scholarly journals Atmospheric circulation influence on the interannual variability of snow pack in the Spanish Pyrenees during the second half of the 20th century

2007 ◽  
Vol 38 (1) ◽  
pp. 33-44 ◽  
Author(s):  
Juan I. López-Moreno ◽  
Sergio M. Vicente-Serrano
Keyword(s):  
Atmospheric Circulation ◽  
20Th Century ◽  
Large Scale ◽  
Spatial Scales ◽  
Cold Season ◽  
Snow Accumulation ◽  
Positive Trend ◽  
Snow Pack ◽  
Weather Types ◽  
Spanish Pyrenees

Large areas in the Spanish Pyrenees are covered by snow between December and April, especially above 1650 m a.s.l., the location of the cold season 0°C isotherm. However, a significant negative trend in Pyrenean snow pack was detected during the second half of the 20th century. This paper analyses the interannual evolution of snow accumulation in these mountains in relation to the variability of atmospheric circulation. The study considers two spatial scales, from weather types over the Iberian Peninsula to hemispheric atmospheric patterns. The results show strong relationships between the annual occurrence of several weather types and spring snow accumulation. Changes in the frequency of several weather types are explained by the evolution of large scale hemispheric circulation patterns, especially the North Atlantic Oscillation (NAO). Thus, the positive trend observed in the NAO index leads to a decrease in the occurrence of types that favour snow accumulation and an increase in unfavourable conditions for snow pack during the second half of the 20th century.

scholarly journals Dendroclimatology in the Eastern Mediterranean

Radiocarbon ◽  
2014 ◽  
Vol 56 (04) ◽  
pp. S61-S68
Author(s):  
Ramzi Touchan ◽  
David M. Meko ◽  
Kevin J. Anchukaitis
Keyword(s):  
Resource Management ◽  
Climate Variability ◽  
20Th Century ◽  
Tree Ring ◽  
Large Scale ◽  
Eastern Mediterranean ◽  
Spatial Scales ◽  
Climatic Variation ◽  
Ring Network ◽  
The Past

Dendroclimatology in the Eastern Mediterranean (EM) region has made important contributions to the understanding of climate variability on timescales of decades to centuries. These contributions, beginning in the mid-20th century, have value for resource management, archaeology, and climatology. A gradually expanding tree-ring network developed by the first author over the past 15 years has been the framework for some of the most important recent advances in EM dendroclimatology. The network, now consisting of 79 sites, has been widely applied in large-scale climatic reconstruction and in helping to identify drivers of climatic variation on regional to global spatial scales. This article reviews EM dendroclimatology and highlights contributions on the national and international scale.

Savanna Biome

Ecology ◽  
2013 ◽  
Author(s):  
Michael J. Hill
Keyword(s):  
South America ◽  
20Th Century ◽  
Ecosystem Function ◽  
Large Scale ◽  
Restoration Ecology ◽  
Vegetation Index ◽  
Spatial Scales ◽  
Scenario Development ◽  
Tall Grass ◽  
Agricultural Conversion

