Using a global climate model to evaluate the influences of water vapor, snow cover and atmospheric aerosol on warming in the Tibetan Plateau during the twenty-first century

We examine trends in climate variables and their interrelationships over the Tibetan Plateau using global climate model simulations to elucidate the mechanisms for the pattern of warming observed over the plateau during the latter half of the twentieth century and to investigate the warming trend during the twenty-first century under the SRES A1B scenario. Our analysis suggests a 4°C warming over the plateau between 1950 and 2100. The largest warming rates occur during winter and spring. For the 1961–2000 period, the simulated warming is similar to the observed trend over the plateau. Moreover, the largest warming occurs at the highest elevation sites between 1950 and 2100. We find that increases in (1) downward longwave radiation (DLR) influenced by increases in surface specific humidity (q), and (2) absorbed solar radiation (ASR) influenced by decreases in snow cover extent are, in part, the reason for a large warming trend over the plateau, particularly during winter and spring. Furthermore, elevation-based increases in DLR (influenced by q) and ASR (influenced by snow cover and atmospheric aerosols) appear to affect the elevation dependent warming trend simulated in the model.     

Interdecadal change in North Korean winter mean rainfall

In the present study, it was found that there was a significant climate regime shift in 1993 from average rainfall amounts in winter (December of a year and January and February of the next year) in North Korea over the last 30 years (1982–2011). This significant climate regime shift in 1993 also appeared in empirical orthogonal function analysis conducted using the winter mean rainfall amounts observed at 26 weather observation stations in North Korea. The reason why winter mean rainfall amounts in North Korea were smaller during the period of 1994–2011 than during the period of 1982–1994 was that anomalous anticyclone was reinforced in regions near Lake Baikal while anomalous cyclone was reinforced on the sea on the east of Japan so that the winter pressure system pattern (west high-east low pattern) appeared and thus anomalous cold and dry northerlies were reinforced in most East Asian regions including North Korea. To figure out the reason why anomalous anticyclone was reinforced further in the East Asian continent in winters during the period of 1994–2011, differences in water equivalent of accumulated snow depths between the two periods were analyzed. As a result, more snow was observed in most East Asian regions during the period of 1994–2011. Therefore, anomalous anticyclone could be further reinforced in the East Asian continent because surface air temperature dropped further due to snow-albedo effect. The surface air temperature cooling deepened further in the East Asian continent during the period of 1994–2011 due to snow-albedo effect was identified through differences in sensible heat net flux between the two periods.     

Use of atmospheric radiation measurement program data from Barrow, Alaska, for evaluation and development of snow-albedo parameterizations

Summary Snow albedo is determined from the ratio of out-going to incoming solar radiation using three years of broadband shortwave radiometer data obtained from the Barrow, Alaska, Atmospheric Radiation Measurement (ARM) site. These data are used for the evaluation of various types of snow-albedo parameterizations applied in numerical weather prediction or climate models. These snow-albedo parameterizations are based on environmental conditions (e.g., air or snow temperature), snow related characteristics (e.g., snow depth, snow age), or combinations of both. The ARM data proved to be well suited for snow-albedo evaluation purposes for a low-precipitation tundra environment. The evaluation confirms that snow-age dependent parameterizations of snow albedo work well during snowmelt, while parameterizations considering meteorological conditions often perform better during snow accumulation. Current difficulties in parameterizing snow albedo occur for long episodes of snow-event free conditions and episodes with a high frequency of snow events or strong snowfall. In a further step, the first two years of the ARM albedo dataset is used to develop a snow-albedo parameterization, and the third year’s data serves for its evaluation. This parameterization considers snow depth, wind speed, and air temperature which are found to be significant parameters for snow-albedo modeling under various conditions. Comparison of all evaluated snow-albedo parameterizations with this new parameterization shows improved snow-albedo prediction. Correspondence: Nicole M?lders, Geophysical Institute and College of Natural Science and Mathematics, University of Alaska Fairbanks, 903 Koyukuk Drive, P.O. Box 757320, Fairbanks, AK 99775-7320, USA     

