Longwave Radiation Flux Research Articles

Impact of Cold Surge (CS) on Net Surface Heat Flux (NSHF) in Natuna Sea

Cold Surge (CS) events are often associated with rainfall occurrences in the Jakarta area. However, there is still limited literature on how CS affects other parameters in Indonesia. This study aims to contribute to this literature, particularly regarding the crucial role of CS in the interaction between the ocean and the atmosphere. This research uses the composite difference method to compare changes in Wind Speed (WS), Latent Heat Flux (LHF), Sensible Heat Flux (SHF), Shortwave Radiation (SWR), Longwave Radiation (LWR), and Net Surface Heat Flux (NSHF) during CS phases versus neutral conditions no CS (nCS). The composite difference results indicate an increase in wind speed in the study area, Natuna Sea, with values of 1.17 m/s, 1.45 m/s, and 1.69 m/s for December, January, and February, respectively. This finding explains that the increase in wind speed significantly influences LHF in the negative direction, meaning more LHF is transferred from the ocean to the atmosphere during the CS phase. LHF also predominantly affects NSHF in the study area during the CS period, indicating that more NSHF is leaving the ocean and entering the atmosphere compared to the amount entering the ocean from the atmosphere during the CS phase.

Dependence of longwave broadband clear-sky radiative fluxes and heating rates on water vapour continuum model updates

Dependence of longwave broadband clear-sky radiative fluxes and heating rates on water vapour continuum model updates

Reduction of Pacific Double‐ITCZ Bias by Convection Parameterization in NCAR CESM2.2

AbstractThe impact of convective closure on the double‐ITCZ bias in the NCAR CESM2.2 is investigated in this study. The standard CESM2.2 simulates a remarkable double‐ITCZ bias in the central and eastern Pacific, especially in boreal winter and spring. Modifications to the closure in convection parameterization scheme greatly reduce the double‐ITCZ bias in all seasons, demonstrating that convection parameterization can substantially influence the double‐ITCZ bias in CESM2.2. Further analyses suggest that convection parameterization can modulate the tropical atmosphere‐ocean feedback processes, through which it influences the SST in the southern ITCZ region and hence the double‐ITCZ bias. The changes in the upper ocean temperature advection induced by modified convective closure plays important roles in reducing the warm SST bias and double‐ITCZ precipitation bias in the southern ITCZ region. The modified convective closure improves the low‐level cloud and shortwave cloud radiative forcing in the southeastern Pacific. However, surface heat flux plays only a limited role in reducing warm SST bias and double ITCZ bias because the impacts of shortwave radiation changes are largely canceled by changes in longwave radiation and latent heat flux.

Description and validation of the Japanese algorithm for radiative flux and heating rate products with all four EarthCARE instruments: pre-launch test with A-Train

Abstract. This study developed an algorithm for the Level 2 (L2) atmospheric radiation flux and heating rate product by a Japanese team for Earth Cloud, Aerosol and Radiation Explorer (EarthCARE). This product offers vertical profiles of downward and upward longwave (LW) and shortwave (SW) radiative fluxes and their atmospheric heating rates. This paper describes the algorithm developed for generating products, including the atmospheric radiative transfer model and input datasets, and its validation against measurement data of radiative fluxes. In the testing phase before the EarthCARE launch, we utilized A-Train data that provided input and output variables analogous to EarthCARE, so that the developed algorithm could be directly applied to EarthCARE after its launch. The results include comparisons of radiative fluxes between radiative transfer simulations and satellite and ground-based observations that quantify errors in computed radiative fluxes at the top of the atmosphere against Clouds and the Earth's Radiant Energy System (CERES) observations and their dependence on cloud type with varying thermodynamic phases. For SW fluxes, the bias was 24.4 W m−2, and the root mean square error (RMSE) was 36.3 W m−2 relative to the CERES observations at spatial and temporal scales of 5° and 1 month, respectively. On the other hand, LW exhibits a bias of −10.7 W m−2 and an RMSE of 14.2 W m−2. When considering different cloud phases, the SW water cloud exhibited a bias of −11.7 W m−2 and an RMSE of 46.2 W m−2, while the LW showed a bias of 0.8 W m−2 and an RMSE of 6.0 W m−2. When ice clouds were included, the SW bias ranged from 58.7 to 81.5 W m−2 and the RMSE from 72.8 to 91.6 W m−2 depending on the ice-containing cloud types, while the corresponding LW bias ranged from −8.8 to −28.4 W m−2 and the RMSE from 25.9 to 31.8 W m−2, indicating that the primary source of error was ice-containing clouds. The comparisons were further extended to various spatiotemporal scales to investigate the scale dependency of the flux errors. The SW component of this product exhibited an RMSE of approximately 30 W m−2 at spatial and temporal scales of 40° and 40 d, respectively, whereas the LW component did not show a significant decrease in RMSE with increasing spatiotemporal scale. Radiative transfer simulations were also compared with ground-based observations of the surface downward SW and LW radiative fluxes at selected locations. The results show that the bias and RMSE for SW are −17.6 and 172.0 W m−2, respectively, which are larger than those for LW that are −5.6 and 19.0 W m−2, respectively.

