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Liu Y.,Institute of Desert Meteorology | Liu Y.,Xinjiang University | He Q.,Institute of Desert Meteorology | Zhang H.,Peking University | Mamtimin A.,Institute of Desert Meteorology
Advances in Atmospheric Sciences | Year: 2012

Improving and validating land surface models based on integrated observations in deserts is one of the challenges in land modeling. Particularly, key parameters and parameterization schemes in desert regions need to be evaluated in-situ to improve the models. In this study, we calibrated the land-surface key parameters and evaluated several formulations or schemes for thermal roughness length (z 0h) in the common land model (CoLM). Our parameter calibration and scheme evaluation were based on the observed data during a torrid summer (29 July to 11 September 2009) over the Taklimakan Desert hinterland. First, the importance of the key parameters in the experiment was evaluated based on their physics principles and the significance of these key parameters were further validated using sensitivity test. Second, difference schemes (or physics-based formulas) of z 0h were adopted to simulate the variations of energy-related variables (e. g., sensible heat flux and surface skin temperature) and the simulated variations were then compared with the observed data. Third, the z 0h scheme that performed best (i. e., Y07) was then selected to replace the defaulted one (i. e., Z98); the revised scheme and the superiority of Y07 over Z98 was further demonstrated by comparing the simulated results with the observed data. Admittedly, the revised model did a relatively poor job of simulating the diurnal variations of surface soil heat flux, and nighttime soil temperature was also underestimated, calling for further improvement of the model for desert regions. © 2012 Chinese National Committee for International Association of Meteorology and Atmospheric Sciences, Institute of Atmospheric Physics, Science Press and Springer-Verlag Berlin Heidelberg.

Zhang G.,Institute of Desert Meteorology | Sun S.,Urumqi Meteorological Bureau | Ma Y.,Institute of Desert Meteorology | Zhao L.,Institute of Desert Meteorology
Journal of Geographical Sciences | Year: 2010

According to climate features and river runoff conditions, Xinjiang could be divided into three research areas: The Altay-Tacheng region, the Tianshan Mountain region and the northern slope of the Kunlun Mountains. Utilizing daily observations from 12 sounding stations and the annual runoff dataset from 34 hydrographical stations in Xinjiang for the period 1960-2002, the variance of the summertime 0°C level height and the changing trends of river runoff are analyzed both qualitatively and quantitatively, through trend contrast of curves processed by a 5-point smoothing procedure and linear correlation. The variance of the summertime 0°C level height in Xinjiang correlates well with that of the annual river runoff, especially since the early 1990s, but it differs from region to region, with both the average height of the 0°C level and runoff quantity significantly increasing over time in the Altay-Tacheng and Tianshan Mountain regions but decreasing on the northern slope of the Kunlun Mountains. The correlation holds for the whole of Xinjiang as well as the three individual regions, with a 0. 01 significance level. This indicates that in recent years, climate change in Xinjiang has affected not only the surface layer but also the upper levels of the atmosphere, and this raising and lowering of the summertime 0°C level has a direct impact on the warming and wetting process in Xinjiang and the amount of river runoff. Warming due to climate change increases the height of the 0°C level, but also speeds up, ice-snow melting in mountain regions, which in turn increases river runoff, leading to a season of plentiful water instead of the more normal low flow period. © 2010 Science in China Press and Springer-Verlag Berlin Heidelberg.

Zhou Y.,Nanjing University | Jiang J.,Nanjing University | Huang A.,Nanjing University | La M.,Nanjing University | And 2 more authors.
Environmental Research Letters | Year: 2013

A regional climate model (RegCM4.1) is used to conduct two sets of sensitivity experiments. There are 20-year runs in each set of experiments. The experiments in each set include the variation of anthropogenic SO2 emissions during 1989-2008 but exclude natural variations of the atmosphere and sea surface temperature. The model results suggest that the high-speed emission of SO2 and its uneven distribution over eastern China can contribute to the change in May-August rainfall over eastern China between the two decades of 1999-2008 and 1989-1998, especially to the decrease (increase) of rainfall in the Yangtze River valley (Huang-Huai River region). Furthermore, the areas of decreasing (increasing) rainfall correspond to the downward (upward) currents of the anomalous atmospheric circulation, which is caused by the two humps of the difference in sulfate concentration between the two decades. © 2013 IOP Publishing Ltd.

