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In order to study the imprints of solar-ENSO-geomagnetic activity on the Indian Subcontinent, we have applied the Singular Spectral Analysis (SSA) and wavelet analysis to the tree ring temperature variability record from the western Himalayas. The data used in the present study are the Solar Sunspot Number (SSN), Geomagnetic Indices (aa Index), Southern Oscillation Index (SOI) and tree ring temperature record from western Himalayas (WH), for the period of 1876-2000. The SSA and wavelet spectra reveal the presence of 5 years short term ENSO variations to 11 year solar cycle indicating the influence of both the solar-geomagnetic and ENSO imprints in the tree ring data. The presence of 33-year cycle periodicity suggests the Sun-temperature variability probably involving the induced changes in the basic state of the atmosphere. Our wavelet analysis for the SSA reconstructed time series agrees with our previous results and also enhance the amplitude of the signals by removing the noise and showing a strong influence of solar-geomagnetic and ENSO patterns throughout the record. The solar flares are considered to be responsible for cause in the circulation patterns in the atmosphere. The net effect of solar-geomagnetic processes on temperature record thus appears to be the result of counteracting influences on shorter (about 5-6 years) and longer (about 11-12 years) time scales. The present analysis thus suggests that the influence of solar processes on Indian temperature variability operates in part indirectly through ENSO, but on more than one time scale. The analyses hence provides credible evidence for teleconnections of tropical pacific climatic variability with Indian climate ranging from interannual-decadal time scales and also demonstrate the possible role of exogenic triggering in reorganizing the global earth-ocean-atmospheric systems. [ABSTRACT FROM AUTHOR]

Recent climate and environment over the Tibetan Plateau (TP) have undergone significant changes, dominated by variations in the Westerlies and the Indian summer monsoon. However, long‐term shifts in atmospheric circulation during the transitional seasons are still lacking. Here we investigate the modern distribution of Tsuga pollen over the central‐western TP and confirm it as an indicator of variable atmospheric circulation in spring. By combining our Tsuga record from Taro Co with existing records in the Tsuga pollen source area, we suggest that a potential particle transport pathway from the southern slope of the Himalayas to the interior of the plateau appeared in the spring of the late Holocene. Our results show that the springtime atmospheric circulation over the southwestern TP during the early and late Holocene is closely related to the substantial remnants of ice sheets at northern high latitudes and the frequency of El Niño events, respectively. Plain Language Summary: The spring climate over the Tibetan Plateau (TP) is undergoing significant changes that yield profound impacts on environmental changes such as variations in vegetation phenology and alpine treeline. Knowledge of long‐term variations in atmospheric circulation during spring can improve the understanding of current climatic and environmental change and the projection of future variability. In this paper, we use an exotic pollen grain, which can be transported long distances in the air, as an indicator to trace the variability of spring atmospheric circulation over the TP. The results indicate that the spring meridional atmospheric circulation from the southern slope of the TP to its interior has been enhanced in the last four thousand years, which is mainly influenced by the frequency of El Niño events. Key Points: Spring atmospheric circulation change over the southwestern Tibetan Plateau (TP) during Holocene is reconstructedMeridional atmospheric circulation in spring over the southwestern TP is strengthened in the late HoloceneHigh‐(low‐) latitude forcing mainly influence the variations in spring atmospheric circulation during the early (late) Holocene [ABSTRACT FROM AUTHOR]

