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 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.

The Source of the Midwinter Suppression in Storminess over the North Pacific

2010 ◽  
Vol 23 (3) ◽  
pp. 634-648 ◽  
Author(s):  
Sandra Penny ◽  
Gerard H. Roe ◽  
David S. Battisti
Keyword(s):  
Growth Rates ◽  
Feature Tracking ◽  
Storm Track ◽  
Static Stability ◽  
The Tibetan Plateau ◽  
The North ◽  
The Pacific ◽  
Upper Level ◽  
The North Pacific ◽  
Midwinter Suppression

Abstract Feature-tracking techniques are employed to investigate why there is a relative minimum in storminess during winter within the Pacific storm track (the midwinter suppression). It is found that the frequency and amplitude of disturbances entering the Pacific storm track from midlatitude Asia are substantially reduced during winter relative to fall and spring and that the magnitude of this reduction is more than sufficient to account for the midwinter supression. Growth rates of individual disturbances are calculated and compared to expectations from linear theory for several regions of interest. Although there are discrepancies between linear expectations and observed growth rates over the Pacific, the growth of disturbances within the Pacific storm track cannot explain why the midwinter suppression exists. Furthermore, it is determined that the development of a wintertime reduction in storminess over midlatitude Asia is consistent with linear expectations, which predict a wintertime minimum in Eady growth rates in this region, mainly because of increased static stability. Several other mechanisms that may contribute to the initiation of the midwinter suppression over midlatitude Asia are discussed, including the interaction between upper-level waves and topography, the behavior of waves upwind of the Tibetan Plateau, and the initiation of lee cyclones.

Baroclinic Development in Observations and NASA GSFC General Circulation Models

2006 ◽  
Vol 134 (4) ◽  
pp. 1161-1173 ◽  
Author(s):  
Dennis P. Robinson ◽  
Robert X. Black
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
General Circulation ◽  
Storm Track ◽  
Model Simulations ◽  
The North ◽  
The Pacific ◽  
The North Atlantic ◽  
The North Pacific ◽  
Midwinter Suppression

Abstract Comparative diagnostic analyses of developing synoptic-scale baroclinic disturbances in NCEP–NCAR reanalyses and the NASA–NCAR (NASCAR) and Aries [NASA’s Seasonal-to-Interannual Prediction Project (NSIPP)] general circulation model simulations are performed. In particular, lag composite analyses of wintertime cyclonic and anticyclonic events occurring in the North Pacific and North Atlantic storm tracks are constructed to pursue a synoptic and dynamic characterization of eddy development. The data are also seasonally stratified to study aspects of the North Pacific midwinter suppression phenomenon. Winter-averaged results indicate that the model-simulated events are generally too weak in amplitude, particularly in the upper troposphere. For the North Pacific storm track, model-simulated events are also anomalously distended in the meridional direction. The existing model biases in eddy structure and magnitude lead to anomalously weak baroclinic energy conversions for both cyclonic and anticyclonic events over the North Pacific. For the North Atlantic storm track the NASCAR model provides a very good representation of the structure of developing cyclonic events. However, growing North Atlantic cyclones in the NSIPP model are anomalously weak and horizontally too isotropic (meridionally retracted). These latter two characteristics are also observed in both models for developing anticyclonic flow anomalies over the North Atlantic. The relative weakness of NSIPP synoptic events over the North Atlantic region is largely responsible for the 50% deficiency in areal-averaged baroclinic energy conversions. Conversely, the NASCAR model climatology features anomalously strong temperature gradients over the western North Atlantic that provide local enhancements to the baroclinic energy conversion field. A seasonally stratified diagnostic analysis reveals that the simulated climatological storm tracks over the North Pacific undergo larger spatial migrations during the cool season compared to observations. It is further determined that the suppression of synoptic eddy activity observed in the Pacific storm track is associated with a relative midwinter weakness in the magnitude of the growing cyclonic anomalies. Specifically, during midwinter the cyclonic perturbations entering the Pacific storm track are deficient in magnitude compared to their early and late winter counterparts. It is also discovered that the midwinter suppression pattern over the North Pacific region has a clear organized extension upstream into Siberia, the region from which incipient upper-tropospheric short-wave features emanate. This behavior is found in both observations and the model simulations. The results herein support the idea that the North Pacific midwinter suppression phenomenon is linked to a midwinter weakness in the upstream formation of upper-level short waves, leading to anomalously weak “seeding” of baroclinic disturbances in the Pacific storm track.

