The Experts below are selected from a list of 5670 Experts worldwide ranked by ideXlab platform
Kaicun Wang - One of the best experts on this subject based on the ideXlab platform.
-
quantifying the sensitivity of precipitation to the long term warming trend and interannual Decadal Variation of surface air temperature over china
2017Co-Authors: Chunlue Zhou, Kaicun WangAbstract:AbstractPrecipitation is expected to increase under global warming. However, large discrepancies in precipitation sensitivities to global warming among observations and models have been reported, partly owing to the large natural variability of precipitation, which accounts for over 90% of its total variance in China. Here, the authors first elucidated precipitation sensitivities to the long-term warming trend and interannual–Decadal Variations of surface air temperature Ta over China based on daily data from approximately 2000 stations from 1961 to 2014. The results show that the number of dry, trace, and light precipitation days has stronger sensitivities to the warming trend than to the Ta interannual–Decadal Variation, with 14.1%, −35.7%, and −14.6% K−1 versus 2.7%, −7.9%, and −3.1% K−1, respectively. Total precipitation frequency has significant sensitivities to the warming trend (−18.5% K−1) and the Ta interannual–Decadal Variation (−3.6% K−1) over China. However, very heavy precipitation frequencie...
-
evidence for Decadal Variation in global terrestrial evapotranspiration between 1982 and 2002 2 results
2010Co-Authors: Kaicun Wang, Robert E Dickinson, Martin Wild, Shunlin LiangAbstract:[1] Terrestrial evapotranspiration (ET) cools the surface and moistens the atmosphere near the Earth's surface. Variations in this important climate factor have major environmental and socioeconomic impacts. How terrestrial ET has varied in the past and what caused the Variations, however, have remained quite uncertain. These issues are addressed by calculating monthly global ET from 1982 to 2002 at 1120 globally distributed stations, using a modified Penman-Monteith method that was developed in the first part of the two-part paper. Our analyses show that ET has a significant Decadal Variation (∼10%) regionally and globally. Over the period analyzed ET for global land increased by 0.6 W m−2 per decade equal to 1.2 W m−2 (about 2.2% in relative value) or 15 mm yr−1 in water flux during the study period. We show that long-term Variations of ET in humid areas such as the tropics, Europe, and humid areas of Asia are primarily controlled by Variations in incident solar radiation Rs connected to changes in cloudiness and aerosols. However, soil water supply, estimated here by RH, and connected to precipitation, is the dominant factor in controlling long-term Variations of ET in arid areas. A correlation analysis demonstrates that the dependence of ET on Rs switches to negative in dry regions. Furthermore, its dependence on relative humidity switches from negative in moist regions to positive in dry regions. Its dependence on normalized difference vegetation index is uniformly positive.
-
evidence for Decadal Variation in global terrestrial evapotranspiration between 1982 and 2002 1 model development
2010Co-Authors: Kaicun Wang, Robert E Dickinson, Martin Wild, Shunlin LiangAbstract:[1] Estimating interannual to Decadal variability of terrestrial evapotranspiration (ET) requires use of standard meteorological data complemented with some high-resolution satellite data. A semiempirical expression for this purpose is developed and validated with data from 2000 to 2007. These data were collected at 64 globally distributed sites, including the continuous measurements collected by the Atmospheric Radiation Measurement (ARM) and FLUXNET projects, and are the longest available, with continuous worldwide multisite measurements of ET, and a total of 274 site years. The sites are mainly located in North America and Asia, with the exception of three sites in Australia, two in Europe, and one in Africa. The climates of the sites vary from tropical to subarctic and from arid to humid. The land cover types of the sites vary from desert, croplands, grasslands, and shrub land to forests. On average, the 16 day average daily ET can be estimated with an error (standard deviation) of 17 W m−2 (25% in relative value), and with an average correlation coefficient of 0.94. The standard deviation of the comparison between measured and predicted site-averaged daily ET is 9 W m−2 (14%), with a correlation coefficient of 0.93. The model is also satisfactory in reproducing the interannual variability at sites with 5 years of data in both humid and arid regions. The correlation coefficient between measured and predicted annual ET anomalies is 0.85. This simple but accurate method permits us to investigate Decadal Variation in global ET over the land as will be demonstrated in part two of this paper series.