The physicochemical properties and origins of atmospheric aerosols in the Tibetan Plateau (TP) region are a research topic of great interest, but an in‐depth understanding of this topic is challenging, partially due to a lack of intensive in situ observations. Thus, a field campaign was conducted over Yadong, a remote area on the south slope of the TP from June 11 to 31 August 2021. The aerosol loading was low, with a black carbon mass concentration of 147.4 ± 98.4 ng·m−3. Aerosol single‐scattering albedo was low (0.73 ± 0.11 at 550 nm) and increased from 450 to 700 nm wavelength. Organic matter (OM) accounting for 69.6% of the total aerosol mass and relatively high secondary organic carbon ratios, highlighting the importance of secondary formation. An interesting phenomenon observed was that the evolution of aerosols was mainly characterized by diurnal variation, which could not be explained by large‐scale atmospheric processes such as Indian summer monsoon. Instead, it was found that regional mountain‐valley winds between the Himalayas and South Asia transported polluted air masses toward the TP, especially in the afternoon when regional valley wind are expected to be the strongest and the boundary layer in South Asia is deepest. Additionally, daytime local valley wind further elevated these aerosols to higher altitudes on the TP. This paper provides insights into the transport mechanisms of aerosols from South Asia to the TP. These findings are of great importance since aerosols exhibit significant diurnal variations in the TP region. Plain Language Summary: Previous studies focused on the analysis of the physical or chemical properties of aerosols on the Tibetan Plateau, but this study provides a comprehensive examination of both. The findings reveal that aerosols on the southern slope of the Tibetan Plateau exhibit strong absorption efficiency. Aerosol single‐scattering albedo was low (0.73 ± 0.11 at 550 nm), which may be attributed to aerosol secondary generation and coating. Finally, the mechanism of pollutant transport from South Asia to the Tibetan Plateau was analyzed relies on site observations, satellite, and reanalysis data to highlight the link between diurnal variations of pollutants and transport mechanism. The specific transport mechanism be understood uniformly across different scales, including Indian summer monsoon, regional mountain‐valley winds between the Himalayas and South Asia, and local mountain‐valley winds circulation. Key Points: Aerosol single‐scattering albedo was low (0.73 ± 0.11 at 550 nm) and secondary organic matter was the major aerosol componentThe evolution of aerosols was mainly characterized by diurnal variation that was related to transport mechanism over YadongThe Himalayas‐South Asia regional mountain‐valley winds combined with local mountain‐valley winds transport aerosols to the Tibetan Plateau [ABSTRACT FROM AUTHOR]

Extreme glacier melt has important implications for climate change studies and glacier‐related hazards. Few attempts have been made to study the characteristics and mechanisms of extreme melt on the Tibetan Plateau (TP) and surroundings, one of the largest concentrations of glaciers beyond the polar regions. To address this gap, we investigated the magnitude and possible drivers of anomalous early spring glacier melt in 2022 on the central TP using multi‐source observations (October 2020–July 2022) of Kuoqionggangri and Sangqu glaciers and an energy and mass balance model. Our results show that anomalous melt of both glaciers occurred in early spring (18 March–10 April 2022), when glaciers are traditionally expected to be frozen. There were 89 cumulative hours with air temperatures above 0°C, with a positive cumulative air temperature of 121.80°C hour at 5,700 m on Kuoqionggangri Glacier. The glacier‐wide cumulative melts on Kuoqionggangri and Sangqu glaciers from 18 March to 10 April 2022 were 22 ± 14.2 and 48 ± 37.5 mm w.e., respectively. Such anomalous glacier melt was driven by high incoming shortwave radiation and sensible heat flux, which were influenced by low cloud fraction and precipitation, and high air temperature during early spring. The weakening and northward‐shift of the westerlies, coupled with descending air motions over the central TP, reduced cloud fraction and hindered the transport of cold, moist air to the central TP. These changes occurred both in the central TP and the Himalaya, indicating the influence of macroscale atmospheric circulation patterns on this extreme glacier melt. Plain Language Summary: The Tibetan Plateau (TP) and surroundings have the largest amount of ice outside of the Arctic and Antarctic. Extreme glacier melt not only accelerates glacier mass loss, but is also important for changing climates and triggering glacier‐related disasters. Here, results show that extreme weather conditions and anomalous glacier melt occurred in early spring 2022 on the central TP. High air temperature, low cloud fraction and precipitation were the main characteristics of extreme weather events. Accompanying this extreme event, anomalously high incoming shortwave radiation and sensible heat flux control extreme glacier melt. We found that extreme weather conditions occurred in both the central TP and the northern foothills of the Himalaya. Our results indicate that extreme weather events and glacier melt were linked to large‐scale atmospheric circulation and regional climate conditions. This study contributes to a deeper insight into the characteristics and processes of glacier melt. In the future, more efforts are needed to monitor glacier melt and identify the causes of extreme glacier melt on the TP, which holds significant scientific and practical importance. Key Points: Extreme weather conditions and glacier melt occurred in the early spring of 2022 on central Tibetan PlateauExtreme glacier melt was driven by anomalously high incoming shortwave radiation and sensible heat fluxA strong northward shift of westerly winds in early spring 2022 led to extreme weather conditions and glacier melt [ABSTRACT FROM AUTHOR]

