scholarly journals Seamless Detection of Cutoff Lows and Preexisting Troughs

2021 ◽  
Author(s):  
Satoru Kasuga ◽  
Meiji Honda ◽  
Jinro Ukita ◽  
Shozo Yamane ◽  
Hiroaki Kawase ◽  
...  
Keyword(s):  
Geopotential Height ◽  
Geometric Features ◽  
Height Field ◽  
Height Profile ◽  
Distribution Maps ◽  
Adverse Weather ◽  
Local Background ◽  
Cutoff Low ◽  
Torrential Rainfall ◽  
Height Fields

AbstractWe propose a new scheme based on geopotential height fields to detect cutoff lows starting in the preexisting trough stage. The intensity and scale derived from the proposed scheme will allow for a better understanding of the cutoff low life cycle. These cutoff lows often accompany mesoscale disturbances, causing adverse weather-related events, such as intense torrential rainfall and/or tornadoes. The proposed scheme quantifies the geometric features of a depression from its horizontal height profile. The height slope of a line intersecting the depression bottom and the nearest tangential point (optimal slope) locally indicates the intensity and scale of an isolated depression.The strength of the proposed scheme is that, by removing a local background height slope from a geopotential height field, the cutoff low and its preexisting trough are seamlessly detected as an identical depression. The distribution maps for the detected cutoff lows and preexisting troughs are illustrated along with their intensities, sizes, and local background flows estimated from snapshot height fields. We conducted climatological comparisons of cutoff lows to determine the utility of the proposed scheme.

Seamless Detection of Cutoff Low and Preexisting Trough

2020 ◽  
Author(s):  
Meiji Honda ◽  
Satoru Kasuga ◽  
Jinro Ukita ◽  
Shozo Yamane ◽  
Hiroaki Kawase ◽  
...  
Keyword(s):  
Life Cycle ◽  
Lead Time ◽  
Isobaric Surface ◽  
Background Flow ◽  
Upper Troposphere ◽  
Local Background ◽  
Geometric Character ◽  
Cutoff Low ◽  
Height Fields ◽  
Meso Scale

<p><strong>Cutoff lows are cyclones existing in the upper troposphere developing from precursory preexisting troughs. We introduce a new method to seamlessly detect cutoff lows and even preexisting troughs aiming to improve lead time of meso scale disturbances like tornadoes. The method is based on a geometric character; in this method, a slope defined as the tangential line from a minimum point of each height depression is measured on an isobaric surface. This slope evaluates an intensity and horizontal extension (radius) of each depression. Adopting a mathematical assumption, we successfully achieved to make an algorithm to separate the depression and the local background flow. To remove the background flow enables us to detect both cutoff lows and preexisting troughs seamlessly in reanalysis height fields. So, our method would allow the life cycle to be illustrated continuously from the birth of the cutoff low, that is, from the precursory preexisting trough, and is expected to contribute to the improvement of the lead time for predicting severe weathers. Some further application examples, including tornado accompanying cases, and even for blocking highs, would be shown.</strong></p>

scholarly journals Probabilistic Forecasting of the 500 hPa Geopotential Height over the Northern Hemisphere Using TIGGE Multi-model Ensemble Forecasts

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 253
Author(s):  
Luying Ji ◽  
Qixiang Luo ◽  
Yan Ji ◽  
Xiefei Zhi
Keyword(s):  
Northern Hemisphere ◽  
Geopotential Height ◽  
Prediction Skill ◽  
Ensemble Prediction ◽  
Lead Times ◽  
Height Distribution ◽  
Height Field ◽  
Probabilistic Forecasting ◽  
Ensemble Forecasts ◽  
Geopotential Height Field

Bayesian model averaging (BMA) and ensemble model output statistics (EMOS) were used to improve the prediction skill of the 500 hPa geopotential height field over the northern hemisphere with lead times of 1–7 days based on ensemble forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF), National Centers for Environmental Prediction (NCEP), and UK Met Office (UKMO) ensemble prediction systems. The performance of BMA and EMOS were compared with each other and with the raw ensembles and climatological forecasts from the perspective of both deterministic and probabilistic forecasting. The results show that the deterministic forecasts of the 500 hPa geopotential height distribution obtained from BMA and EMOS are more similar to the observed distribution than the raw ensembles, especially for the prediction of the western Pacific subtropical high. BMA and EMOS provide a better calibrated and sharper probability density function than the raw ensembles. They are also superior to the raw ensembles and climatological forecasts according to the Brier score and the Brier skill score. Comparisons between BMA and EMOS show that EMOS performs slightly better for lead times of 1–4 days, whereas BMA performs better for longer lead times. In general, BMA and EMOS both improve the prediction skill of the 500 hPa geopotential height field.

A complex network analysis of extreme cyclones in the Arctic

2021 ◽  
Author(s):  
Dörthe Handorf ◽  
Ozan Sahin ◽  
Annette Rinke ◽  
Jürgen Kurths
Keyword(s):  
Complex Network ◽  
Northern Hemisphere ◽  
Extreme Events ◽  
Geopotential Height ◽  
Winter Season ◽  
Climate Extremes ◽  
The Arctic ◽  
Weather And Climate ◽  
Class 1 ◽  
Height Fields

