scholarly journals Increased Quasi Stationarity and Persistence of Winter Ural Blocking and Eurasian Extreme Cold Events in Response to Arctic Warming. Part II: A Theoretical Explanation

2017 ◽  
Vol 30 (10) ◽  
pp. 3569-3587 ◽  
Author(s):  
Dehai Luo ◽  
Yao Yao ◽  
Aiguo Dai ◽  
Ian Simmonds ◽  
Linhao Zhong
Keyword(s):  
Zonal Wind ◽  
Large Amplitude ◽  
Multiscale Model ◽  
Theoretical Explanation ◽  
Vertical Shear ◽  
Synoptic Scale ◽  
Dynamical Mechanism ◽  
Arctic Warming ◽  
Westward Movement ◽  
Cold Events

Abstract In Part I of this study, it was shown that the Eurasian cold anomalies related to Arctic warming depend strongly on the quasi stationarity and persistence of the Ural blocking (UB). The analysis here revealed that under weak mean westerly wind (MWW) and vertical shear (VS) (quasi barotropic) conditions with weak synoptic-scale eddies and a large planetary wave anomaly, the growth of UB is slow and its amplitude is small. For this case, a quasi-stationary and persistent UB is seen. However, under strong MWW and VS (quasi baroclinic) conditions, synoptic-scale eddies are stronger and the growth of UB is rapid; the resulting UB is less persistent and has large amplitude. In this case, a marked retrogression of the UB is observed. The dynamical mechanism behind the dependence of the movement and persistence of UB upon the background conditions is further examined using a nonlinear multiscale model. The results show that when the blocking has large amplitude under quasi-baroclinic conditions, the blocking-induced westward displacement greatly exceeds the strong mean zonal-wind-induced eastward movement and hence generates a marked retrogression of the blocking. By contrast, under quasi-barotropic conditions because the UB amplitude is relatively small the blocking-induced westward movement is less distinct, giving rise to a quasi-stationary and persistent blocking. It is further shown that the strong mid–high-latitude North Atlantic mean zonal wind is the quasi-barotropic condition that suppresses UB’s retrogression and thus is conducive to the quasi stationarity and persistence of the UB. The model results show that the blocking duration is longer when the mean zonal wind in the blocking region or eddy strength is weaker.

scholarly journals Increased Quasi Stationarity and Persistence of Winter Ural Blocking and Eurasian Extreme Cold Events in Response to Arctic Warming. Part I: Insights from Observational Analyses

2017 ◽  
Vol 30 (10) ◽  
pp. 3549-3568 ◽  
Author(s):  
Yao Yao ◽  
Dehai Luo ◽  
Aiguo Dai ◽  
Ian Simmonds
Keyword(s):  
Reanalysis Data ◽  
Heat Fluxes ◽  
Vertical Shear ◽  
Arctic Warming ◽  
Surface Heat Fluxes ◽  
Narrow Region ◽  
Westward Movement ◽  
Cold Anomaly ◽  
Cold Events ◽  
Barents And Kara Seas

Abstract Part I of this study examines the relationship among winter cold anomalies over Eurasia, Ural blocking (UB), and the background conditions associated with Arctic warming over the Barents and Kara Seas (BKS) using reanalysis data. It is found that the intensity, persistence, and occurrence region of UB-related Eurasian cold anomalies depend strongly on the strength and vertical shear (VS) of the mean westerly wind (MWW) over mid–high-latitude Eurasia related to BKS warming. Observational analysis reveals that during 1951–2015 UB days are 64% (54%) more frequent during weak MWW (VS) winters, with 26.9 (28.4) days per winter, than during strong MWW (VS) winters. During weak MWW or VS winters, as frequently observed during 2000–15, persistent and large UB-related warming is seen over the BKS together with large and widespread midlatitude Eurasian cold anomalies resulting from increased quasi stationarity and persistence of the UB. By contrast, when the MWW or VS is strong as frequently observed during 1979–99, the cold anomaly is less intense and persistent and confined to a narrow region of Europe because of a rapid westward movement of the strong UB. For this case, the BKS warming is relatively weak and less persistent. The midlatitude cold anomalies are maintained primarily by reduced downward infrared radiation (IR), while the surface heat fluxes, IR, and advection all contribute to the BKS warming. Thus, the large BKS warming since 2000 weakens the meridional temperature gradient, MWW, and VS, which increases quasi stationarity and persistence of the UB (rather than its amplitude) and then leads to more widespread Eurasian cold events and further enhances the BKS warming.

