Atmospheric Moisture Transport Research Articles

Global Climatology of Low‐Level‐Jets: Occurrence, Characteristics, and Meteorological Drivers

AbstractLow‐level jets (LLJs), vertical profiles with a wind speed maxima in the lowest hundred meters of the troposphere, have multiple impacts in the Earth system, but a global present‐day climatology based on contemporary data does not exist. We use the spatially and temporally complete data set from ERA5 reanalysis to compile a global climatology of LLJs for studying the formation mechanisms, characteristics, and trends during the period of 1992–2021. In the global mean, LLJs are detected 21% of the time with more cases over land (32%) than over the ocean (15%). We classified the LLJs into three categories: non‐polar land (LLLJ), polar land (PLLJ), and coastal (CLLJ) LLJs. For LLLJ, the averaged frequency of occurrence is 20% and 75% of them are associated with a near‐surface temperature inversion as a prerequisite for an inertial oscillation. PLLJs are also associated with a temperature inversion and occur even more frequently with 59% of the time. These are also the lowest and the strongest LLJs among the three categories. CLLJs are particularly frequent in some marine hotspots, situated along the west coast of continents, with neutral to unstable stratification close to the surfaces and a stably stratified layer aloft. We found distinct regional trends in both the frequency and intensity of LLJs over the past decades, which can have implications for the emission and transport of aerosols, and the transport of atmospheric moisture. Future studies could address changes in LLJs and the associated implications in more detail, based on the here released ERA5‐based LLJ data.

Spatiotemporal dynamics of stable isotopes of different water sources in Western Himalayas: Insights into regional hydrological processes

The spatiotemporal variations in stable isotope ratios are primarily related to atmospheric moisture transport. However, the isotopic composition of stream water is significantly influenced by the diverse landscape of glaciated and snow-dominated basins. The present study investigates the spatiotemporal variation of the isotopic composition of stream water and potential water sources such as rain, snowmelt, glacier melt, lakes, and groundwater in the Upper Jhelum River Basin (UJRB). Our findings reveal that the significant seasonal variability of precipitation is mainly associated with the transition between westerlies (WDs) and the Indian Southwest Monsoon (ISWM), each conveying distinct moisture to the UJRB. The isotopic signature in rain is actively controlled by the combined effect of temperature (T) and relative humidity (RH) during WDs. However, the impact of “amount effect” with lower condensation temperature is dominant during the latter half of ISWM. Seasonal variations in δ18O and d-excess in stream water are distinct, influenced by different contributing sources and topographic controls. A linear relationship is observed between δ18O vs. altitude and glacier area ratio (GAR). Lower δ18O in stream water and higher d-excess values are observed towards the southwest at higher elevations in glacier-fed tributaries. In the northern UJRB, higher δ18O in stream water indicates contributions from non-glacier fed tributaries and enhanced groundwater contributions rather than merely following the lower δ18O of precipitation along the strengthened WDs gradient. The δ18O isotopic lapse rate (ILR) of rain (−0.19‰/100 m) is higher compared to ILR for the river (−0.05‰/100 m), reflecting the mixing of water sources in river water. However, both are lower than the global average (−0.28‰/100 m). This study helps in understanding the influence of meteorological, topographic factors and other water sources on stream water, a prerequisite for projecting a potential future change in the complex Himalayan region.

Effects of idealized land cover and land management changes on the atmospheric water cycle