During the pre-monsoon season, the Northwest Himalayas region receives a significantly larger proportion of precipitation than the pan Indian average. This heightened precipitation makes the region vulnerable to the repercussions of extreme weather events. Therefore, this study delves into the variations in precipitation during the pre-monsoon period over the Northwest Himalayas spanning from 1979 to 2018. It has been observed that since 1998, the mean baseline for precipitation has shifted downward, signifying a bi-decadal transition. Notably, the seasonal average precipitation has dropped to 50% of the levels recorded before 1998, with March emerging as the primary contributor to this overall decline. Subsequent analysis revealed that western disturbances (WDs) predominantly account for the precipitation in this region during this season. This dominance arises due to the lack of conducive local atmospheric conditions for any other significant source of moisture and precipitation. However, the strength of zonal moisture transport and WDs aided vorticities are seen to be weakening post 1998 which also interestingly coincides with the strongest El Nino phase on record and the start of a negative Pacific decadal oscillation (PDO) cycle. As a result, the role of global teleconnections is investigated, which concluded that negative PDO conditions after 1998 are responsible for changes in the atmospheric circulation pattern. Such changes resulted in air subsidence over the study region which increased the atmospheric stability while weakening the lower-level convergence and the westerly component of moisture transport. Consequently, the pre-monsoon precipitation has experienced a steep decline in the recent decades. To further examine this hypothesis, a threefold process is employed, which encompasses the study of changes in circulation patterns, cause-effect cluster analysis, and case study comparisons. [ABSTRACT FROM AUTHOR]

Profiles of aerosols and cloud layers have been investigated over a high-altitude urban atmosphere in the eastern Himalayas in India, for the first time, using a Raman LIDAR. The study was conducted post-monsoon season over Darjeeling (latitude 27°01 ′ N longitude 88°36 ′ E, 2200 masl), a tourist destination in north-eastern India. In addition to the aerosols and cloud characterization and atmospheric boundary layer detection, the profile of the water vapor mixing ratio has also been analyzed. Effects of atmospheric dynamics have been studied using the vertical profiles of the normalized standard deviation of RCS along with the water vapor mixing ratio. The aerosol optical characteristics below and above the Atmospheric Boundary Layer (ABL) region were studied separately, along with the interrelation of their optical and microphysical properties with synoptic meteorological parameters. The backscatter coefficient and the extinction coefficient were found in the range from 7.15 × 10 − 10 m − 1 sr − 1 to 3.01 × 10 − 5 m − 1 sr − 1 and from 1.02 × 10 − 5 m − 1 to 2.28 × 10 − 3 m − 1 , respectively. The LIDAR ratio varies between 3.9 to 78.39 sr over all altitudes. The variation of the linear depolarization ratio from 0.19 to 0.32 indicates the dominance, of non-spherical particles. The periodicity observed in different parameters may be indicative of atmospheric wave phenomena. Cloud parameters, such as scattering coefficients, top and bottom height, and optical depth for different cloud phases, have been evaluated. A co-located Micro Rain Radar has been used with LIDAR for cloud life cycle study. [ABSTRACT FROM AUTHOR]

The role of the diurnal atmospheric circulation cycle around the eastern Indian subcontinent, leeward of the monsoon westerlies, on the hydroclimate of South Asia remains unknown. Here, we reveal that low‐level moist southerlies are greatly enhanced at night parallel to the coastline over the western Bay of Bengal (BoB), and then flow onto the Gangetic Plain enhancing onshore moisture flux and nocturnal precipitation over the Himalayas and the Meghalaya Plateau. This nocturnal surge is strongly controlled by the diurnal cycle of dynamic and thermodynamic effects around the subcontinent. At night, nocturnal westerly low‐level jets appear over the subcontinent. Strong low‐level southwesterly flow with a low‐level jet structure also appears parallel to the coastline over the western BoB, extending from the west of Sri Lanka. The low‐level westerlies from the subcontinent and the low‐level southwesterlies merge into a single strong southwesterly flow, forming the low‐level moist surge. Plain Language Summary: Nocturnal precipitation is a well‐known phenomenon around the Himalayas and the Meghalaya Plateau in South Asia in summer. Such precipitation is a major supply source for glaciers in the central–eastern Himalayas and the headwaters of major rivers such as the Ganges and the Brahmaputra. In this study, we show that low‐level moist southerlies are greatly enhanced at night parallel to the coastline over the western Bay of Bengal (BoB) and then flow onto the Gangetic Plain, enhancing moisture transport toward land and nocturnal precipitation in South Asia. Here, we refer to the phenomenon as the nocturnal southerly moist surge. This nocturnal surge is strongly affected by the diurnal cycle of the thermal and topographic effects of the Indian subcontinent. At night, a strong low‐level westerly jet appears above the nocturnal stable layer over the Indian subcontinent. Strong low‐level southwesterlies with a low‐level jet structure also appear over the western BoB, extending from the strait between the southernmost tip of the Indian subcontinent and Sri Lanka. The low‐level westerlies flowing from the subcontinent and the southwesterlies merge into a single strong southwesterly flow, forming the low‐level moist surge over the western BoB. Key Points: Nocturnal low‐level southerly moist surge occurs parallel to the western Bay of Bengal coastline and flows over the Gangetic PlainThe surge consists of strong low‐level westerlies from the Indian subcontinent and southwesterlies extending from the west of Sri LankaDynamic and thermodynamic effects of the Indian subcontinent likely play an important role in forming the nocturnal surge [ABSTRACT FROM AUTHOR]