Zhao Y.,Institute of Desert Meteorology | Zhang H.,Bureau of Meteorology
Climate Dynamics | Year: 2015

Based on the historical and RCP8.5 experiments from 25 Coupled Model Intercomparison Project phase 5 (CMIP5) models, the impacts of sea surface temperature (SST) warming in the tropical Indian Ocean (IO) on the projected change in summer rainfall over Central Asia (CA) are investigated. The analysis is designed to answer three questions: (1) Can CMIP5 models reproduce the observed influence of the IO sea surface temperatures (SSTs) on the CA rainfall variations and the associated dynamical processes? (2) How well do the models agree on their projected rainfall changes over CA under warmed climate? (3) How much of the uncertainty in such rainfall projections is due to different impacts of IO SSTs in these models? The historical experiments show that in most models summer rainfall over CA are positively correlated to the SSTs in the IO. Furthermore, for models with higher rainfall-SSTs correlations, the dynamical processes accountable for such impacts are much closer to what have been revealed in observational data: warmer SSTs tend to favor the development of anti-cyclonic circulation patterns at low troposphere over north and northwest of the Arabian Sea and the Bay of Bengal. These anomalous circulation patterns correspond to significantly enhanced southerly flow which carries warm and moisture air mass from the IO region up to the northeast. At the same time, there is a cyclonic flow over the central and eastern part of the CA which further brings the tropical moisture into the CA and provides essential moist conditions for its rainfall generation. In the second half of twenty-first century, although all the 25 models simulate warmed SSTs, significant uncertainty exists in their projected rainfall changes over CA: half of them suggest summer rainfall increases, but the other half project rainfall decreases. However, when we select seven models out of the 25 based on their skills in capturing the dynamical processes as observed, then the model projected changes are much closer. Five out of the seven models predicted more rainfall over CA. Such a result is helpful for allowing us to attribute part of the observed upward rainfall trend in the CA region in the last several decades to the IO SST warming. © 2015 The Author(s)

Chen F.,Institute of Desert Meteorology | Yuan Y.,Institute of Desert Meteorology | Wei W.,Institute of Desert Meteorology
Journal of Arid Environments | Year: 2011

Cores of thick leaf spruce from the western Qilian Mountains were subjected to densitometric analysis to obtain data for seven tree-ring parameters (tree-ring width, earlywood width, latewood width, maximum density, minimum density, mean earlywood density and mean latewood density). The chronologies were analyzed individually and then compared with each other. Most of these variables show moderately high values of common variance and mean interseries correlation except latewood and maximum densities. The relationships between the different tree-ring parameters and climate data are also presented. The growth/climate response analyses reveal that the radial growth of thick leaf spruce is the mainly controlled by total annual precipitation (July-June). Herein the residual ring width chronology was used to reconstruct annual (July-June) precipitation of Jiuquan for the period 1768-2009 A.D., and it accounted for 45.0% of the precipitation variance. Multi-taper spectral analysis reveals the existence of significant 11.1-year, 4.9-year, and 2.0- to 3.4-year periods of variability. Spatial analysis shows that the precipitation of Jiuquan has strong common signals for the northern margin of the Tibetan Plateau and Hexi Corridor. Drought events in our reconstruction are compared to the historical archives and other moisture-sensitive tree ring width series in the Hexi Corridor. The results reveal common climatic extremes over much of the Hexi Corridor. Many of these events have had profound impacts on the peoples of the Hexi Corridor over the past several centuries. © 2011 Elsevier Ltd.

Saumel I.,TU Berlin | Ziche D.,Johann Heinrich Von Thunen Institute | Yu R.,Institute of Desert Meteorology | Kowarik I.,TU Berlin | Overdieck D.,TU Berlin
Journal of Arid Environments | Year: 2011

The endangered river plain woodlands of semi-arid Central Asia provide numerous ecosystem services. Previous studies have focused mainly on changes in water supply and salinity as the underlying mechanisms of Populus euphratica woodland's decline. We tested whether vegetative regeneration of P. euphratica serves as an alternative pathway to propagation from seeds for reproduction in a degraded tree steppe in northwestern China and whether this method also works on grazed sites. We measured the effects of different grazing pressures on tree growth, survival, and vegetative regeneration. When subjected to high or moderate grazing pressure, P. euphratica populations failed to regenerate vegetatively, indicating recruitment limitation. A 25% increase of grazing pressure decreased the ramet density to 50% and the ramet height to 25%, as well as reducing the average age of ramets to one year. As overgrazing seriously limits the potential of natural recovery of P. euphratica a balance between livestock grazing and the regeneration of the Tugai forests is needed to sustain positive effects of increasing water tables and floods on tree vitality and regeneration. To restore population structure, and to support early vegetative regeneration long-term livestock management interventions to exclude livestock from degraded and recovered land need to be developed. © 2010 Elsevier Ltd.

Liu Y.,Institute of Desert Meteorology | Zhang P.,Institute of Desert Meteorology | Li Y.,Institute of Desert Meteorology
Hongwai Yu Haomibo Xuebao/Journal of Infrared and Millimeter Waves | Year: 2011

The purpose of the study was to approach the feasibility of the snow water equivalent retrieved with optical remote sensing data. Field measurement for separate layer snow density and other snow parameters was made in Feb 2009 and 2010. For different snow types, by using continuum removal method, spectral absorption characteristics of snow were analyzed. It comes to the conclusion that snow depth has a significant effect on its spectral absorption at near 1028 nm, 1252 nm, 1494 nm and 1940 nm. The deeper the depth, the smaller the absorption depth is. The image of moderate-resolution imaging spectroradiometer with spatial 500 m resolution was used as the experimental optical remote sensing data in this study. Based on correlation analysis of the test sample, including reflectance of MODIS channel 5 and 6, elevation and snow pressure, the remote sensing model for the retrieval of snow pressure was built by statistical regression equations. The evaluation results of the model showed that its root mean square error is 0.075 and correlation coefficient between predicted and measured values is 0.72 when snow depth is less than 30 cm.