scholarly journals Future Changes in the Ozone Quasi-Biennial Oscillation with Increasing GHGs and Ozone Recovery in CCMI Simulations

2017 ◽  
Vol 30 (17) ◽  
pp. 6977-6997 ◽  
Author(s):  
Hiroaki Naoe ◽  
Makoto Deushi ◽  
Kohei Yoshida ◽  
Kiyotaka Shibata
Keyword(s):  
Zonal Wind ◽  
Climate Model ◽  
Vertical Shear ◽  
Quasi Biennial Oscillation ◽  
The Past ◽  
Meteorological Research Institute ◽  
Climate Simulations ◽  
The Future ◽  
Ozone Depleting Substances ◽  
Biennial Oscillation

The future quasi-biennial oscillation (QBO) in ozone in the equatorial stratosphere is examined by analyzing transient climate simulations due to increasing greenhouse gases (GHGs) and decreasing ozone-depleting substances under the auspices of the Chemistry–Climate Model Initiative. The future (1960–2100) and historical (1979–2010) simulations are conducted with the Meteorological Research Institute Earth System Model. Three climate periods, 1960–85 (past), 1990–2020 (present), and 2040–70 (future) are selected, corresponding to the periods before, during, and after ozone depletion. The future ozone QBO is characterized by increases in amplitude by 15%–30% at 5–10 hPa and decreases by 20%–30% at 40 hPa, compared with the past and present climates; the future and present ozone QBOs increase in amplitude by up to 60% at 70 hPa, compared with the past climate. The increased amplitude at 5–10 hPa suggests that the temperature-dependent photochemistry plays an important role in the enhanced future ozone QBO. The weakening of vertical shear in the zonal wind QBO is responsible for the decreased amplitude at 40 hPa in the future ozone QBO. An interesting finding is that the weakened zonal wind QBO in the lowermost tropical stratosphere is accompanied by amplified QBOs in ozone, vertical velocity, and temperature. Further study is needed to elucidate the causality of amplification about the ozone and temperature QBOs under climate change in conditions of zonal wind QBO weakening.

Developing versus Nondeveloping Disturbances for Tropical Cyclone Formation. Part I: North Atlantic

2012 ◽  
Vol 140 (4) ◽  
pp. 1047-1066 ◽  
Author(s):  
Melinda S. Peng ◽  
Bing Fu ◽  
Tim Li ◽  
Duane E. Stevens
Keyword(s):  
Water Vapor ◽  
North Atlantic ◽  
Large Scale ◽  
Relative Vorticity ◽  
Water Vapor Content ◽  
Vertical Shear ◽  
Horizontal Shear ◽  
Synoptic Scale ◽  
The North ◽  
The North Atlantic

This study investigates the characteristic differences of tropical disturbances that eventually develop into tropical cyclones (TCs) versus those that did not, using global daily analysis fields of the Navy Operational Global Atmospheric Prediction System (NOGAPS) from the years 2003 to 2008. Time filtering is applied to the data to extract tropical waves with different frequencies. Waves with a 3–8-day period represent the synoptic-scale disturbances that are representatives as precursors of TCs, and waves with periods greater than 20 days represent the large-scale background environmental flow. Composites are made for the developing and nondeveloping synoptic-scale disturbances in a Lagrangian frame following the disturbances. Similarities and differences between them are analyzed to understand the dynamics and thermodynamics of TC genesis. Part I of this study focuses on events in the North Atlantic, while Part II focuses on the western North Pacific. A box difference index (BDI), accounting for both the mean and variability of the individual sample, is introduced to subjectively and quantitatively identify controlling parameters measuring the differences between developing and nondeveloping disturbances. Larger amplitude of the BDI implies a greater possibility to differentiate the difference between two groups. Based on their BDI values, the following parameters are identified as the best predictors for cyclogenesis in the North Atlantic, in the order of importance: 1) water vapor content within 925 and 400 hPa, 2) rain rate, 3) sea surface temperature (SST), 4) 700-hPa maximum relative vorticity, 5) 1000–600-hPa vertical shear, 6) translational speed, and 7) vertically averaged horizontal shear. This list identifies thermodynamic variables as more important controlling parameters than dynamic variables for TC genesis in the North Atlantic. When the east and west (separated by 40°W) Atlantic are examined separately, the 925–400-hPa water vapor content remains as the most important parameter for both regions. The SST and maximum vorticity at 700 hPa have higher importance in the east Atlantic, while SST becomes less important and the vertically averaged horizontal shear and horizontal divergence become more important in the west Atlantic.

