Convective heat transfer of spring meltwater accelerates active layer phase change in Tibet permafrost areas

Abstract

Abstract. Convective heat transfer (CHT) is one of the important processes that control the near-ground surface heat transfer in permafrost areas. However, this process has often not been considered in most permafrost studies, and its influence on freezing–thawing processes in the active layer lacks quantitative investigation. The Simultaneous Heat and Water (SHAW) model, one of the few land surface models in which the CHT process is well incorporated into the soil heat–mass transport processes, was applied in this study to investigate the impacts of CHT on the thermal dynamics of the active layer at the Tanggula station, a typical permafrost site on the eastern Qinghai–Tibet Plateau with abundant meteorological and soil temperature and soil moisture observation data. A control experiment was carried out to quantify the changes in active layer temperature affected by vertical advection of liquid water. Three experimental setups were used: (1) the original SHAW model with full consideration of CHT, (2) a modified SHAW model that ignores CHT due to infiltration from the surface, and (3) a modified SHAW model that completely ignores CHT processes in the system. The results show that the CHT events occurred mainly during thaw periods in melted shallow (0–0.2 m) and intermediate (0.4–1.3 m) soil depths, and their impacts on soil temperature at shallow depths were significantly greater during spring melting periods than summer. The impact was minimal during freeze periods and in deep soil layers. During thaw periods, temperatures at the shallow and intermediate soil depths simulated under the scenario considering CHT were on average about 0.9 and 0.4 ∘C higher, respectively, than under the scenarios ignoring CHT. The ending dates of the zero-curtain effect were substantially advanced when CHT was considered due to its heating effect. However, the opposite cooling effect was also present but not as frequently as heating due to upward liquid fluxes and thermal differences between soil layers. In some periods, the advection flow from the cold layer reduced the shallow and intermediate depth temperatures by an average of about −1.0 and −0.4 ∘C, respectively. The overall annual effect of CHT due to liquid flux is to increase soil temperature in the active layer and favor thawing of frozen ground at the study site.

Divergent responses of permafrost degradation to precipitation increases at different seasons on the eastern Qinghai–Tibet Plateau based on modeling approach

“…However, since the effects of increasing precipitation in different seasons offset each other, the overall impact of the precipitation increase is not substantial. On the other hand, some studies argued that the rainfall in the warm summer penetrating into soil could accelerate active layer deepening through enhanced convective heat transfer (Mekonnen et al 2021, Magnusson et al 2022, Zhao et al 2022. In this study, the increased convective heat transfer due to rainwater penetration is limited compared with the decreased conductive heat and increased latent heat, which is also consistent with the findings of Zhang et al (2021b).…”

Evaluation of Parameterization Schemes for Matric Potential in Frozen Soil in Land Surface Models: A Modeling Perspective

“…Numerous applications of the SHAW model have proven its satisfactory performance in cold regions (Flerchinger & Pierson, 1997; Flerchinger & Saxton, 1989b), covering a wide spectrum of topics, such as permafrost evolution (Wei et al., 2011), freeze‐thaw cycle characteristics (Chen et al., 2019; Cui et al., 2020), and permafrost responses to climate and land ecosystem changes (Huang & Gallichand, 2006; Kahimba et al., 2009; Link et al., 2004; Zuo et al., 2019). Our previous study (Zhao et al., 2022) on a SHAW simulation at the TGL site showed that the simulation accuracy of soil temperature and moisture content can exceed 0.7 and 0.4, respectively, in terms of the Nash‐Sutcliffe coefficient of efficiency (NSE) at most active layer depth, indicating the satisfactory performance of the SHAW model at the TGL.…”

“…It should be noted that the other model parameters were not exposed to uncertainty analysis, and their values were determined based on the TGL conditions with reference to our previous study (Zhao et al., 2022). Additionally, as the original SHAW model did not specify a residual UWC when using the Campbell scheme, we defined a minimum liquid content of 0.02 m 3 · m −3 as a threshold to avoid the occurrence of extremely low UWC simulated by the modified schemes.…”

“…5 of 21 to climate and land ecosystem changes (Huang & Gallichand, 2006;Kahimba et al, 2009;Link et al, 2004;Zuo et al, 2019). Our previous study (Zhao et al, 2022) on a SHAW simulation at the TGL site showed that the simulation accuracy of soil temperature and moisture content can exceed 0.7 and 0.4, respectively, in terms of the Nash-Sutcliffe coefficient of efficiency (NSE) at most active layer depth, indicating the satisfactory performance of the SHAW model at the TGL.…”

Analysis of free and forced convections in the flow of radiative viscous fluid with oxytactic microorganisms

“…They deduced that the efficiency of the heat exchanger is conclusively dependent on the orientation of fins. Formation of thermal boundary layer thickness in hydrothermal flow of viscous fluid over a vertical surface along with advection phenomenon was investigated by (Zhao et al, 2022). Density differences generated due to the diffusion of microorganisms is known as bioconvection.…”