scholarly journals Synoptic atmospheric circulation patterns associated with deep persistent slab avalanches in the western United States

2021 ◽  
Vol 21 (2) ◽  
pp. 757-774
Author(s):  
Andrew R. Schauer ◽  
Jordy Hendrikx ◽  
Karl W. Birkeland ◽  
Cary J. Mock
Keyword(s):  
Atmospheric Circulation ◽  
Winter Season ◽  
Heavy Precipitation ◽  
Self Organizing Maps ◽  
Synoptic Type ◽  
Additional Tool ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Unique Distribution ◽  
In The Beginning

Abstract. Deep persistent slab avalanches are capable of destroying infrastructure and are usually unsurvivable for those who are caught. Formation of a snowpack conducive to deep persistent slab avalanches is typically driven by meteorological conditions occurring in the beginning weeks to months of the winter season, and yet the avalanche event may not occur for several weeks to months later. While predicting the exact timing of the release of deep persistent slab avalanches is difficult, onset of avalanche activity is commonly preceded by rapid warming, heavy precipitation, or high winds. This work investigates the synoptic drivers of deep persistent slab avalanches at three sites in the western USA with long records: Bridger Bowl, Montana; Jackson, Wyoming; and Mammoth Mountain, California. We use self-organizing maps to generate 20 synoptic types that summarize 5899 daily 500 mbar geopotential height maps for the winters (November–March) of 1979/80–2017/18. For each of the three locations, we identify major and minor deep persistent slab avalanche seasons and analyze the number of days represented by each synoptic type during the beginning (November–January) of the major and minor seasons. We also examine the number of days assigned to each synoptic type during the 72 h preceding deep persistent slab avalanche activity for both dry and wet slab events. Each of the three sites exhibits a unique distribution of the number of days assigned to each synoptic type during November–January of major and minor seasons and for the 72 h period preceding deep persistent slab avalanche activity. This work identifies the synoptic-scale atmospheric circulation patterns contributing to deep persistent slab instabilities and the patterns that commonly precede deep persistent slab avalanche activity. By identifying these patterns, we provide an improved understanding of deep persistent slab avalanches and an additional tool to anticipate the timing of these difficult-to-predict events.

scholarly journals Synoptic atmospheric circulation patterns associated with deep persistent slab avalanches in the western United States

2020 ◽  
Author(s):  
Andrew R. Schauer ◽  
Jordy Hendrikx ◽  
Karl W. Birkeland ◽  
Cary J. Mock
Keyword(s):  
Atmospheric Circulation ◽  
Winter Season ◽  
Heavy Precipitation ◽  
Self Organizing Maps ◽  
Synoptic Type ◽  
Additional Tool ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Unique Distribution ◽  
In The Beginning

Abstract. Deep persistent slab avalanches are capable of destroying infrastructure and are usually unsurvivable to those who are caught. Formation of a snowpack conducive to deep persistent slab avalanches is typically driven by meteorological conditions occurring in the beginning weeks to months of the winter season, and yet the avalanche event may not occur for several weeks to months later. While predicting the exact timing of the release of deep persistent slab avalanches is difficult, onset of avalanche activity is commonly preceded by rapid warming, heavy precipitation, or high winds. This work investigates the synoptic drivers of deep persistent slab avalanches at three sites in the Western USA with long records: Bridger Bowl, Montana; Jackson, Wyoming; and Mammoth Mountain, California. We use self-organizing maps to generate twenty synoptic types that summarize 5,899 daily 500 mb geopotential height maps for the winters (November–March) of 1979/80–2017/18. For each of the three locations, we identify major and minor deep persistent slab avalanche seasons, and analyze the number of days represented by each synoptic type during the beginning (November–January) of the major and minor seasons. We also examine the number of days assigned to each synoptic type during the 72 hours preceding deep persistent slab avalanche activity for both dry and wet slab events. Each of the three sites exhibits a unique distribution of the number of days assigned to each synoptic type during November–January of major and minor seasons, and for the 72-hour period preceding deep persistent slab avalanche activity. This work identifies the synoptic scale atmospheric circulation patterns contributing to deep persistent slab instabilities, and the patterns that commonly precede deep persistent slab avalanche activity. By identifying these patterns, we provide an improved understanding of deep persistent slab avalanches, and an additional tool to anticipate the timing of these difficult-to-predict events.

