scholarly journals The Predictability of Blocking Character in the Northern Hemisphere Using an Ensemble Forecast System

2019 ◽  
Vol 13 (1) ◽  
pp. 13-28 ◽  
Author(s):  
DeVondria D. Reynolds ◽  
Anthony R. Lupo ◽  
Andrew D. Jensen ◽  
Patrick S. Market
Keyword(s):  
Northern Hemisphere ◽  
Large Scale ◽  
Weather Conditions ◽  
Atmospheric Blocking ◽  
Weather Extremes ◽  
University Of Missouri ◽  
Weather Patterns ◽  
Temperature And Precipitation ◽  
Environmental Prediction ◽  
The University

Introduction: Some weather extremes are the result of atmospheric blocking, which can be responsible for the stagnation of weather patterns. These large-scale quasi-stationary mid-latitude flow regimes can result in significant temperature and precipitation anomalies over the regions that the blocking event impacts or in the upstream and downstream regions. Methods: The ability to predict periods of anomalous weather conditions due to atmospheric blocking is a major problem for medium-range forecasting. Analyzing the National Centers for Environmental Prediction (NCEP) Ensemble 500-hPa pressure level heights (240 hrs.) ten-day forecasts, and using the University of Missouri blocking archive to identify blocking events, the forecasted onset, duration, and intensity of model blocking events are compared to observed blocks. Results and Discussion: The observed blocking events were identified using the University of Missouri blocking archive. Comparing these differences using four Northern Hemisphere case studies occurring over a one-year period across the Northern Hemisphere has shown the continued need for improvement in the duration and intensity of blocking events. Additionally, a comparison of the block intensity to a diagnostic known as the Integrated Regional Enstrophy (IRE) was performed in order to determine if there is a correlation between IRE and these quantities. Conclusion: Having a better understanding of block persistence and their associated anomalies can help society prepare for the damage they can cause.

scholarly journals The predictability of northern hemispheric blocking using an ensemble mean forecast system

2017 ◽  
Author(s):  
◽  
Devondria D. Reynolds
Keyword(s):  
Large Scale ◽  
Weather Conditions ◽  
Atmospheric Blocking ◽  
Weather Extremes ◽  
University Of Missouri ◽  
Knowing How ◽  
Weather Patterns ◽  
Intensity Index ◽  
Temperature And Precipitation ◽  
Blocking Event

Some weather extremes can be the result of atmospheric blocking. Like atmospheric patterns that tend to repeat themselves, atmospheric blocking leads to the stagnation of weather patterns. This repetition can last for several days to weeks. These large-scale quasi-stationary mid-latitude flow regimes can result in significant temperature and precipitation anomalies in the regions that the blocking event impacts. Being able to predict periods of anomalous weather conditions due to atmospheric blocking is a major problem for medium-range forecasting. Analyzing the NCEP Ensemble 500-mb pressure heights (240 hrs.) ten-day forecasts and using the University of Missouri blocking archive to identify blocking event, the duration of blocks, intensity prediction in comparison to observed blocks. Comparing these differences over a oneyear period across the Northern Hemisphere has shown the possibility for improved predictability of these blocks and their intensity. Having a better understanding of knowing how long each block will last and their associated anomalies can help society prepare for the damage they can cause. Knowing how to correctly identify blocks is important in improving forecast issues. Lastly, it is demonstrated that the Integrated Regional Enstrophy (IRE) for these events correlates with a block intensity index (BI).

New method to detect and quantify weather persistence associated with hydro-climatic extremes

2021 ◽  
Author(s):  
Peter Hoffmann ◽  
Jascha Lehmann ◽  
Bijan Fallah ◽  
Fred Hattermann
Keyword(s):  
Climate Models ◽  
Heat Waves ◽  
Weather Conditions ◽  
Reanalysis Data ◽  
New Method ◽  
Climate Projections ◽  
Weather Extremes ◽  
Weather Patterns ◽  
Temperature And Precipitation ◽  
Height Fields

<p>Changes in weather persistence are of particular concern in the context of climate change as periods of longer persistence can reinforce weather extremes. In our study we apply structural image recognition methods to global ERA5 reanalysis data to identify when, where and how long isolines of atmospheric geopotential height fields run in similar tracks. We identify regions and episodes around the world in which, retrospectively, unusually long-lasting weather patterns repeatedly occurred. Concerning the temperature and precipitation meteorological fields, we derive a connection between the occurrence of weather persistence and hydro-climatic extreme events.</p><p>Based on our new method we find that weather persistence has been particularly increasing in Northern Hemisphere mid-latitudes in summer confirming earlier studies. Here, highly populated regions like Central Europe have experienced long-term increases in persistent weather conditions of up to 4-5% between 1981 and 2019 amplifying the risk of prolonged heat waves and droughts. Further, we show that climate models tend to have difficulties in capturing the dynamics of weather persistence and thus may severely underestimate the frequency and magnitude of future extremes events in their climate projections.</p>

