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Snow cover days (SCD) have increased significantly in winter on the Western Kunlun Mountains and Eastern Pamir Plateau (hereafter referred to as KMPP for short), however the causes have not been well understood so far. Here, we use remote sensing data to analyze the abnormal increase in SCD on the KMPP and explore its causes from the perspective of the local factors and water vapor transport caused by sea surface temperatures (SST) warming. We discover that the winter SCD on the KMPP increased significantly at a rate of 4.75 days/decade (significant at the 0.01 level) during 1989–2020, while there has been a significant decrease on the Tibetan Plateau (TP), with a rate of −1.50 days/decade (significant at the 0.1 level). Based on ERA5, GPCP, GHCN, and station data, we find that, in contrast to the significant warming observed on the TP, temperature changes on the KMPP are negligible, while precipitation is increasing, differing from the decreasing precipitation trend observed on the TP. The differences in local temperature and precipitation changes cause different variations in SCD between the KMPP and the TP. The increase in SCD on the KMPP is primarily driven by increased precipitation (over 97% contribution), with minimal impact from the more or less unchanged temperature. In contrast, the decline in SCD on the TP results from decreased precipitation and significantly increased temperature. Furthermore, we found that changes in SCD on the KMPP are significantly correlated with SST in the northern North Atlantic Ocean. Based on the correlation vector, the anomaly field in the high/low SCD years of water vapor transport, and the FLEXPART model, we show that the northern North Atlantic Ocean is one of the major water vapor sources affecting the SCD on the KMPP. The warming SST in the northern North Atlantic Ocean enhances water vapor transport to the KMPP in winter, leading to an abnormal increase in the SCD that differs from the overall trend on the TP. The findings are conductive to further understand the peculiarity of winter precipitation and SCD on the KMPP, and the "Western Kunlun Mountains Oddity" in mountain glacial change. [ABSTRACT FROM AUTHOR]

The Three-Rivers Headwater (TRH) region has experienced notable dry-to-wet shift in summer precipitation in recent decades. Despite the widespread efforts of scientific community, the causes of such climate shift remain not well-understood. Building upon an ensemble of high-resolution Lagrangian simulations and moisture source diagnostic, this study investigated the long-term changes in moisture sources with the ERA-Interim reanalysis from 1980 to 2017, particularly aiming to pose a complimentary understanding on this shift from a perspective of moisture source changes. The results show that the variability of moisture sources for the water vapor reaching the TRH region is closely and quantitatively linked to its regional summer precipitation. The dry-to-wet shift in summer precipitation in TRH is regulated by the changes in moisture sources across multiple transport time scales (from 1 to 10 days), and could be attributed to the enhanced contribution by the moisture sources originated from the Tibetan Plateau (TP), the Central Eastern Asian region (CEA), and the Arabian Peninsula (ARP), of which regional accumulative moisture contribution increased by 11.3 (0.33%), 8.61 (0.27%) and 8.53 (0.52%) mm per year, respectively. This result implies that the terrestrial source ranks the leading role in regulating the decadal shift of TRH summer precipitation, rather than that directly from the oceanic regions. Although the moisture sources are across multiple transport timescales, the relatively shorter transport distance and steady contribution (lasting 1 to 10 days) from the TP highlight the significance of strengthened local precipitation recycling process in this dry-to-wet shift. Further analysis indicates the variations in mid-latitudinal meridional winds and the low-latitudinal SST play a role of 'bridge' connecting the changes in moisture sources to enhanced precipitation during the summer season. Key points: The decadal variation of regional precipitation over the TRH region is closely and quantitatively linked with the changes in moisture sources. The moisture sources responsible for the dry-to-wet shift in summer rainfall over the TRH have been detected. The weakened mid-latitudinal meridional winds and the warming low-latitudinal sea surface temperature bridge the moisture source changes and summer precipitation over the TRH region. [ABSTRACT FROM AUTHOR]