Chen Y.,CAS Institute of Tibetan Plateau Research | Chen Y.,University of Chinese Academy of Sciences | Yang K.,CAS Institute of Tibetan Plateau Research | He J.,CAS Institute of Atmospheric Physics | And 4 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2011

The parameterization of thermal roughness length z0h plays a key role in land surface modeling. Previous studies have found that the daytime land surface temperature (LST) on dry land (arid and semiarid regions) is commonly underestimated by land surface models (LSMs). This paper presents two improvements of Noah land surface modeling for China's dry-land areas. The first improvement is the replacement of the model's z0h scheme with a new one. A previous study has validated the revised Noah model at several dry-land stations, and this study tests the revised model's performance on a regional scale. Both the original Noah and the revised one are driven by the Global Land Data Assimilation System (GLDAS) forcing data. The comparison between the simulations and the daytime Moderate Resolution Imaging Spectroradiometer- (MODIS-) Aqua LST products indicates that the original LSM produces a mean bias in the early afternoon (around 1330, local solar time) of about -6 K, and this revision reduces the mean bias by 3 K. Second, the mean bias in early afternoon is further reduced by more than 2 K when a newly developed forcing data set for China (Institute of Tibetan Plateau Research, Chinese Academy of Sciences (ITPCAS) forcing data) is used to drive the revised model. A similar reduction is also found when the original Noah model is driven by the new data set. Finally, the original Noah model, when driven by the new forcing data, performs satisfactorily in reproducing the LST for forest, shrubland and cropland. It may be sensible to select the z0h scheme according to the vegetation type present on the land surface for practical applications of the Noah LSM. Copyright 2011 by the American Geophysical Union.

Huang A.,Nanjing University | Zhou Y.,Nanjing University | Zhang Y.,Nanjing University | Huang D.,Nanjing University | And 2 more authors.
Journal of Climate | Year: 2014

Based on the outputs of historical and future representative concentration pathway (RCP) experiments produced by 28 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5), future changes in climatic mean, interannual standard deviation (ISD), and long-term trends of the annual precipitation over central Asia (CA) have been estimated. Under different emission scenarios during the twenty-first century, the climatic mean and ISD (long-term trends) of the annual precipitation over CA projected by the five best models' ensemble mean show very similar (quite different) spatial patterns to those in the twentieth century. Relatively stronger increasing rates (over 3mmdecade-1 in RCP2.6 and over 6mmdecade-1 in RCP4.5 and RCP8.5) are located over northern CA and the northeastern Tibetan Plateau. Compared to the situations in the twentieth century, the climatic mean, ISD, and long-term trends of the projected annual precipitation over most of CA under different emission scenarios exhibit robust increasing changes during the twenty-first century. The projected increasing changes in the climatic mean (ISD) of theCAannual mean range from 10% to 35% (10%-90%) under different emission scenarios with relatively large increases over Xinjiang, China (northern CA and Xinjiang). The increasing trends of the annual precipitation over most of CA are projected to intensify with relatively large increases (over 3-9mmdecade-1) located over northern CA, the Tian Shan Mountains, and northern Tibet during the twenty-first century. In addition, the intensities of the increasing changes in the climatic mean, ISD, and trends of CA annual precipitation are intensified with the emissions increased correspondingly. Further analyses of the possible mechanisms related to the projected changes in precipitation indicate that the increases of the annual precipitation over CA in the twenty-first century are mainly attributed to the enhanced precipitable water that results from strengthened water vapor transport and surface evaporation. © 2014 American Meteorological Society.

Li M.,Ocean University of China | Li M.,Institute of Desert Meteorology | Zhang S.,Ocean University of China
Journal of Ocean University of China | Year: 2013

A stratus-sea fog event that occurred over the Yellow and East China Seas on 3 June 2011 is investigated using observations and a numerical model, with a focus on the effects of background circulation and Sea Surface Temperature Front (SSTF) on the transition of stratus into sea fog. Southerly winds of a synoptic high-pressure circulation transport water vapor to the Yellow Sea, creating conditions favorable for sea fog/stratus formation. The subsidence from the high-pressure contributes to the temperature inversion at the top of the stratus. The SSTF forces a secondary circulation within the ABL (Atmospheric Boundary Layer), the sinking branch of which on the cold flank of SSTF helps lower the stratus layer further to reach the sea surface. The cooling effect over the cold sea surface counteracts the adiabatic warming induced by subsidence. The secondary circulation becomes weak and the fog patches are shrunk heavily with the smoothed SSTF. A conceptual model is proposed for the transition of stratus into sea fog over the Yellow and East China Seas. Finally, the analyses suggest that sea fog frequency will probably decrease due to the weakened SSTF and the reduced subsidence of secondary circulation under global warming. © 2013 Science Press, Ocean University of China and Springer-Verlag Berlin Heidelberg.

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