Abstract. Land cover and land management changes (LCLMCs) play an important role in achieving low-end warming scenarios through land-based mitigation. However, their effects on moisture fluxes and recycling remain uncertain, although they have important implications for the future viability of such strategies. Here, we analyse the impact of idealized LCLMC scenarios on atmospheric moisture transport in three different Earth system model (ESMs): the Community Earth System Model (CESM), the Max Planck Institute Earth System Model (MPI-ESM), and the European Consortium Earth System Model (EC-EARTH). The LCLMC scenarios comprise of a full cropland world, a fully afforested world, and a cropland world with unlimited irrigation expansion. The effects of these LCLMC in the different ESMs are analysed for precipitation, evaporation, and vertically integrated moisture flux convergence to understand the LCLMC-induced changes in the atmospheric moisture cycle. Then, a moisture tracking algorithm is applied to assess the effects of LCLMC on moisture recycling at the local (grid cell level) and the global scale (continental moisture recycling). By applying a moisture tracking algorithm on fully coupled ESM simulations we are able to quantify the complete effects of LCLMC on moisture recycling (including circulation changes), which are generally not considered in moisture recycling studies. Our results indicate that cropland expansion is generally causing a drying and reduced local moisture recycling, while afforestation and irrigation expansion generally cause wetting and increased local moisture recycling. However, the strength of this effect varies across ESMs and shows a large dependency on the dominant driver. Some ESMs show a dominance of large-scale atmospheric circulation changes while other ESMs show a dominance of local to regional changes in the atmospheric water cycle only within the vicinity of the LCLMC. Overall, these results corroborate that LCLMC can induce substantial effects on the atmospheric water cycle and moisture recycling, both through local effects and changes in atmospheric circulation. However, more research is needed to constrain the uncertainty of these effects within ESMs to better inform future land-based mitigation strategies.

Differing roles of North Atlantic oceanic and atmospheric transports in the winter Eurasian Arctic sea-ice interannual-to-decadal variability

In recent decades, winter Arctic sea-ice concentration (SIC) has experienced a most prominent decline over Barents-Kara Seas (BKS). However, what regulates the time scale and spatial structure of the SIC variability over the Eurasian Arctic is unclear. Here, we find that the SIC variability over the Eurasian Arctic exhibits two major modes: decadal dipole mode with antiphase variation between the BKS and East Greenland (EG), and interannual monopole mode with in-phase variation between the BKS and EG. This decadal mode mainly results from interdecadal changes in ocean heat transports (OHTs) through Barents Sea Opening (BSO) and EG, lagging the Atlantic Multidecadal Oscillation by 7–16 years. The positive SIC dipole mode with a decrease over the BKS and an increase over the EG is also tied to the negative Arctic Oscillation comprised of Ural blocking and the negative North Atlantic Oscillation (NAO). However, the SIC loss of the interannual monopole mode mainly stems from the positive Arctic dipole comprised of Ural blocking and positive NAO through interannual changes in the BSO OHT and atmospheric moisture or heat transport. We further highlight that interannual atmospheric transports and BSO OHT associated with the Arctic dipole contribute to ~66% and ~34% of the interannual variability of the Eurasian Arctic SIC during 1960-2017, respectively. On decadal timescales, the relative contributions of atmospheric transports associated with Arctic Oscillation and OHT to the Eurasian Arctic SIC variability are ~19% and ~81%, respectively. Especially, the contribution of decadal atmospheric transports is significantly intensified during 2000–2017.

The Important Role of Reduced Moisture Supplies from the Monsoon Region in the Formation of Spring and Summer Droughts over Northeast China

