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Accelerating glacier shrinkage is one of the most consequential of global warming. Yet, projections for the region remain ambiguous because of the tremendous spatial heterogeneity, especially in the Qilian Mountains, where glacier melt runoff is a vital water resource for the arid downstream area. To better understand glacier changes in this region, this study took regional representative Qiyi Glacier as an example and applied an enhanced distributed surface mass balance (SMB) model to glimpse the SMB variation and possible impacts on melt runoff under the RCP 4.5 and RCP 8.5 scenarios. Further, we combined a modified volume-scaling method to update the glacier geometry gradually to enhance long-term reliability. When forced with observed daily temperature and precipitation, the reconstructed glacier SMB, from 1957 through 2013, agrees well with the in situ observations. The result indicates an abrupt change for SMB from positive to negative in 1992 and subsequent mass accelerated loss after 2000. The increased summer air temperature and the pattern of large-scale atmospheric circulation shifts might both cause these changes. Using projected climate forcing from as many as 31 coupled GCMs from the CMIP 5 ensemble, the Qiyi Glacier is projected to undergo sustained SMB loss throughout the 21st century for both RCPs. By 2100, the Qiyi Glacier will lose ~25 m water equivalent (w.e.) for RCP 4.5 and ~37 m w.e. for RCP 8.5. Whereas the glacier area will shrink by 43% for RCP 4.5 and 54% for RCP 8.5 relative to 2013 glacier content, corresponding to the volume of the Qiyi Glacier will lose by 54% for RCP 4.5 and by 65% for RCP 8.5, accordingly. Simultaneously, the glacier terminus will experience extreme melts. The terminus elevation of the Qiyi Glacier will retreat from 4310 m a.s.l. in 2013 to 4810 m a.s.l. (RCP 4.5) and 4838 m a.s.l. (RCP 8.5) by the end of 2100, which will exceed the multi-year average ELA (4749 m) from 1957 to 2013. If the warming trends keep and glaciers melt like the Qiyi Glacier with this 'shocking' rate, it will raise the possibility of crippling, long-term water shortages for Hexi corridors. [ABSTRACT FROM AUTHOR]

The interdecadal changes in the dominant mode of the summer precipitation over the central‐eastern Tibetan Plateau (TP) are investigated around the mid‐1990s. It is found that the leading empirical orthogonal function mode of the interannual variations of summer precipitation over the central‐eastern TP is shown an out‐of‐phase pattern, with opposite variation between the southeastern and northeastern TP during 1961–1996, while the dominant mode become an in‐phase pattern during 1997–2019. During 1961–1996, the dipole pattern of TP precipitation is mainly related to the North Atlantic Oscillation (NAO) and associated circulation anomalies. However, the impact of NAO on the dipole pattern of TP precipitation has weakened since the mid‐1990s. In contrast, during 1997–2019, more pronounced positive height anomalies in the upper troposphere are observed over the whole TP regions. Meanwhile, the southerly moisture flux from the Bay of Bengal and the Philippine Sea is prevalent significantly with strong moisture convergence. Further analysis demonstrates that this interdecadal spatial change is mainly linked to the significant increasing of the sea surface temperature in the North Atlantic, South Atlantic, and Indo‐Pacific warm pool, via wave trains propagation. The wave train‐related positive height anomalies over the TP regions are in favor of the strengthening of the South Asian high (SAH). Moreover, the zonal and meridional mean temperature advections by SAH‐related circulation anomalies are primarily responsible for the intense vertical flow anomalies. Consequently, the summer precipitation anomalies over the entire TP regions are largely enhanced and formed the mono‐sign pattern during 1997–2019. Key Points: The dominant mode of precipitation in central‐eastern Tibetan Plateau (TP) changes from a dipole pattern to mono‐sign pattern in mid‐1990sThe change in the TP precipitation pattern is linked to the increasing of sea surface temperature anomalies in the Atlantic Ocean and Indo‐Pacific warm poolThe circulation anomalies related to the strengthening of South Asian high mainly contribute to the mono‐sign pattern of TP precipitation [ABSTRACT FROM AUTHOR]