Analysis of climatic variability and snow cover in the Kaligandaki River Basin,Himalaya, Nepal

Various remote sensing products and observed data sets were used to determine spatial and temporal trends in climatic variables and their relationship with snow cover area in the higher Himalayas, Nepal. The remote sensing techniques can detect spatial as well as temporal patterns in temperature and snow cover across the inaccessible terrain. Non-parametric methods (i.e. the Mann–Kendall method and Sen's slope) were used to identify trends in climatic variables. Increasing trends in temperature, approximately by 0.03 to 0.08 °C year^?1 based on the station data in different season, and mixed trends in seasonal precipitation were found for the studied basin. The accuracy of MOD10A1 snow cover and fractional snow cover in the Kaligandaki Basin was assessed with respect to the Advanced Spaceborne Thermal Emission and Reflection Radiometer-based snow cover area. With increasing trends in winter and spring temperature and decreasing trends in precipitation, a significant negative trend in snow cover area during these seasons was also identified. Results indicate the possible impact of global warming on precipitation and snow cover area in the higher mountainous area. Similar investigations in other regions of Himalayas are warranted to further strengthen the understanding of impact of climate change on hydrology and water resources and extreme hydrologic events.     

Manipulating snow cover in an alpine bog: effects on ecosystem respiration and nutrient content in soil and microbes

Snow amount is expected to decline in the Northern hemisphere as an effect of climate warming. However, snow amount in alpine regions will probably undergo stronger interannual fluctuations than elsewhere. We set up a short-term (1?year) experiment in which we manipulated snow cover in an alpine bog, with the following protocol: snow removal at the end of winter; snow removal in spring; snow addition in spring; removal of all aboveground plant tissues with no snow manipulation; no manipulation at all. We measured, at different dates from late spring to early autumn: ecosystem respiration (ER), and concentrations of carbon (C), nitrogen (N) and phosphorus (P) in the soil and in microbes. We hypothesized that longer duration of snow cover will lead to: i) higher ER rates associated with increased microbial biomass; and ii) decreased soil nutrient availability. Contrary to our first hypothesis, ER and microbial C content were unaffected by the snow cover manipulations, probably because ER was decoupled from microbial biomass especially in summer, when CO₂ efflux was dominated by autotrophic respiration. Our second hypothesis also was partially contradicted because nutrient content in the soil and in plants did not vary in relation to snow cover. However, we observed unexpected effects of snow cover manipulations on the N : P ratio in the microbial biomass, which declined after increasing snow cover. This probably depended on stimulation of microbial activity, which enhanced absorption of P, rather than N, by microbes. This may eventually reduce P availability for plant uptake.     

Albedo of coastal landfast sea ice in Prydz Bay,Antarctica: Observations and parameterization

The snow/sea-ice albedo was measured over coastal landfast sea ice in Prydz Bay, East Antarctica(off Zhongshan Station)during the austral spring and summer of 2010 and 2011. The variation of the observed albedo was a combination of a gradual seasonal transition from spring to summer and abrupt changes resulting from synoptic events, including snowfall, blowing snow, and overcast skies. The measured albedo ranged from 0.94 over thick fresh snow to 0.36 over melting sea ice. It was found that snow thickness was the most important factor influencing the albedo variation, while synoptic events and overcast skies could increase the albedo by about 0.18 and 0.06, respectively. The in-situ measured albedo and related physical parameters(e.g., snow thickness, ice thickness, surface temperature, and air temperature) were then used to evaluate four different snow/ice albedo parameterizations used in a variety of climate models. The parameterized albedos showed substantial discrepancies compared to the observed albedo, particularly during the summer melt period, even though more complex parameterizations yielded more realistic variations than simple ones. A modified parameterization was developed,which further considered synoptic events, cloud cover, and the local landfast sea-ice surface characteristics. The resulting parameterized albedo showed very good agreement with the observed albedo.     