Abstract Anomalies in atmospheric moisture transport are critical for drought formation, with East Asian monsoon anomalies identified as the primary driver of droughts in East Asia. However, the drought mechanism for the border region between monsoon and nonmonsoon land areas remains unclear due to complex interactions between latitudinal circulation patterns. Using a Lagrangian framework, we quantify moisture supply (MS) during spring and summer drought events within the border region, specifically Northeast China (NEC). Our results reveal that decreased MS from monsoon land areas is more crucial than nonmonsoon land areas and local areas for NEC droughts, with the local water recycling playing a more substantial role in summer than in spring. On average, summer droughts are 4 times more intense than spring droughts. Contributions to MS deficits from monsoon land areas, nonmonsoon land areas, and local areas during spring (summer) droughts are 43.2% (43.8%), 25.1% (19.2%), and 22% (33.8%), respectively. The weakened atmospheric circulation from source regions to NEC contributes to over 80% of MS deficits during droughts. Atmospheric wave trains triggered by North Atlantic sea surface temperature anomalies (SSTA) gradients, along with the weakening of the East Asian subtropical westerly jet in spring and a positive phase of the polar–Eurasian teleconnection in summer, contribute to spring and summer droughts, respectively. A sustained, record-breaking positive SSTA along the western European coast from the spring to summer excited a wave train, and resulted in the extreme 2017 spring–summer drought. These findings provide valuable insights into the drought mechanism within the interaction zone of circulation systems from different latitudes. Significance Statement The complex interactions between atmospheric circulation patterns at different latitudes have led to an insufficient understanding of the mechanisms causing extreme drought in the border region between the monsoon and nonmonsoon land areas. This study aims to investigate the drought mechanisms in the border region from the perspective of moisture tracking. Results indicate a moisture supply deficit from the monsoon region contributes the most (approximately half) to droughts, although the majority of air parcels reaching this region originate from the nonmonsoon region. The weakening of circulation contributes to more than 80% of the moisture supply deficit during droughts, far exceeding the impact of reduced evaporation from the moisture source regions. These findings are conducive to understanding the mechanisms of extreme drought.

Unravelling the origin of the atmospheric moisture deficit that leads to droughts

AbstractDrought is one of the most catastrophic natural hazards, and precipitation plays a major role in the development and intensification of drought events. The amount of precipitation resulting from humidity transported from a given moisture source can be key in revealing the origin of the atmospheric moisture deficit underlying drought occurrence. Here this study demonstrates, for the first time, the predominant role of moisture transport deficit in drought genesis. In most land areas, the estimated conditional probability of drought given an equivalent moisture deficit received either from the ocean or from the continents is higher than 10%. This probability is over 15% in the regions where the main atmospheric moisture transport mechanisms are active and over 20% in some hotspot regions, such as central-east North America, south-east South America and east Europe, where lower incoming moisture is almost synonymous with drought occurrence. Our results indicated that the contribution deficit of the dominant moisture source to the precipitation of a region could improve the predictability of droughts, with enormous hydrological, socioeconomic and environmental implications.

Future trends in the vertical structure of Arctic warming and moistening in different emission scenarios

Arctic warming is a pressing global concern, and understanding its future vertical structure is crucial for Arctic-mid-latitude connections. In this study, we employed the Coupled Model Intercomparison Project Phase 6 (CMIP6) multi-model simulations to investigate the vertical structure of Arctic warming concerning its current evolving (1980–2030) and future change (2050–2100). In addition to the dry atmosphere described only by temperature, this study analyzed humidity and moist static energy (MSE) for the moist (with the effect of moisture explicitly presented) atmosphere. Under the high-emission scenario, Arctic warming is projected to accelerate, while maintaining its existing bottom-heavy structure. Amplified humidity increases are anticipated in both the tropics and the Arctic, with the Arctic exhibiting greater moisture increases in percentage. Furthermore, we find that MSE, serving as a comprehensive metric for moist atmospheric warming, is projected to accelerate in the Arctic under the high-emission scenario. As a result, the warming of both the dry and moist atmospheres will intensify in the future, with the bottom-heavy vertical structure persisting due to enhanced warming and moistening in the lower troposphere. The accelerated Arctic moistening in the future is due to meridional atmospheric moisture transport in the summer and local moisture source in the winter. In contrast, under the intermediate-emission scenario, Arctic warming and moistening are not projected to accelerate. Despite the inter-model discrepancy, our findings underscore the reliability of projections derived from the high-emission scenario. In summary, our findings highlight that the bottom-heavy vertical structure of Arctic warming will not change and that enhanced upper-level Arctic warming will not occur in the future.