The Pan‐Third Pole contains the largest number of glaciers outside the polar region that plays a crucial role in atmospheric circulation and the hydrological cycle. However, this pristine region has undergone rapid change through complex interactions including the black carbon (BC) enhanced warming effect and glacier melting. Study shows, Weather Research and Forecasting coupled with Chemistry (WRF‐Chem) simulation is able to capture distinctive seasonal variability of BC. The result from our sensitivity experiments revealed that South Asia (SA; 60.7%) and East Asia (EA; 32.9%) contributed more toward the Tibetan Plateau (TP). Our analysis on aerosol‐boundary feedback interaction revealed BC expand planetary boundary layer height by 5.0% and 4.8% over SA and EA, respectively, which facilitates BC dispersion and transportation. Whereas, we also found that under the influence of different wind regimes the significant BC transport flux aloft over the TP and the upper troposphere and lower stratosphere. Additionally, mountain‐valley channel and synoptic and local meteorological processes also facilitated BC transport to the TP. This study also evaluated the effect of BC on direct radiative forcing and calculated subsequent temperature changes. A strong dimming effect of BC corroborated with the following negative surface temperature changes. However, enhanced BC concentration during winter and spring caused the increase in temperature over the TP. Here, the WRF‐Chem model, synergy on aerosol‐boundary feedback, BC transport flux, and source‐receptor methods confirmed the significant BC contribution and transportation, and notable BC‐induced warming over TP. Such trans‐Himalayan BC transport and associated warming could grim glacier melt and water availability in the region. Key Points: Trans‐Himalaya long‐range transport is evident with significant black carbon (BC) transport flux aloft above Himalayas and Tibetan Plateau and free troposphere from South Asia (SA) and East Asia (EA) regionSynergy on aerosol‐boundary feedback interaction manifested that BC expand planetary boundary layer height by 5.01% and 4.80% over SA and EA, respectivelyElevated BC caused notable warming over Tibetan Plateau that could pose a threat in the cryosphere over that region [ABSTRACT FROM AUTHOR]

Starting in January 2020, the novel coronavirus, now known as acute respiratory syndrome coronavirus (SARS‐CoV‐2) and the disease that it causes (COVID‐19) has had significant impacts on human health, the environment, and the economy globally. The rapid lockdown that occurred as well as its well documented timing allows for an unprecedented opportunity to examine the impact of air pollution from densely populated regions has on adjacent and pristine environments. Here, we use in situ and satellite observations to show that there was a step function decrease in two key indicators of air quality, nitrogen dioxide and airborne particulates, in locations within the Indo‐Gangetic Plan (IGP) as a result of the Spring 2020 lockdown. Based on anomaly patterns, we find a dipole response with a statistically significant reduction in air pollution along the western IGP and Himalaya and an increase in air pollution in the eastern IGP and Himalaya. We show that spatial variability in the reductions in economic activity across northern India and the adjoining countries of Nepal, Pakistan, and Bangladesh contributed to this dipole as did a persistent atmospheric circulation anomaly across the region during the lockdown. Key Points: The COVID‐19 lockdown provides an opportunity to assess the impact of air pollution from the Indo‐Gangetic Plain on the Himalaya.Air pollutions levels in cities in the western Indo‐Gangetic Plain experienced marked drops that coincided with the lockdown.Across the Indo‐Gangetic Plain and Himalaya, there were reductions in air pollution in the west and increases in the east. [ABSTRACT FROM AUTHOR]