-
global atmospheric downward longwave radiation over land surface under all sky conditions from 1973 to 2008
2009Co-Authors: Kaicun Wang, Shunlin LiangAbstract:[1] In this article, we first evaluate two widely accepted methods to estimate global atmospheric downward longwave radiation (Ld) under both clear and cloudy conditions, using meteorological observations from 1996 to 2007 at 36 globally distributed sites, operated by the Surface Radiation Budget Network (SURFRAD), AmeriFlux, and AsiaFlux Projects. The breakdown of locations is North America (20 sites), Asia (12 sites), Australia (2 sites), Africa (1 site), and Europe (1 site). Latitudes for these sites range from 0° at the equator to ±50°; elevation ranges from 98 to 4700 m, and six different land cover types are represented (deserts, semideserts, croplands, grasslands, forests, and wetlands). The evaluation shows that the instantaneous Ld under all-sky conditions is estimated with an average bias of 2 W m−2 (0.6%), an average standard deviation (SD) of 20 W m−2 (6%), and an average correlation coefficient (R) of 0.86. Daily Ld under all-sky conditions is estimated with a SD of 12 W m−2 (3.7%) and an average R of 0.93. These results suggest that these two methods could be applied to most of the Earth's land surfaces. Accordingly, we applied them to globally available meteorological observations to estimate Decadal Variation in Ld. The Decadal Variations in global Ld under both clear and cloudy conditions at about 3200 stations from 1973 to 2008 are presented. We found that daily Ld increased at an average rate of 2.2 W m−2 per decade from 1973 to 2008. The rising trend results from increases in air temperature, atmospheric water vapor, and CO2 concentration.
Alan H Taylor - One of the best experts on this subject based on the ideXlab platform.
-
fire history and the structure and dynamics of a mixed conifer forest landscape in the northern sierra nevada lake tahoe basin california usa
2008Co-Authors: Matthew R Beaty, Alan H TaylorAbstract:Abstract The goal of this study was to understand how fire regimes promote fine- and coarse-grain vegetation patterns in an old-growth mixed conifer forest dominated landscape in the General Creek watershed on the west shore of Lake Tahoe, California. We quantified the structure (e.g., composition, age, and size) of old-growth mixed conifer stands located across a range of environmental settings. Fire histories were reconstructed using fire-scar dendrochronology, and the influence of regional climatic variability on fire occurrence was assessed by relating the fire record to regional climate reconstructions. Fire regimes parameters varied across topographic gradients at landscape scales promoting fine grain forest structural patterns. The timing and extent of fires was related to inter-annual and inter-Decadal Variation in drought which was linked to the El Nino-Southern Oscillation and the Pacific Decadal Oscillation. Coarse scale vegetation patterns where related to upper slope positions and relatively infrequent high severity fires. Fire regimes and forest structure have changed since EuroAmerican settlement with virtually no fires and structural shifts towards higher stand densities and a greater representation of fire intolerant species. At the landscape scale, fire regimes and forests patterns in mixed conifer forests are influenced by a variety of process operating at multiple spatial and temporal scales. Coarse scale heterogeneity related to topography and moderate to high severity fire is superimposed on fine scale variability related to topographic gradients and local variability in fuel and forest structural characteristics. Fire suppression has resulted in a more homogenous landscape particularly with regard to the loss of coarse scale heterogeneity.
-
fire history and the structure and dynamics of a mixed conifer forest landscape in the northern sierra nevada lake tahoe basin california usa
2008Co-Authors: Matthew R Beaty, Alan H TaylorAbstract:Abstract The goal of this study was to understand how fire regimes promote fine- and coarse-grain vegetation patterns in an old-growth mixed conifer forest dominated landscape in the General Creek watershed on the west shore of Lake Tahoe, California. We quantified the structure (e.g., composition, age, and size) of old-growth mixed conifer stands located across a range of environmental settings. Fire histories were reconstructed using fire-scar dendrochronology, and the influence of regional climatic variability on fire occurrence was assessed by relating the fire record to regional climate reconstructions. Fire regimes parameters varied across topographic gradients at landscape scales promoting fine grain forest structural patterns. The timing and extent of fires was related to inter-annual and inter-Decadal Variation in drought which was linked to the El Nino-Southern Oscillation and the Pacific Decadal Oscillation. Coarse scale vegetation patterns where related to upper slope positions and relatively infrequent high severity fires. Fire regimes and forest structure have changed since EuroAmerican settlement with virtually no fires and structural shifts towards higher stand densities and a greater representation of fire intolerant species. At the landscape scale, fire regimes and forests patterns in mixed conifer forests are influenced by a variety of process operating at multiple spatial and temporal scales. Coarse scale heterogeneity related to topography and moderate to high severity fire is superimposed on fine scale variability related to topographic gradients and local variability in fuel and forest structural characteristics. Fire suppression has resulted in a more homogenous landscape particularly with regard to the loss of coarse scale heterogeneity.