Glacier mass balance change is among the best indicators of glacier response to climate change. Due to its inaccessibility and limited observation, little is known about the change to the Dongkemadi Ice Field (DIF) in the Tanggula Mountains located in the source region of the Yangtze River in central Tibetan Plateau. Here, an enhanced temperature index--based glacier model considering glacier area change was applied to study the temporal--spatial variation in mass balance on the DIF from 1989 to 2012 and to assess its response to climate change. The model was forced by reconstructed temperature and precipitation from adjacent national meteorological stations and validated by comparing with field observations from the Xiao Dongkemadi Glacier (XDG). Results show that the simulated mass balance is in good agreement with the observations (R² = 0.75, p < .001), and the model can reasonably reproduce well the glacier mass change. Then the model was applied to twenty individual glaciers in DIF and forced by the highresolution regional climate model (RegCM3) from 2013 to 2050 to project their further variation. In the future, the mass balance of glaciers in DIF shows a continuously negative trend with a linear rate of -0.16 m water equivalent (w.e.) a-1 in representative concentration pathway (RCP) 4.5 and -0.35 m w.e. a-1 in RCP 8.5. Most of the glaciers' equilibrium line altitudes (ELAs) will reach or exceed their maximum elevation after the 2030s. By coupling a modified volume--area scaling method with the mass balance model, results showed that areas of the individual glaciers in DIF will lose about 12.10 to 30.66 percent under RCP4.5 and 14.06 to 38.76 percent under RCP8.5, and the volume of the DIF will lose about 1.18 km³ in RCP4.5 and 1.44 km3 in RCP8.5 by the end of 2050. In addition, the terminuses of glaciers experienced the largest percentage losses and most of the glaciers' front position will reach ~5,520 m a.s.l. in RCP 4.5 and 5,570 m a.s.l. in RCP 8.5, the latter of which is nearly close to the DIF average ELA in 1989. The clearly increasing summer air temperature may be the main reason for glacier shrinkage in the DIF. If the warming trend continues, glaciers in DIF may further retreat with continued glacial melt or even mostly disappear by the end of the century. [ABSTRACT FROM AUTHOR]

The variation of freezing level height (FLH) is significantly indicated the cryosphere change under global warming. In this study, the FLH during boreal summer in the TP regions is investigated, with the leading mode of a mono-sign pattern both on interannual and interdecadal timescales. The interannual variation of the summer FLH is dominantly coupled with the summer Arctic Oscillation (AO). When the AO is in positive phase, positive geopotential height anomalies are prolonged in the mid-latitude and negative anomalies are present over the Arctic regions. Meanwhile, the westerly shifts northward and strengthened, preventing the cold air propagating southward. These conditions are beneficial for the surface and free-air temperature increasing and thus enhance the FLH over the TP. On the interdecadal timescale, the Pacific Decadal Oscillation (PDO) has mainly contributed to the variation of summer FLH. In the negative PDO phase, the warming sea surface temperature anomalies appear in the North Pacific, which could drive wave trains propagating eastward and induce high pressure around the northern TP. With the anomalous anticyclone from TP to western North Pacific, the southeasterly wind is prevalent in the TP. Consequently, the northern TP becomes warming remarkably and leads to the rising of FLH. This study provides an insight perspective for understanding the changes of FLH over the TP, which also suggests the influence on the cryosphere processes at multi-timescale variations. • The summer freezing level height (FLH) in the Tibetan Plateau (TP) shows interannual and interdecadal variations. • The interannual variation is dominantly coupled with the summer Arctic Oscillation. • The Pacific Decadal Oscillation has mainly contributed to the interdecadal component variation. • The results indicate the cryosphere processes changes in the TP at multi-timescales. [ABSTRACT FROM AUTHOR]