An Increase in Autumn Marine Heatwaves Caused by the Indian Ocean Dipole in the Bay of Bengal

Abstract This study investigates the interannual variability of marine heatwaves (MHWs) in the Bay of Bengal (BOB) associated with the Indian Ocean dipole (IOD) from 1982 to 2021. The results revealed a significant positive correlation at the 95% confidence level between the IOD and MHW days in the central bay at the peak of the IOD in autumn. During positive IOD (pIOD) events, the central bay experienced more MHW days in autumn, with an average increase of 7.4 days. The increased MHW days in the central bay could be primarily attributed to the enhanced net heat flux (TQ), which is 9.7 times the contribution of ocean dynamic processes (horizontal advection + entrainment). The reduced latent heat flux loss and enhanced shortwave radiation due to the anomalous atmospheric low-level high pressure associated with the pIOD account for 63% and 50%, respectively, of the anomalous enhanced TQ, while the longwave radiation and sensible heat flux make smaller contributions of −20% and 7%. In addition, thermocline deepening in the southwestern bay, caused by this anomalous high pressure and associated anticyclonic wind anomalies, favors the occurrence and persistence of MHWs by reducing the mixed-layer cooling rate. In addition to the influence of the IOD, El Niño–Southern Oscillation mainly affects MHWs from winter to the following summer, which confirms the result of a previous study.

Effect of microphysics scheme and data assimilation on hydrometeor and radiative flux simulations in the Arctic.

Although clouds are a major factor influencing atmospheric environments in the Arctic, numerical simulations of Arctic clouds are uncertain. In this study, the effects of microphysics scheme and data assimilation (DA) on the simulation of clouds, hydrometeors and radiative fluxes in the Arctic were investigated using the polar weather research and forecasting (WRF) model and three-dimensional variational DA. Compared with the WRF 5-class (WSM5) microphysics scheme, when the Morrison double-moment (Morrison) scheme was used, the simulated amount of cloud ice water decreased by approximately 68%. In contrast, the amount of water vapour, cloud liquid water, snow and rain in the atmosphere increased. With DA, the amount of water vapour increased, leading to increased hydrometeors. The cloud liquid water increased in the middle and low atmospheres when Morrison was used, whereas it increased in the low atmosphere when DA was used. The increase in cloud liquid water by using Morrison resulted in a decrease in the downward short-wave radiative flux at the surface, whereas using DA increased the downward long-wave radiative flux. Changing the microphysics scheme induced redistribution of the region and amounts of hydrometeors, whereas DA induced an increase in hydrometeors in specific regions by adding observation information to the model states.

