined seasonality, being generally larger in cold seasons and smaller in the warmest season, and this seasonality is stronger in the Northern Hemisphere than in the Southern Hemisphere. This study also reveals a mid- to late winter (January–March) suppression of the EIG rate in the Northern Hemisphere, which indicates a reduced eddy feedback efficiency and may be largely attributed to the eddy kinetic energy suppression and the midlatitude zonal wind maximum in the midwinter of the Northern Hemisphere.

Role of the Tibetan Plateau on the Annual Variation of Mean Atmospheric Circulation and Storm-Track Activity*

2013 ◽  
Vol 26 (14) ◽  
pp. 5270-5286 ◽  
Author(s):  
Sun-Seon Lee ◽  
June-Yi Lee ◽  
Kyung-Ja Ha ◽  
Bin Wang ◽  
Akio Kitoh ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Atmospheric Circulation ◽  
North Pacific ◽  
Annual Variation ◽  
Storm Track ◽  
Monsoon Circulation ◽  
The Tibetan Plateau ◽  
The Pacific ◽  
Storm Track Activity ◽  
Midwinter Suppression

Abstract This study reexamines how the Tibetan Plateau (TP) modulates the annual variation of atmospheric circulation and storm-track activity based on the Meteorological Research Institute's atmosphere–ocean coupled model experiments with a progressive TP uplift from 0% to 100% of the present height. Three major roles of the TP on atmospheric circulation and storm-track activity are identified. First, consistent with a previous finding, the TP tends to intensify the upper-level jet and enhance baroclinicity in the North Pacific Ocean but significantly weaken storm-track activity over the TP, East Asia, and the western North Pacific during the cold season. Second, the TP amplifies stationary waves that are closely linked to transient eddies. In particular, the TP enhances the Siberian high and the Aleutian low, which together contribute to the strengthening of the East Asian winter monsoon circulation and the weakening of storm-track activity. Third, the TP significantly modulates the subseasonal variability of the Pacific storm-track (PST) activity. In particular, the TP tends to suppress PST activity during midwinter despite the fact that it strengthens baroclinicity along the Pacific jet. The midwinter suppression of PST activity, which is well reproduced in a control run with a realistic TP, gradually disappears as the TP height decreases. Major factors for the midwinter suppression of the PST associated with the TP include the 1) destructive effect of an excessively strong jet leading to an inefficiency of barotropic energy conversion, 2) reduction of baroclinicity over the northern part of the TP, and 3) subseasonally varying SST change and resulting moist static energy.

scholarly journals Comments on “The Source of the Midwinter Suppression in Storminess over the North Pacific”

2011 ◽  
Vol 24 (19) ◽  
pp. 5187-5191 ◽  
Author(s):  
Edmund K. M. Chang ◽  
Yanjuan Guo
Keyword(s):  
North Pacific ◽  
Feature Tracking ◽  
Storm Track ◽  
Northern Asia ◽  
The North ◽  
Relative Minimum ◽  
The Pacific ◽  
Storm Track Activity ◽  
The North Pacific ◽  
Midwinter Suppression

In a recent paper, Penny et al. employed feature tracking to investigate why there is a relative minimum in storminess during winter within the Pacific storm track. They concluded that reduced upstream seeding, especially seeding from northern Asia, is the main “source” of the midwinter suppression of the Pacific storm track. Results presented here show that during midwinter months when upstream seeding is as strong as that in spring/fall, the Pacific storm track is not significantly stronger than average and is still much weaker than that in spring/fall, suggesting that the strength of upstream seeding cannot be the primary cause of the midwinter suppression of Pacific storm-track activity.

scholarly journals Changing Northern Hemisphere Storm Tracks in an Ensemble of IPCC Climate Change Simulations

2008 ◽  
Vol 21 (8) ◽  
pp. 1669-1679 ◽  
Author(s):  
U. Ulbrich ◽  
J. G. Pinto ◽  
H. Kupfer ◽  
G. C. Leckebusch ◽  
T. Spangehl ◽  
...  
Keyword(s):  
Climate Change ◽  
Northern Hemisphere ◽  
Climate Models ◽  
Global Climate ◽  
Storm Track ◽  
Global Climate Models ◽  
The North ◽  
Storm Track Activity ◽  
Eastern North Atlantic ◽  
The Individual

Abstract Winter storm-track activity over the Northern Hemisphere and its changes in a greenhouse gas scenario (the Special Report on Emission Scenarios A1B forcing) are computed from an ensemble of 23 single runs from 16 coupled global climate models (CGCMs). All models reproduce the general structures of the observed climatological storm-track pattern under present-day forcing conditions. Ensemble mean changes resulting from anthropogenic forcing include an increase of baroclinic wave activity over the eastern North Atlantic, amounting to 5%–8% by the end of the twenty-first century. Enhanced activity is also found over the Asian continent and over the North Pacific near the Aleutian Islands. At high latitudes and over parts of the subtropics, activity is reduced. Variations of the individual models around the ensemble average signal are not small, with a median of the pattern correlation near r = 0.5. There is, however, no evidence for a link between deviations in present-day climatology and deviations with respect to climate change.

scholarly journals Is Pacific Storm-Track Activity Correlated with the Strength of Upstream Wave Seeding?