Streamflow in source region of Yellow River (SRYR) matters with regard to the adjacent and downstream water resources. Intraseasonal oscillation (ISO) in the streamflow in SRYR is of great significance to the sub-seasonal prediction of streamflow in SRYR, but is unknown. Here, we first report a 30–60-day ISO in the streamflow in SRYR, which is regulated by the atmospheric 30–60-day ISO at mid-high latitude over North Eurasia. The 30–60-day ISO in atmosphere is featured by a Rossby wavetrain, and the wave energy propagates southward onto the TP, which causes anomalous wind response over TP. The leading anomalous high (low) with anti-cyclonic (cyclonic) wind anomalies over the TP favors dry (wet) air in lower troposphere in SRYR, via enhancing the water vapor divergence (convergence). Dry (wet) air always results in strong (weak) evaporation from the Yellow River, which causes the later streamflow valley (peak) and thereby the 30–60-day ISO in the streamflow in SRYR. [ABSTRACT FROM AUTHOR]

Based on long-term observational and reanalysis datasets from 1901 through 2014, this study investigates the characteristics and physical causes of the interdecadal variations in the summer precipitation over the East Asian monsoon boundary zone (EAMBZ), which is a peculiar domain defined from the perspective of the interplay between climatic systems (i.e., mid-latitude westerly and East Asian summer monsoon). Observational evidence reveals that, similarly to previous studies, the EAMBZ precipitation featured prominent interdecadal fluctuations, e.g., with dry summers during the periods preceding 1927, 1939–1945, 1968–1982, and 1998–2010 and wet summers during the periods of 1928–1938, 1946–1967, and 2011 onwards. Further analyses identify that, amongst the major interdecadal oceanic forcings (e.g., Atlantic multidecadal oscillation and Pacific decadal oscillation), the Indian Ocean basin mode (IOBM) is a significant oceanic forcing responsible for the interdecadal variations of the EAMBZ precipitation, playing an independent and critical modulation role. When the cold phase of the IOBM occurs, an anomalous cyclonic circulation is excited around the northeast corner of the tropical Indian Ocean, which further induces a north-low–south-high meridional seesaw pattern over the Northeast China–subtropical western Pacific (SWP) sector. Such seesaw pattern is conducive to the enhanced EAMBZ precipitation by linking favorable environments for the transportation of water vapor from the SWP and the convergence over the EAMBZ at interdecadal timescales. For this reason, a physical–empirical model for the EAMBZ precipitation is developed in terms of the IOBM cooling. Despite the fact that the extreme summer EAMBZ precipitation cannot be captured by this model, it can still well capture its interdecadal fluctuations and reflect their steady relationship. The key physical pathway connecting the IOBM cooling with the interdecadal variations of the summer EAMBZ precipitation is supported by the numerical results based on the large ensemble experiment and the Indian Ocean pacemaker experiment. Our findings may provide new insights into the understanding of the causes of the interdecadal variations in the summer EAMBZ precipitation, which may favor the long-term policy decision-making for the local hydrometeorological planning. [ABSTRACT FROM AUTHOR]

The Yarlung Zsangbo Grand Canyon (YGC) is an important pathway for water vapor transport from southern Asia to the Tibetan Plateau (TP). This area exhibits one of the highest frequencies of convective activity in China, and precipitation often induces natural disasters in local communities, which can dramatically affect their livelihoods. In addition, the produced precipitation gives rise to vast glaciers and large rivers around the YGC. In 2018, the Second Tibetan Plateau Scientific Expedition and Research Program tasked a research team to conduct an "investigation of the precipitation process in the water vapor channel of the Yarlung Zsangbo Grand Canyon" (INVC) in the southeastern TP. This team subsequently established a comprehensive observation system of land–air interaction, water vapor, clouds, and rainfall activity in the YGC. This paper introduces the developed observation system and summarizes the preliminary results obtained during the first two years of the project. Using this INVC observation network, herein, we focus on the development of rainfall events on the southeastern TP. This project also helps to monitor geohazards in the key area of the Sichuan–Tibet railway, which traverses the northern YGC. The observation datasets will benefit future research on mountain meteorology. [ABSTRACT FROM AUTHOR]