A drier Orinoco basin during the twenty-first century: the role of the Orinoco low-level jet

AbstractThis study focuses on the analysis of the simulation of the main climatological features of the Orinoco low-level jet (OLLJ) by a set of models included in the Sixth Phase of the Coupled Model Intercomparison Project (CMIP6) and their projected changes under three Shared Socioeconomic Pathways (SSPs): SSP2-4.5, SSP3-7.0, and SSP5-8.5. We consider the 1979–2014 period to evaluate the historical simulations using the ERA5 reanalysis as the reference dataset. In general, CMIP6 models are able to capture the activation of the OLLJ during December-January–February (DJF) in the Orinoco basin, as well as the main links between this circulation and low-level moisture transport patterns in northern South America. Regarding the analysis of projections, CMIP6 models suggest a weakening and shrinking of the OLLJ, especially in its exit region, by the end of the twenty-first century, which in turn induces changes in atmospheric moisture transport patterns in the region during DJF. The projected changes of the OLLJ are associated with variations in the regional gradients of mean sea level pressure, near-surface air temperature, and surface sensible heat flux in association with drier conditions in the Orinoco basin. These projections are consistent with previous studies suggesting a drier Orinoco river basin throughout the twenty-first century. Assessing the projected changes of this low-level jet in northern South America improves our understanding of the different phenomena that modulate atmospheric moisture transport in the region, which is particularly important given its high vulnerability to climate change.

Changes in the Indian Ocean surface hydrography driven by the seaway closure and monsoonal circulation since the late Oligocene

Closure of the East Tethyan and Indonesian gateways and development of the Indian or South Asian monsoon (SAM) wind system had profound control on Indian Ocean circulation. However, the dynamics of the Indian Ocean surface hydrography since the late Oligocene hitherto remains poorly constrained. Planktic foraminiferal relative abundance and stable isotope data from ODP Site 758A, eastern equatorial Indian Ocean (EEIO) reveal a conspicuous thick mixed layer between ∼25.6 and 14.7 Ma, except for a short-lived thinning from 20.7 to 19.4 Ma. We suggest that existence of a thick mixed layer and perhaps higher sea surface temperatures in the EEIO increased convection and atmospheric moisture transport to the southern hemisphere, which contributed to the expansion of Antarctic ice volume. The East Tethyan Seaway closure and constriction of the Indonesian Gateways cooled the surface and deep waters at ∼14.7 Ma when the mixed layer thickness began to decrease and thermocline began to shoal. Seasonal fluctuations between mixed layer and thermocline were secular from 25.6 to 12.9 Ma which became more intense and frequent in the younger interval. A shift in the surface hydrography with high frequency changes at ∼12.9 Ma was driven by the onset of the SAM wind system, leading to the development of the modern summer monsoon surface circulation in the Indian Ocean.

Present‐Day Regional Antarctic Sea Ice Response to Extratropical Cyclones

AbstractBoth atmospheric warming and poleward moisture transport increase the likelihood of sea ice surface melt. In the Southern Hemisphere, short‐lived extratropical cyclones (ETCs) are responsible for a bulk of total heat and moisture transport toward high latitudes. Although these storms form ubiquitously in the midlatitudes, moisture availability and temperature characteristics vary by source region. In this study, we assess atmospheric, oceanic, and sea ice concentration (SIC) anomalies associated with austral winter ETCs over different Antarctic regions using ERA5 reanalysis data. Between 1990 and 2019, we find a total of 514 ETCs, with greater storm frequency in the eastern hemisphere groups. Compared to the climatology, sea ice melts (grows) behind the warm (cold) front of each system and is negatively correlated with atmospheric poleward moisture transport, temperature, meridional winds, and sea surface temperature for all ETCs. We find that Bellingshausen storms move moisture and warm air furthest poleward over their lifespan. However, East Weddell and East Antarctic ETCs are responsible for greater absolute poleward moisture transport than Bellingshausen and Ross systems. More intense ETCs correspond to greater SIC through Day 1, suggesting that SIC impacts ETC strength, regardless of ETC region. From cyclogenesis to cyclolysis, sea ice extent declines underneath composite ETCs, trends are generally not significant. Overall, while sea ice response produced by ETC‐induced atmospheric and oceanic changes varies regionally, the long‐term impacts of ETCs on regional sea ice are negligible over the study period.