The savanna biome represents the complex of vegetation made up of grassland with trees in varying densities and arrangements that occupies the transition zone between forests and grasslands. Whereas the lay observer could usually identify a forest or grassland, the savanna biome would provide a challenge, greatly influenced by the scale of observation, since it is characterized by high variability in density, arrangement, clumping, and structure of grassland and trees. The large-scale savannas of the world are quite different on the major continents of Africa, South America, and Australia, and distributed in smaller, highly variable arrangements and formations in North America and Eurasia. The nature and stability of the savanna biome has received increasing attention because of its perceived dependence on disturbance by fire and herbivory to maintain tree-grass balance and because some savannas are biodiversity hotspots. Evolution of savannas is thought to be associated with a lower CO2world where tropical grasses gain advantage from highly efficient photosynthetic systems and fire and grazing control woody encroachment. The explorer botanists of the early 20th century paid significant attention to the neotropical and peri-Amazonian savannas of South America with their extraordinary biodiversity. In the 1980s, the West African savannas became the terrestrial focus of the genesis of remote sensing of land systems and the development of the Normalized Difference Vegetation Index (NDVI) as a global monitoring tool. During the early to mid-20th century, many temperate savannas were heavily converted to agriculture in the New World, and a similar trend is now continuing and potentially accelerating in tropical savannas of South America and Africa. The Australian tropical savanna has remained largely intact as it is generally too arid for agricultural conversion. As a result it has become increasingly important for ecological and process studies on tree-grass ecosystem function across spatial scales. Tropical tall grass-tree systems in Asia tend to have been extirpated by dense human activity but have also been treated differently in vegetation classifications and so do not clearly appear in global land cover maps. There has been limited attention paid to these systems in the literature. With global population and food demand potentially ballooning in the 21st century, accelerated conversion of savannas is likely to intensify both concerns about decline in ecosystem function, and competition for ecosystem services that will necessitate a significant expansion in integrated, interdisciplinary research, sophisticated modeling and future scenario development and research on restoration ecology and amelioration of land degradation.

Transition probabilities between synoptic weather types as a fingerprint for climate model evaluation

2021 ◽  
Author(s):  
Juan Antonio Fernandez-Granja ◽  
Ana Casanueva ◽  
Joaquín Bedia ◽  
Jesús Fernández
Keyword(s):  
Atmospheric Circulation ◽  
Large Scale ◽  
Transition Probabilities ◽  
Transition Probability ◽  
Transition Probability Matrix ◽  
Weather Types ◽  
Observational Uncertainty ◽  
Leibler Divergence ◽  
Synoptic Conditions ◽  
Large Scale Atmospheric Circulation

<p>Global Climate Models (GCMs) generally exhibit significant biases in the representation of large-scale atmospheric circulation. Even after bias adjustment, these errors remain and are inherited to some extent by the derived downscaling products, impairing the credibility of future regional projections. </p><p>We perform a process-based evaluation of state-of-the-art GCMs from CMIP5 and CMIP6, with a focus on the simulation of the synoptic climatological patterns having a most prominent effect on the European climate. To this aim, we use the Lamb Weather Type Classification (LWT, Lamb, 1972). We undertake a comprehensive assessment based on several evaluation measures, such as Kullback-Leibler divergence (KL), Relative Bias and Transition Probability Matrix Score (TPMS), used to assess the ability of the GCMs in reproducing not only the frequencies of the different Lamb Weather Types (LWTs), but also the daily probabilities of transitions among them. We show that the novel TPMS score poses a stringent test on the GCM performance, allowing for a convenient model ranking based on each model’s transition probability matrix fingerprint. Deficiencies in the transition probabilities from one LWT to another might explain the misrepresentation of the synoptic conditions and their frequencies by the GCMs. Four different reanalysis products of varying characteristics are considered as pseudo-observational reference in order to assess observational uncertainty. </p><p>Our results unveil an overall improvement of salient atmospheric circulation features of CMIP6 with respect to CMIP5, demonstrating the ability of the new models to better capture key synoptic conditions. The improvement is consistent across observational references, although it is uneven across models and large frequency biases still remain for the dominant LWTs in many cases. In particular, some CMIP6 models attain similar or even worse results than their CMIP5 counterparts. In light of the large differences found across models, we advocate for a careful selection of driving GCMs in downscaling experiments with a special focus on large-scale atmospheric circulation aspects.</p><p> </p>

Compiling a chemistry database from Antarctic ice cores records spanning the past 2000 years

2021 ◽  
Author(s):  
Diana Vladimirova ◽  
Elizabeth Thomas ◽  
on behalf of CLIVASH2k
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
Large Scale ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Sea Ice Extent ◽  
Large Variability ◽  
The Past ◽  
Direct Observations ◽  
Past 2000 Years