In recent years, rapid global warming has led to a dramatic cryosphere retreat and caused environmental disasters on the Tibetan Plateau (TP). To better understand the near-surface air temperature variation on the TP in response to global warming in the 21st century, we systematically detected temperature changes on the TP relative to global warming regarding warming time, warming amplitude, and elevation-dependent warming (EDW) using the multi-model ensemble (MME) means of 24 CMIP6 models. The results showed that the warming rate on the TP is 1.3–1.45 times more than that of mean global warming from 2015 to 2100, with the TP having already warmed by 1.5 °C above the pre-industrial levels in 2016/2015 and will warm by 2 °C by 2028/2027 under the Shared Socioeconomic Pathway (SSP) scenarios, SSP2–4.5 and SSP5–8.5. In addition, the warming amplitude on the TP in response to global warming levels of 1.5 and 2 °C would be 1.97 and 2.69 °C under the SSP2–4.5 scenario and 1.94 and 2.68 °C under the SSP5–8.5 scenario. Furthermore, EDW amplifies the warming amplitude at high elevations, mainly because of the decrease in surface albedo. The most sensitive warming amplitude in the cryosphere region, with an elevation of 5–5.5 km, would exceed 2.06, 2.79, 4.29, and 5.73 °C when global warming reaches 1.5, 2, 3, and 4 °C under the SSP5–8.5 scenario. This additional 0.56–1.73 °C warming in the high elevation relative to the global mean will intensify the cryosphere ablation on the TP. Thus, considering the projected larger warming trend and amplitude, the high-elevation region on the TP would be particularly sensitive and vulnerable, which is unfavorable for the TP from the perspective of the Paris Agreement warming target. • Temperature changes on the Tibetan Plateau (TP) are sensitive to global warming. • The warming rate of the TP is 1.3–1.45 times greater than the global mean during 2015–2100. • The TP has warmed by 1.5 °C in 2016 and will warm by 2 °C in 2028 under the SSP2–4.5. • The EDW phenomenon will continue to amplify the warming amplitude at high elevations. • As global warming reaches 2.0 °C, the mean warming over TP could be 2.7 °C, which would cause disastrous effects on the cryosphere. [ABSTRACT FROM AUTHOR]

A regional climate model, WRF-Chem, was used to investigate the feedback between aerosols and meteorological conditions in the planetary boundary layer (PBL) over the Tibetan Plateau (TP) and Indo-Gangetic Plain (IGP). The numerical experiments (15-km horizontal resolution) with and without the aerosol effects are driven by reanalysis of data for 1-31 March 2009, when a heavy pollution event (13-19 March) occurred. The results showed that the model captured the spatial and temporal meteorological conditions and aerosol optical characteristics during the heavy pollution days. Aerosols induced cooling at the surface and warming in the middle troposphere due to their radiative effects, and resulted in a more stable PBL over the IGP. Aerosol-induced 2-m relative humidity (RH) was increased. The stable PBL likely led to the surface PM concentration increase of up to 21 μg m (15 %) over the IGP. For the TP, the atmospheric profile did not drastically change due to fewer radiative effects of aerosols in the PBL compared with those over the IGP. The aerosol-induced RH decreased due to cloud albedo and cloud lifetime effect, and led to a reduction in surface PM concentration of up to 17 μg m (13 %). These results suggest a negative and positive feedback over the TP and IGP, respectively, between aerosol concentrations and changes of aerosol-induced meteorological conditions. Similar positive feedbacks have been observed in other heavily polluted regions (e.g., the North China Plain). The results have implications for the study of air pollution on weather and environment over the TP and IGP. [ABSTRACT FROM AUTHOR]

