Temperature In Tibetan Plateau Research Articles

Linkage between the boreal spring Antarctic oscillation and the temperature dipole mode over the Tibetan Plateau in summer

As the extratropical Southern Hemispheric most prominent atmospheric mode, Antarctic oscillation (AAO) can impact the climate system via multi-spherical interactions, whereas its potential influence on the temperature anomaly over the Tibetan Plateau (TP) remains unclear. By employing ERA5 reanalysis during 1979–2018, we have identified a significant in-phase relationship between April–May AAO and the boreal summer (June–August) temperature anomaly over the TP. The AAO significantly modulates the meridional circulation in the Atlantic sector where the climatic subtropical jet is weaker than other regions in the subtropics as well as the equatorward extension of midlatitude jet. The divergence of transient eddy momentum related to the positive AAO strengthens the northward movement of the South American meridional circulation and cross-equatorial airflow in the low troposphere. Due to the Coriolis force, the cross-equatorial airflow turns southwesterly above the tropical North Atlantic, weakening the climatic northeasterly and the feedback of wind-evaporation-sea surface temperature (SST). Consequently, an anomalous warm SST persists into the boreal summer and triggers a Rossby wave train, which propagates along the North Atlantic-TP pathway. As a result, the positive phase of TP's temperature dipole mode with an eastern warm anomaly and a western cold anomaly appears. The numerical experiments conducted by the linear baroclinic model provide further evidence for the Rossby wave origination and propagation. The AAO, therefore, may act as a valuable predictor for the climate predictions around the TP.

Spring Land Temperature in Tibetan Plateau and Global-Scale Summer Precipitation: Initialization and Improved Prediction

Abstract Subseasonal-to-seasonal (S2S) precipitation prediction in boreal spring and summer months, which contains a significant number of high-signal events, is scientifically challenging and prediction skill has remained poor for years. Tibetan Plateau (TP) spring observed surface ­temperatures show a lag correlation with summer precipitation in several remote regions, but current global land–atmosphere coupled models are unable to represent this behavior due to significant errors in producing observed TP surface temperatures. To address these issues, the Global Energy and Water Exchanges (GEWEX) program launched the “Impact of Initialized Land Temperature and Snowpack on Subseasonal-to-Seasonal Prediction” (LS4P) initiative as a community effort to test the impact of land temperature in high-mountain regions on S2S prediction by climate models: more than 40 institutions worldwide are participating in this project. After using an innovative new land state initialization approach based on observed surface 2-m temperature over the TP in the LS4P experiment, results from a multimodel ensemble provide evidence for a causal relationship in the observed association between the Plateau spring land temperature and summer precipitation over several regions across the world through teleconnections. The influence is underscored by an out-of-phase oscillation between the TP and Rocky Mountain surface temperatures. This study reveals for the first time that high-mountain land temperature could be a substantial source of S2S precipitation predictability, and its effect is probably as large as ocean surface temperature over global “hotspot” regions identified here; the ensemble means in some “hotspots” produce more than 40% of the observed anomalies. This LS4P approach should stimulate more follow-on explorations.

The altered drivers of evapotranspiration trends around the recent warming hiatus in China

AbstractThis study focuses on the trends and the causes of variation in actual evapotranspiration (AET) around the warming hiatus over China by a comprehensive analysis applying various temporal–spatial methods. It is observed that the annual AET showed a different trend around 2000 for China as a whole. By employing segmented regression analysis for detecting warming hiatus points, high temporal inconsistency can be found in eight climatic regions of China. The impacts of meteorological variables on AET were further identified by affecting the intensity and relative change of meteorological factors. AET was highly correlated (p < .01) with solar radiation in the southeast (R = 0.80) and air specific humidity in the northwest areas (R = 0.83). AET changes presented the highest sensitivity to specific humidity in Northwest before 2006 and in north central China after 2003, with sensitivity coefficients of 1.48 and 1.74, respectively. Three variables, including air specific humidity (with an average contribution rate of ~17% in the northwest), short‐wave radiation and air temperature, can be the main factors that lead to the changes in AET. The specific meteorological factors varied from region to region: the changes in AET can be ascribed to the increased wind and short‐wave radiation in north central China and east China, the decreased air temperature in Tibetan Plateau, the increased specific humidity in southeast China during warming hiatus, and so on. After the warming hiatus occurred, the dominant factor of AET trends changed from air specific humidity to short‐wave radiation and other factors. Generally, air specific humidity and air temperature have played leading roles in AET trends during the past 30 years.