<p>Trends in sea ice extent and atmospheric circulation around Antarctica have exhibited large variability over recent decades. Direct observations such as satellite data cover the past four decades only. Thus, a comparison with paleoclimate archives is essential to understand the natural and anthropogenic components of these recent changes. We have initiated a data call within CLIVASH2k community (http://pastglobalchanges.org/science/wg/2k-network/projects/clivash) to collect all available sodium (Na+) and sulfate (SO42-) concentration and fluxes from Antarctic ice cores. We aim to improve our understanding of large-scale sea-ice variability and atmospheric circulation over the past 2000 years. In this respect, ice cores are a unique archive.</p><p>Here we present the new database, which builds on previous efforts by the PAGES community in gathering snow accumulation (Thomas et al. 2017) and stable water isotope data (Stenni et al. 2017).  To date, 88 published and 14 unpublished records have been submitted, 10 of which span the full 2000 years. The data, especially 2000 years-long records are equally distributed over the Antarctic continent and all coastal regions are well represented.  The new data will allow us to investigate interannual and decadal-to-centennial scale variability in sea ice extent and atmospheric circulation and its regional differences over the past 2000 years.</p>

scholarly journals Mapping Weather-Type Influence on Senegal Precipitation Based on a Spatial–Temporal Statistical Model*

2013 ◽  
Vol 26 (20) ◽  
pp. 8189-8209 ◽  
Author(s):  
Henning W. Rust ◽  
Mathieu Vrac ◽  
Benjamin Sultan ◽  
Matthieu Lengaigne
Keyword(s):  
Atmospheric Circulation ◽  
Large Scale ◽  
Pearson Correlation ◽  
Precipitation Amount ◽  
Correlation Coefficients ◽  
Drought Risk ◽  
Synoptic Scale ◽  
Weather Types ◽  
Easterly Waves ◽  
Precipitation Occurrence

Abstract Senegal is particularly vulnerable to precipitation variability. To investigate the influence of large-scale circulation on local-scale precipitation, a full spatial–statistical description of precipitation occurrence and amount for Senegal is developed. These regression-type models have been built on the basis of daily records at 137 locations and were developed in two stages: (i) a baseline model describing the expected daily occurrence probability and precipitation amount as spatial fields from monsoon onset to offset, and (ii) the inclusion of weather types defined from the NCEP–NCAR reanalysis 850-hPa winds and 925-hPa relative humidity establishing the link to the synoptic-scale atmospheric circulation. During peak phase, the resulting types appear in two main cycles that can be linked to passing African easterly waves. The models allow the investigation of the spatial response of precipitation occurrence and amount to a discrete set of preferred states of the atmospheric circulation. As such, they can be used for drought risk mapping and the downscaling of climate change projections. Necessary choices, such as filtering and scaling of the atmospheric data (as well as the number of weather types to be used), have been made on the basis of the precipitation models' performance instead of relying on external criteria. It could be demonstrated that the inclusion of the synoptic-scale weather types lead to skill on the local and daily scale. On the interannual scale, the models for precipitation occurrence and amount capture 26% and 38% of the interannual spatially averaged variability, corresponding to Pearson correlation coefficients of rO = 0.52 and ri = 0.65, respectively.

scholarly journals Variability of sea ice deformation rates in the Arctic and their relationship with basin-scale wind forcing

2012 ◽  
Vol 6 (6) ◽  
pp. 1553-1559 ◽  
Author(s):  
A. Herman ◽  
O. Glowacki
Keyword(s):  
Sea Ice ◽  
Wind Stress ◽  
Large Scale ◽  
Spatial Scales ◽  
Distribution Functions ◽  
Wind Forcing ◽  
The Arctic ◽  
Positive Trend ◽  
Strongly Correlated ◽  
Basin Scale