To improve the simulation performance of mesoscale models in the northeastern Tibetan Plateau, two reanalysis initial datasets (NCEP FNL and ERA-Interim) and two MODIS (Moderate-Resolution Imaging Spectroradiometer) land-use datasets (from 2001 and 2010) are used in WRF (Weather Research and Forecasting) modeling. The model can reproduce the variations of 2 m temperature (T2) and 2 m relative humidity (RH2), but T2 is overestimated and RH2 is underestimated in the control experiment. After using the new initial drive and land use data, the simulation precision in T2 is improved by the correction of overestimated net energy flux at surface and the RH2 is improved due to the lower T2 and larger soil moisture. Due to systematic bias in WRF modeling for wind speed, we design another experiment that includes the Jimenez subgrid-scale orography scheme, which reduces the frequency of low wind speed and increases the frequency of high wind speed and that is more consistent with the observation. Meanwhile, the new drive and land-use data lead to lower boundary layer height and influence the potential temperature and wind speed in both the lower atmosphere and the upper layer, while the impact on water vapor mixing ratio is primarily concentrated in the lower atmosphere. [ABSTRACT FROM AUTHOR]

An analysis of the spatiotemporal variability in summer precipitation during the period 1961-2010 is presented based on monthly precipitation datasets from 66 meteorological stations in the central and eastern Tibetan Plateau (TP). By applying empirical orthogonal function (EOF) analysis, a strong reversal is found in the variability of summer precipitation between the northeastern and the southeastern TP on the inter-annual timescale; this reversal is defined as theDipole Oscillation in summer precipitation over the TP. Our analysis shows that the North Atlantic Oscillation (NAO) greatly controls the Dipole Oscillation in TP summer precipitation by modifying the atmospheric circulation over and around the TP. With the increased stationary wave activity spreading eastward from theNorthAtlantic to the TP, a pronouncedwave train pattern bridges the NorthAtlantic Ocean and the TP. During the positive phase of the NAO, warm moist air from the oceans around Asia is transported by the southeastern flank of the anticyclonic anomaly over East Asia to the northeastern TP. This northward-moving warm moist air encounters cold air masses transported by the northwestern flank of the cyclonic anomaly over the northeastern TP. The confluence of the cold and warm air masses subsequently strengthens cumulus convective activities and ultimately results in excessive precipitation over the northeastern TP. Meanwhile, as a cyclonic anomaly sets up over northwestern India and Pakistan, water vapour condenses into precipitation over northwestern India and Pakistan, inhibiting Arabian Sea moisture inflows into the southeastern TP and northeastern India. As a result, a precipitation deficit occurs over the southeastern TP. The opposite scenario occurs during the negative phase of the NAO. [ABSTRACT FROM AUTHOR]

Precipitation changes over the Tibetan Plateau (TP) substantially impact the downstream river runoff. However, future precipitation variation over the TP remains unclear. Here, we evaluated the historical (1961–2014) precipitation of 25 CMIP6 models based on the observations. The multi-model ensemble mean of the five best models (BMME) was in stronger agreement with observations than the single model. Then, seasonal precipitation changes in 2015–2099 were projected using the BMME under four Shared Socioeconomic Pathway (SSP) scenarios. The results showed that seasonal precipitation would increase over the TP in the 21st century, with a higher rate of precipitation increase under the higher emission scenarios. Precipitation is projected to increase by 29.3% (11.5%), 27.1% (12.7%), 23.2% (9.4%), and 16.7% (2.9%) in spring, summer, autumn, and winter by end of the 21st century relative to 1995–2014 under the high-emission SSP5‐8.5 (low-emission SSP1‐2.6) scenario, respectively. The largest precipitation increases in summer and autumn during 2040–2059 and 2080–2099 will occur in the southeastern TP, whereas the largest increases in winter and spring will appear in the Pamirs, where precipitation will increase by >40% during 2080–2099 relative to 1995–2014. The spatial discrepancy in seasonal precipitation changes indicates a potential glacier expansion over the Pamirs and increased flood risks over the southeastern TP. • Future precipitation changes over the Tibetan Plateau (TP) are predicted by CMIP6 models • Performances of 25 CMIP6 models in predicting precipitation variations are reported • Multi-model ensemble means of the five best models provided the highest accuracy • Results show seasonal precipitation will increase over the TP in the 21st century • Seasonal precipitation changes suggest glacier expansion over the Pamirs and increased flood risks over the southeastern TP [ABSTRACT FROM AUTHOR]