Assessing Arctic wetting: Performances of CMIP6 models and projections of precipitation changes

The Arctic region is experiencing a notable increase in precipitation, known as Arctic wetting, amidst the backdrop of Arctic warming. This phenomenon has implications for the Arctic hydrological cycle and numerous socio-ecological systems. However, the ability of climate models to accurately simulate changes in Arctic wetting has not been thoroughly assessed. In this study, we analyze total precipitation in the Arctic using station data, multiple reanalyses, and 35 models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6). By employing the moisture budget equation and an evaluation method for model performance with ERA5 reanalysis as a reference, we evaluated the models' capability to reproduce past Arctic wetting patterns. Our findings indicate that most reanalyses and models are able to replicate Arctic wetting. However, the CMIP6 models generally exhibit an overestimation of Arctic wetting during the warm season and an underestimation during the cold season from 1979 to 2014 when compared to the ERA5 reanalysis. Further investigation reveals that the overestimation of wetting during the warm season is largest over the Arctic Ocean's northern part, specifically the Canadian Arctic Archipelago, and is associated with an overestimation of atmospheric moisture transport. Conversely, the models significantly underestimate wetting over the Barents-Kara Sea during the cold season, which can be attributed to an underestimation of evaporation resulting from the models' inadequate representation of sea ice reduction in that region. The models with the best performance in simulating historical Arctic wetting indicate a projected intensification of Arctic wetting, and optimal models significantly reduce uncertainties in future projections compared to the original models, particularly in the cold season and oceanic regions. Our study highlights significant biases in the CMIP6 models' simulation of Arctic precipitation, and improving the model's ability to simulate historical Arctic precipitation could reduce uncertainties in future projections.

Projected changes in atmospheric moisture transport contributions associated with climate warming in the North Atlantic

Global warming and associated changes in atmospheric circulation patterns are expected to alter the hydrological cycle, including the intensity and position of moisture sources. This study presents predicted changes for the middle and end of the 21st century under the SSP5-8.5 scenario for two important extratropical moisture sources: the North Atlantic Ocean (NATL) and Mediterranean Sea (MED). Changes over the Iberian Peninsula—considered as a strategic moisture sink for its location—are also studied in detail. By the end of the century, moisture from the NATL will increase precipitation over eastern North America in winter and autumn and on the British Isles in winter. Moisture from the MED will increase precipitation over the southern and western portions of the Mediterranean continental area. Precipitation associated with the MED moisture source will decrease mainly over eastern Europe, while that associated with the NATL will decrease over western Europe and Africa. Precipitation recycling on the Iberian Peninsula will increase in all seasons except summer for mid-century. Climate change, as simulated by CESM2 thus modifies atmospheric moisture transport, affecting regional hydrological cycles.

Unraveling atmospheric moisture transport linkages to extreme precipitation events and associated synoptic features over India

This study explores the physical mechanisms underlying extreme precipitation events linked to atmospheric moisture transport (IVT-P). It identifies regions where IVT influences extreme precipitation and investigates changes in synoptic-scale weather patterns over the Indian subcontinent. The study finds a strong association between daily IVT and precipitation over the core monsoon region and complex terrains of the Western Ghats and Himalayas. Event Coincidence Analysis reveals that extreme IVT can be used to forecast extreme precipitation in these regions. The dynamic component of moisture transport strongly influences daily and extreme precipitation over complex terrains, while the thermodynamic component influences precipitation over regions with abundant water vapor and weak horizontal winds. The study also identifies synoptic features and moisture transport ahead of IVT-P events and finds intense low-pressure anomalies, transition from ridge to trough patterns, and intense 700 hPa relative humidity in the specified regions. Overall, the study provides insights into the physical mechanisms underlying IVT linked extreme precipitation events.