Interdecadal changes in the storm track activity over the North Pacific and North Atlantic

2011 ◽  
Vol 39 (1-2) ◽  
pp. 313-327 ◽  
Author(s):  
Sun-Seon Lee ◽  
June-Yi Lee ◽  
Bin Wang ◽  
Kyung-Ja Ha ◽  
Ki-Young Heo ◽  
...  
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Storm Track ◽  
The North ◽  
Storm Track Activity ◽  
The North Pacific ◽  
Interdecadal Changes

scholarly journals Energetics of transient eddies related to the midwinter minimum of the North Pacific storm-track activity

2021 ◽  
pp. 1-55
Keyword(s):  
Energy Conversion ◽  
North Pacific ◽  
Storm Track ◽  
Generation Rate ◽  
Net Energy ◽  
The North ◽  
Eddy Heat Flux ◽  
Storm Track Activity ◽  
Baroclinic Energy Conversion ◽  
The North Pacific

Abstract Storm-track activity over the North Pacific climatologically exhibits a clear minimum in midwinter, when the westerly jet speed sharply maximizes. This counterintuitive phenomenon, referred to as the “midwinter minimum (MWM)”, has been investigated from various perspectives, but the mechanisms are still to be unrevealed. Toward better understanding of this phenomenon, the present study delineates the detailed seasonal evolution of climatological-mean Eulerian statistics and energetics of migratory eddies along the NP storm-track over 60 years. As a comprehensive investigation of the mechanisms for the MWM, this study has revealed that the net eddy conversion/generation rate normalized by the eddy total energy, which is independent of eddy amplitude, is indeed reduced in midwinter. The reduction from early winter occurs mainly due to the decreased effectiveness of the baroclinic energy conversion through seasonally weakened temperature fluctuations and the resultant poleward eddy heat flux. The reduced net normalized conversion/generation rate in midwinter is also found to arise in part from the seasonally enhanced kinetic energy conversion from eddies into the strongly diffluent Pacific jet around its exit. The seasonality of the net energy influx also contributes especially to the spring recovery of the net normalized conversion/generation rate. The midwinter reduction in the normalized rates of both the net energy conversion/generation and baroclinic energy conversion was more pronounced in the period before the late 1980s, during which the MWM of the storm-track activity was climatologically more prominent.

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.

Nature of the Differences in the Intraseasonal Variability of the Pacific and Atlantic Storm Tracks: A Diagnostic Study

2006 ◽  
Vol 63 (10) ◽  
pp. 2602-2615 ◽  
Author(s):  
Yi Deng ◽  
Mankin Mak
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Intraseasonal Variability ◽  
Storm Track ◽  
Late Winter ◽  
The North ◽  
The Pacific ◽  
The North Atlantic ◽  
Early Late ◽  
The North Pacific

Abstract On the basis of an intraseasonal variability index of storm track evaluated for 40 winters (1963–64 through 2003–04) of NCEP–NCAR reanalysis data, it is found that well-defined midwinter minimum [MWMIN; (midwinter maximum MWMAX)] occurs in 21 (8) winters over the North Pacific. In contrast, MWMIN (MWMAX) occurs in 4 (25) of the 40 winters over the North Atlantic. The power spectrum of such an index for the Pacific has a broad peak between 5 and 10 yr, whereas the spectrum of the index for the Atlantic has comparable power in two spectral bands: 2–2.8 and 3.5–8 yr. Over the North Pacific, the increase in the zonal asymmetry of the background baroclinicity as well as in the corresponding horizontal deformation of the time-mean jet from early/late winter to midwinter is distinctly larger in an MWMIN winter. Associated with these changes, there is a distinctly stronger barotropic damping rate in the January of an MWMIN winter. The increase in the net conversion rate of eddy kinetic energy from early/late winter to midwinter is much larger in an MWMAX winter than that in an MWMIN winter. Even though there is a modest increase in the barotropic damping from early/late winter to midwinter over the North Atlantic, it is overcompensated by a larger increase in the baroclinic conversion rate. That would result in MWMAX. These results are empirical evidences in support of a hypothesis that a significant enhancement of the barotropic damping relative to the baroclinic growth from early/late winter to midwinter is a major contributing factor to MWMIN of the Pacific storm track.

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