Drivers of the mean biases of the tropical atmospheric circulation in a moist static energy framework

In this study, we apply the moist static energy for first baroclinic mode (MSEB) model to examine the drivers of the mean tropical atmospheric circulation biases over oceanic regions. The model diagnoses the vertical motion in an air column of the tropical regions based on net energy heat flux and advection of moisture or heat into the air column in relation to the stability of the air column due to the gradients in moist static energy. Analysis of Coupled Model Intercomparison Project (CMIP) and Atmospheric Model Intercomparison Project (AMIP) simulations helped to identified errors intrinsic to the atmospheric models or errors due to atmosphere–ocean coupling process. Despite some limitations of the MSEB model, our multi-model mean analysis over the entire tropical ocean reveals that the primary drivers of the tropical circulation biases mostly result from intrinsic atmospheric model errors in top of the atmosphere longwave radiation and surface latent heats fluxes, suggesting a link to biases in the hydrological cycle. Oceanic coupling significantly enhanced some of the biases. Biases in the advection of moist static energy also play an important role, while biases in the gross moist stability profiles play only a minor role. Further, we examine the inter-model variations in four main regional large-scale biases (double-ITCZ, Pacific cold tongue, southward shift of ITCZ over the Atlantic, and dipole bias over the Indian Ocean). The analysis suggests that regional bias patterns across general circulation models are primarily driven by coupling errors, except for the bias in the Indian Ocean, which is intrinsic to the atmospheric model but amplified by coupling. Notably, longwave radiation biases at the top of the atmosphere are prevalent among the four bias patterns, as well as biases in moisture advection over the Atlantic. Our results underscore the significant role of net longwave radiation at the top of the atmosphere, an aspect not sufficiently emphasized in previous studies.

HEAT BUDGET OF THE BARENTS SEA SURFACE IN WINTER

Variability of the total heat balance (HB) of the Barents Sea during the cold period of the year has been studied. The cold period is that of cooling of the sea surface when the heat flux is permanently oriented towards the atmosphere. The contribution of two major components of the HB, i. e. sensible and latent heat fluxes, to the observed increase of the total winter heat transfer at the sea-atmosphere interface has been estimated. Data on short-wave and long-wave radiation fluxes, and sensible and latent heat values were obtained from the atmos-pheric reanalysis of the European Center for Medium-term Weather Forecasting ERA5. HB of the sea surface was calculated as a sum of short-wave and long-wave radiation fluxes and those of sensible and latent heat. The total HB, as well as the total flux of sensible and latent heat for the cold period were calculated by summing up the corresponding values between the start and end dates of the cooling season. Calculations demonstrated an increase in the sum of HB over the cold season for the northern part of the Barents Sea (up to 2000 MJ/m2 over 40 years), and a decrease in the southern part of the sea (up to 1000 MJ/m2 over 40 years). In the northern part of the sea, the contribution of sensible and latent heat fluxes decreases to 0,3-0,4. The observed trend of sum of HB over the cold season and its turbulent components could with high probability be explained by increasing difference between air temperature and sea surface temperature.

SENSITIVITY OF A 1D LAKE MODEL TO THE INPUT METEOROLOGICAL DATA

The paper evaluates how the choice of a source of meteorological data used as boundary conditions and the changes in model calibration parameters affect the adequate performance of a model of lake thermo- and hydrodynamics. The quality of simulation of water temperature dynamics in a small lake by a onedimensional GLM model using data from an automatic meteorological station on the lake shore, a state weather station and two global reanalyses was quantitatively assessed. It is shown that the best modeling result (RMSE of water temperature calculation 0,8-2,0°C, Nash-Sutcliffe efficiency >0,7) can be achieved using data sets that explicitly provide incoming shortwave and longwave radiation fluxes. At the same time, good representation of the bottom water temperature requires correct setting of wind regime, which is only possible if data from instrumental ground-based observations at a stationary weather station are applied. Combining ground-based observations of wind speed, air temperature and humidity with radiation fluxes from global reanalyses makes it possible to achieve a calculation error ≤1°C at all depths.The analysis of model sensitivity to calibration parameters in case when the reanalysis data are applied showed that parameters related to wind mixing, i.e. the scaling factor for wind speed and constants related to the in-model description of wind impact energy, have the greatest influence on the final calculation error. If we change the intensity coefficients of other types of mixing during calibration it does not lead to an obvious trend in the quantitative estimates of modeling quality. It could also be reasonable to introduce correction multipliers to the values of air temperature and solar radiation fluxes, thus neutralizing the effect of unrepresentativeness of the meteorological data applied for a particular lake, as well as to correct the value of solar radiation extinction coefficient relative to the value obtained from the Secchi depth. The results of the study could be used to justify the choice of meteorological data source and to optimize the methods of calibration of lake thermal stratification models