Спутниковые оценки вариаций увлажненности внутреннего Тянь-Шаня в период 1982–2022 гг. на примере хребта Ат-Баши (Киргизия)

Introduction. Western atmospheric jet streams carry moisture over the Northern Tian Shan ridges into the Inner Tian Shan. Long-term weather changes in the Inner Tian Shan diagnose climatic fluctuations in atmospheric moisture transport. This is of considerable interest for understanding the direction of modern climate change in Central Asia. Materials. The area of the At-Bashi Ridge (2700 км2) in Inner Tian Shan, including a large high-altitude Lake Chatyr-Kul (170 km2, 3530 m), were considered. The ridge, with a peak of 4786 m, has a length of 135 km and is characterized by an Alpine type of relief. The initial information related to the period 1982-2022. The list of data used included: FLDASSnowDepth_inst; JRC Monthly Water History, v1.4; ECMWF/ERA5_LAND/MONTHLY (precipitation); NOAA/NCEP_DOE_RE2 (cloud fraction). Also, to diagnose the mountain glaciation state of the At-Bashi Ridge, three satellite images of sub meter resolution dated 09/21/2002, 07/27/2013 and 09/13/2021 were used. The purpose of the work. The aim of the research was to study the humidity regime of the At-Bashi Ridge area during 1982-2022. Research methodology. The change in the average annual snow depth in the test area in the period 1982-2022 was analyzed, as well as the degree of correlation of this parameter with other weather characteristics.Fischer’s criterion acted as a quantitative basis for estimates. Satellite images of sub meter resolution were used to analyze long–term changes in the area of rock outcrops from ice on the slopes of glacial chambers, which diagnoses the glacier state (degradation – stability – growth). Satellite data recorded the process of mountain glaciation growth above the height of 4000 m in the period between 2002–2013. Research results. In order of increasing correlation (F-criterion), with the snowiness of the cold period (October-May) of the At-Bashi Ridge area, the parameters considered were arranged as follows (F=2.11; α=0.01): cloud fraction, F= 3.02; precipitation, F=12.42; the Lake Chatyr-Kul area, F= 12.53; the balance of snow deposits between the windward (north-western) and leeward (south-eastern) At-Bashi Ridge slopes, F= 22.01. According to satellite data, the growth of mountain glaciation in the zone with an altitude above 4000 m in the period 2002-2013 was recorded. Discussion. The At-Bashi Ridge area has three different periods in terms of humidity: dry in 1982-1999 with an average annual snow depth of 0.099± 0.051 m; wet in 2000-2012; 0.192± 0.074 m; and moderately humid in 2013-2022; 0.133± 0.058 m. Ultra-high-resolution satellite images recorded the growth of the mountain glaciation of the At-Bashi Ridge at altitudes of more than 4000 m in the period from 2002 to 2013. This confirms the actual existence of the wet period of 2001-2012. Conclusion. Thus, the current trend of humidity changes of the At-Bashi Ridge does not have an unambiguous direction, but in general, for the period 1982-2022, it is aimed at a certain increase in the snow content in mountains and the area of the Lake Chatyr-Kul. Apparently, the current climate change is accompanied by an increase in the ability of western atmospheric jet fluxes to transfer moisture over the front Northern Tian Shan ranges into the Inner and Central Tian Shan ridges, which may even be accompanied by an increase in the mountain glaciation of these territories in certain periods of time.