Tropical cyclone genesis and trajectory characteristics in the western north Pacific

2020 ◽  
Author(s):  
Rui Xiong ◽  
Mengqian Lu
Keyword(s):  
Tropical Cyclone ◽  
Zonal Wind ◽  
Environmental Conditions ◽  
North Pacific ◽  
Western North Pacific ◽  
Data Science ◽  
Clustering Algorithm ◽  
The Philippines ◽  
Vertical Shear ◽  
Gaussian Kernel

<p>The western North Pacific (WNP) is one of the most active tropical cyclone (TC) regions, which can inflict enormous death and massive property damage to surrounding areas. Although many studies about tropical cyclone activities on multi-timescales have been done, most of them focus on the entire basin, variations within the basin deserve more investigations. Besides TC characteristics on different timescales, to investigate the impacts of environment variables on TC and provide informative factors for prediction is another concern in the research community. In this study, we adopt several data science techniques, including Gaussian kernel estimator, wavelet, cross-wavelet coherence and regression analyses, to explore the spatiotemporal variations of TC genesis and associated environmental conditions. Significant semiannual and annual variations of TC genesis have been found in the northern South China Sea (NSCS) and oceanic areas east of the Philippines (OAEP). In the southeast part of WNP (SEWNP), TC genesis shows prominent variations on ENSO time scale. With reconstructed TC series on those frequencies, we further quantify the influences of environmental variables on the primary TC signals over WNP. About 40% of the identified TC variance over NSCS and OAEP can be explained by variability in vertical shear of zonal wind and relative humidity. In the SEWNP, TC genesis reveals strong nonlinear and non-stationary relationships with vertical shear of zonal wind and absolute vorticity. Besides, A probabilistic clustering algorithm is used to describe the TC tracks in the WNP. The best track dataset from JMA is decomposed into three clusters based on genesis location and curvature. For each cluster, we analyze the relationships between TC properties, such as genesis location, trajectory and intensity, and associated environmental conditions using the self-organizing map. The spatial patterns of sea surface temperature have huge impacts on TC genesis location, while the trajectory is largely influenced by geopotential height.</p>

scholarly journals A Synoptic-Scale Cold-Reservoir Hypothesis on the Origin of the Mature-Stage Super Cloud Cluster: A Case Study with a Global Nonhydrostatic Model

2016 ◽  
Vol 56 ◽  
pp. 14.1-14.24 ◽  
Author(s):  
Kazuyoshi Oouchi ◽  
Masaki Satoh
Keyword(s):  
Indian Ocean ◽  
Warm Pool ◽  
Vertical Shear ◽  
Fundamental Aspect ◽  
Boreal Summer ◽  
Squall Line ◽  
Synoptic Scale ◽  
Zonal Circulation ◽  
Nonhydrostatic Model ◽  
Cloud Cluster