<p>Under the rapid and amplified warming of the Arctic, changes in the occurrence of Arctic weather and climate extremes are evident which have substantial cryospheric and biophysical impacts like floods, droughts, coastal erosion or wildfires. Furthermore, these changes in weather and climate extremes have the potential to further amplify Arctic warming. <br>Here we study extreme cyclone events in the Arctic, which often occur during winter and are associated with extreme warming events that are caused by cyclone-related heat and moisture transport into the Arctic. In that way Arctic extreme cyclones have the potential to retard sea-ice growth in autumn and winter or to initiate an earlier melt-season onset. <br>To get a better understanding of these extreme cyclones and their occurrences in the Arctic, it is important to reveal the related atmospheric teleconnection patterns and understand their underlying mechanisms. In this study, the methodology of complex networks is used to identify teleconnections associated with extreme cyclones events (ECE) over Spitzbergen. We have chosen Spitzbergen, representative for the Arctic North Atlantic region which is a hot spot of Arctic climate change showing also significant recent changes in the occurrence of extreme cyclone events. <br>Complex climate networks have been successfully applied in the analysis of climate teleconnections during the last decade. To analyze time series of unevenly distributed extreme events, event synchronization (ES) networks are appropriate. Using this framework, we analyze the spatial patterns of significant synchronization between extreme cyclone events over the Spitzbergen area and extreme events in sea-level pressure (SLP) in the rest of the Northern hemisphere for the extended winter season from November to March. Based on the SLP fields from the newest atmospheric reanalysis ERA5, we constructed the ES networks over the time period 1979-2019.<br>The spatial features of the complex network topology like Eigenvector centrality, betweenness centrality and network divergence are determined and their general relation to storm tracks, jet streams and waveguides position is discussed. Link bundles in the maps of statistically significant links of ECEs over Spitzbergen with the rest of the Northern Hemisphere have revealed two classes of teleconnections: Class 1 comprises links from various regions of the Northern hemisphere to Spitzbergen, class 2 comprises links from Spitzbergen to various regions of the Northern hemisphere. For each class three specific teleconnections have been determined. By means of composite analysis, the corresponding atmospheric conditions are characterized.<br>As representative of class 1, the teleconnection between extreme events in SLP over the subtropical West Pacific and delayed ECEs at Spitzbergen is investigated. The corresponding lead-lag analysis of atmospheric fields of SLP, geopotential height fields and meridional wind fields suggests that the class 1 teleconnections are caused by tropical forcing of poleward emanating Rossby wave trains. As representative of class 2, the teleconnection between ECEs at Spitzbergen and delayed extreme events in SLP over Northwest Russia is analyzed. The corresponding lead-lag analysis of atmospheric fields of SLP and geopotential height fields from the troposphere to the stratosphere suggests that the class 2 teleconnections are caused by troposphere-stratosphere coupling processes.</p>

Analysis of the arrival of southern cyclones to the Republic of Bashkortostan

2021 ◽  
Vol 2 ◽  
pp. 66-76
Author(s):  
O.V. Volobueva ◽  
◽  
O.N. Toptunova ◽  
Y.V. Drobzheva ◽  
◽  
...  
Keyword(s):  
Environmental Monitoring ◽  
Black Sea ◽  
Geopotential Height ◽  
The Black Sea ◽  
Front Part ◽  
Observational Network ◽  
Republic Of Bashkortostan ◽  
Adverse Weather ◽  
The Republic

Analysis of the arrival of southern cyclones to the Republic of Bashkortostan / Volobueva O.V., Toptunova O.N., Drobzheva Y.V. // Hydrometeorological Research and Forecasting, 2021, no. 2 (380), pp. 66-76. The results of the analysis of the arrival of southern cyclones to the territory of the Republic of Bashkortostan for the period of 1993-2018 are presented. Typical trajectories of cyclones, areas of their origin, as well as accompanying adverse weather phenomena are identified according to the observational network of the Bashkir Administration for Hydrometeorology and Environmental Monitoring. In 70 % of cases, southern cyclones move through the territory of the republic and leave it in the southern direction. About 50 % of the depressions come to the Republic of Bashkortostan from the Black Sea and its coast. The upper-air field for the arrival of southern cyclones is the front part of the pressure trough with high geopotential height gradients. The arrivals of southern cyclones have a significant impact on the study area and are closely related to the formation of severe hydrometeorological events. Keywords: southern cyclone, typical territories, the Republic of Bashkortost

scholarly journals Identifying Weather Regimes in the Wintertime 500-hPa Geopotential Height Field for the Pacific–North American Sector Using a Limited-Contour Clustering Technique

2007 ◽  
Vol 46 (10) ◽  
pp. 1619-1630 ◽  
Author(s):  
Joseph H. Casola ◽  
John M. Wallace
Keyword(s):  
North American ◽  
Significant Relationship ◽  
Geopotential Height ◽  
Field Method ◽  
Contour Method ◽  
Regime Type ◽  
Height Field ◽  
Full Field ◽  
Geopotential Height Field ◽  
The Pacific

Abstract A hierarchical clustering algorithm using Ward’s method has been applied to the 500-hPa geopotential height field in the Pacific–North American sector. In contrast to previous clustering studies that measure distance between records by using all the grid points within the domain (full-field method), the procedure outlined here, referred to as the limited-contour method, focuses on the coordinates of the 540-dam contour as the distance measure. Comparison between the regimes emerging from the two methods shows that the limited-contour method is more efficient than the full-field method with respect to grouping maps with ridges located at similar longitudes. The four regimes emerging from the limited-contour clustering analysis have been named as follows: Off-Shore Trough, Alaskan Ridge, Coastal Ridge, and Rockies Ridge. The frequencies of occurrence of the regimes have a significant relationship with the phase of the El Niño–Southern Oscillation. El Niño winters exhibit a strong preference for the Rockies Ridge pattern; La Niña winters exhibit a greater diversity of regimes. The frequencies of occurrence of extreme cold outbreaks and episodes of heavy precipitation in the Pacific Northwest show a relatively strong connection to the regime type. For other regions in the western portion of the United States, only the frequency of occurrence of cold outbreaks exhibits a significant relationship to regime type.

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