Characteristics of clustered heavy precipitation events at Northeast China and associated atmospheric circulations

AbstractHeavy precipitation events can exert greater impact than general precipitation on the economy, ecology, and people’s livelihoods. Based on CN05.1 daily precipitation data and the NCEP/NCAR global daily reanalysis dataset, this study analyzes the characteristics of clustered heavy precipitation (CHP) events during summer in Northeast China (NEC) during 1961–2020, with consideration of associated atmospheric circulations and moisture transport. Results indicate that CHP events occurred mainly during midsummer, especially in July. Both the frequency and the intensity of CHP events decrease after the mid-1970s, increase after the early 1980s, and then diminish again after the 2000s. The CHP events occur in association with an anomalous lower-tropospheric cyclone centered over NEC, northward and westward shifts of the western North Pacific subtropical high in the middle troposphere, and northward shift of an intensified westerly jet in the upper troposphere, in conjunction with strengthened local convective motion. Additionally, the net moisture budget begins to increase 2 days before the occurrence of CHP and peaks 6 h earlier than the CHP. Further results indicate that net moisture influx across the southern boundary of NEC made a dominant contribution to the net moisture budget. The results of this study have importance regarding the prediction of CHP events over NEC.

The Hydrologic Cycle and Atmospheric Rivers in CESM2 Simulations of the Last Glacial Maximum

AbstractProxy reconstructions and model simulations of precipitation during Earth's glacial periods suggest that the locations and mechanisms of atmospheric moisture transport have changed considerably during Earth's past. We investigate the hydroclimate of the Last Glacial Maximum (LGM) using simulations with the Community Earth System Model, with a focus on the extratropics and the influence of atmospheric rivers (ARs), a key driver of modern‐day moisture transport globally. Mean and extreme precipitation increase significantly over southwestern Patagonia, Iberia, and southwestern North America—mid‐latitude regions affected by ARs in the modern climate—despite overall decreases elsewhere. In each, the associated moisture transport changes are different, with increased transport and AR activity mainly occurring in the North Atlantic. The overall LGM response is dominated by the response to ice sheets, with other forcings causing additional cooling and drying over the extratropics and a strong decrease of moisture transport over the subpolar North Atlantic.

Atmospheric Moisture Transport Associated with Precipitation in Present and Simulated Future Climates

Abstract Precipitation and the atmospheric moisture budget are analyzed for 40-yr periods of recent and future climate simulated by the 10 CMIP6 models from which the vertically integrated moisture flux data are available. This allows new assessments of this important atmospheric transport, which can typically only be approximated. Seasonal climatological fields are compared with those from the ERA5 reanalysis. Using the four-season average M skill score for the globe, precipitation from the 10 models is similar in skill to that from a further 25 models. The scores for six moisture variables, including flux and its convergence, demonstrate global skill for each model. The 10-model average fields have better skill than any individual model. Changes are calculated for 2040–79 under the SSP5-8.5 forcing scenario. The focus is on the 10-model average scaled as a projection of change for a global warming of 2°C. The changes in precipitation, temperature, and pressure in each season are largely consistent with those from the larger ensemble. The changes in flux, convergence, water column, and winds at three levels are presented. The role of convergence in balancing precipitation changes over many land regions is evident. Flux, convergence, and precipitation are shown in detail for selected cases, including central North America, the South American monsoon, southern Africa in summer, southern South America in winter, Europe in summer, and both polar regions. Typically, flux is enhanced, but the associated convergence may shift. The production of the vertically integrated flux vector as a standard output from climate models is supported.

Impact of ENSO on Wintertime Land Surface Variables in Northern Hemisphere Extratropics: Role of Atmospheric Moisture Processes