The Flood‐Drought condition over the Three‐River Headwater region (TRHR) of the Tibetan Plateau (TP) exerts vital impacts on regional climate and downstream livelihoods. However, the reasons behind precipitation variability over this region remain elusive. In this study, the multi‐year moisture sources of water vapour reaching the TRHR were identified to reveal their connection to the interannual variability of summer precipitation by utilizing a Lagrangian diagnosis analysis. The results show that the moisture sources could be tracked backward covering vast areas, with the peak values located mostly at the northern Indian continent and adjacent regions of TRH itself. The variability of integrated moisture sources' contribution agrees well with the summer precipitation on the interannual scale; However, the role of different regions varies in line with their geographical location. More specifically, summer precipitation is positively correlated with the moisture source over the adjacent areas of TRH and the remote terrestrial‐oceanic regions, in contrast to a negative correlation to the water vapour departing from the Northeastern Asian and western regions to the TP. The Indian summer monsoon circulation and local recycling process play a dominant role in modulating the summer precipitation on the interannual scale, whereas the role of the westerlies is almost negligible. The abnormal atmosphere circulations triggered by mid‐high latitude wave trains and anomalies in SST in the central and eastern Pacific Ocean and Indian Ocean could serve as possible drivers for the precipitation variability over TRHR. [ABSTRACT FROM AUTHOR]

Based on long-term observational and reanalysis datasets from 1901 through 2014, this study investigates the characteristics and physical causes of the interdecadal variations in the summer precipitation over the East Asian monsoon boundary zone (EAMBZ). Observational evidence reveals that the EAMBZ precipitation featured prominent interdecadal fluctuations, e.g., with dry summers during the periods preceding 1927, 1968–1982, and 1998–2010, and wet summers during the periods of 1928–1938, 1946–1967, and 2011 onwards. Further analyses identify that the Indian Ocean basin mode (IOBM) is an important oceanic modulator responsible for the interdecadal variations of the EAMBZ precipitation. When the cold phase of the IOBM occurs, an anomalous cyclonic circulation is excited around the northeast corner of the tropical Indian Ocean, which further induces a "north-low–south-high" meridional seesaw pattern over the Northeast China–subtropical western Pacific (SWP) sector. Such seesaw pattern is conducive to the enhanced EAMBZ precipitation through linking favorable environments for the transportation of water vapor from the SWP and the convergence over EAMBZ at interdecadal timescales. For this reason, a physical-empirical model for the EAMBZ precipitation is developed in terms of the IOBM cooling, which can well capture its interdecadal fluctuations and reflect their steady relationship. The key physical pathway connecting the IOBM cooling with the interdecadal variations of the summer EAMBZ precipitation is supported by the numerical results based on the large ensemble experiment and the Indian Ocean pacemaker experiment. Our findings may provide new insights into the understanding of the causes of the interdecadal variations in the summer EAMBZ precipitation, which may favor the long-term policy decision making for the local hydrometeorological planning. [ABSTRACT FROM AUTHOR]

The correlation characteristics between anomalous changes in summer precipitation on the Qinghai–Tibet Plateau (QTP) and the high-impact areas of global sea-surface temperature (SST) are mainly studied in this paper. The results show that the interdecadal change of the regional "warming-wetting" in China is especially prominent in the northern part of the main body of the QTP, which is therefore identified as the high-value area of precipitation variability. Investigations have revealed that the high-value areas of summer precipitation variability in the northern QTP are significantly correlated with four high-value areas of SST variability, namely the western North Pacific, the western Central Pacific, the Southwest Pacific, and the central Indian Ocean. In these four high-impact areas, a synchronous tendency is found in the SST increase and sea-surface specific humidity. Through the tracking analysis of the correlated vectors of the water vapor source for the warming-wetting of the QTP, it further confirms that the four high-value areas of SST variability in the Indo-Pacific Ocean are the major impact sources of water vapor transport for the warming-wetting of the QTP. Moreover, the comparison of the characteristics of various interdecadal global water vapor transport circulations show that from 1991 to 2020, the trans-equatorial water vapor transport from the Southern Hemisphere witnessed a notable increase, which furthermore suggests that the interdecadal change of SST increase in the Southwest Pacific and central Indian Ocean is the key reason for the warming-wetting of the QTP. In addition, a comprehensive image of high-impact marine water vapor sources for modulating the warming-wetting tendency in the QTP is proposed. [ABSTRACT FROM AUTHOR]