Western Himalayan snow cover and Indian monsoon rainfall: A re-examination with INSAT and NCEP/NCAR data

Summary ?This study presents the monthly climatology and variability of the INSAT (Indian National Satellite) derived snow cover estimates over the western Himalayan region. The winter/spring snow estimates over the region are related to the subsequent summer monsoon rainfall over India. The NCEP/NCAR data are used to understand the physical mechanism of the snow-monsoon links. 15 years (1986–2000) of recent data are utilized to investigate these features in the present global warming environment. Results reveal that the spring snow cover area has been declining and snow has been melting faster from winter to spring after 1993. Connections between snow cover estimates and Indian monsoon rainfall (IMR) show that spring snow cover area is negatively related with maximum during May, while snow melt during the February–May period is positively related with subsequent IMR, implying that smaller snow cover area during May and faster snow melt from winter to spring is conducive for good monsoon activity over India. NCEP/NCAR data further shows that the heat low over northwest India and the monsoon circulation over the Indian subcontinent, in particular the cross-equatorial flow, during May are intensified (weakened) when the snow cover area during May is smaller (extensive) and snow melts faster (slower) during the February–May period. The well-documented negative relationship between winter snow and summer rainfall seems to have altered recently and changed to a positive relationship. The changes observed in snow cover extent and snow depth due to global warming may be a possible cause for the weakening winter snow–IMR relationship. Received January 15, 2002; revised May 5, 2002; accepted June 23, 2002     

Local climatic drivers of changes in phenology at a boreal-temperate ecotone in eastern North America

Ecosystems in biogeographical transition zones, or ecotones, tend to be highly sensitive to climate and can provide early indications of future change. To evaluate recent climatic changes and their impacts in a boreal-temperate ecotone in eastern North America, we analyzed ice phenology records (1975?C2007) for five lakes in the Adirondack Mountains of northern New York State. We observed rapidly decreasing trends of up to 21?days less ice cover, mostly due to later freeze-up and partially due to earlier break-up. To evaluate the local drivers of these lake ice changes, we modeled ice phenology based on local climate data, derived climatic predictors from the models, and evaluated trends in those predictors to determine which were responsible for observed changes in lake ice. November and December temperature and snow depth consistently predicted ice-in, and recent trends of warming and decreasing snow during these months were consistent with later ice formation. March and April temperature and snow depth consistently predicted ice-out, but the absence of trends in snow depth during these months, despite concurrent warming, resulted in much weaker trends for ice-out. Recent rates of warming in the Adirondacks are among the highest regionally, although with a different seasonality of changes (early winter > late winter) that is consistent with other lake ice records in the surrounding area. Projected future declines in snow cover could create positive feedbacks and accelerate current rates of ice loss due to warming. Climate sensitivity was greatest for the larger lakes in our study, including Wolf Lake, considered one of the most ecologically intact ??wilderness lakes?? in eastern North America. Our study provides further evidence of climate sensitivity of the boreal-temperate ecotone of eastern North America and points to emergent conservation challenges posed by climate change in legally protected yet vulnerable landscapes like the Adirondack Park.     

近44年青藏高原东部积雪的年代际变化特征及其与降雪和气温的关系

选取青藏高原东部地区1967~2010年61个测站的积雪数据,分析比较了整年和不同季节高原积雪的年代际变化特征及其与降雪和气温的关系,结果表明:除了秋季以外,高原东部积雪表现出“少雪-多雪-少雪“的显著年代际变化特征,80年代末发生的由少到多突变仅在冬季积雪中表现显著,20世纪末发生的由多到少突变在冬春两季积雪中均表现显著;降雪和气温的变化是影响高原东部积雪的重要因素,降雪变化的影响更加显著,尤其是秋季降雪;在冬春季降雪偏多时段,降雪的变化主导着积雪的变化;在冬春季降雪偏少时段,气温变化的影响增大,某些时段会超过降雪,甚至达到主导积雪变化的程度。      

Properties of the snow-firn cover of greenlandic glaciers from the satellite measurements of its scattering index

A new approach to the daily monitoring of properties of the snow-firn cover of Greenlandic glaciers based on the maps of the scattering index computed from the AMSU satellite radiometer measurements is considered. The boundaries of areas with different dispersing properties of snow and their seasonal variations in 2010?C2011 are determined. A high daily variability of the scattering index of snow-firn cover in summer and in transitional seasons is revealed. The analysis of probable reasons for the variability of the scattering index of snow-firn cover of glaciers is carried out.     