The 3D Structure of Atmospheric Blocking: Role of Moisture and Response to Climate Change

2021 ◽  
Author(s):  
Ebrahim Nabizadeh ◽  
Sandro Lubis ◽  
Pedram Hassanzadeh
Keyword(s):  
Climate Change ◽  
Surface Temperature ◽  
Northern Hemisphere ◽  
Large Scale ◽  
3D Structure ◽  
Winter Season ◽  
Temperature Response ◽  
Atmospheric Blocking ◽  
Weather Extremes ◽  
Large Ensemble

<p>Atmospheric blocking is a large-scale weather phenomenon that interrupts the prevailing eastward progression of pressure systems and can result in weather extremes in the midlatitudes. Due to their devastating consequences, understanding the changes of blocking in response to climate change has been of great interest in recent years. In this study, we investigate the 3D structure of blocking events in reanalysis and two large-ensemble, fully coupled GCM simulations: NCAR’s CESM1 Large-Ensemble Project (LENS) and GFDL-CM3 large-ensemble project. Here we compare the climatology of blocks in the models with reanalysis and show that the structure of the blocks is remarkably reproduced well in the GCMs, given that these models are known to have biases in reproducing the climatological Northern Hemisphere large-scale circulation. The results of our composite analysis indicate that the blocks exhibit an equivalent-barotropic structure in both summer and winter seasons over both oceans and continents in the northern hemisphere. However, blocking events are stronger in winters compared to summers. We also notice a significant latent heating associated with ascending airstream on the east side of blocks. This warming, which is stronger in winter especially over the ocean basins, leads to a westward shift in the temperature anomaly during blocking episodes. Furthermore, we study the response of the blocks to climate change (RCP8.5) and find that blocking events will be weakened in the summer of three different northern hemisphere regions. However, wintertime blocks’ responses to climate change are more complex than those in summers and depend on the regions and atmospheric pressure levels. Finally, we examined the response of surface temperature associated with blocking events. We have found that the surface temperature response associated with blocking events will be weaker over all the regions in the winter season. However, during summer, the temperature responses will be slightly stronger over Russia and partially over the two ocean basins. Our results suggest that summertime blocking events over Russia are going to be more impactful compared to those over the ocean basins.</p>

scholarly journals Evidence linking rapid Arctic warming to mid-latitude weather patterns

2015 ◽  
Vol 373 (2045) ◽  
pp. 20140170 ◽  
Author(s):  
Jennifer Francis ◽  
Natasa Skific
Keyword(s):  
Northern Hemisphere ◽  
Weather Conditions ◽  
Extreme Weather Events ◽  
Jet Stream ◽  
Self Organizing Maps ◽  
Arctic Warming ◽  
Scientific Debate ◽  
Weather Patterns ◽  
Enhanced Sensitivity ◽  
Active Research

The effects of rapid Arctic warming and ice loss on weather patterns in the Northern Hemisphere is a topic of active research, lively scientific debate and high societal impact. The emergence of Arctic amplification—the enhanced sensitivity of high-latitude temperature to global warming—in only the last 10–20 years presents a challenge to identifying statistically robust atmospheric responses using observations. Several recent studies have proposed and demonstrated new mechanisms by which the changing Arctic may be affecting weather patterns in mid-latitudes, and these linkages differ fundamentally from tropics/jet-stream interactions through the transfer of wave energy. In this study, new metrics and evidence are presented that suggest disproportionate Arctic warming—and resulting weakening of the poleward temperature gradient—is causing the Northern Hemisphere circulation to assume a more meridional character (i.e. wavier), although not uniformly in space or by season, and that highly amplified jet-stream patterns are occurring more frequently. Further analysis based on self-organizing maps supports this finding. These changes in circulation are expected to lead to persistent weather patterns that are known to cause extreme weather events. As emissions of greenhouse gases continue unabated, therefore, the continued amplification of Arctic warming should favour an increased occurrence of extreme events caused by prolonged weather conditions.

scholarly journals Atmosphere similarity patterns in boreal summer show an increase of persistent weather conditions connected to hydro-climatic risks

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Peter Hoffmann ◽  
Jascha Lehmann ◽  
Bijan H. Fallah ◽  
Fred F. Hattermann
Keyword(s):  
Northern Hemisphere ◽  
Climate Models ◽  
Weather Conditions ◽  
Boreal Summer ◽  
Climatic Extremes ◽  
Weather Patterns ◽  
Dry Conditions ◽  
Climatic Risks ◽  
Long Term Trend