The numerical weather prediction (NWP) is gaining more attention in providing high-resolution rainfall forecasts in the arid and semiarid region. However, the modeling accuracy is negatively affected by errors in the initial conditions. Here we investigate the potential of data assimilation in improving the NWP rainfall forecasts in the northeastern Tibetan Plateau. Three of three-dimensional variational (3DVar) data assimilation experiments were designed on running the advanced research weather research forecast (WRF) model. Two heavy rain events selected with different rainfall distribution in space and time are utilized to examine the improvement for rainfall forecast after data assimilation. For the spatial distribution, the improvement of rainfall accumulation and area is obvious for the both two events. But for the temporal variation, the improvement is more obvious for the event with even rainfall distribution in time, while the effect of data assimilation is not ideal for the rainfall event with uneven distribution in space and time. It is noteworthy that, for both the spatial and temporal distribution of rainfall, satellite radiances have greater effect on rainfall forecasts than surface and upper-air meteorological observations in this high-altitude region. Moreover, the data assimilation experiments provide more detail information to the initial fields. [ABSTRACT FROM AUTHOR]

By the analyses of Guliya ice core on the Tibetan Plateau, it was found that the calcium (Ca2+) originated from the terrestrial source is the main cation of soluble aerosol and a good proxy of the atmospheric component and environment in the mountain ice core located in the mid-low latitude arid regions. Evident variation of Ca2+ concentration has been found in the Guliya ice core since the Last Interglaelation with two relatively strong increase periods and two weak increase periods. These variations are generally related to climatic changes: high Ca2+ concentration periods coincide with cold periods and low Ca2+ concentration periods coincide with warm periods. However, Ca2+ concentration does not always decrease (increase) with climate warming (cooling). The magnitude and phase of Ca2+ concentration does not always match temperature either. The changes of atmospheric circulation, land surface condition and atmospheric humidity might be important factors which influence Ca2+ concentration besides temperature. [ABSTRACT FROM AUTHOR]

Based on the Guliya ice core records, the precipitation in the past 400 years was retrieved. Its relations with other regions were also analyzed. The results demonstrated that there were two high-precipitation periods and two low-precipitation periods in Guliya ice core since 1571 AD. The average precipitation in the two high-precipitation periods was 42 mm (21%) higher than that in the two low-precipitation periods. The precipitation recorded in the ' Guliya ice core was consistent with that in Dunde ice core. The variation trends of precipitation in the Guliya ice core and the northern hemisphere are similar. During the extremely wet years in the northern hemisphere, the precipitation recorded in the Guliya ice core was two times the long-term average. However, the annual precipitation was 38% less than that of the long-term average in extremely dry years. Based on the Guliya ice core records, the precipitation in the past 400 years was retrieved. Its relations with other regions were also analyzed. The results demonstrated that there were two high-precipitation periods and two low-precipitation periods in Guliya ice core since 1571 AD. The average precipitation in the two high-precipitation periods was 42 mm (21%) higher than that in the two low-precipitation periods. The precipitation recorded in the ' Guliya ice core was consistent with that in Dunde ice core. The variation trends of precipitation in the Guliya ice core and the northern hemisphere are similar. During the extremely wet years in the northern hemisphere, the precipitation recorded in the Guliya ice core was two times the long-term average. However, the annual precipitation was 38% less than that of the long-term average in extremely dry years. [ABSTRACT FROM AUTHOR]