2012 ◽  
Vol 25 (17) ◽  
pp. 5768-5776 ◽  
Author(s):  
Edmund K. M. Chang ◽  
Yanjuan Guo
Keyword(s):  
Feature Tracking ◽  
Storm Track ◽  
Central Pacific ◽  
The North ◽  
The Pacific ◽  
North Asia ◽  
Storm Track Activity ◽  
The Relationship ◽  
The North Pacific ◽  
Midwinter Suppression

Abstract In this paper, the relationship between upstream seeding over north Asia and downstream storm-track activity over the North Pacific in midwinter and spring/fall has been analyzed using 45 years of variance and feature-tracking statistics. It is shown that for each season, interannual variations in upstream seeding and downstream storm-track activity are largely uncorrelated. Moreover, during midwinter months in which the upstream seeding from north Asia is about as strong as that during a typical spring/fall month, the downstream storm track in central Pacific is still significantly weaker during midwinter than that during spring/fall. In addition, during cool seasons in which the midwinter suppression is more pronounced in the upstream seeding region, the suppression is not significantly enhanced in the downstream Pacific storm track. A recent study suggested that reduced upstream seeding from north Asia is the main “source” of the midwinter suppression of the Pacific storm track. Results presented in this study suggest that it is unlikely that the weakness in upstream seeding is the primary cause of the midwinter suppression.

scholarly journals Assessing the Increasing Trend in Northern Hemisphere Winter Storm Track Activity Using Surface Ship Observations and a Statistical Storm Track Model

2007 ◽  
Vol 20 (22) ◽  
pp. 5607-5628 ◽  
Author(s):  
Edmund K. M. Chang
Keyword(s):  
Northern Hemisphere ◽  
Storm Track ◽  
Winter Storm ◽  
Surface Ship ◽  
The Pacific ◽  
Increasing Trend ◽  
Storm Track Activity ◽  
Observational Errors ◽  
Hemisphere Winter ◽  
Northern Hemisphere Winter

Abstract Recent studies, based largely on analyses of reanalysis datasets, suggest that the Northern Hemisphere winter storm track activity has increased significantly during the second half of the twentieth century. In this study, this increasing trend, in terms of filtered mean sea level pressure (MSLP) variance statistics, is assessed using surface ship observations and a statistical storm track model. MSLP observations made by ships, archived as part of the reanalysis project conducted by the National Centers for Environmental Prediction–National Center for Atmospheric Research, have been analyzed. Observational errors are estimated by comparing reports of nearly collocated observations. Consistent with previous studies, the observational errors of ship pressure observations are found to be very large during the late 1960s and early 1970s. Without correcting for observational errors, the storm track activity over the Pacific, computed based on ship observations, is found to be decreasing with time, while the upward trend in the Atlantic is much smaller than that found in the reanalysis data. Even after corrections have been made to account for secular changes in observational error statistics, the ship-based trend in the Pacific is still found to be much smaller than that found in the reanalysis, while over the Atlantic, the corrected ship-based trend is consistent with that found in the reanalysis. The robustness of the results is tested by application of data trimming based on the reanalysis products. Ship observations that are different from the reanalysis by more than a prescribed limit are removed before the statistics are computed. As the prescribed limit is reduced from 30 to 2.5 hPa, the ship-based storm track activity becomes increasingly consistent with that based on the reanalysis. However, even when the smallest limit is used, the trends computed from the ship observations are still smaller than those computed from the reanalysis, strongly suggesting that the trends in the reanalysis are biased high. Nevertheless, the results suggest that decadal-scale variability of the Atlantic storm track activity is not very sensitive to the trimming limit, while results for the Pacific storm track are not as robust. As an independent corroboration of the ship observation results, a statistical model is used to test whether the storm track trend found in the reanalysis is dynamically consistent with observed mean flow change. Five hundred winters of GCM simulations are used to construct a linear model based on canonical correlation analysis (CCA), using monthly mean distribution of MSLP anomalies as a predictor to hindcast monthly mean MSLP variance. The Atlantic storm track in the CCA model hindcast is well correlated with the storm track in the reanalysis on both interannual and decadal time scales, with the hindcast trend being 82% of that found in the reanalysis. Over the Pacific, the CCA hindcast does not perform as well, and the hindcast trend is only 32% of that found in the reanalysis. The results of this study suggest that the actual trend in Pacific storm track activity is probably only about 20%–60% of that found in the reanalysis, while over the Atlantic, the actual trend is likely to be about 70%–80% of that found in the reanalysis. Two new basinwide storm track indices, which should contain less bias in the secular trends, have been defined based mainly on ship observations.

scholarly journals On non-elliptic regions and solvability of balance equations for atmosphere dynamics

2007 ◽  
Vol 22 (3) ◽  
pp. 329-337
Author(s):  
Andrei Bourchtein ◽  
Ludmila Bourchtein
Keyword(s):  
Gravitational Waves ◽  
Southern Hemisphere ◽  
Numerical Schemes ◽  
Balance Equations ◽  
Tropical Zone ◽  
The Real ◽  
Modeling Systems ◽  
Great Amplitude ◽  
Real Atmosphere ◽  
Elliptic Regions

To eliminate the fast gravitational waves of great amplitude, which are not observed in the real atmosphere, the initial fields for numerical schemes of atmosphere forecasting and modeling systems are usually adjusted dynamically by applying balance relations. In this study we consider different forms of the balance equations and for each of them we detect the nonelliptic regions in the gridded atmosphere data of the Southern Hemisphere. The performed analysis reveals the geographical, vertical and zonally averaged distributions of nonelliptic regions with the most concentration in the tropical zone. The area of these regions is essentially smaller and less intensive for more complete and physically justified balance relations. The obtained results confirm the Kasaharas assumption that ellipticity conditions are violated in the actual atmospheric fields essentially due to approximations made under deriving the balance equations.

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