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Tree-ring δ18 O values are a sensitive proxy for regional physical climate, while their δ13 C values are a strong predictor of local ecohydrology. Utilizing available ice-core and tree-ring δ18 O records from the central Himalaya (CH), we found an increase in east–west climate heterogeneity since the 1960s. Further, δ13 C records from transitional western glaciated valleys provide a robust basis for reconstructing about 3 centuries of glacier mass balance (GMB) dynamics. We reconstructed annually resolved GMB since 1743 CE based on regionally dominant tree species of diverse plant functional types. Three major phases became apparent: positive GMB up to the mid-19th century, the middle phase (1870–1960) of slightly negative but stable GMB, and an exponential ice mass loss since the 1960s. Reasons for accelerated mass loss are largely attributed to anthropogenic climate change, including concurrent alterations in atmospheric circulations (weakening of the westerlies and the Arabian Sea branch of the Indian summer monsoon). Multi-decadal isotopic and climate coherency analyses specify an eastward declining influence of the westerlies in the monsoon-dominated CH region. Besides, our study provides a long-term context for recent GMB variability, which is essential for its reliable projection and attribution. [ABSTRACT FROM AUTHOR]

Cenozoic atmospheric circulation, climatic changes, sedimentation and weathering over the Indian sub‐continent were mainly influenced by the northward drift of the Indian Plate, the shrinking Paratethys, India‐Asia collision and the rise of the Himalayas. This study is aimed at exploring the fluvial sedimentary record of the north‐west part of the Himalayan Foreland Basin to interpret weathering and pedogenesis during early Oligocene to Mid‐Miocene time. Palaeopedological investigation of a 3.1 km thick succession from Kangra sub‐basin of the Himalayan Foreland Basin shows that the lower 2 km part of the succession is characterized by the red (10R hue) and the upper 1.1 km part of the succession by the yellow (2.5Y hue) palaeosols with varying intensity of weathering and pedogenesis. The association of sedimentary rocks and pedogenic expression in palaeosols indicate four (Type‐A to Type‐D) pedofacies in the entire Oligocene–Miocene succession. The pedofacies are defined by a decrease in the intensity of palaeopedogenic development from strongly‐developed palaeopedofeatures in Type‐A, moderately‐developed palaeopedofeatures in Type‐B, weakly‐developed palaeopedofeatures in Type‐C and to the only incipient stage of palaeopedogenesis in Type‐D pedofacies. The palaeolatitudinal shift during the convergence of the Indian Plate played a major role in weathering and palaeopedogenesis with the inception of seasonality during the early Oligocene, which is demonstrated by the formation of the red palaeosols with pedogenic CaCO3 and vertic features in tropical conditions. The transition to yellow palaeosols at about 20 Ma is marked by increased humidity, rapid aggradation, pronounced uplift and enhanced erosion of the hinterland. These yellow palaeosols are characterized by the abundance of weakly‐developed Bw and Bss horizons, pure clay pedofeatures and absence of any pedogenic CaCO3 during short pedogenic intervals in subtropical conditions. [ABSTRACT FROM AUTHOR]

This study provides the first comprehensive assessment of Regional Climate Model version 4.6.1 (RegCM4) for the Tibetan Plateau (TP) region. A wide range of model configurations were analyzed with different parameterizations employed to represent cumulus convection (Kuo, Grell, Emanuel, Kain, and Tiedtke), land surface processes (BATS and CLM), planetary boundary layer turbulence (Holtslag and UW PBL), and radiation (CCM3 and RRTM). In addition to the above experiments at a 30-km horizontal resolution, another experiment was conducted based upon the use of a double-nested dynamic downscaling method to construct a simulation at a 10-km resolution to study the sensitivity to the model resolution. We evaluated a 20-year simulation for precipitation, cloud cover, surface radiation budget, 2-m air temperature, and the surface atmospheric circulation against ground and satellite-based observations during the period 1989–2008. Among the factors analyzed regarding sensitivity, precipitation was unsurprisingly found to be sensitive to the cumulus parameterization scheme, and the CLM is found to reduce rainfall compared with BATS, which is satisfactory for both the Emanuel and Tiedtke schemes. Compared with the cumulus convection schemes, the cloud cover and surface radiation budget are sensitive to the land surface, PBL, and radiation schemes. Generally, the CLM is characterized by reduced mean cloud cover and enhanced surface longwave and shortwave radiation compared with BATS. Conversely, the UW PBL and RRTM radiation schemes result in increased cloud cover and less surface radiation compared with the default options in RegCM4. All experiments, except those employing the Kuo scheme, represent the mean 2-m air temperature and regional circulation patterns reasonably well. At the basin scale, the seasonal cycle and interannual variations of precipitation are found to be not well depicted by most model configurations, although the temperature field was well reproduced. Considering all the analyzed variables collectively, the Tiedtke scheme combined with the CLM land surface model is demonstrated to provide the best performance over the TP. However, the higher-resolution version of the model improves the precipitation simulation significantly, particularly in the Brahmaputra river basin, which is located in the north of the Himalayas. [ABSTRACT FROM AUTHOR]