AbstractRecent studies have shown that hydro-climatic extremes have increased significantly in number and intensity in the last decades. In the Northern Hemisphere such events were often associated with long lasting persistent weather patterns. In 2018, hot and dry conditions prevailed for several months over Central Europe leading to record-breaking temperatures and severe harvest losses. The underlying circulation processes are still not fully understood and there is a need for improved methodologies to detect and quantify persistent weather conditions. Here, we propose a new method to detect, compare and quantify persistence through atmosphere similarity patterns by applying established image recognition methods to day to day atmospheric fields. We find that persistent weather patterns have increased in number and intensity over the last decades in Northern Hemisphere mid-latitude summer, link this to hydro-climatic risks and evaluate the extreme summers of 2010 (Russian heat wave) and of 2018 (European drought). We further evaluate the ability of climate models to reproduce long-term trend patterns of weather persistence and the result is a notable discrepancy to observed developments.

scholarly journals Global Trends in the Occurrence and Characteristics of Blocking Anticylones Using Sen Innovative Trend Analysis

2021 ◽  
Vol 8 (1) ◽  
pp. 41
Author(s):  
Bahtiyar Efe ◽  
Anthony R. Lupo
Keyword(s):  
Trend Analysis ◽  
Pacific Region ◽  
Atmospheric Blocking ◽  
University Of Missouri ◽  
Global Trends ◽  
Innovative Trend Analysis ◽  
Increasing Trend ◽  
The University ◽  
Increasing Trends ◽  
High Cluster

Atmospheric blocking plays an important role in modulating mid-latitude weather, in particular in the Northern Hemisphere (NH). Trend analysis of atmospheric blocking for both hemispheres by using Şen’s Innovative Trend Analysis (ITA) is performed in this study. The blocking data archived in the University of Missouri covers the period of 1968–2019 for the NH and 1970–2019 for the Southern Hemisphere is used in the study. Block occurrence, duration and blocking intensity (BI) is analysed by classifying the NH (and SH) into three groups according to the preferred blocking locations: Atlantic, Pacific and Continental (Atlantic, Pacific and Indian). In the NH, blocking intensity showed mixed results. It showed a decreasing trend for the entire hemisphere and Atlantic Region, whilst a different trend was shown for different BI clusters. For blocking numbers and duration, the entire hemisphere and regions showed increasing trends. These increasing trend values were also statistically significant. In the SH, blocking intensity showed a decreasing trend for low clusters, whilst medium and high cluster increased for the entire hemisphere. Block duration showed an increasing trend for the entire SH. Block numbers showed increasing trends, except for one point in the low cluster. Blocking characteristics showed different trends for different preferred blocking locations. Increasing trends of blocking numbers for the overall SH and Pacific region are statistically significant at 95% level. Increasing trends of blocking duration for the overall SH, Atlantic and Pacific region are statistically significant at 90%, 95% and 95% level, respectively.

scholarly journals Large-Scale Gravity Current over the Middle Hills of the Nepal Himalaya: Implications for Aircraft Accidents

2017 ◽  
Vol 56 (2) ◽  
pp. 371-390 ◽  
Author(s):  
Ram P. Regmi ◽  
Toshihiro Kitada ◽  
Jimy Dudhia ◽  
Sangeeta Maharjan
Keyword(s):  
Large Scale ◽  
Gravity Current ◽  
Weather Conditions ◽  
Civil Aviation ◽  
Mountain Waves ◽  
Aircraft Accidents ◽  
Nepal Himalaya ◽  
Weather Patterns ◽  
Weather Situation ◽  
Wrf Modeling

AbstractNepal has been the location of a series of fatal aircraft accidents, raising serious concerns about civil aviation security and the safety of passengers. However, significant studies on weather patterns associated with the airports and air routes of the Himalayan complex terrain and their implications for aviation activities are yet to be carried out. The present study numerically reconstructs the prevailing weather conditions and puts forward some possible causes behind the most recent fatal aircraft accident in the foothills of the western Nepal Himalaya at 0730 UTC (1315 LST) 16 February 2014. The weather patterns have been numerically simulated at 1-km2 horizontal grid resolution using the Weather Research and Forecasting (WRF) modeling system. The reconstructed weather situation shows the existence of a low-level cloud ceiling, supercooled cloud water and hail, trapped mountain waves, supercritical descent of a strong tail wind, and the development of turbulence at the altitude of the flight path followed by the aircraft. The aircraft might have gone through a series of weather hazards including visibility obstruction, moderate turbulence, abnormal loss in altitude, and icing. It is concluded that the weather situation over the region was adverse enough to affect small aircraft and therefore that it might have played an important role leading to the fatal accident. The development of hazardous weather over the region may be attributed to a previously unanticipated large-scale easterly gravity current over the middle hills of the Nepal Himalaya. The gravity current originated from the central high Himalayan mountainous region located northeast of the Kathmandu valley and traveled more than 200 km, reaching the foothills of the western Nepal Himalaya.

