Trends in Persistent Seasonal-Scale Atmospheric Circulation Patterns Responsible for Seasonal Precipitation Totals and Occurrences of Precipitation Extremes over Canada

2019 ◽  
Vol 32 (21) ◽  
pp. 7105-7126 ◽  
Author(s):  
Xuezhi Tan ◽  
Thian Yew Gan ◽  
Shu Chen ◽  
Daniel E. Horton ◽  
Xiaohong Chen ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
Extreme Precipitation ◽  
Circulation Pattern ◽  
Atmospheric Moisture ◽  
Dynamic Changes ◽  
Extreme Precipitation Events ◽  
Circulation Patterns ◽  
Precipitation Changes ◽  
Synoptic Circulation ◽  
Precipitation Events

Abstract Both large-scale atmospheric circulation and moisture content in the atmosphere govern regional precipitation. We partition recent changes in mean, heavy, and extreme precipitation for all seasons over Canada to changes in synoptic circulation patterns (dynamic changes) and in atmospheric moisture conditions (thermodynamic changes) using 500-hPa geopotential height and precipitation data over 1979–2014. Using the self-organizing map (SOM) cluster analysis, we identify statistically significant trends in occurrences of certain synoptic circulation patterns over the Canadian landmass, which have dynamically contributed to observed changes in precipitation totals and occurrence of heavy and extreme precipitation events over Canada. Occurrences of circulation patterns such as westerlies and ridges over western North America and the North Pacific have considerably affected regional precipitation over Canada. Precipitation intensity and occurrences of precipitation extremes associated with each SOM circulation pattern also showed statistically significant trends resulting from thermodynamic changes in the atmospheric moisture supply for precipitation events. A partition analysis based on the thermodynamic–dynamic partition method indicates that most (~90%) changes in mean and extreme precipitation over Canada resulted from changes in precipitation regimes occurring under each synoptic circulation pattern (thermodynamic changes). Other regional precipitation changes resulted from changes in occurrences of synoptic circulation patterns (dynamic changes). Because of the high spatial variability of precipitation response to changes in thermodynamic and dynamic conditions, dynamic contributions could offset thermodynamic contributions to precipitation changes over some regions if thermodynamic and dynamic contributions are in opposition to each other (negative or positive), which would result in minimal changes in precipitation intensity and occurrences of heavy and extreme precipitation events.

scholarly journals Investigating changes in atmospheric circulation patterns connected to extreme precipitation in Norway

2021 ◽  
Author(s):  
Karianne Ødemark ◽  
Malte Müller ◽  
Ole Einar Tveito ◽  
Cyril Palerme
Keyword(s):  
Atmospheric Circulation ◽  
Extreme Precipitation ◽  
Good Description ◽  
Construction Technique ◽  
Sea Ice Concentration ◽  
Data Set ◽  
Atmospheric Circulation Patterns ◽  
Extreme Precipitation Events ◽  
Circulation Patterns ◽  
Precipitation Events

<p>Extreme precipitation events that lead to excess surface water and flood are becoming an amplifying societal cost as a result of both the increasing precipitation amounts in recent years and urbanization. Knowledge about extreme precipitation events is important for the ability to predict them, but also to know how often they occur with various intensities in order to estimate design values for constructions and critical infrastructure. A good description of extreme precipitaton is a challenge since observation networks are often too sparse to describe the spatial structure of precipitation, and the highest amounts are most likely not captured by a precipitation gauge. For the study of extreme precipitation events by means of statistical analysis, long timesteries are required, which is a major challenge when using conventional or new observational data records.  Here, a data set constructed from the numerical seasonal prediction system at ECMWF, SEAS5, has been applied to evaluate mechanisms controlling extreme precipitation events. The construction technique gives the ability to increase the event sample size compared to conventional data sets. We analyze 3-day  maximum precipitation events in the September-October-November season for an area on the west coast of Norway, an area subject to the largest precipitation amounts in Europe. A principal component analysis of the 500 hPa geopotential anomaly has been performed to identify atmospheric circulation patterns related to the extreme precipitation events. We find that two of the EOFs are related to precipitation with high return values for the selected area. These two EOFs have a significant trend over the data period, but with opposing signs. We also investigate the connection between both sea surface temperature (SST) and sea-ice concentration in the Barents-Kara sea and the occurrence of extreme precipitation.</p>

scholarly journals Spring Extreme Precipitation Days in North China and Their Reliance on Atmospheric Circulation Patterns During 1979–2019