By using the multi-source data of meteorology over recent decades, this study discovered a summertime "hollow wet pool" in the troposphere with a center of high water vapor over the Asian water tower (AWT) on the Tibetan Plateau (TP), which is indicated by a vertical transport "window" in the troposphere. The water vapor transport in the upper troposphere extends from the vertical transport window over the TP with significant connections among the Arctic, Antarctic and TP regions, highlighting the effect of the TP's vertical transport window of water vapor in the troposphere on global change in water vapor. The vertical transport window is built by the AWT's thermal forcing in association with the dynamic effect of the TP's "hollow heat island". Our study improves the understanding of the vapor transport over the TP with important implication for global climate change. [ABSTRACT FROM AUTHOR]

A Lagrangian approach is utilized to identify and compare the sources of water vapor transported to the four subregions of Tibetan Plateau (TP) during the wet season (May–August) of 1980–2016. We focus on the time scale and subseasonal variability of water vapor transport and the relationship between moisture supply and precipitation at the interannual scale. This study finds that: (1) The moisture sources for the four subregions differ significantly in both spatial pattern and magnitude and depend heavily on the combined effects of the summer monsoons, local recycling and the westerlies. (2) The spatial evolution of the moisture sources based on the backward trajectory analysis reveals that, although approximately 80% of the moisture is delivered to the target regions within 1–4 days, the individual subregions feature different transport pathways and associated time scales. (3) The subseasonal migration of the Indian summer monsoon regulates the importance of different moisture sources for the southern TP but not for the northern TP. Additionally, the subseasonal moisture source evolution differs greatly between the southeastern TP and the southwestern TP. (4) The interannual variability of precipitation over the whole TP during summer is negatively correlated with the variation in the moisture transported by the westerlies and is positively related to the moisture conveyed by the Indian summer monsoon for the northern TP and by adjacent moisture transport for the southern TP. [ABSTRACT FROM AUTHOR]

This paper introduces the X-band weather radar dual-polarization parameters of isolated convective cell precipitation and meso/microscale snowfall on Mount Everest and presents the first precipitation observations based on dual-polarization weather radar in this area. Compared with the Chengdu Plain, Mount Everest experienced convective precipitation on smaller horizontal and vertical scales with a narrower Zdr probability density spectrum (uniformly distributed around approximately 0). The Zh profile on Mount Everest displayed two peaks, unlike that over the plains, and the precipitation at the strong convective core was denser. Furthermore, during winter snowfall on the northern slope of Mount Everest, when the boundary layer exhibited sufficient water vapor and dynamic uplift, due to the low boundary layer temperature (<0 °C), water vapor produced stratiform clouds in the middle and lower layers (approximately 1.5 km above ground level (AGL)). Water vapor condensation at 1.5–2.5 km AGL led to latent heat release, which increased the temperature of regional stratiform clouds with increasing height. Consequently, the temperature at the stratiform cloud top height (2.5 km AGL) unexpectedly exceeded 0 °C. Additionally, the −20 °C isotherm was at approximately 4 km AGL, indicating that the middle- and upper-layer atmospheric temperatures remained low. Therefore, thermal instability occurred between the stratiform cloud top height and the middle/upper atmosphere, forming convective motion. These findings confirm the occurrence of elevated winter snowfall convection above Mount Everest and may have certain reference value for retrieving raindrop size distributions, quantitatively estimating precipitation, and parameterizing cloud microphysical processes in numerical prediction models for the Qinghai-Tibetan Plateau. [ABSTRACT FROM AUTHOR]