The mountainous regions of southern Tibetan Plateau and surroundings (hereafter mountainous southern TP), mainly including Himalayas, Gangdise, Nyainqentanglha and Hengduan Mountains, are characterized by high mountains and a complex terrain, and play a crucial role in the redistribution of monsoon water vapor and consequently determine the spatial distribution of precipitation over the TP. However, numerical simulations generally have large precipitation deviation in this focus area. Therefore, optimizing simulation of summer precipitation by Weather Research and Forecasting (WRF) model with two-way nested domains was carried out. A matrix of 11 model experiments, including four cumulus convection (CU) schemes, four microphysics (MP) schemes and four planetary boundary layer (PBL) schemes, were designed. In situ observations from 44 stations, TRMM 3B42 v7 precipitation product, and statistical and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) methods were utilized for the model evaluation. The results showed that physical parameterization schemes, Kain-Fritsch-Cumulus Potential scheme (CU), Thompson scheme (MP), Mellor-Yamada-Janjic scheme (PBL), Unified Noah land surface model, and Eta similarity surface layer scheme, greatly reduced the summer precipitation simulation error of newly High Asia Refined analysis (HAR v2) over the mountainous southern TP, with the better reproduction of the spatiotemporal distribution and vertical variability of precipitation. Compared to NCEP-FNL reanalysis data, the performance of this model setup forced by ERA5 was notably improved, especially with perspective to the vertical variability of precipitation. Our findings suggested that summer precipitation simulation was more sensitive to the CU scheme, and the choice of Kain-Fritsch-Cumulus Potential scheme (ERA5 as initial conditions) significantly improved the precipitation simulation, especially with the lowest MAE (2.00 mm/d), RMSE (2.89 mm/d) and highest Rs (0.74). Further analysis implied that accurate description of shallow convection and proper suppression of deep convection should be considered in precipitation simulations over the TP, especially in mountainous regions. This study could provide a firm foundation for the production of more realistic dynamic downscaling precipitation dataset over the TP. [Display omitted] • An optimizing simulation of summer precipitation by WRF was carried out for the mountainous southern TP for the first time. • The determined optimal model setup greatly reduced the summer precipitation simulation error of HAR v2. • ERA5 was a more superior forcing data than FNL reanalysis data for TP summer precipitation simulation. • The key role of KF-Cup scheme implied the importance of accurate description of TP convective activities. [ABSTRACT FROM AUTHOR]