Diurnal variations of rainfall and winds are pronounced over the Asian summer monsoon region, but their activities under different monsoon conditions are not clarified. Here, the diurnal cycle of monsoon flow and its influence are examined using 20-yr satellite rainfall and reanalysis data. A total of 1840 summer days are partitioned into four dynamic groups of strong or weak background flows with large or small diurnal amplitudes of low-level meridional wind. Large-scale southerly wind is found to be strongest after midnight, with a large diurnal amplitude on strong monsoon days over central-north India and southeast China. Such a nocturnal speed-up is closely associated with the Blackadar boundary layer inertial oscillation due to the diurnal heating over low-lying landmass. It acts like a large air pump that injects moisture poleward at night and strengthens monsoonal circulation with anomalous rising motion at the northern rainband of the Asian monsoon. In particular, monsoon southerlies with large nighttime speed-up converge with downslope winds from the Himalayas or northerly anomaly from midlatitudes. Enhanced water vapor convergence facilitates the growth of organized convection, producing substantial rainfall at the Himalayan foothills in predawn hours and at the mei-yu–baiu zone from predawn to noon. When monsoon flow undergoes a small diurnal cycle, rainfall is instead displaced south and mostly recorded in daytime. Both the daily mean and morning peak of rainfall are suppressed on land under weak monsoon southerlies. Moreover, the monsoon diurnal cycle exhibits evident intraseasonal/interannual variations and contributes to rainfall variability. The results highlight that monsoon flow couples with subdaily forcings to strongly regulate the detailed patterns of rainfall and moisture budget over the Asian monsoon regions. [ABSTRACT FROM AUTHOR]

Driven by the strength in local land–atmosphere coupling, inter‐annual variability of larger‐scale atmospheric circulations primarily determines a glacier's response to warming in high Asia. In this study, micrometeorological measurements in conjunction with regional reanalysis data set were analysed to examine seasonal land–atmosphere coupling strength at a typical central Himalayan (CH) glacier where the influence of Indian summer monsoon (ISM) predominates relative to winter‐westerlies. Energy–water (E–W) exchange and coupling behaviour were studied for the Pindari glacier based on sub‐hourly measurements of radiative–convective flux, state parameters, and sub‐surface thermal profiles using cross‐correlations between various E–W balance components. Coupling was positive in summer and winter accumulation seasons. However, it remained strongest during ISM. Coupling reversed during seasonal transition phases concurrent with distinct seasonality in E–W components. Lead–lag relation between some variables showed strong association at diurnal‐scale (VPD–Rn; VPD–LE; Rn–G), whereas some persisted beyond months (Rn–LE; Bowen ratio–precipitation; surface–air temperature). Weak association of variation of latent heat flux (LE) and rainfall was found during ISM at local scale than at regional scale, but with a lag, which was more prominent at regional scale. These observations indicate a seasonally variable coupling between E–W balance components through response–feedback mechanisms. Cross‐correlations of daily mean values of energy fluxes and meteorological variables reveal that Rn and air temperature are the prime drivers of energy balance. Net radiative energy (Rn) dominates energy exchanges at the glacier–atmosphere interface (governed primarily by the variation in net shortwave radiation), contributed on average 62% of the melt energy. However, sub‐surface heat flux along with the turbulent fluxes was the energy sinks of 24 and 15%, respectively. This study would help understand and parameterize E–W exchange pathways for ISM dominated CH glaciers in coupled glacier–climate models. [ABSTRACT FROM AUTHOR]

The seasonal variability of strong afternoon winds in a northern Himalayan valley and their relationship with the synoptic circulation were examined using in situ meteorological data from March 2006 to February 2007 and numerical simulations. Meteorological observations were focused on the lower Rongbuk valley, on the north side of the Himalayas (4270m MSL), where a wind profile radar was available. In the monsoon season (21 May-4 October), the strong afternoon wind was southeasterly, whereas it was southwesterly in the nonmonsoon season. Numerical simulations were performed using the Weather Research and Forecasting Model to investigate the mechanism causing these afternoon strong winds. The study found that during the nonmonsoon season the strong winds are produced by downward momentum transport from the westerly winds aloft, whereas those during the monsoon season are driven by the inflow into the Arun Valley east of Mount Everest. The air in the Arun Valley was found to be colder than that of the surroundings during the daytime, and there was a horizontal pressure gradient from the Arun Valley to Qomolangma Station (QOMS), China Academy of Sciences, at the 5200-m level. This explains the formation of the strong afternoon southeasterly wind over QOMS in the monsoon season. In the nonmonsoon season, the colder air from Arun Valley is confined below the ridge by westerly winds associated with the subtropical jet. [ABSTRACT FROM AUTHOR]