2022 ◽  
pp. 1-41
Keyword(s):  
Climate Variability ◽  
Atmospheric Circulation ◽  
Extreme Precipitation ◽  
Interannual Variation ◽  
North China ◽  
Circulation Pattern ◽  
Southerly Wind ◽  
Atmospheric Circulation Patterns ◽  
Rain Gauges ◽  
Circulation Patterns

Abstract The interannual variation of springtime extreme precipitation (SEP) days in North China (NC) and their reliance on atmospheric circulation patterns are studied by using the continuous daily record of 396 rain gauges and the fifth generation of the European Centre for Medium-Range Weather Forecasts atmospheric reanalysis during 1979–2019. The SEP days are defined as the days when at least 10% of rain gauges in NC record daily precipitation no less than 10.5 mm. Results show that the number of SEP days shows large interannual variability but no significant trend in the study period. Using the objective classification method of the obliquely rotated principal analysis in T-mode, we classify the atmospheric circulation into five different patterns based on the geopotential height at 700 hPa. Three circulation patterns all have fronts and are associated with strong southerly wind, leading to 88% of SEP days in NC. The strong southerly wind may provide moisture and dynamic forcing for the frontal precipitation. The interannual variation of SEP days is related with the number of the three above-mentioned dominant circulation patterns. Further analysis shows that the West Pacific pattern could be one of the possible climate variability modes related to SEP days. This study reveals that the daily circulation pattern may be the linkage between SEP days and climate variability modes in NC.

scholarly journals Characterisation of extreme winter precipitation in Mediterranean coastal sites and associated anomalous atmospheric circulation patterns

2010 ◽  
Vol 10 (5) ◽  
pp. 1037-1050 ◽  
Author(s):  
A. Toreti ◽  
E. Xoplaki ◽  
D. Maraun ◽  
F. G. Kuglitsch ◽  
H. Wanner ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
Extreme Precipitation ◽  
Large Scale ◽  
Western Mediterranean ◽  
Precipitation Extremes ◽  
Return Level ◽  
Jet Stream ◽  
Eastern Basin ◽  
Extreme Precipitation Events ◽  
Precipitation Events

Abstract. We present an analysis of daily extreme precipitation events for the extended winter season (October–March) at 20 Mediterranean coastal sites covering the period 1950–2006. The heavy tailed behaviour of precipitation extremes and estimated return levels, including associated uncertainties, are derived applying a procedure based on the Generalized Pareto Distribution, in combination with recently developed methods. Precipitation extremes have an important contribution to make seasonal totals (approximately 60% for all series). Three stations (one in the western Mediterranean and the others in the eastern basin) have a 5-year return level above 100 mm, while the lowest value (estimated for two Italian series) is equal to 58 mm. As for the 50-year return level, an Italian station (Genoa) has the highest value of 264 mm, while the other values range from 82 to 200 mm. Furthermore, six series (from stations located in France, Italy, Greece, and Cyprus) show a significant negative tendency in the probability of observing an extreme event. The relationship between extreme precipitation events and the large scale atmospheric circulation at the upper, mid and low troposphere is investigated by using NCEP/NCAR reanalysis data. A 2-step classification procedure identifies three significant anomaly patterns both for the western-central and eastern part of the Mediterranean basin. In the western Mediterranean, the anomalous southwesterly surface to mid-tropospheric flow is connected with enhanced moisture transport from the Atlantic. During ≥5-year return level events, the subtropical jet stream axis is aligned with the African coastline and interacts with the eddy-driven jet stream. This is connected with enhanced large scale ascending motions, instability and leads to the development of severe precipitation events. For the eastern Mediterranean extreme precipitation events, the identified anomaly patterns suggest warm air advection connected with anomalous ascent motions and an increase of the low- to mid-tropospheric moisture. Furthermore, the jet stream position (during ≥5-year return level events) supports the eastern basin being in a divergence area, where ascent motions are favoured. Our results contribute to an improved understanding of daily precipitation extremes in the cold season and associated large scale atmospheric features.

scholarly journals Impacts of the Sahel-Sahara Interface Reforestation on West African Climate: Intraseasonal Variability and Extreme Precipitation Events

