Exploring the complex relationship between the freeze-thaw cycle and the surface energy budget (SEB) is crucial for deepening our comprehension of climate change. Drawing upon extensive field monitoring data of the Qinghai-Tibet Plateau, this study examines how surface energy accumulation influences the thawing depth. Combined with Community Land Model 5.0 (CLM5.0), a sensitivity test was designed to explore the interplay between the freeze-thaw cycle and the SEB. It is found that the freeze-thaw cycle process significantly alters the distribution of surface energy fluxes, intensifying energy exchange between the surface and atmosphere during phase transitions. In particular, an increase of 65.6% is observed in the ground heat flux during the freezing phase, which subsequently influences the sensible and latent heat fluxes. However, it should be noted that CLM5.0 has limitations in capturing the minor changes in soil moisture content and thermal conductivity during localized freezing events, resulting in an imprecise representation of the complex freeze-thaw dynamics in cold regions. Nevertheless, these results offer valuable insights and suggestions for improving the parameterization schemes of land surface models, enhancing the accuracy and applicability of remote sensing applications and climate research.

The presence of taliks (perennially unfrozen zones in permafrost areas) adversely affects the thermal stability of infrastructure in cold regions, including roads. The role of heat advection on talik development and feedback on permafrost degradation has not been quantified methodically in this context. We incorporate a surface energy balance model into a coupled groundwater flow and energy transport numerical model (SUTRA-ice). The model, calibrated with long-term observations (1997-2018 on the Alaska Highway), is used to investigate and quantify the role of heat advection on talik initiation and development under a road embankment. Over the 25-year simulation period, the new model is driven by reconstructed meteorological data and has a good agreement with near surface soil temperatures. The model successfully reproduces the increasing depth to the permafrost table (mean absolute error <0.2 m), and talik development. The results demonstrate that heat advection provides an additional energy source that expedites the rate of permafrost thaw and roughly doubles the rate of permafrost table deepening, compared to purely conductive thawing. Talik initially formed and grew over time under the combined effect of water flow, snow insulation, road construction and climate warming. Talik formation creates a new thermal state under the road embankment, resulting in acceleration of underlying permafrost degradation, due to the positive feedback of heat accumulation created by trapped unfrozen water. In a changing climate, mobile water flow will play a more important role in permafrost thaw and talik development under road embankments, and is likely to significantly increase maintenance costs and reduce the long-term stability of the infrastructure.

The surface energy budget over the Qinghai-Tibet Plateau (QTP) and the Arctic significantly influences the climate system with global consequences. The performances of 30 selected Coupled Model Intercomparison Project Phase 6 (CMIP6) models were evaluated based on six sites in the QTP and Arctic. The simulation results for latent heat flux (LE) were more accurate in the QTP, where the correlation coefficient and root mean square error (RMSE) were 0.9 and 30 W m(-2), respectively. The results for sensible heat flux (H) were more accurate in the Arctic, the correlation coefficient and RMSE were 0.8 and 24 W m(-2), respectively. Furthermore, the multiple models mean results revealed that the surface energy flux had seasonal variation and regional differences over the QTP and the Arctic. In the QTP, H was the lowest in winter, increased in spring, and reached the maximum in summer. However, the transitional changes in spring and autumn were not apparent in the Arctic, mainly due to seasonal net radiation difference between the two places. LE was affected by precipitation and surface soil moisture content. This work is important for understanding land-atmosphere interactions and useful for improving the accuracy of land surface models simulations.

The surface energy budget is closely related to freeze-thaw processes and is also a key issue for land surface process research in permafrost regions. In this study, in situ data collected from 2005 to 2015 at the Tanggula site were used to analyze surface energy regimes, the interaction between surface energy budget and freeze-thaw processes. The results confirmed that surface energy flux in the permafrost region of the Qinghai-Tibetan Plateau exhibited obvious seasonal variations. Annual average net radiation (R-n) for 2010 was 86.5 W m(-2), with the largest being in July and smallest in November. Surface soil heat flux (G(0)) was positive during warm seasons but negative in cold seasons with annual average value of 2.7 W m(-2). Variations in R-n and G(0) were closely related to freeze-thaw processes. Sensible heat flux (H) was the main energy budget component during cold seasons, whereas latent heat flux (LE) dominated surface energy distribution in warm seasons. Freeze-thaw processes, snow cover, precipitation, and surface conditions were important influence factors for surface energy flux. Albedo was strongly dependent on soil moisture content and ground surface state, increasing significantly when land surface was covered with deep snow, and exhibited negative correlation with surface soil moisture content. Energy variation was significantly related to active layer thaw depth. Soil heat balance coefficient K was > 1 during the investigation time period, indicating the permafrost in the Tanggula area tended to degrade.