Abstract This chapter proposes a working assumption as a way of conceptual simplification of the origin of Madden–Julian oscillation (MJO)-associated convection, or super cloud cluster (SCC). To develop the simplification, the importance of the synoptic-scale cold reservoir underlying the convection and its interaction with the accompanying zonal–vertical circulation is highlighted. The position of the convection with respect to that of climatological warm pool is postulated to determine the effectiveness of this framework. The authors introduce a prototype hypothesis to illustrate the usefulness of the above assumption based on a numerical simulation experiment with a global nonhydrostatic model for the boreal summer season. Premises for the hypothesis include 1) that the cloud cluster (CC) is a basic building block of tropical convection accompanying the precipitation-generated cold reservoir in its subcloud layer and 2) that a warm-pool-induced quasi-persistent zonal circulation is key for the upscale organization of CCs. The theory of squall-line structure by Rotunno, Klemp, and Weisman (hereafter RKW) is employed for the interpretation. No account is taken regarding the influences of equatorial waves as a first-order approximation. Given the premises, an SCC of O(1000) km scale is interpretable as a gigantic analog of a multicellular squall line embedded in the quasi-stationary westerly shear branch of the zonal circulation east of the warm water pool. A CC corresponds to the “cell,” and its successive formation to the east and westward movement represents an upshear-tilting core of intense updraft. The upshear-tilted SCC is favorably maintained with the precipitating area being separated from the gust front boundary between the cold reservoir and a low-level easterly, which is supported in the realm of the RKW theory where two horizontal vortices associated with the cold reservoir and vertical shear are opposite in sign but cold reservoir’s vorticity can be inferred to be larger, leading to upshear-tilted and multicellular behavior. As a counterexample, CCs to the west of the warm pool (Indian Ocean and Arabian Sea) are embedded in the easterly shear and organized into a less coherent cloud cluster complex (CCC) given the situation of RKW where two horizontal vortices associated with the cold reservoir and vertical shear are still opposite in sign, but the smaller vertical shear west of the warm pool causes even more suboptimal vorticity imbalance in the western flank of cold reservoir, leading to larger tilt with height and intermittent, less viable storm situations. A cold pool or cold reservoir, having been prevalent in mesoscale convection research, is argued to be important for the MJO as pointed out by the emerging evidence in the international field campaign for the MJO called Cooperative Indian Ocean Experiment on Intraseasonal Variability (CINDY)/DYNAMO. The simplified and idealistic hypothesis proposed here does not cover all aspects of MJO and its validation awaits further modeling and observational studies, but it can offer a framework for characterizing a fundamental aspect of the origin of MJO-associated convection.

Process understanding of a linkage between East-Asian cold-surge wiith the unprecedented Arctic warming event in early 2016

2020 ◽  
Author(s):  
Kwang-hee Han ◽  
Ho-young Ku ◽  
Baek-min Kim
Keyword(s):  
Sea Ice ◽  
Mountain Region ◽  
The Arctic ◽  
Height Anomaly ◽  
Ural Mountain ◽  
Arctic Warming ◽  
Synoptic Analysis ◽  
Eurasian Continent ◽  
Process Understanding ◽  
Cold Events

<p>At the end of December 2015, Storm Frank, a major Atlantic windstorm, intruded into the Arctic-circle along with warm air and a large amount of moisture, resulting in an unprecedented Arctic high-temperature phenomenon. In late January 2016, the Eurasian continent suffered a series of strong cold events. This study performed a synoptic analysis of a daily Northern Hemisphere SLP and 500hPa, 300hPa height anomaly using JRA-reanalysis data focusing on the process understanding of the sequential development and strengthening of Siberian high in association with the generation of the Ural blocking after the Arctic warming event. From synoptic analysis , we found that, within one month period, there exist several spells of Ural blocking occurrence instead of steady occupation of persistent high pressure over Ural Mountain region. The heat intrusion from midlatitude in association with Storm Frank caused a large wave breaking event over Atlantic sector of Arctic and initiated Ural blocking. The unprecedented warm temperature in early 10 days of January 2016 caused a large sea-ice loss and further heat injection from Barents/Kara seas helping anchoring the blocking over Ural Mountain region. In January 2016, several cold events over Eurasian continent well matched with the several spell of Ural blocking events. We suggest that daily scale interactions among warm advection, downward longwave radiation, sea-ice loss, and blocking occurrence need to be carefully considered to understand true nature of Arctic-Midlatitude linkage issue.</p>

scholarly journals Asymmetry of atmospheric microstructure over synoptic scales

2001 ◽  
Vol 19 (8) ◽  
pp. 921-924 ◽  
Author(s):  
R. M. Worthington
Keyword(s):  
Western Europe ◽  
Lower Stratosphere ◽  
Middle Atmosphere ◽  
Radar Data ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Synoptic Scale ◽  
Wind Maximum ◽  
Vhf Radar