Winter precipitation over the Hindu Kush-Karakoram (HKK) range in the western Himalayas is generated by westerly perturbations whose dynamics is affected by the North Atlantic Oscillation (NAO). Larger precipitation is typically recorded during the positive NAO phase. In this work, the relationship between the NAO and winter precipitation in the HKK is explored further, using an ensemble of precipitation datasets and the 40-yr ECMWF Re-Analysis (ERA-40) and Twentieth Century Reanalysis (20CR) data. The mechanisms underlying this relationship are discussed, with a focus on the secular variations that occurred in the last century. The NAO exerts its control on HKK precipitation by altering the intensity of westerly winds in the region of the Middle East jet stream (MEJS). Results indicate that evaporation from the Persian Gulf, the northern Arabian Sea, and the Red Sea plays an important role. During positive NAO phases, westerlies are strengthened and enhanced evaporation occurs from these basins owing to higher surface wind speed. The extra moisture combines with stronger westerlies and results in enhanced moisture transport toward the HKK. Precipitation datasets covering the twentieth century show an alternation of periods of strong and weaker influence of the NAO on precipitation in the HKK. It is found that these variations are associated with changes in the spatial pattern of the NAO: the relative position of the two centers of action of the NAO determines to what extent it can modulate the MEJS, affecting precipitation in the HKK. [ABSTRACT FROM AUTHOR]

Observations and model simulations were conducted in a typical Himalayan valley to investigate the role of snow/ice cover in the formation of the local diurnal wind. An unusual local circulation was observed in the Himalayas with a strong down-valley flow dominant from noon to midnight, greatly differing from those in other mountainous regions. Two experiments with snow/ice cover included/excluded were performed using the Regional Atmospheric Modeling System (RAMS) to reconstruct the Himalayan circulation, and to reveal the role of snow/ice in this circulation. The results show that the wind system in the Himalayas is composed of both glacier winds driven by the snow/ice cover and classical mountain-valley winds. In particular, the glacier winds establish the distinctive feature of the Himalayan local circulation, i.e., the strong down-valley flow in the afternoon. [ABSTRACT FROM AUTHOR]

In this work, we present the first systematic identification of episodes of air mass transport from the lower stratosphere/upper troposphere (LS/UT) in the middle troposphere of the southern Himalayas. For this purpose, we developed an algorithm to detect LS/UT transport events on a daily basis at the Everest-Pyramid GAW station (EV-PYR, 5079 m a.s.l., Nepal). In particular, in situ surface ozone and atmospheric pressure variations as well as total ozone values from OMI satellite measurements have been analysed. Further insight is gained from three-dimensional backward trajectories and potential vorticity calculated with the LAGRANTO model. According to the algorithm outputs, 9.0% of the considered data set (365 days from March 2006 to February 2007) was influenced by this class of phenomena with a maximum of frequency during dry and pre-monsoon seasons. During 25 days of LS/UT transport events for which any influence of anthropogenic pollution was excluded, the daily ozone mixing ratio increased by 9.3% compared to the seasonal values. This indicates that under favourable conditions, downward air mass transport from the LS/UT can play a considerable role in determining the concentrations of surface ozone in the southern Himalayas. [ABSTRACT FROM AUTHOR]

A 16.8 m firn core of middle Himalayas was recovered on the col of Dasuopu glacier in August 2006, being 7000 m above sea level. A total of 317 samples were measured for stable oxygen isotope ratios (δ18O) and major ion concentrations (Na+, NH4+, K+, Mg2+, Ca2+, Cl-, SO42-, and NO3-). The firn core dating and seasonal partitioning were carried out based on the marked seasonal variations along the stable oxygen isotopes and crustal species (Ca2+, Mg2+) profiles. The multi-parameters and high-resolution glaciochemical data set of Dasuopu firn core recorded the detailed chemical characteristics of precipitation in high-elevation region, middle Himalayas, since 1991 A.D., which mainly originated from the crustal and anthropogenic sources, while the sea-salt contribution was minor. The seasonal variability of major ion concentrations was dominated by the seasonal alternation of the prevalent air mass, atmospheric circulation situation and precipitation regime. Linear regression analysis indicated that most of the variance in annual ionic fluxes can be explained by a linear dependence on snow accumulation rate. [ABSTRACT FROM AUTHOR]