Changing Relationship Between Tibetan Plateau Temperature and South China Sea Summer Monsoon Precipitation

The present study documents the changes in the relationship between the Tibetan Plateau summer surface temperature (TPST) and the South China Sea summer monsoon precipitation (SCSSMP). A stepwise regression model is used to exclude the signals of global warming, El Niño–Southern Oscillation (ENSO), western North Pacific Subtropical High (WNPSH), Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO). The results indicate that the relationship between TPST–SCSSMP changes with time, going from a negative correlation during the period of 1980–1994 to an obvious positive correlation during 1998–2016 in the South China Sea. Meanwhile, the negative correlation between TPST and the East Asia subtropical front (Meiyu) is enhanced during 1998–2016. This change in the TPST–SCSSMP relationship is associated with the change of the atmospheric circulation, which is mainly due to TPST interdecadal variation. A wave–like structure at the low latitude moves eastward along the low–level monsoon flow, and a strong cyclonic circulation is apparent in the southwestern part of the Plateau, including the Indochina Peninsula, South China Sea, and the ocean to the east of the Philippines, which is consistent with the negative correlation between TPST and Outgoing Longwave Radiation (OLR). The increase in water–vapor convergence and more favorable convection conditions lead to more precipitation in the region after the late 1990s. The present results suggest that, in a changing climate, we should be cautious when using predictor with interdecadal variations.

Simulation Analysis of the Long-Term Stability for Frozen Soil Roadbed

The global warming will lead to rising temperature in Tibetan plateau which will cause some trouble to the long-term stability of frozen soil roadbed. Of course, the temperature is the most important to stability analysis and study of frozen soil roadbed. In this paper, taking the frozen soil roadbed in Tibetan plateau as an example, the numerical simulation model is established. Firstly, the characteristics of temperature fields of frozen soil roadbed in the future 50 years are analyzed, and then the vertical and horizontal displacements without load and under dynamic load are analyzed.

Temperature and Moisture Effects on Soil Respiration in Alpine Grasslands

The Tibetan Plateau, the low-latitude and high-altitude cold region, has a variety of soils rich in organic carbon (C). Climate change will have large impacts on soil carbon dioxide (CO2) efflux in the region. These impacts will subsequently affect global-scale climate and C cycle links. However, the magnitude of this feedback is still uncertain. Here we use a laboratory incubation experiment to investigate how soil temperature and moisture affected the rate and temperature sensitivity of heterotrophic respiration of three alpine ecosystems (alpine meadow [M], alpine shrubland [SB], alpine swamp [SP]) on the Tibetan Plateau. Soil samples were incubated under three temperature (0 degrees C, 15 degrees C, and 30 degrees C) and two moisture (50% and 100% water-holding capacity) conditions. The response of soil respiration to temperature and moisture varied with ecosystems. Soil respiration in SP was the most temperature sensitive, and higher moisture increased its temperature sensitivity (Q(10)). The respiration and Q(10) depended on total nitrogen in soils. Moreover, high moisture increased the dependence of Q(10) on total nitrogen. Our results suggest that rising temperature in Tibetan Plateau may cause a positive feedback to the soil C cycle, particularly coupled with increasing precipitation and N addition.

Numerical analysis for the ventilated embankment with thermal insulation layer in Qing–Tibetan railway

The ventilated embankment is widely used in the Qinghai–Tibet railway. In order to decrease heat transfer from embankment downwards to ground when the height of embankment is relatively high, absorbing more heat in warm season, the ventilated embankment with thermal insulation layer is proposed. In this paper, a piece of heat insulator, 20 mm thick, is paved on a plane away 20 cm from the upper surface of ducts. Using finite element method, formulated for non-linear heat conduction, allows the solution of practically any ground freezing problem, the temperature distributions of the ventilated embankment with and without thermal insulation layers are calculated, respectively, on condition that the mean annual air temperature in Tibetan Plateau will be warmed up by 2.6 °C and the mean annual temperature at the native surface is about −1.0 °C in the future 50 years. The conclusions are given in term of the analyzing and comparing results.