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).

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.

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>

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%.

scholarly journals Atmospheric Blocking and Weather Extremes over the Euro-Atlantic Sector – A Review

2021 ◽  
Author(s):  
Lisa-Ann Kautz ◽  
Olivia Martius ◽  
Stephan Pfahl ◽  
Joaquim G. Pinto ◽  
Alexandre M. Ramos ◽  
...  
Keyword(s):  
Flow Pattern ◽  
Large Scale ◽  
Extreme Event ◽  
Heat Waves ◽  
Storm Track ◽  
Extreme Weather Events ◽  
Atmospheric Blocking ◽  
Weather Extremes ◽  
Atmospheric Flow ◽  
Atlantic Sector

Abstract. The physical understanding and timely prediction of extreme weather events are of enormous importance to society regarding associated impacts. In this article, we highlight several types of weather extremes occurring in Europe in connection with a particular atmospheric flow pattern, known as atmospheric blocking. This flow pattern effectively blocks the prevailing westerly large-scale atmospheric flow, resulting in changing flow anomalies in the vicinity of the blocking system and persistent conditions in the immediate region of its occurrence. Blockings are long-lasting, quasi-stationary, self-sustaining systems that occur frequently over certain regions. Their presence and characteristics have an impact on the predictability of weather extremes and can thus be used as potential indicators. The phasing between the surface and the upper-level blocking anomalies is of major importance for the development of the extreme event. In summer, heat waves and droughts form below the blocking anticyclone primarily via large-scale subsidence that leads to cloud-free skies and thus, persistent longwave radiative warming of the ground. In winter, cold waves that occur during atmospheric blocking are normally observed downstream or south of these systems. Here, horizontal advection of cold air masses from higher latitudes plays a decisive role. Extreme snowfall can also occur with the lower temperatures, indicating a shift of the storm track due to the blocking system. Such a shift is also crucial in the connection of blocking with wind and precipitation anomalies in general. Due to this multifaceted linkages, compound events are often observed in conjunction with blocking conditions.

scholarly journals Increased persistence of large-scale circulation regimes over Asia in the era of amplified Arctic warming, past and future

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Jennifer A. Francis ◽  
Natasa Skific ◽  
Stephen J. Vavrus
Keyword(s):  
Large Scale ◽  
Weather Conditions ◽  
First Century ◽  
The Arctic ◽  
Extreme Weather Events ◽  
Temperature And Precipitation ◽  
Weather Events ◽  
Long Duration ◽  
Pattern Recognition Approach ◽  
Insight Into

Abstract Extreme weather events in Asia have been occurring with increasing frequency as the globe warms in response to rising concentrations of greenhouse gases. Many of these events arise from weather regimes that persist over a region for days or even weeks, resulting in disruptive heatwaves, droughts, flooding, snowfalls, and cold spells. We investigate changes in the persistence of large-scale weather systems through a pattern-recognition approach based on daily 500 hPa geopotential height anomalies over the Asian continent. By tracking consecutive days that the atmosphere resides in a particular pattern, we identify long-duration events (LDEs), defined as lasting longer than three days, and measure their frequency of occurrence over time in each pattern. We find that regimes featuring positive height anomalies in high latitudes are occurring more often as the Arctic warms faster than mid-latitudes, both in the recent past and in model projections for the twenty-first century assuming unabated greenhouse gas emissions. The increased dominance of these patterns corresponds to a higher likelihood of LDEs, suggesting that persistent weather conditions will occur more frequently. By mapping observed temperature and precipitation extremes onto each atmospheric regime, we gain insight into the types of disruptive weather events that will become more prevalent as particular patterns become more common.

scholarly journals Weather Patterns Driving Atmospheric Rivers, Santa Ana Winds, Floods, and Wildfires During California Winters Provide Evidence for Increasing Fire Risk

2021 ◽  
Author(s):  
Kristen Guirguis ◽  
Alexander Gershunov ◽  
Benjamin Hatchett ◽  
Tamara Shulgina ◽  
Michael J. DeFlorio ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
Large Scale ◽  
North Pacific Ocean ◽  
Winter Weather ◽  
Weather Extremes ◽  
Atmospheric Rivers ◽  
Santa Ana ◽  
Weather Patterns ◽  
Atmospheric River ◽  
Santa Ana Winds