Abstract. The temporal variability of the moments of probability distribution functions (pdfs) of total sea ice deformation rates in the Arctic is analyzed in the context of the basin-scale wind forcing acting on the ice. The pdfs are estimated for 594 satellite-derived sea ice deformation maps from 11 winter seasons between 1996/1997 and 2007/2008, provided by the RADARSAT Geophysical Processor System. The temporal scale analyzed equals 3 days. The moments of the pdfs, calculated for a range of spatial scales (12.5–900 km), have two dominating components of variability: a seasonal cycle, with deformation rates decreasing throughout winter towards a minimum in March; and a short-term, synoptic variability, strongly correlated with the area-averaged magnitude of the wind stress over the Arctic, estimated based on the NCEP-DOE Reanalysis-2 data (correlation coefficient of 0.71 for the mean deformation rate). Due to scaling properties of the moments, logarithms of higher moments are strongly correlated with the wind stress as well. Exceptions are observed only at small spatial scales, as a result of extreme deformation events, not directly associated with large-scale wind forcing. By repeating the analysis within regions of different sizes and locations, we show that the wind–ice deformation correlation is largest at the basin scale and decreases with decreasing size of the area of study. Finally, we suggest that a positive trend in seasonally averaged correlation between sea ice deformation rates and the wind forcing, present in the analyzed data, may be related to an observed decrease in the multi-year ice area in the Arctic, indicating possibly even stronger correlations in the future.

scholarly journals Influence of atmospheric circulation on glacier mass balance in western Tibet: an analysis based on observations and modeling

2021 ◽  
pp. 1-55
Author(s):  
Meilin Zhu ◽  
Lonnie G. Thompson ◽  
Huabiao Zhao ◽  
Tandong Yao ◽  
Wei Yang ◽  
...  
Keyword(s):  
Mass Balance ◽  
Atmospheric Circulation ◽  
Air Temperature ◽  
Large Scale ◽  
Snow Accumulation ◽  
Balance Model ◽  
Glacier Mass Balance ◽  
The Tibetan Plateau ◽  
Local Climate ◽  
Average Mass

AbstractGlacier changes on the Tibetan Plateau (TP) have been spatially heterogeneous in recent decades. The understanding of glacier mass changes in western Tibet, a transitional area between the monsoon-dominated region and the westerlies-dominated region, is still incomplete. For this study, we used an energy-mass balance model to reconstruct annual mass balances from October 1967 to September 2019 to explore the effects of local climate and large-scale atmospheric circulation on glacier mass changes in western Tibet. The results showed Xiao Anglong Glacier is close to a balanced condition, with an average value of -53±185 mm w.e. a-1 for 1968-2019. The interannual mass balance variability during 1968-2019 was primary driven by ablation-season precipitation, which determined changes in the snow accumulation and strongly influenced melt processes. The interannual mass balance variability during 1968-2019 was less affected by ablation-season air temperature, which only weakly affected snowfall and melt energy. Further analysis suggests that the southward (or northward) shift of the westerlies caused low (or high) ablation-season precipitation, and therefore low (or high) annual mass balance for glaciers in western Tibet. In addition, the average mass balance for Xiao Anglong Glacier was 83±185, -210±185, and -10±185 mm w.e. a-1 for 1968-1990, 1991-2012, and 2013-2019, respectively. These mass changes were associated with the variations in precipitation and air temperature during the ablation season on interdecadal time scales.

scholarly journals Controls on Spatial and Temporal Variation in Snow Accumulation on Glaciers in the Southern Alps, New Zealand

2021 ◽  
Author(s):  
◽  
Heather Purdie
Keyword(s):  
New Zealand ◽  
Atmospheric Circulation ◽  
Southern Oscillation ◽  
Snow Accumulation ◽  
Southern Alps ◽  
Substantial Contribution ◽  
Spatial And Temporal Variation ◽  
Glacier Mass Balance ◽  
Positive Trend ◽  
Unexpected Result