Strengthened impact of late autumn Arctic sea ice on Asian winter cold extremes after 1999/2000

Winter cold extremes (WCEs) frequently plague densely populated areas of Asia, leading to substantial economic losses and even fatalities. It has been found that the late autumn sea ice concentration (SIC) anomalies in the northern (SICN) and southern Arctic (SICS) are significantly positively and negatively correlated with the occurrence frequency of WCE in Asia, respectively (Wang and Su 2024). Our study demonstrates that the impacts of SICN and SICS have strengthened after 1999/2000. Specifically, before 1999/2000, the influences of SICN and SICS on the Asian WCE (AWCE) were relatively weak, possibly related to the weak intensity of SICS and the limited correlation between SICN and SICS. After 1999/2000, the interannual variability of SICS became larger and anti-correlated with that of SICN, resulting in a stronger teleconnection between the Arctic SIC and AWCE. It is revealed that after 1999/2000, the greater loss of SICS modified atmospheric stability through changes in surface heat fluxes and surface upward longwave radiation fluxes. This alteration weakened the magnitudes of westerly winds and increased the frequency of blocking events over the northern Eurasian continent, leading directly to a higher occurrence of cold extremes in Asia. These interdecadal differences in the influence of Arctic SIC on AWCE may be associated with long-term climate change.

Projected energy and hydrological budgets over the Indus River Basin under a CORDEX-SA regional climate model framework

The Indus River is one of the largest transboundary rivers in Asia originating from Tibet autonomous region of China. This supplies water to the great plains of Punjab, significantly influencing agricultural productivity and shaping the socioeconomic conditions of the region's inhabitants. The present study investigates the potential impact of climate change on the water resources of the Indus River Basin (IRB). The study utilized the output from a regional climate model, REMO, to examine the projected change in energy and hydrological budget at 1.5, 2 specific warming levels and at the end of the century over IRB under three different representative concentration pathways (RCPs). The projected rise in the temperature from the historical period to the end of the century (both summer and winter) can be attributed to the increase in net downward energy flux compared to net upward energy flux. In the mid-century, the downward longwave radiation flux (sensible and latent heat flux) plays a dominant role in determining the surface energy balance during winter (summer). While, the combined impact of the energy components becomes more dominant at the end of the century for both seasons. Rainfall is projected to increase in the mountains of the upper Indus basin and gradually decline on the plains of the lower Indus basin till the end of the century. The projected decline in water storage over the plains of IRB can be attributed to the combination of declining rainfall and increasing evaporation. This will exert significant pressure on agriculture, industry and more importantly on the potable water supply. The IRB is found to be highly susceptible to climate extremes such as floods and drought. Climate change information is crucial for policy planners, governance, decision-makers, management authorities, etc. as it enables the implementation of better management practices, Additionally, it provides both short-term and long-term goals for a mitigation-based approach to reduce the impact of climate change.

Low-Level Liquid-Bearing Clouds Contribute to Seasonal Lower Atmosphere Stability and Surface Energy Forcing over a High-Mountain Watershed Environment

Abstract Measurements of atmospheric structure and surface energy budgets distributed along a high-altitude mountain watershed environment near Crested Butte, Colorado, from two separate, but coordinated, field campaigns, Surface Atmosphere Integrated field Laboratory (SAIL) and Study of Precipitation, the Lower Atmosphere, and Surface for Hydrometeorology (SPLASH), are analyzed. This study identifies similarities and differences in how clouds influence the radiative budget over one snow-free summer season (2022) and two snow-covered seasons (2021/22; 2022/23) for this alpine location. A relationship between lower-tropospheric stability stratification and longwave radiative flux from the presence or absence of clouds is identified. When low clouds persisted, often with signatures of supercooled liquid in winter, the lower troposphere experienced weaker stability, while radiatively clear skies that are less likely to be influenced by liquid droplets were associated with appreciably stronger lower-tropospheric stratification. Corresponding surface turbulent heat fluxes partitioned differently based upon the cloud–stability stratification regime derived from early morning radiosounding profiles. Combined with the differences in the radiative budget largely resulting from dramatic seasonal differences in surface albedo, the lower atmosphere stratification, surface energy budget, and near-surface thermodynamics are shown to be modified by the effective longwave radiative forcing of clouds. The diurnal evolution of thermodynamics and surface energy components varied depending on the early morning stratification state. Thus, the importance of quiescent versus synoptically active large-scale meteorology is hypothesized as a critical forcing for cloud properties and associated surface energy budget variations. The physical relationships between clouds, radiation, and stratification can provide a useful suite of metrics for process understanding and to evaluate numerical models in such an undersampled, highly complex terrain environment.