Abstract Floods caused by atmospheric rivers and wildfires fanned by Santa Ana winds are common occurrences in California with devastating societal impacts. Planning for these types of events is critical to protect life and property, and extending the lead-times of predictability for these types of events improves emergency response. A better understanding of linkages between large-scale atmospheric circulation patterns and extreme weather represents an important step towards improving predictability and preparedness on subseasonal-to-seasonal (S2S) timescales and for climate change adaptation. In this work, we show that winter weather variability in California, including the occurrence of extreme and impactful events, is linked to four atmospheric circulation regimes over the North Pacific Ocean previously named and identified as the “NP4 modes”. These modes interact on daily timescales to produce recurring winter weather patterns that are major drivers of atmospheric river landfalls, Santa Ana winds, floods, and wildfires. Many recent California natural hazard events resulted from compounding and cascading extremes including frequent atmospheric river landfalls (wet, fuel-producing years) or lack thereof (drought) and followed by Sana Ana-driven wildfires that render the landscape susceptible to hydrologic hazards posed by short-duration high-intensity precipitation events. This historical perspective of atmospheric circulation and impacts over 70 years reveals that weather patterns are changing in a way that enhances wildfire risk in California, while the frequency of weather patterns linked to historical floods is not diminishing. These changes highlight the rising hazards of compounding weather extremes in California’s present and future.

scholarly journals An Investigation of Critical Fire Weather Patterns: A Case Study

2021 ◽  
Vol 8 (1) ◽  
pp. 37
Author(s):  
Sama Al-Dabbagh ◽  
Hadil AL-Shouhani ◽  
Nabaa Hussein
Keyword(s):  
Weather Conditions ◽  
Reanalysis Data ◽  
Fire Weather ◽  
Atmospheric Blocking ◽  
Weather Factors ◽  
Weather Patterns ◽  
Hot Weather ◽  
Maximum Temperatures ◽  
Main Factor

A series of huge wildfires occurred in some regions of Lebanon in mid-October 2019, when the region witnessed a heat wave with high averages of minimum and maximum temperatures, accompanied by dry weather conditions. This study aimed to investigate the weather pattern that predominated over Lebanon between 10 and 18 October 2019, and to study the weather factors that ignited and spread the fire in several places. The study focused on the Chouf district, in Mount Lebanon Governorate, which witnessed the most severe wildfire outbreak, based on ERA5 atmospheric reanalysis data at the surface and upper levels between 10 and 18 October 2019. It was found that the existence of an atmospheric blocking system over the region for many days was the main factor in the creation of the dry and extremely hot weather, and that the breakdown of the ridge ignited the fire, reinforcing the wildfire’s intensity and spreading fire patches to other regions.

scholarly journals Links between Large-Scale Modes of Climate Variability and Synoptic Weather Patterns in the Southern Indian Ocean

2021 ◽  
Vol 34 (3) ◽  
pp. 883-899
Author(s):  
Danielle G. Udy ◽  
Tessa R. Vance ◽  
Anthony S. Kiem ◽  
Neil J. Holbrook ◽  
Mark A. J. Curran
Keyword(s):  
Indian Ocean ◽  
Large Scale ◽  
Weather Conditions ◽  
Southern Annular Mode ◽  
Southern Indian Ocean ◽  
Regional Variability ◽  
Self Organizing Maps ◽  
Weather Patterns ◽  
Proxy Records ◽  
Synoptic Conditions

AbstractWeather systems in the southern Indian Ocean (SIO) drive synoptic-scale precipitation variability in East Antarctica and southern Australia. Improved understanding of these dynamical linkages is beneficial to diagnose long-term climate changes from climate proxy records as well as informing regional weather and climate forecasts. Self-organizing maps (SOMs) are used to group daily 500-hPa geopotential height (z500; ERA-Interim) anomalies into nine regional synoptic types based on their dominant patterns over the SIO (30°–75°S, 40°–180°E) from January 1979 to October 2018. The pattern anomalies represented include four meridional, three mixed meridional–zonal, one zonal, and one transitional node. The frequency of the meridional nodes shows limited association with the phase of the southern annular mode (SAM), especially during September–November. The zonal and mixed patterns were nevertheless strongly and significantly correlated with SAM, although the regional synoptic representation of SAM+ conditions was not zonally symmetric and was represented by three separate nodes. We recommend consideration of how different synoptic conditions vary the atmospheric representation of SAM+ in any given season in the SIO. These different types of SAM+ mean a hemispheric index fails to capture the regional variability in surface weather conditions that is primarily driven by the synoptic variability rather than the absolute polarity of the SAM.

Sign in / Sign up

Export Citation Format

Share Document