Matthew R Beaty - One of the best experts on this subject based on the ideXlab platform.
-
fire history and the structure and dynamics of a mixed conifer forest landscape in the northern sierra nevada lake tahoe basin california usa
2008Co-Authors: Matthew R Beaty, Alan H TaylorAbstract:Abstract The goal of this study was to understand how fire regimes promote fine- and coarse-grain vegetation patterns in an old-growth mixed conifer forest dominated landscape in the General Creek watershed on the west shore of Lake Tahoe, California. We quantified the structure (e.g., composition, age, and size) of old-growth mixed conifer stands located across a range of environmental settings. Fire histories were reconstructed using fire-scar dendrochronology, and the influence of regional climatic variability on fire occurrence was assessed by relating the fire record to regional climate reconstructions. Fire regimes parameters varied across topographic gradients at landscape scales promoting fine grain forest structural patterns. The timing and extent of fires was related to inter-annual and inter-Decadal Variation in drought which was linked to the El Nino-Southern Oscillation and the Pacific Decadal Oscillation. Coarse scale vegetation patterns where related to upper slope positions and relatively infrequent high severity fires. Fire regimes and forest structure have changed since EuroAmerican settlement with virtually no fires and structural shifts towards higher stand densities and a greater representation of fire intolerant species. At the landscape scale, fire regimes and forests patterns in mixed conifer forests are influenced by a variety of process operating at multiple spatial and temporal scales. Coarse scale heterogeneity related to topography and moderate to high severity fire is superimposed on fine scale variability related to topographic gradients and local variability in fuel and forest structural characteristics. Fire suppression has resulted in a more homogenous landscape particularly with regard to the loss of coarse scale heterogeneity.
-
fire history and the structure and dynamics of a mixed conifer forest landscape in the northern sierra nevada lake tahoe basin california usa
2008Co-Authors: Matthew R Beaty, Alan H TaylorAbstract:Abstract The goal of this study was to understand how fire regimes promote fine- and coarse-grain vegetation patterns in an old-growth mixed conifer forest dominated landscape in the General Creek watershed on the west shore of Lake Tahoe, California. We quantified the structure (e.g., composition, age, and size) of old-growth mixed conifer stands located across a range of environmental settings. Fire histories were reconstructed using fire-scar dendrochronology, and the influence of regional climatic variability on fire occurrence was assessed by relating the fire record to regional climate reconstructions. Fire regimes parameters varied across topographic gradients at landscape scales promoting fine grain forest structural patterns. The timing and extent of fires was related to inter-annual and inter-Decadal Variation in drought which was linked to the El Nino-Southern Oscillation and the Pacific Decadal Oscillation. Coarse scale vegetation patterns where related to upper slope positions and relatively infrequent high severity fires. Fire regimes and forest structure have changed since EuroAmerican settlement with virtually no fires and structural shifts towards higher stand densities and a greater representation of fire intolerant species. At the landscape scale, fire regimes and forests patterns in mixed conifer forests are influenced by a variety of process operating at multiple spatial and temporal scales. Coarse scale heterogeneity related to topography and moderate to high severity fire is superimposed on fine scale variability related to topographic gradients and local variability in fuel and forest structural characteristics. Fire suppression has resulted in a more homogenous landscape particularly with regard to the loss of coarse scale heterogeneity.
Shunlin Liang - One of the best experts on this subject based on the ideXlab platform.