Abstract El Niño–Southern Oscillation (ENSO) is the strongest interannual signature in the tropical air–sea system and can affect global atmospheric variables, but ENSO’s climatic impact on land surface variables such as skin temperature, snow cover, and soil moisture that can serve as seasonal climate predictors remains relatively little known. Here we examine ENSO’s impact on the three land surface variables in Northern Hemisphere extratropics by regression analysis, using a combination of ERA5 reanalysis, GLDAS, satellite-based observations, and CESM2 simulations. Our results show that during El Niño winters anomalous land surface warming occurs in Northern Hemisphere midlatitudes, accompanied by snow cover reduction, especially in northern North America and eastern Europe, while anomalous cooling occurs in southern North America and the Tibetan Plateau, accompanied by increased snow cover. Meanwhile, increased soil moisture is observed in southern North America, central Asia, and southeast China. Further analysis indicates that atmospheric moisture processes dominate the formation of the land surface anomalies, for which the changes in water vapor and precipitation induced by the ENSO-related large-scale atmospheric teleconnection are critical. The anomalous land surface warming in midlatitudes mainly results from the increased downward longwave radiation due to the increase of water vapor, whereas the physical pathway causing water vapor anomalies is different over North America and Eurasia. Controlled by ENSO-induced changes in atmospheric circulation and moisture transport, anomalous precipitation explains most of the snow cover and soil moisture anomalies, which play a certain role in shaping the skin temperature anomalies in some regions through snow–albedo feedback and evaporation, respectively.

The role of external and local atmospheric moisture fluxes in the interannual variability of peak summer precipitation over the northern fringe of the East Asian summer monsoon

On the northern fringe of the East Asian summer monsoon (NFEASM), both external atmospheric moisture transport and local evaporation are important moisture sources of moisture that feed peak summer precipitation, but their relative importance in regulating the precipitation variability remains unclear. This study uses the atmospheric water budget analysis to investigate the contributions of external and local atmospheric moisture fluxes to the interannual variability of peak summer (July and August) precipitation over the NFEASM between 1980 and 2015. The results show that, compared with the net atmospheric moisture flux (i.e., moisture flux convergence, MFC), although climatologically evaporation is of the same magnitude as precipitation, its standard deviation is much smaller than that of precipitation and MFC. With respect to moisture conservation, the atmospheric moisture budget indicates that the interannual variability in summer precipitation is derived primarily from changes in MFC. Moreover, the closer correlation between MFC and precipitation than between MFC and evaporation also implies that the variability of summer precipitation over the NFEASM is controlled mainly by fluctuations in the external atmospheric moisture fluxes, particularly by the moisture transport from the southwest, which is closely linked to the anticyclonic anomalous circulation over eastern China. In addition, although the westerly does not bring substantial moisture, its meridional movement can change the upper-level zonal wind divergence pattern, thereby affecting peak summer precipitation over the NFEASM.

Surface energy balance on a polythermal glacier, Arctic, and the role of poleward atmospheric moisture transport

In recent years, increasing moisture over the Arctic and subarctic regions shows that the Arctic is experiencing wetting conditions, and poleward atmospheric moisture transport (PAMT) plays a vital role in the atmosphere-ice/snow interactions in the Arctic. To identify the effect of PAMT on the surface energy balance (SEB) for the Arctic glacier, meteorological data from an automatic weather station (AWS) at 377 m a.s.l. on the Austre Lovénbreen glacier, as well as the ERA5 reanalysis data from 30 April 2014 to 30 April 2015, were analyzed in this paper. Our results show that the net shortwave radiation (Snet) (18 W m−2, 55%), turbulent sensible (H) (14 W m−2, 43%) and subsurface heat flux (G) (1 W m−2, 2%) act as the energy sources, while the net longwave radiation (Lnet) (−19 W m−2, 56%), melt energy (Qm) (−12 W m−2, 35%) and turbulent latent heat flux (LE) (−3 W m−2, 9%) represent the heat sink. The development process of Atmospheric River (AR), primary form of PAMT, near the Svalbard in February 2015 was revealed according to the total column water vapor, 850 hPa winds and geopotential height fields. Compared to summer, the glacier SEB was more affected in winter by PAMT, leading to a frequent overcast and thus increasing air temperature, moisture, and wind speed, all of which are variables governing the SEB by decreasing H, LE and G less than increasing the Lnet. Our findings obtained here can help to better understand the diverse SEB change on the high Arctic glacier from the perspective of PAMT and large-scale atmospheric circulations anomalies.