Seasonal cycle of snow cover changes in Eastern Siberia and its synoptic preconditions

The seasonal cycle of snow cover in Eastern Siberia is characterized, and synoptic preconditions of snow accumulation in winter and snow ablation in spring are determined using daily datasets. It was ascertained that cyclone activity has a strong impact on the occurrence of abundant snowfalls in Eastern Siberia. Negative anomalies of sea level pressure (SLP) usually spread westward or southwestward from the place of recorded substantial snowfalls, and they are associated with positive anomalies of air temperature located to the east or northeast of SLP depressions. Cyclonic circulation causes inflow of relatively warm and humid southern air masses originating from the Pacific Ocean, to the eastern parts of cyclones. During the days with snow ablation in spring much lower SLP anomalies occur than during snow accumulation in winter. This may suggest smaller influence of air circulation on snow cover reduction in spring and higher impact of insolation; both result in strong positive anomalies of air temperature which extend over entire Asia. These findings imply that the position, intensity, and dimension of pressure patterns are crucial for determining the location and intensity of rapid changes in snow cover depth during the snow cover season in Eastern Siberia.     

The extent and intensity of the urban heat island in Iași city,Romania

The study underlines the characteristics of the urban heat island of Ia?i (Ia?i’s UHI) on the basis of 3 years of air temperature measurements obtained by fixed-point observations. We focus on the identification of UHI development and intensity as it is expressed by the temperature differences between the city centre and the rural surroundings. Annual, seasonal and daily characteristics of Ia?i’s UHI are investigated at the level of the classical weather observation. In brief, an intensity of 0.8 °C of UHI and a spatial extension which corresponds to the densely built area of the city were delineated. The Ia?i UHI is stronger during summer calm nights—when the inner city is warmer with 2.5–3 °C than the surroundings—and is weaker during windy spring days. The specific features of Ia?i’s UHI bear a profound connection to the specificity of the urban structure, the high atmospheric stability in the region and the local topography. Also, the effects of Ia?i’s UHI upon some environmental aspects are presented as study cases. For instance, under the direct influence of UHI, we have observed that in the city centre, the apricot tree blossoms earlier (with up to 4 days) and the depth of the snow cover is significantly lower (with up to 10 cm for a rural snow depth of 30 cm) than in the surrounding areas.     

Long-term snow and weather observations at Weissfluhjoch and its relation to other high-altitude observatories in the Alps

Snow and weather observations at Weissfluhjoch were initiated in 1936, when a research team set a snow stake and started digging snow pits on a plateau located at 2,540?m asl above Davos, Switzerland. This was the beginning of what is now the longest series of daily snow depth, new snow height and bi-monthly snow water equivalent measurements from a high-altitude research station. Our investigations reveal that the snow depth at Weissfluhjoch with regard to the evolution and inter-annual variability represents a good proxy for the entire Swiss Alps. In order to set the snow and weather observations from Weissfluhjoch in a broader context, this paper also shows some comparisons with measurements from five other high-altitude observatories in the European Alps. The results show a surprisingly uniform warming of 0.8°C during the last three decades at the six investigated mountain stations. The long-term snow measurements reveal no change in mid-winter, but decreasing trends (especially since the 1980s) for the solid precipitation ratio, snow fall, snow water equivalent and snow depth during the melt season due to a strong temperature increase of 2.5°C in the spring and summer months of the last three decades.     