Analysis of Precipitation Patterns and Extremes in European Lowlands

2020 ◽  
Author(s):  
Alexandra Berényi ◽  
Judit Bartholy ◽  
Rita Pongrácz
Keyword(s):  
Large Scale ◽  
Western Europe ◽  
Precipitation Amount ◽  
Weather Conditions ◽  
East European Plain ◽  
Climate Indices ◽  
East European ◽  
Precipitation Patterns ◽  
Weather Patterns ◽  
Management Actions

<p>It is well-known that climate change affects large scale weather patterns and local extremes all over the world as well as in Europe. These changes include the changes of precipitation occurences, amounts, and spatial patterns, which may require appropriate risk management actions. For this purpose, the first step is a thorough analysis of possible hazards associated to specific precipitation-related weather phenomena.</p><p>The primary goals of this study are (i) to examine the changes in precipitation patterns and extremes, and (ii) to explore the possible connections between changes in different lowlands across Europe. Precipitation time series are used from the E-OBS v.20 datasets on a 0.1° regular grid. Datasets are based on station measurements from Europe and are available from 1950 onward with daily temporal resolution. Altogether 14 plain regions are selected in this study to represent different parts within Europe. More specifically, five plain regions are parts of the East European Plain, two regions are located in the Scandinavian basin, five regions are located in Western Europe, and the Pannonian Plain (including mostly Hungary) is also selected. For choosing the plains and their spatial representations, objective criteria are used, namely, the elevation remains under 200 m throughout the defined area and difference between the neighbouring gridpoints within the plain region does not exceed 40 m. Daily precipitation times series are analyzed and compared for these plain regions using various statistical tools. The results represent annual and seasonal changes in average and extreme precipitation amount as well as in the frequency of precipitation occurences. Climate indices and the occurence of extreme weather conditions including wet and dry spells are also analyzed.</p><p> </p>

El Niño and its impact on fire weather conditions in Alaska

2001 ◽  
Vol 10 (1) ◽  
pp. 1 ◽  
Author(s):  
Jason C. Hess ◽  
Carven A. Scott ◽  
Gary L. Hufford ◽  
Michael D. Fleming
Keyword(s):  
Weather Conditions ◽  
Weather Patterns ◽  
Area Burned ◽  
Temperature And Precipitation ◽  
Northern Latitudes ◽  
Dry Conditions ◽  
Alaskan Coast ◽  
The Tropics ◽  
Relationship Of ◽  
The Relationship

Examining the relationship of El Niño to weather patterns in Alaska shows wide climate variances that depend on the teleconnection between the tropics and the northern latitudes. However, the weather patterns exhibited in Alaska during and just after moderate to strong El Niño episodes are generally consistent: above normal temperature and precipitation along the Alaskan coast, and above normal temperature and below normal precipitation in the interior, especially through the winter. The warm, dry conditions in the Alaskan interior increase summer wildfire potential. Statistics on the area burned since 1940 show that 15 out of 17 of the biggest fire years occurred during a moderate to strong El Niño episode. These 15 years account for nearly 63% of the total area burned over the last 58 years. Evidence points to increased dry thunderstorms and associated lightning activity during an El Niño episode; the percentage of total area burned by lightning caused fires during five episodes increased from a normal of less than 40% to a high of about 96%.

Problems of Large-Scale Kinetic Energy Balance—A Diagnostic Analysis in GARP

1974 ◽  
Vol 55 (7) ◽  
pp. 768-778 ◽  
Author(s):  
Ernest C. Kung ◽  
Phillip J. Smith
Keyword(s):  
Energy Balance ◽  
Kinetic Energy ◽  
General Circulation ◽  
Large Scale ◽  
Synoptic Scale ◽  
University Of Missouri ◽  
Diagnostic Studies ◽  
Middle Latitudes ◽  
The University ◽  
Balance Problems

Currently available diagnostic studies on kinetic energy balance in the general circulation are reviewed as one of the basic scientific problems in GARP. The kinetic energy equation and several different approaches in the evaluation of energy variables are discussed in relation to real and modeled atmospheric data. Energy balance problems in the middle latitudes are examined in terms of linkages between processes from energy conversion to dissipation, balance within various systems of circulation, and interactions with sub-synoptic scale disturbances. The kinetic energy budget in large-scale disturbances and the general flow of the tropical circulation are contrasted with those in the middle latitudes. By clarifying the current essential problems in the energetics of the middle latitudes and tropics, ongoing diagnostic studies at the University of Missouri—Columbia and Purdue University are identified in the context of the GARP.

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