The Himalayan region of north India is composed of complex mountain ranges with different altitudes and orientations, causing prevailing weather conditions to be complex. Wintertime eastward moving synoptic weather systems `Western Disturbances' (WDs) yield large amounts of precipitation over this region. Numerous micro/mesoscale circulations become generated along with prevailing weather due to surface heterogeneity and land-use variability of the Himalayan region. WDs along with these circulations may give rise to very adverse weather conditions over the region. Intraseasonal variability of surface climate over the Himalayas is studied using regional climate model (RegCM3) with 60 km resolution. A 6-month (Oct. 1999–Mar. 2000) period, as this period has received an enormous amount of precipitation in the form of snow, is considered to study surface climate variability in terms of temperature, precipitation and snow amount. Model simulations show cold bias over the Himalayan region and warm bias over the northwest India. Average monthly distribution of temperature indicates that a controlled experiment could capture the areas of lowest temperature regime. Precipitation fields could be simulated only up to a certain degree of satisfaction and the influence of topographic elevation and valleys needs to be seen. RegCM3 provides a representation of resolvable atmospheric circulations that results in explaining mean variability during winter. [ABSTRACT FROM AUTHOR]

A mean climatology is studied to examine atmospheric circulation characteristics to assess the wintertime (December, January, February and March - DJFM) synoptic weather system affecting northern India. The main objective is to study the mean circulation and mean energetics distribution pertaining to the winter season, which are embedded with an eastward moving synoptic weather system in westerlies, called Western Disturbances (WDs). Forty years (1958–1997) of uninitialized daily re-analysis data of the National Center for Environmental Prediction - National Center for Atmospheric Research (NCEP- NCAR, henceafter NCEP), U.S. has been considered for this study. Winter circulations are considered over the domain 15°S–45°N and 30°E–120°E. This domain is considered particularly to illustrate the impact of wintertime synoptic weather system Western Disturbances (WDs), which travel towards the east over the western Himalayas during winter and yield an enormous amount of precipitation in the form of snow. Large-scale balances of kinetic energy, vorticity, angular momentum, heat and moisture budget terms are analyzed. The main findings of the study show that strong rising motion in the extratropical region brings a significant amount of precipitation over the region of study. Also, horizontal flux of kinetic energy converges in the tropical region and diverges over the extratropical region. It is seen that both the zonal and meridional component of kinetic energy contributes to the production of kinetic energy in the upper troposphere. Vorticity budget shows that wintertime circulation over the western Himalayas is characterized by a negative generation of vorticity. The relative and planetary vorticity advection contributes to the horizontal transport of vorticity. The moisture flux transported into the region shows that in the middle tropospheric levels moisture undergoes phase transformation due to turbulent exchange and hence releases latent heat. [ABSTRACT FROM AUTHOR]

Contrasting features associated with surplus and deficient precipitation years are studied to examine atmospheric circulation characteristics during the winter season viz., December, January February and March (DJFM) to assess the wintertime synoptic weather system affecting the western Himalayas. Large-scale balances of kinetic energy, vorticity, angular momentum, heat and moisture fields are analyzed. Winter circulations are studied over the domain 15°S–45°S and 30°E–120°E. This domain is considered particularly to illustrate the distribution of precipitation due to wintertime eastward moving synoptic weather systems called western disturbances. Surplus and deficient years of seasonal (DJFM) precipitation are identified using±20% departure from mean from uninitialized daily reanalysis data of fourty (1958–1997) years of the National Center for Environmental Prediction (NCEP), USA. The years 1965–1969, 1973 and 1991 are found to be surplus years and years 1962, 1963, 1971, 1977 and 1985 are found to be deficient years. Composites of these two categories are made. Comparative study is made using Students t-test of significance. Examining the aspects associated with energetics during the two extreme categories of winter seasonal precipitation years, higher heat flux convergence in excess years in the area of study of precipitation takes place. Diabatic heating shows cooling. Higher flux of convergence of kinetic energy and higher dissipation of kinetic energy are observed during surplus years. [ABSTRACT FROM AUTHOR]