scholarly journals Trends and variability in extreme precipitation indices over Maghreb countries

2013 ◽  
Vol 13 (12) ◽  
pp. 3235-3248 ◽  
Author(s):  
Y. Tramblay ◽  
S. El Adlouni ◽  
E. Servat
Keyword(s):  
Atmospheric Circulation ◽  
Large Scale ◽  
Heavy Precipitation ◽  
Climate Indices ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Precipitation Indices ◽  
Precipitation Records ◽  
Mediterranean Oscillation ◽  
Large Scale Atmospheric Circulation

Abstract. Maghreb countries are highly vulnerable to extreme hydrological events, such as floods and droughts, driven by the strong variability of precipitation. While several studies have analyzed the presence of trends in precipitation records for the Euro-Mediterranean basin, this study provides a regional assessment of trends on its southernmost shores. A database of 22 stations located in Algeria, Morocco and Tunisia with between 33 and 59 yr of daily precipitation records is considered. The change points and trends are analyzed for eleven climate indices, describing several features of the precipitation regime. The issue of conducting multiple hypothesis tests is addressed through the implementation of a false discovery rate procedure. The spatial and interannual variability of the precipitation indices at the different stations are analyzed and compared with large-scale atmospheric circulation patterns, including the North Atlantic Oscillation (NAO), western Mediterranean Oscillation (WEMO), Mediterranean Oscillation (MO) and El Niño–Southern Oscillation (ENSO). Results show a strong tendency towards a decrease of precipitation totals and wet days together with an increase in the duration of dry periods, mainly for Morocco and western Algeria. On the other hand, only a few significant trends are detected for heavy precipitation indices. The NAO and MO patterns are well correlated with precipitation indices describing precipitation amounts, the number of dry days and the length of wet and dry periods, whereas heavy precipitation indices exhibit a strong spatial variability and are only moderately correlated with large-scale atmospheric circulation patterns.

scholarly journals Influence of springtime atmospheric circulation types on the distribution of air pollutants in the Arctic

2021 ◽  
Author(s):  
Manu Anna Thomas ◽  
Abhay Devasthale ◽  
Tiina Nygård
Keyword(s):  
Atmospheric Circulation ◽  
The Arctic ◽  
Transport Models ◽  
Self Organizing Maps ◽  
Atmospheric Circulation Patterns ◽  
Circulation Types ◽  
Circulation Patterns ◽  
European Arctic ◽  
Pollutant Distribution ◽  
Almost All

Abstract. The transport and distribution of short-lived climate forcers in the Arctic is influenced by the prevailing atmospheric circulation patterns. Understanding the coupling between pollutant distribution and dominant atmospheric circulation types is therefore important, not least to understand the processes governing the local processing of pollutants in the Arctic, but also to test the fidelity of chemistry transport models to simulate the transport from the southerly latitudes. Here, we use a combination of satellite based and reanalysis datasets spanning over 12 years (2007–2018) and investigate the concentrations of NO2, O3, CO and aerosols and their co-variability during 20 different atmospheric circulation types in the spring season (March, April and May) over the Arctic. We carried out a Self-Organizing Maps analysis of MSLP to derive these circulation types. Although almost all pollutants investigated here show statistically significant sensitivity to the circulation types, NO2 exhibits the strongest sensitivity among them. The circulation types with low-pressure systems located over the northeast Atlantic show a clear enhancement of NO2 and AOD in the European Arctic. The O3 concentrations are, however, decreased. The free tropospheric CO is increased over the Arctic during such events. The circulation types with atmospheric blocking over Greenland and northern Scandinavia show the opposite signal in which the NO2 concentrations are decreased and AODs are smaller than the climatological values. The O3 concentrations are, however, increased and the free tropospheric CO decreased during such events. The study provides the most comprehensive assessment so far of the sensitivity of springtime pollutant distribution to the atmospheric circulation types in the Arctic and also provides an observational basis for the evaluation of chemistry transport models.