Abstract. Distortions are often seen in the angular distribution of echo-power from VHF wind-profiling radars, suggesting that thin stable layers, within the air flow, are distorted and tilted from horizontal. In vertical shear of the horizontal wind, the distribution of the layer tilt angles becomes skewed. A case study using six days of VHF radar data and synoptic charts above western Europe indicates that this asymmetry of atmospheric microstructure can exist throughout the troposphere and lower stratosphere, above and below the jet wind maximum, over horizontal scales of thousands of kilometres.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; synoptic-scale meteorology; turbulence).

scholarly journals Climate index; Cold events; Extreme; Precipitations.

2021 ◽  
Vol 32 (2) ◽  
pp. 63
Author(s):  
Ali. J. Mohammed ◽  
Samir K. Mohammed ◽  
Jasim H. Kadhum
Keyword(s):  
Extreme Events ◽  
Large Scale ◽  
Grid Point ◽  
Significant Negative Correlation ◽  
Hysplit Model ◽  
Dynamical Mechanism ◽  
East Region ◽  
Cold Events ◽  
Extreme Cold ◽  
Middle East Region

The cold events and Precipitation conditions having special attention in the last years due to their impact on human health, ecosystems, and other aspects such as agriculture, hydrology. The ECMWF ERA-Interim 12-hourly (03 and 15 UTC) total precipitations and Tmin in a 1º x 1º grid covering Iraq, from 29° N to 38° N and from 39° W to 48° E, with a total of 10 by 10 cells, was used. At each grid point, extremes were defined as those events in which total precipitations were above 99th percentile for the 25 years period 1994-2018. For more investigation, the Hybrid Single-Particle Lagrangian Integrated The trajectory (HYSPLIT) model was used to study the dynamical mechanism that led to producing the cold events in Iraq. The number of extreme precipitations patterns shows an increasing behavior in the number of extreme events especially in the last decade, farther more there is a significant increase in the number of extreme precipitations in the last three years ago. No correlations were found with NAO, EA index, in contrast, there is a significant negative correlation with winter Arctic oscillations index. The aim of this work is studying the precipitation and cold extreme events in Iraq and their relations of most hemispheric pattern which influence in the Middle East region such as North Atlantic Oscillation (NAO), East Atlantic index (EA), Artic oscillation index (AO) and Mediterranean index (MOi). We speculate that the results of this study can provide a better understanding of extreme cold and precipitations anomalies in Iraq from a large-scale view.The cold events and Precipitations conditions having special attention in the last years due to their impact on human health, ecosystems and other aspects such as agriculture, hydrology. The ECMWF ERA-Interim 12-hourly (03 and 15 UTC) total precipitations and Tmin in a 1º x 1º grid covering the Iraq, from 29° N to 38° N and from 39° W to 48° E, with a total of 10 by 10 cells, was used. At each grid point, extremes were defined as those events in which total precipitations were above its 99th percentile for the 25 years’ period 1994-2018. For more investigation, the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model was used to study the dynamical mechanism that led to produce the cold events over Iraq. The number of extreme precipitations pattern shows an increasing behavior in the number of extreme events especially in last decade, farther more there is a significant increase in the number of extreme precipitations in last three years ago. No correlations were found with NAO, EA index, in contrast, there is a significant negative correlation with winter Arctic oscillations index. The aim of this work is studying the precipitation and cold extreme events in Iraq and their relations of most hemispheric pattern which influence in the Middle East region such as North Atlantic Oscillation (NAO), East Atlantic index (EA), Artic oscillation index (AO) and Mediterranean index (MOi). We speculate that the results of this study can provide a better understanding of extreme cold and precipitations anomalies in Iraq a large-scale view.

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