近46年重庆地区气温变化特征分析

利用1961~2006年期间重庆地区的气温资料,对重庆气温变化的特征进行分析。结果表明:近46年,重庆年平均、年平均最高气温都经历了先降温后升温的过程,而且前期1961~1985年的降温趋势和后期1986~2006年的升温趋势都很显著,均通过了0.01的显著性水平检验。而年平均最低气温近46年的整体上升趋势明显,通过了0.01的显著性水平检验。对于重庆平均气温和平均最高气温,在前期降温过程中,春季和夏季的下降趋势显著;而在后期的升温过程中,春季和秋季的增温趋势显著。      

Interpreting observed northern hemisphere snow trends with large ensembles of climate simulations

Simulated variability and trends in Northern Hemisphere seasonal snow cover are analyzed in large ensembles of climate integrations of the National Center for Atmospheric Research’s Community Earth System Model. Two 40-member ensembles driven by historical radiative forcings are generated, one coupled to a dynamical ocean and the other driven by observed sea surface temperatures (SSTs) over the period 1981–2010. The simulations reproduce many aspects of the observed climatology and variability of snow cover extent as characterized by the NOAA snow chart climate data record. Major features of the simulated snow water equivalent (SWE) also agree with observations (GlobSnow Northern Hemisphere SWE data record), although with a lesser degree of fidelity. Ensemble spread in the climate response quantifies the impact of natural climate variability in the presence and absence of coupling to the ocean. Both coupled and uncoupled ensembles indicate an overall decrease in springtime snow cover that is consistent with observations, although springtime trends in most climate realizations are weaker than observed. In the coupled ensemble, a tendency towards excessive warming in wintertime leads to a strong wintertime snow cover loss that is not found in observations. The wintertime warming bias and snow cover reduction trends are reduced in the uncoupled ensemble with observed SSTs. Natural climate variability generates widely different regional patterns of snow trends across realizations; these patterns are related in an intuitive way to temperature, precipitation and circulation trends in individual realizations. In particular, regional snow loss over North America in individual realizations is strongly influenced by North Pacific SST trends (manifested as Pacific Decadal Oscillation variability) and by sea level pressure trends in the North Pacific/North Atlantic sectors.     

北疆积雪深度和积雪日数的变化趋势

 选取新疆北疆20个站1961-2006年积雪及稳定积雪日数、最大积雪深度资料,同时选择冬季降水量和气温稳定通过0℃以下的日数作为积雪的影响因子,分析了46 a来北疆积雪的变化趋势。结果表明：46 a来最大积雪深度呈显著增加趋势,平均年增长0.8%,其变化与冬季降水量增加有关,呈正相关;积雪日数和稳定积雪日数也呈稍增加趋势,增加主要发生在1960-1980年代,1990年代以来有所减少,其变化与气温稳定通过0℃以下的日数呈显著正相关。     

Elevation gradients of European climate change in the regional climate model COSMO-CLM

A transient climate scenario experiment of the regional climate model COSMO-CLM is analyzed to assess the elevation dependency of 21st century European climate change. A focus is put on near-surface conditions. Model evaluation reveals that COSMO-CLM is able to approximately reproduce the observed altitudinal variation of 2 m temperature and precipitation in most regions and most seasons. The analysis of climate change signals suggests that 21st century climate change might considerably depend on elevation. Over most parts of Europe and in most seasons, near-surface warming significantly increases with elevation. This is consistent with the simulated changes of the free-tropospheric air temperature, but can only be fully explained by taking into account regional-scale processes involving the land surface. In winter and spring, the anomalous high-elevation warming is typically connected to a decrease in the number of snow days and the snow-albedo feedback. Further factors are changes in cloud cover and soil moisture and the proximity of low-elevation regions to the sea. The amplified warming at high elevations becomes apparent during the first half of the 21st century and results in a general decrease of near-surface lapse rates. It does not imply an early detection potential of large-scale temperature changes. For precipitation, only few consistent signals arise. In many regions precipitation changes show a pronounced elevation dependency but the details strongly depend on the season and the region under consideration. There is a tendency towards a larger relative decrease of summer precipitation at low elevations, but there are exceptions to this as well.     