The surface energy budget is closely related to freeze-thaw processes and is also a key issue for land surface process research in permafrost regions. In this study, in situ data collected from 2005 to 2015 at the Tanggula site were used to analyze surface energy regimes, the interaction between surface energy budget and freeze-thaw processes. The results confirmed that surface energy flux in the permafrost region of the Qinghai-Tibetan Plateau exhibited obvious seasonal variations. Annual average net radiation (R-n) for 2010 was 86.5 W m(-2), with the largest being in July and smallest in November. Surface soil heat flux (G(0)) was positive during warm seasons but negative in cold seasons with annual average value of 2.7 W m(-2). Variations in R-n and G(0) were closely related to freeze-thaw processes. Sensible heat flux (H) was the main energy budget component during cold seasons, whereas latent heat flux (LE) dominated surface energy distribution in warm seasons. Freeze-thaw processes, snow cover, precipitation, and surface conditions were important influence factors for surface energy flux. Albedo was strongly dependent on soil moisture content and ground surface state, increasing significantly when land surface was covered with deep snow, and exhibited negative correlation with surface soil moisture content. Energy variation was significantly related to active layer thaw depth. Soil heat balance coefficient K was > 1 during the investigation time period, indicating the permafrost in the Tanggula area tended to degrade.

Impacts of absorbing and scattering aerosols on global energy balance are investigated with a global climate model. A series of sensitivity experiments perturbing emissions of black carbon and sulfate aerosols individually is conducted with the model to explore how components of global energy budget change in response to the instantaneous radiative forcing due to the two types of aerosols. It is demonstrated how differing vertical structures of the instantaneous radiative forcing between the two aerosols induce distinctively different proportions of fast and slow climate responses through different energy redistribution into atmosphere and surface. These characteristics are quantified in the form of the whole picture of global energy budget perturbations normalized by the top-of-atmosphere instantaneous radiative forcing. The energy budget perturbation per unit instantaneous forcing thus quantified reveals relative magnitudes of changes to different component fluxes in restoring atmospheric and surface energy balances through fast and slow responses. The normalized picture then directly links the initial forcing to the eventual climate responses, thereby explaining how starkly different responses of the global-mean temperature and precipitation are induced by the two types of aerosols. The study underscores a critical need for better quantifications of the forcings' vertical structure and atmospheric rapid adjustment for reliable estimates of climatic impact of absorbing and scattering aerosols. In particular, cloud responses through the indirect and semidirect effects and the sensible heat decrease in response to stabilized atmosphere due to the black carbon heating are identified as key uncertain components in the global energy budget perturbation. Plain Language Summary The minute particles suspended in the atmosphere, called aerosols, have warming or cooling impacts on climate depending on their color that determines their ability to scatter or absorb the sunlight. The black aerosols, like black carbon, enhance the heating on atmosphere and reduce the sunlight reaching the surface through absorbing the sunlight, while the white aerosols, like sulfate, directly cool the surface with little influence on atmosphere through scattering the sunlight. This study analyzes simulations with a global climate model to quantify how the two types of aerosols with such different characteristics modulate the Earth's energy budget differently to induce distinctively different responses of the global-mean temperature and precipitation. The results explain why the global temperature response to perturbations of black carbon tends to be muted in contrast to the pronounced response to perturbations of sulfate. The energy budget picture also illustrates how increased black carbon can increase and decrease the global precipitation through two competing pathways to result a net decrease while increased sulfate monotonically decreases the global precipitation. The findings of this study provide a theoretical basis for better quantifying the climate change driven by future emission changes of different types of aerosols.

Understanding the dynamics of heat transfer mechanisms is critical for forecasting the effects of climate change on arctic river temperatures. Climate influences on arctic river temperatures can be particularly important due to corresponding effects on nutrient dynamics and ecological responses. It was hypothesized that the same heat and mass fluxes affect arctic and temperate rivers, but that relative importance and variability over time and space differ. Through data collection and application of a river temperature model that accounts for the primary heat fluxes relevant in temperate climates, heat fluxes were estimated for a large arctic basin over wide ranges of hydrologic conditions. Heat flux influences similar to temperate systems included dominant shortwave radiation, shifts from positive to negative sensible heat flux with distance downstream, and greater influences of lateral inflows in the headwater region. Heat fluxes that differed from many temperate systems included consistently negative net longwave radiation and small average latent heat fluxes. Radiative heat fluxes comprised 88% of total absolute heat flux while all other heat fluxes contributed less than 5% on average. Periodic significance was seen for lateral inflows (up to 26%) and latent heat flux (up to 18%) in the lower and higher stream order portions of the watershed, respectively. Evenly distributed lateral inflows from large scale flow differencing and temperatures from representative tributaries provided a data efficient method for estimating the associated heat loads. Poor model performance under low flows demonstrated need for further testing and data collection to support the inclusion of additional heat fluxes.

Global warming will bring about changes in surface energy balance of Arctic ecosystems, which will have implications for ecosystem structure and functioning, as well as for climate system feedback mechanisms. In this study, we present a unique, long-term (2000-2010) record of summer-time energy balance components (net radiation, R-n; sensible heat flux, H; latent heat flux, LE; and soil heat flux, G) from a high Arctic tundra heath in Zackenberg, Northeast Greenland. This area has been subjected to strong summer-time warming with increasing active layer depths (ALD) during the last decades. We observe high energy partitioning into H, low partitioning into LE and high Bowen ratio (beta = H/LE) compared with other Arctic sites, associated with local climatic conditions dominated by onshore winds, slender vegetation with low transpiration activity and relatively dry soils. Surface saturation vapour pressure deficit (D-s) was found to be an important variable controlling within-year surface energy partitioning. Throughout the study period, we observe increasing H/R-n and LE/R-n and decreasing G/R-n and beta, related to increasing ALD and decreasing soil wetness. Thus, changes in summer-time surface energy balance partitioning in Arctic ecosystems may be of importance for the climate system.