Local and Nonlocal Biophysical Effects of Historical Land Use and Land Cover Changes in CMIP6 Models and the Intermodel Uncertainty

AbstractLand use and land cover changes (LULCCs) can influence surface temperature through local and nonlocal biophysical processes, which remain inadequately addressed. In this study, we separate the local and nonlocal effects of historical (1850–2014) LULCCs based on model outputs from the Coupled Model Intercomparison Project Phase 6. We also attempt to explore the sources of intermodel differences in the effects of LULCCs. The multimodel mean shows a cooling effect of −0.05°C (with an intermodel range of −0.24–0.06°C) at the global scale due to cropland and pastureland expansion, consisting of dominant nonlocal cooling of −0.06°C (with an intermodel range of −0.26–0.06°C) and slight local warming of 0.01°C (with an intermodel range of −0.01–0.05°C). The modeling results show some clear consistency in the effects of LULCCs despite considerable intermodel uncertainties. The local effects cause warming at low latitudes and cooling in boreal regions via changes in upward shortwave radiation and sensible and latent heat fluxes. The nonlocal effects mainly cause cooling via decreases in downward longwave radiation and increases in upward shortwave radiation. Intermodel differences in the total effects are dominated by those in the nonlocal effects, which are further attributed to divergent changes in downward longwave radiation and sensible heat flux across the models. This study highlights the importance of the nonlocal effects of LULCCs in terms of strength and intermodel uncertainty, with implications for designing land‐based solutions aimed at climate change mitigation.

Aerosol impacts on the East Asian winter monsoon: Insights from TaiESM1 and CMIP6 simulations

AbstractThe East Asian winter monsoon (EAWM) is an important climate pattern in Southeast Asia. This study delved into the aerosol effects on the EAWM by analysing simulations conducted with the Taiwan Earth System Model version 1 (TaiESM1) model, part of the Coupled Model Intercomparison Project Phase 6 (CMIP6). Our assessment, validated against observational and reanalysis data, revealed that TaiESM1 effectively replicates the robust circulation of the EAWM and aerosol concentrations, placing its performance above average level among CMIP6 models. Notably, the simulated global mean aerosol optical thickness exhibited an approximately 20% increase from 1850 to 2014. The increased aerosols corresponded to a weakened Aleutian Low and an intensified Siberian High, leading to a weakened EAWM in the lower atmosphere over extratropical areas. In addition, the cooling across the Northern Hemisphere might affect enhanced northerly winds at approximately 10°N, which are situated in the southern part of the EAWM. An analysis of the near‐surface temperature budget indicated that the aerosol‐induced cooling in East China and India was primarily driven by changes in shortwave and longwave radiation fluxes, albeit slightly offset by sensible heat and latent heat fluxes. Furthermore, our study also reveals that while the mechanisms through which anthropogenic aerosols affect the northern portion of the EAWM vary across most CMIP6 models, their impacts on the tropical region remain consistent.

A simple three-cylinder radiometer and low-speed anemometer to characterize human extreme heat exposure.