-
evidence for Decadal Variation in global terrestrial evapotranspiration between 1982 and 2002 2 results
2010Co-Authors: Kaicun Wang, Robert E Dickinson, Martin Wild, Shunlin LiangAbstract:[1] Terrestrial evapotranspiration (ET) cools the surface and moistens the atmosphere near the Earth's surface. Variations in this important climate factor have major environmental and socioeconomic impacts. How terrestrial ET has varied in the past and what caused the Variations, however, have remained quite uncertain. These issues are addressed by calculating monthly global ET from 1982 to 2002 at 1120 globally distributed stations, using a modified Penman-Monteith method that was developed in the first part of the two-part paper. Our analyses show that ET has a significant Decadal Variation (∼10%) regionally and globally. Over the period analyzed ET for global land increased by 0.6 W m−2 per decade equal to 1.2 W m−2 (about 2.2% in relative value) or 15 mm yr−1 in water flux during the study period. We show that long-term Variations of ET in humid areas such as the tropics, Europe, and humid areas of Asia are primarily controlled by Variations in incident solar radiation Rs connected to changes in cloudiness and aerosols. However, soil water supply, estimated here by RH, and connected to precipitation, is the dominant factor in controlling long-term Variations of ET in arid areas. A correlation analysis demonstrates that the dependence of ET on Rs switches to negative in dry regions. Furthermore, its dependence on relative humidity switches from negative in moist regions to positive in dry regions. Its dependence on normalized difference vegetation index is uniformly positive.
-
evidence for Decadal Variation in global terrestrial evapotranspiration between 1982 and 2002 1 model development
2010Co-Authors: Kaicun Wang, Robert E Dickinson, Martin Wild, Shunlin LiangAbstract:[1] Estimating interannual to Decadal variability of terrestrial evapotranspiration (ET) requires use of standard meteorological data complemented with some high-resolution satellite data. A semiempirical expression for this purpose is developed and validated with data from 2000 to 2007. These data were collected at 64 globally distributed sites, including the continuous measurements collected by the Atmospheric Radiation Measurement (ARM) and FLUXNET projects, and are the longest available, with continuous worldwide multisite measurements of ET, and a total of 274 site years. The sites are mainly located in North America and Asia, with the exception of three sites in Australia, two in Europe, and one in Africa. The climates of the sites vary from tropical to subarctic and from arid to humid. The land cover types of the sites vary from desert, croplands, grasslands, and shrub land to forests. On average, the 16 day average daily ET can be estimated with an error (standard deviation) of 17 W m−2 (25% in relative value), and with an average correlation coefficient of 0.94. The standard deviation of the comparison between measured and predicted site-averaged daily ET is 9 W m−2 (14%), with a correlation coefficient of 0.93. The model is also satisfactory in reproducing the interannual variability at sites with 5 years of data in both humid and arid regions. The correlation coefficient between measured and predicted annual ET anomalies is 0.85. This simple but accurate method permits us to investigate Decadal Variation in global ET over the land as will be demonstrated in part two of this paper series.
-
global atmospheric downward longwave radiation over land surface under all sky conditions from 1973 to 2008
2009Co-Authors: Kaicun Wang, Shunlin LiangAbstract:[1] In this article, we first evaluate two widely accepted methods to estimate global atmospheric downward longwave radiation (Ld) under both clear and cloudy conditions, using meteorological observations from 1996 to 2007 at 36 globally distributed sites, operated by the Surface Radiation Budget Network (SURFRAD), AmeriFlux, and AsiaFlux Projects. The breakdown of locations is North America (20 sites), Asia (12 sites), Australia (2 sites), Africa (1 site), and Europe (1 site). Latitudes for these sites range from 0° at the equator to ±50°; elevation ranges from 98 to 4700 m, and six different land cover types are represented (deserts, semideserts, croplands, grasslands, forests, and wetlands). The evaluation shows that the instantaneous Ld under all-sky conditions is estimated with an average bias of 2 W m−2 (0.6%), an average standard deviation (SD) of 20 W m−2 (6%), and an average correlation coefficient (R) of 0.86. Daily Ld under all-sky conditions is estimated with a SD of 12 W m−2 (3.7%) and an average R of 0.93. These results suggest that these two methods could be applied to most of the Earth's land surfaces. Accordingly, we applied them to globally available meteorological observations to estimate Decadal Variation in Ld. The Decadal Variations in global Ld under both clear and cloudy conditions at about 3200 stations from 1973 to 2008 are presented. We found that daily Ld increased at an average rate of 2.2 W m−2 per decade from 1973 to 2008. The rising trend results from increases in air temperature, atmospheric water vapor, and CO2 concentration.
Ying Sun - One of the best experts on this subject based on the ideXlab platform.