Climatic changes in Estonia during the second half of the 20th century in relationship with changes in large-scale atmospheric circulation

Summary Trends in the time series of air temperature, precipitation, snow cover duration and onset of climatic seasons at ten stations in Estonia during 1951–2000 are analysed. Using the conditional Mann-Kendall test, these trends are compared with trends in the characteristics of large-scale atmospheric circulation: the NAO and AO indices, frequency of circulation forms according to the Vangengeim-Girs’ classification, and the northern hemisphere teleconnection indices. The objective of the study is to estimate the influence of trends in circulation on climate changes in Estonia. Statistically significant increasing trends in air temperature are detected in January, February, March, April and May, in winter (DJF), spring (MAM) and in the cold period (NDJFM). The trends in precipitation, as a rule, differ from station to station. Increasing trends are present during the cold half-year – from October until March – and also in June. Snow cover duration has decreased in Estonia by 17–20 days inland and by 21–36 days on the coast. The onsets of early spring and spring have shifted to an earlier date. Some important changes have occurred in the parameters of atmospheric circulation during 1951–2000. Intensity of zonal circulation, i.e. westerlies, has increased during the cold period, especially in February and March. Results of the conditional Mann-Kendall test indicate that the intensification of westerlies in winter is significantly related to climate changes in winter and also in spring. A negative trend in the East Atlantic Jet (EJ) index, i.e. the weakening of the westerlies in May has caused warming during that month. Decrease in northerly circulation, i.e. in frequency of circulation form C and in East Atlantic/West Russia teleconnection index (EW) is related to an increase in precipitation in October.     

1961-2014年青藏高原积雪时空特征及其影响因子

利用青藏高原(下称高原)1961-2014年地面110个气象站积雪深度、积雪日数、气温和降水逐日资料,系统地分析了高原积雪深度和积雪日数时空特征,并进一步探究了高原积雪深度和积雪日数与气候因子和地理因子之间的关系。研究发现:1961-2014年高原年平均积雪深度和积雪日数分别为0.26 cm和23.78 d,空间和季节尺度上分布不均匀,且积雪深度和积雪日数大值并不完全重合;在整体变化趋势上,积雪深度和积雪日数均呈缓慢下降趋势,分别为-0.0080±0.0086 cm·(10a)^-1(p=0.36)和-0.64±0.47 d·(10a)^-1(p=0.17),但在数理统计上不显著,且各站点差异性大;积雪深度和积雪日数在春季、冬季和年表现为“减-增-减”的年代际变化特征,而在秋季为“增-减”的变化特征;气温与积雪深度和积雪日数均有较好的相关性,冬季的降水与积雪深度和积雪日数高度相关;积雪深度和积雪日数随海拔呈增加趋势,积雪日数与纬度也高度相关,但积雪深度与纬度的相关性不明显。     

Response of the water balance in Greece to temperature and precipitation trends

This paper deals with the most recent trends in meteorological and hydrological variables, which include air temperature and precipitation (P), potential and actual (ET) evapotranspiration, surface runoff (RO), water recharge into the soil (R) and water loss from the soil (L). Most hydrological variables were calculated via Palmer's algorithm. For this purpose, two rank-based statistical tests (the Mann?CKendall (MK) and a change-point analysis (CPA) approach) and the basic linear regression-based model were applied on the weekly precipitation and temperature from 17 stations all over Greece, during 1961?C2006. Only in winter, all variables except for R, which showed no clear signal, presented downward trends. The declining trends of P and L in spring and summer were counterbalanced by reductions in RO (and R in the case of summer) as opposed to increases in ET. In autumn, the declining tendencies of P and L were offset by RO reductions and R increases. Annually, the trends in water cycle components were analogous to that of spring, summer and autumn. The number of stations with statistically significant (at 95%) trends greatly varied with season and meteorological/hydrological variable.