2016 ◽  
Vol 2016 ◽  
pp. 1-20 ◽  
Author(s):  
Ibrahima Diba ◽  
Moctar Camara ◽  
Alioune Badara Sarr
Keyword(s):  
West Africa ◽  
Extreme Precipitation ◽  
Land Surface ◽  
Summer Rainfall ◽  
Maximum Length ◽  
Spatiotemporal Variability ◽  
Content Increase ◽  
Atmospheric Moisture ◽  
Extreme Precipitation Events ◽  
Precipitation Events

This study aims to evaluate the impacts of the Sahel-Sahara interface reforestation on spatiotemporal variability of the summer rainfall and extreme precipitation events over West Africa using the RegCM4 model. The land surface scheme of RegCM4 was modified to incorporate an East-West reforested zone (15°N and 20°N). Two runs were performed using the standard version of RegCM4 and the modified one of the same model taking into account the incorporated forest. The reforestation significantly modifies rainfall signal over West Africa by increasing it over the reforested zone and the Fouta Jallon highlands (FJH). This rainfall increase is associated with a strengthening of the atmospheric moisture over the reforested area. This atmospheric moisture content increase associated with the wind dynamic may explain the spatiotemporal change of the rainfall and extreme precipitation events. The analysis of the impacts of the reforestation on some rainfall indices shows an increase of the 90th, 95th, and 99th percentiles over the reforested zone and off the FJH. This reforestation also causes an increase of the maximum length of the consecutive wet days over and off FJH and a decrease of the maximum length of the consecutive dry days over the northern Sahel and the reforested zone.

scholarly journals Extreme Precipitation Changes in the Semiarid Region of Xinjiang, Northwest China

2015 ◽  
Vol 2015 ◽  
pp. 1-7 ◽  
Author(s):  
Yanwei Zhang ◽  
Quansheng Ge ◽  
Minzhe Liu
Keyword(s):  
Extreme Precipitation ◽  
Daily Precipitation ◽  
Statistical Tests ◽  
Northwest China ◽  
Semiarid Region ◽  
Extreme Precipitation Events ◽  
Precipitation Records ◽  
Precipitation Changes ◽  
Climate Disasters ◽  
Precipitation Events

This study focuses on extreme precipitation changes in Xinjiang Province of Northwest China, which has experienced an increase in climate disasters in recent years. This paper investigates extreme precipitation events in Xinjiang, using 54 stations with daily precipitation records from the period 1961–2008. Different statistical tests and approaches were used to check the significance of trends of single and Xinjiang regionally aggregated precipitation series for intensity and in frequency. There were predominantly positive trends in annual maximum precipitation and a remarkable increment in the frequency of extreme precipitation over certain thresholds (from 10 to 40 mm). Although the series of frequencies exceeding thresholds had positive trends, only a minority were statistically significant. This lack of significance is because of the high variability of extreme precipitation in space and time. Thus, significant trends were evident when we assessed the extreme precipitation indicators of intensity and frequency at the regional level, both in intensity and frequency over thresholds, with a clearer signal in Xinjiang.

Lagrangian review of the origin of the humidity for the case of two extreme precipitation events in the Mediterranean region 

2021 ◽  
Author(s):  
Sara Cloux ◽  
Damián Insua-Costa ◽  
Gonzalo Miguez-Macho ◽  
Vicente Perez-Muñuzuri
Keyword(s):  
Relative Humidity ◽  
Extreme Precipitation ◽  
Mediterranean Region ◽  
Weather Data ◽  
Earth System ◽  
Atmospheric Moisture ◽  
Extreme Precipitation Events ◽  
The Mediterranean ◽  
Atmospheric Phenomena ◽  
Precipitation Events

<div> <p>Extreme precipitation events are atmospheric phenomena causing floods that generate great economic and social losses. The Mediterranean region is characterized by a strong variability in time and space that favors the appearance of this type of phenomena. Therefore, determining the origin of humidity must be done.     </p> </div><div> <p>The UTrack-atmospheric-moisture model [1] is a Lagrangian tool to track atmospheric moisture flows forward in time using ERA-5 reanalysis weather data. The labeled moisture is released into the atmosphere in the form of evaporation. After determine the allocated moisture precipitated at each time, this model allows us to know the percentage of relative humidity that has precipitated for each of the labeled sources.  Here we present a comparison of these results with previous results obtained by other Lagrangian methods. </p> </div><div> <p>[1] Tuinenburg, Obbe A., and Arie Staal. Tracking the global flows of atmospheric moisture and associated uncertainties." Hydrology and Earth System Sciences 24.5 (2020): 2419-2435. </p> </div>

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