-
inter Decadal Variation of the summer precipitation in china and its association with decreasing asian summer monsoon part ii possible causes
2009Co-Authors: Yihui Ding, Ying Sun, Zunya Wang, Yuxiang Zhu, Yafang SongAbstract:The present article is the second part of a study on the inter-Decadal variability of the summer precipitation in East China, which mainly addresses the possible cause of this change. Firstly, an updated analysis of the long-term Variations of snow cover, snow days and snow depth in the preceding winter and spring over the Tibetan Plateau (TP) was done by using station and satellite data. The abrupt increase in the winter and spring snow over the TP since around 1977 has been well documented. At that time, the inter-Decadal Variation of the atmospheric heating over the TP in spring and summer had been estimated. It has been revealed that the atmospheric heating fields in subsequent spring and summer over the TP assumed a significant weakening after the late 1970s. This weakening is closely related to the significantly reduced surface sensible heat flux into the atmosphere and subsequent cooling over the TP and its surrounding atmosphere. The latter was produced by the increase of surface albedo and soil hydrological effect of melting snow under the condition of abrupt increase in the preceding winter and spring snow over the TP. On the other hand, three phases of significant inter-Decadal warming of the sea surface temperature (SST) in the tropical central and eastern Pacific, which occurred in the mid-1960s, the late 1970s and the early 1990s, respectively, have been found. The above inter-Decadal variability of heating fields over the land area in the Asian region and neighbouring oceanic region of the West Pacific has consistently reduced the land–sea thermal contrast in summer in the Asian monsoon region based on the estimate of atmospheric heating fields. This cause is likely to lead to weakening of the Asian summer monsoon. In such case, the northward moisture transport in East Asia is greatly weakened and cannot reach North China, thus causing the condition of less precipitation or droughts. In contrast, the Yangtze River basin and South China receive a large amount of moisture supply and have strong upward motion, creating favourable conditions for frequent occurrence of heavy rainfall. In the process of the southward shift of the high-precipitation zone, two abrupt or rapid regime shifts observed in the late 1970s and the early 1990s were possibly in response to the increase in the winter and spring snow over the TP, and two major rapid warming events of the SST in the tropical central and eastern Pacific in the late 1970s and the early 1990s. Correlative analysis has further confirmed that high TP snow and oceanic forcing factors have a positive correlation with the subsequent summer precipitation in the Yangtze River basin and most of South China, and a negative correlation with the summer precipitation in North China. This correlative relationship implies that if the TP has excessive (deficient) snow in the preceding winter and spring and the tropical central and eastern Pacific anomalously warms up (cools down), North China will have decreasing (increasing) summer precipitation, whereas the Yangtze River basin and South China will have increasing (decreasing) summer precipitation. Copyright © 2009 Royal Meteorological Society
-
inter Decadal Variation of the summer precipitation in east china and its association with decreasing asian summer monsoon part i observed evidences
2008Co-Authors: Yihui Ding, Zunya Wang, Ying SunAbstract:In recent two decades, North and Northeast China have suffered from severe and persistent droughts while the Yangtze River basin and South China have undergone much more significant heavy rainfall/floods events. This long-term change in the summer precipitation and associated large-scale monsoon circulation features have been examined by using the new dataset of 740 surface stations for recent 54 years (1951–2004) and about 123-yr (1880–2002) records of precipitation in East China. The following new findings have been highlighted: (1) One dominating mode of the inter-Decadal variability of the summer precipitation in China is the near-80-yr oscillation. Other modes of 12-yr and 30–40-yr oscillations also play an important role in affecting regional inter-Decadal variability. (2) In recent 54 years, the spatial pattern of the inter-Decadal variability of summer precipitation in China is mainly structured with two meridional modes: the dipole pattern and the positive-negative-positive (“+ − + ” pattern). In this period, a regime transition of meridional precipitation mode from “+ − + ” pattern to dipole pattern has been completed. In the process of southward movement of much precipitation zone, two abrupt climate changing points that occurred in 1978 and 1992, respectively, were identified. (3) Accompanying the afore-described precipitation changes, the East Asian summer monsoon have experienced significant weakening, with northward moisture transport and convergence by the East Asian summer monsoon greatly weakened, thus leading to much deficient moisture supply for precipitation in North China. (4) The significant weakening of the component of the tropical upper-level easterly jet (TEJ) has made a dominating contribution to the weakening of the Asian summer monsoon system. The cooling in the high troposphere at mid- and high latitudes and the possible warming at low latitude in the Asian region is likely to be responsible for the inter-Decadal weakening of the TEJ. Copyright © 2007 Royal Meteorological Society