scholarly journals Trends and variability in extreme precipitation indices over Maghreb countries

2013 ◽  
Vol 1 (4) ◽  
pp. 3625-3658 ◽  
Author(s):  
Y. Tramblay ◽  
S. El Adlouni ◽  
E. Servat
Keyword(s):  
Atmospheric Circulation ◽  
Large Scale ◽  
Heavy Precipitation ◽  
Climate Indices ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Precipitation Indices ◽  
Precipitation Records ◽  
Mediterranean Oscillation ◽  
Large Scale Atmospheric Circulation

Abstract. Maghreb countries located in North Africa are highly vulnerable to extreme hydrological events, such as floods and droughts, driven by the strong variability of precipitation. While several studies have analyzed the presence of trends in precipitation records for the Euro-Mediterranean Basin, this study provides the first regional assessment of trends on its southernmost shores. A database of 22 stations located in Algeria, Morocco and Tunisia with between 33 and 59 yr of daily precipitation records is considered. The change points and trends are analyzed for eleven climate indices describing several features of the precipitation regime. The issue of conducting multiple hypothesis tests is addressed through the implementation of a false discovery rate procedure. The spatial and inter-annual variability of the precipitation indices at the different stations are analyzed and compared with large scale atmospheric circulation patterns, including the North Atlantic Oscillation (NAO), Western Mediterranean Oscillation (WEMO), Mediterranean Oscillation (MO) and El Niño Southern Oscillation (ENSO). Results show a strong tendency towards a decrease of precipitation totals and wet days together with an increase in the duration of dry periods, mainly for Morocco and western Algeria. On the opposite, only a few significant trends are detected for heavy precipitation indices. The NAO and MO patterns are well correlated with precipitation indices describing precipitation amounts, the number of dry days and the length of wet and dry periods, whereas heavy precipitation indices exhibit a strong spatial variability and are only moderately correlated with large scale atmospheric circulation patterns.

scholarly journals Statistical analysis of very high-resolution precipitation data and relation to atmospheric circulation in Central Germany

2019 ◽  
Vol 16 ◽  
pp. 69-73
Author(s):  
Annika Brieber ◽  
Andreas Hoy
Keyword(s):  
High Resolution ◽  
Atmospheric Circulation ◽  
Heavy Precipitation ◽  
Precipitation Data ◽  
Short Term ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
The Impact ◽  
Very High ◽  
Precipitation Events

Abstract. The cumulative occurrence of heavy precipitation and flood events during recent years in various Central European locations emphasises the urgent need to improve extreme rainfall observations and forecasts. Precipitation gauges based on a weighing system allow the recording of intense short-term precipitation events with a very high temporal resolution (down to 1 min). In this study, observational data that were collected during the period 2000 to 2016 for 126 stations of two corresponding measuring networks in the Central German state of Hesse were investigated for the first time to answer the following questions: (1) Are the recorded high-resolution precipitation data plausible and comparable between both networks? (2) Which atmospheric circulation patterns were specifically prone to produce short-term intense precipitation events? Although the two networks are equipped with the same measuring technology, systematic differences concerning their maximum 1 min precipitation amounts occur, which may be explained by different instrumental software settings. We could minimise those discrepancies by accumulating the existing 1 min data to 15 min. Subsequently, the 15 min daily maximum values and accumulated daily sums were analysed regarding the impact of large-scale atmospheric circulation patterns, based on the well-known “Großwetterlagen” classification. We identified a clear connection between atmospheric circulation and heavy precipitation over Hesse, while indicating some differences between daily (24 h) and sub-daily (15 min) events. High daily precipitation sums often relate to westerlies and central cyclones, while intense short-term events are frequently generated by warm-humid continental air from southern and eastern Europe as well as trough conditions, where the trough's core is found west of the study area. Our results underline the importance of expanding and enhancing high-resolution precipitation observations in Germany as well as other countries.

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