As populations and temperatures of urban areas swell, more people face extreme heat and are at increasing risk of adverse health outcomes. Radiation accounts for much of human heat exposure but is rarely used as heat metric due to a lack of cost-effective and accurate sensors. To this end, we fuse the concepts of a three-globe radiometer-anemometer with a cylindrical human body shape representation, which is more realistic than a spherical representation. Using cost-effective and readily available materials, we fabricated two combinations of three cylinders with varying surface properties. These simple devices measure the convection coefficient and the shortwave and longwave radiative fluxes. We tested the devices in a wind tunnel and at fourteen outdoor sites during July 2023's record-setting heat wave in Tempe, Arizona. The average difference between pedestrian-level mean radiant temperature (MRT) measured using research-grade 3-way net radiometers and the three-cylinder setup was 0.4 3.0°C ( 1 SD). At most, we observed a 10°C MRT difference on a white roof site with extreme MRT values (70°C to 80°C), which will be addressed through discussed design changes to the system. The measured heat transfer coefficient can be used to calculate wind speed below 2m·s-1; thus, the three cylinders combined also serve as a low-speed anemometer. The novel setup could be used in affordable biometeorological stations and deployed across urban landscapes to build human-relevant heat sensing networks.

Resilience of Amazon rainfall to CO2 removal forcing

Over the Amazon region, rainfall-induced changes to CO2 pathways significantly impact humans and multiple ecosystems. Its resilience is of vital importance, and idealized CO2 removal experiments indicate that declining trends in rainfall amounts are irreversible and exhibit a deficiency when the CO2 concentration returns to the pre-industrial level. The irreversible decline in Amazon rainfall is mainly due to the weakened ascent, further led by two main causes. (1) Enhanced tropospheric warming and a wetter atmospheric boundary layer over the tropics during CO2 removal generate a strong meridional gradient of temperature and specific humidity; driven by prevailing northeasterly winds, negative moist enthalpy advection occurs, which in turn weakens the ascent over the Amazon and results in anomalous drought. (2) The enhanced radiative cooling of atmospheric column. Driven by the negative lapse-rate feedback, the outgoing longwave radiative flux increases in the clear-sky atmosphere. As a result, the anomalous diabatic descent generates to maintain the energy balance of the atmospheric column. This result implies that the symmetric removal of CO2 does not guarantee full recovery of regional precipitation.

Improving indoor environmental quality in an affordable house by using a vegetated wall: A case study in subtropical Brazil

Indoor environmental quality of buildings, including thermal, acoustic, visual comfort, and air quality, directly impacts the comfort, health, and productivity of occupants. However, in Brazil, the high deficit of affordable housing units has led to a situation where environmental quality is often overlooked in favour of low investment costs, prioritizing quantity over quality. Furthermore, the poorest segments of the population, who rely on affordable housing, are disproportionately affected by energy costs. Therefore, it is crucial to conduct research on low-cost energy solutions for social housing to improve the sustainability of people's lives. In this light, a study was conducted to monitor the energy performance of a vegetated wall made of deciduous species and compare it to a bare wall used in an affordable house in subtropical Brazil. Parameters, such as internal and external surface temperatures, nearby microclimatic conditions, and heat transfer through the vegetated and bare walls, were monitored every 5 min over a two-year period. The heat flux analysis revealed that the vegetated wall reduced conductive heat up to 83 % during summer days, significantly lowering the external surface temperature by 8.6 °C due to the presence of the plant layer. Moreover, the vegetated wall generally exhibited lower shortwave and longwave radiative and convective heat fluxes. These findings contribute to our understanding of energy transfer through vegetated walls in subtropical Brazil, including the impact of adjacent microclimatic conditions. Furthermore, the results confirm the potential of vegetated walls to effectively reduce cooling and heating demands at a minimal additional cost.

Projection on elevation-dependent and latitude-dependent warming over Antarctica from CMIP6 under different socioeconomic scenarios