<p>Mountain glaciers are already responding to climatic warming, and are expected to make a substantial contribution to sea-level rise in the coming decades. The aim of this investigation in the New Zealand Southern Alps was to improve our understanding of snow accumulation variability on mid-latitude maritime glaciers, in order to allow for better estimation of future glacier mass balance. The specific aim was to investigate snow accumulation processes at a range of spatial and temporal scales, focussing on synoptic-scale atmospheric circulation influences, moisture sources for snow accumulation and local-scale dependencies of snow accumulation in relation to topography. A range of methods were utilised including direct measurement, snow and ice core analysis, statistical analysis and modelling. Snow accumulation in the Southern Alps was found to be derived predominantly from the Tasman Sea, and deposited during low pressure troughs and fronts. Although precipitation increased with elevation, wind processes redistributed this mass. On a ~monthly timescale this redistribution caused an unexpected result, namely that wind deflation of snow on Franz Josef Glacier countered the effects of greater accumulation, and total accumulation was similar at both Franz Josef and Tasman Glaciers over this period. These processes make it challenging to simulate snow accumulation patterns by simply extrapolating snowfall over an orographic barrier from lowland climate station data. On an inter-annual basis, temperature, especially during the ablation season, had most influence on net accumulation, and warm summers served to homogenise winter variability. Consequently, atmospheric circulation patterns that affect summer temperature, for example the El Niño Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) also influence inter-annual variability in net accumulation. Together, these results highlight the dependence of maritime glaciers in the New Zealand Southern Alps on the prevailing westerly circulation. Although some uncertainty surrounds how global warming will affect atmospheric circulation and synoptic weather patterns, the results of this research indicate that New Zealand glaciers can be expected to lose significant mass in the coming decades if the current positive trend in the SAM continues, and if La Niña events (positive ENSO) become more frequent.</p>

scholarly journals Controls on Spatial and Temporal Variation in Snow Accumulation on Glaciers in the Southern Alps, New Zealand

2021 ◽  
Author(s):  
◽  
Heather Purdie
Keyword(s):  
New Zealand ◽  
Atmospheric Circulation ◽  
Southern Oscillation ◽  
Snow Accumulation ◽  
Southern Alps ◽  
Substantial Contribution ◽  
Spatial And Temporal Variation ◽  
Glacier Mass Balance ◽  
Positive Trend ◽  
Unexpected Result

<p>Mountain glaciers are already responding to climatic warming, and are expected to make a substantial contribution to sea-level rise in the coming decades. The aim of this investigation in the New Zealand Southern Alps was to improve our understanding of snow accumulation variability on mid-latitude maritime glaciers, in order to allow for better estimation of future glacier mass balance. The specific aim was to investigate snow accumulation processes at a range of spatial and temporal scales, focussing on synoptic-scale atmospheric circulation influences, moisture sources for snow accumulation and local-scale dependencies of snow accumulation in relation to topography. A range of methods were utilised including direct measurement, snow and ice core analysis, statistical analysis and modelling. Snow accumulation in the Southern Alps was found to be derived predominantly from the Tasman Sea, and deposited during low pressure troughs and fronts. Although precipitation increased with elevation, wind processes redistributed this mass. On a ~monthly timescale this redistribution caused an unexpected result, namely that wind deflation of snow on Franz Josef Glacier countered the effects of greater accumulation, and total accumulation was similar at both Franz Josef and Tasman Glaciers over this period. These processes make it challenging to simulate snow accumulation patterns by simply extrapolating snowfall over an orographic barrier from lowland climate station data. On an inter-annual basis, temperature, especially during the ablation season, had most influence on net accumulation, and warm summers served to homogenise winter variability. Consequently, atmospheric circulation patterns that affect summer temperature, for example the El Niño Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) also influence inter-annual variability in net accumulation. Together, these results highlight the dependence of maritime glaciers in the New Zealand Southern Alps on the prevailing westerly circulation. Although some uncertainty surrounds how global warming will affect atmospheric circulation and synoptic weather patterns, the results of this research indicate that New Zealand glaciers can be expected to lose significant mass in the coming decades if the current positive trend in the SAM continues, and if La Niña events (positive ENSO) become more frequent.</p>

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