Records of recent climate from ice cores drilled in 2015 on the Guliya ice cap in the western Kunlun Mountains of the Tibetan Plateau, which with the Himalaya comprises the Third Pole (TP), demonstrate that this region has become warmer and moister since at least the middle of the 19th century. Decadal-scale linkages are suggested between ice core temperature and snowfall proxies, North Atlantic oceanic and atmospheric processes, Arctic temperatures, and Indian summer monsoon intensity. Correlations between annual-scale oxygen isotopic ratios (δ 18 O) and tropical western Pacific and Indian Ocean sea surface temperatures are also demonstrated. Comparisons of climate records during the last millennium from ice cores acquired throughout the TP illustrate centennial-scale differences between monsoon and westerlies dominated regions. Among these records, Guliya shows the highest rate of warming since the end of the Little Ice Age, but δ 18 O data over the last millennium from TP ice cores support findings that elevation-dependent warming is most pronounced in the Himalaya. This, along with the decreasing precipitation rates in the Himalaya region, is having detrimental effects on the cryosphere. Although satellite monitoring of glaciers on the TP indicates changes in surface area, only a few have been directly monitored for mass balance and ablation from the surface. This type of ground-based study is essential to obtain a better understanding of the rate of ice shrinkage on the TP. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP), also known as the "Asian Water Tower," includes thousands of lakes containing sizable lacustrine sediments that have been proven to be important carbon pools of inland ecosystems. To develop an in-depth understanding of the status of TP lake carbon storage and its response to global changes and human activities, we accurately quantified the change trend of long-term organic carbon burial in lakes over the TP, compared levels of differentiation within the TP, and explored related driving factors of the carbon accumulation rates (CARs) by compiling 24 lake sediment cores. The results show that the lake CAR over the TP presented a rising trend during the Holocene, with an average of 6.50 g C m−2 yr−1 and levels ranging from 1.75 to 18.41 g C m−2 yr−1. The eastern TP (ETP), with warmer and wetter climate conditions and more vegetation coverage, had almost twice the CAR as that of the central and western TP (CWTP). We demonstrate that climate and vegetation could be the main drivers of the lake CAR on the TP despite environmental heterogeneity contributing to subregional discrepancies. During the early Holocene, superior summer temperatures and precipitation favored vegetation development, providing abundant material for lake carbon deposition. In the middle Holocene, together with vigorous vegetation, decreasing summer temperatures led to a decline in mineralization, which enhanced carbon storage efficiency and resulted in an increase in the CAR across the ETP. In contrast, for the CWTP, herbaceous-dominated vegetation continued to expand during the early-mid Holocene, which constrained detritus supply, thus maintaining a relatively stable CAR. However, intensive human activities could be responsible for the CAR peak in the late Holocene on the TP, especially since 2000 cal yr BP. In addition to the anthropogenic impacts, variations in CAR among lakes resulting from local factors lead to large uncertainties in future C predictions for the whole region of TP. • The eastern TP had almost twice the CAR as that of the central and western TP. • Climate and vegetation could be the main drivers of the lake CAR on the TP. • Intensive human activities possibly lead to the CAR peak since 2000 cal yr BP. [ABSTRACT FROM AUTHOR]

Abstract: Data observed at monitoring stations in the Tanggula Pass (TGLMS) and in the Xidatan region (XDTMS) were used to calculate the surface energy fluxes, that is, net radiation, ground surface heat flux, sensible heat flux, and latent heat flux. The energy closure statuses obtained by the daily accumulated energy fluxes at the TGLMS and XDTMS sites were good and the turbulent fluxes were slightly higher than the available energy, but this was influenced by differing time-scales. From an energy perspective, the phenomenon of turbulent fluxes being greater than the available energy is advantageous to the development of permafrost, and snow cover is advantageous to storing cold energy in soil. The sensible heat flux and the latent heat flux exhibited a seasonal alternation characteristic, that is, the sensible heat flux was higher than the latent heat flux in winter and spring, but was lower than the latent heat flux in summer and autumn. This is mainly related to the precipitation influenced by the monsoon and the freezing-thawing processes of the active layer. Analysis of diurnal flux variations included the daily freezing-thawing processes. Variations of the Bowen ratios at the two sites were greater than 1.0 from June to September, and less than 1.0 in the other months. Negative Bowen ratios appeared when the snow cover reached a certain thickness (in this case, 10 cm). [Copyright &y& Elsevier]

Abstract: The sensible and latent heat fluxes in the Tanggula region were calculated using turbulent flux monitoring data from June 2004 to December 2005. The monitoring site was located on a gentle slope covered by meadow vegetation (91°56′E, 33°04′N; elevation 5100 m). The turbulent flux monitoring was conducted using the eddy covariance system and a meteorological gradient tower. The results indicated that the average surface energy closure ratio (CR) was 1.07 for the period from June to December of 2004, and 1.03 for the year 2005. The surface energy balance was greatly influenced by rainfalls, snowfalls and snow cover. The sensible heat flux was higher in spring and had a heat sink in summer due to the heat consumed in thawing of the active layer. The latent heat flux was much higher in summer because the soil moisture content was higher, resulting from the thawing of the active layer and more precipitation during the summer monsoon season. It also was found that the amplitudes of the energy fluxes on cloudy days were lower than that on clear days. The evapotranspiration was well related to the surface soil moisture content. The freezing and thawing cycles played a significant role in the land surface processes. [Copyright &y& Elsevier]