Many studies have focused on elevation-dependent warming (EDW) across high mountains, but few studies have examined both EDW and LDW (latitude-dependent warming) on Antarctic warming. This study analyzed the Antarctic amplification (AnA) with respect to EDW and LDW under SSP1–2.6, SSP2–4.5, SSP3–7.0 and SSP5–8.5 from Coupled Model Intercomparison Project Phase 6 (CMIP6) during the period 2015–2100. The results show that the AnA appears under all socioeconomic scenarios, and the greatest signal appears in austral autumn. In the future, Antarctic warming is not only elevation-dependent, but also latitude-dependent. Generally, positive EDW of mean temperature (Tmean), maximum temperature (Tmax) and minimum temperature (Tmin) appear in the range of 1.0–4.5 km, and the corresponding altitudinal amplification trends are 0.012/0.012/0.011 (SSP1–2.6)—0.064/0.065/0.053 (SSP5–8.5) °C decade−1•km−1. Antarctic EDW demonstrates seasonal differences, and is strong in summer and autumn and weak in winter under SSP3–7.0 and SSP5–8.5. For Tmean, Tmax and Tmin, the feature of LDW is varies in different latitude ranges, and also shows seasonal differences. The strongest LDW signal appears in autumn, and the warming rate increases with increasing latitude at 64–79°S under SSP1–2.6. The similar phenomenon can be observed at 68–87°S in the other cases. Moreover, the latitude component contributes more to the warming of Tmean and Tmax relative to the corresponding altitude component, which may relates to the much larger range of latitude (∼2600 km) than altitude (∼4.5 km) over Antarctica, while the EDW contributes more warming than LDW in the changes in Tmin in austral summer. Moreover, surface downwelling longwave radiation, water vapor and latent heat flux are the potential factors influencing Antarctic EDW, and the variation in surface downwelling longwave radiation can also be considered as an important influencing factor for Antarctic LDW. Our results provide preliminary insights into EDW and LDW in Antarctica.

Geotextile protection of glacier: Observed and simulated impacts on energy and mass balance

The detailed physical processes involved in slowing glacier ablation by material cover remain poorly understood so far. In the present study, using the snow cover model SNOWPACK, the effect of geotextile cover on the energy and mass balance at the tongue of the Urumqi Glacier No. 1 (Chinese Tien Shan) was simulated between July 12, 2022 and August 31, 2022. The mass changes and the energy fluxes with and without material cover were compared. The results indicated that the geotextile covering reduced glacier ablation by approximately 68% compared to the ablation in the uncovered regions. The high solar reflectivity of the geotextile reduced the net short-wave radiation energy available for the melt by 45%. Thermal insulation of the geotextile reduced the sensible heat flux by 15%. In addition, the wet geotextile exerted a cooling effect through long-wave radiation and negative latent heat flux. This cooling effect reduced the energy available for ablation by 20%. Consequently, only 37% of the energy was used for melting compared to that used in the uncovered regions (67%). Sensitivity experiments revealed that the geotextile cover used at a thickness range of 0.045–0.090 m reduced the ice loss by approximately 68%–72%, and a further increase in the thickness of the geotextile cover led to little improvements. A higher temperature and greater wind speed increased glacier ablation, although their effects were small. When the precipitation was set to zero, it led to a significantly increased melt. Overall, the geotextile effectively protected the glacier tongue from rapid melting, and the observed results have provided inspiration for developing an effective and sustainable approach to protect the glaciers using geotextile cover.

Atmospheric Latent Energy Transport Pathways into the Arctic and Their Connections to Sea Ice Loss during Winter over the Observational Period

Abstract To investigate patterns of horizontal atmospheric latent energy (LE) transport toward the Arctic, we applied the self-organizing maps (SOM) method to the daily vertically integrated horizontal LE flux from ERA5 in winter (January–March) during 1979–2021. A clear picture depicting the LE transport to the Arctic at a synoptic scale then emerged, with four primary transport pathways identified: the northern Europe, the Davis Strait, the Greenland Sea, and the Bering Strait pathways. The four primary pathways occurred at a comparable frequency, and noticeable interannual variability was observed in their time series of frequency during 1979–2021. Further analysis suggested that the northward LE transport through all these pathways is significantly modulated by cyclones, with the northern Europe and the Greenland Sea pathways being mostly affected. Generally, more frequent and stronger cyclones were observed near the entry regions of LE transport compared to other regions. Moreover, this study provides a comprehensive picture of how atmospheric LE transport is related to air temperature, moisture, surface heat flux, and sea ice anomalies over the Arctic Ocean in winter. Through a thermodynamic perspective, we argue that the deleterious impacts of poleward LE transport on Arctic sea ice are to a large extent attributable to the enhanced local atmosphere–ice interactions, which increase downward longwave radiation (DLR) plus turbulent fluxes, consequently warming the surface and promoting the loss of sea ice. According to the quantitative results, among the four primary pathways, LE transport through the Davis Strait and the Greenland Sea could cause the loss of Arctic sea ice most efficiently.