An official website of the United States government
Abstract Improved modeling of permafrost active layer freeze‐thaw plays a crucial role in understanding the response of the Arctic ecosystem to the accelerating warming trend in the region over the past decades. However, modeling the dynamics of the active layer at diurnal time scale remains challenging using the traditional models of freeze‐thaw processes. In this study, a physically based analytical model is formulated to simulate the thaw depth of the active layer under changing boundary conditions of soil heat flux. Conservation of energy for the active layer leads to a nonlinear integral equation of the thaw depth using a temperature profile approximated from the analytical solution of the heat transfer equation forced by ground heat flux. Temporally variable ground heat flux is estimated using non‐gradient models when field observations are not available. Validation of the proposed model conducted against field data obtained from three Arctic forest and tundra sites demonstrates that the model is able to simulate both thaw depth and soil temperature profiles accurately. The model has the potential to estimate regional variability of the thaw depth for permafrost related applications.
more »
« less
Modeling Active Layer Depth of Permafrost under Changing Surface Boundary Conditions
A physically based model is formulated for the active layer depth of permafrost under changing boundary condition instead of constant boundary condition considered in the traditional Stefan problem. Time-varying ground heat flux is obtained from net radiation and surface temperature using the Maximum Entropy Production (MEP) model as the driver of the active layer melting process. Conductive heat flux at the melting front is approximated in terms of an analytical function of ground heat flux. The simulated active layer depth is in good agreement with the field observations.
more »
« less
- Award ID(s):
- 1724633
- PAR ID:
- 10184231
- Date Published:
- Journal Name:
- Agu
- ISSN:
- 2346-6855
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Thwaites Glacier is one of the fastest‐changing ice‐ocean systems in Antarctica. Basal melting beneath Thwaites' floating ice shelf, especially around pinning points and at the grounding line, sets the rate of ice loss and Thwaites' contribution to global sea‐level rise. The rate of basal melting is controlled by the transport of heat into and through the ice–ocean boundary layer toward the ice base. Here we present the first turbulence observations from the grounding line of Thwaites Eastern Ice Shelf. We demonstrate that contrary to expectations, the turbulence‐driven vertical flux of heat into the ice–ocean boundary layer is insufficient to sustain the basal melt rate. Instead, most of the heat required must be delivered by lateral fluxes driven by the large‐scale advective circulation. Lateral processes likely dominate beneath the most unstable warm‐cavity ice shelves, and thus must be fully incorporated into parameterizations of ice shelf basal melting.more » « less
-
Abstract Ground heat flux (G0) is a key component of the land‐surface energy balance of high‐latitude regions. Despite its crucial role in controlling permafrost degradation due to global warming,G0is sparsely measured and not well represented in the outputs of global scale model simulation. In this study, an analytical heat transfer model is tested to reconstructG0across seasons using soil temperature series from field measurements, Global Climate Model, and climate reanalysis outputs. The probability density functions of ground heat flux and of model parameters are inferred using availableG0data (measured or modeled) for snow‐free period as a reference. When observedG0is not available, a numerical model is applied using estimates of surface heat flux (dependent on parameters) as the top boundary condition. These estimates (and thus the corresponding parameters) are verified by comparing the distributions of simulated and measured soil temperature at several depths. Aided by state‐of‐the‐art uncertainty quantification methods, the developedG0reconstruction approach provides novel means for assessing the probabilistic structure of the ground heat flux for regional permafrost change studies.more » « less
-
The atmospheric boundary layer along the coastal-urban transect differs from that of urban or rural regions due to the distinctive interaction between the sea breeze and the urban heat island effect. In this manuscript, we present the observations of the atmospheric boundary layer in the Houston, Texas, area during the Coastal Urban Boundary Layer Experiment (CUBE) from June through September 2022. In order to understand the unique characteristics of the coastal urban boundary layer, we collected mean and turbulence data from micrometeorological towers and ground-based remote sensing instruments installed in the urban, coastal, bay, and rural sections within the greater Houston region. Furthermore, an urbanized weather research and forecast (WRF) model incorporating the Building Effect Parameterization and Building Energy Model (BEP-BEM) scheme is used to recognize the spatial variability of the meteorological conditions in the Houston Metro area. Compared to non-urban sites, the urban site exhibits a higher near-surface temperature throughout the day, with the highest temperature difference occurring at night due to the redistribution of the stored heat as sensible heat. During the dry period in June, we observed comparatively higher sensible heat flux in the urban site, demonstrating the heat island effect and lower latent heat flux due to lack of vegetation. The urban site had higher TKE values throughout the day than other sites because of the uneven roughness of the landscape. One of the unique findings of this study is the shift in spectral characteristics along the coastal-rural-urban transect. The power and co-spectra of zonal and vertical velocities and the vertical heat flux during the convective periods varied significantly across all the sites. The coastal site was influenced mainly by the local bay breeze shifting the peak to higher frequencies. The boundary layer height in the urban site was generally greater than in bay and rural sites due to increased convection in urban areas resulting from anthropogenic modification of land cover and waste heat from air conditioning use. The balance between the urban thermal and mechanical roughness effects was seen during the sea breeze front (SBF) event on the highest heat index day as SBF was triggered and accelerated by UHI.more » « less
-
Abstract Heat flux from the core to the mantle provides driving energy for mantle convection thus powering plate tectonics, and contributes a significant fraction of the geothermal heat budget. Indirect estimates of core‐mantle boundary heat flow are typically based on petrological evidence of mantle temperature, interpretations of temperatures indicated by seismic travel times, experimental measurements of mineral melting points, physical mantle convection models, or physical core convection models. However, previous estimates have not consistently integrated these lines of evidence. In this work, an interdisciplinary analysis is applied to co‐constrain core‐mantle boundary heat flow and test the thermal boundary layer (TBL) theory. The concurrence of TBL models, energy balance to support geomagnetism, seismology, and review of petrologic evidence for historic mantle temperatures supportsQCMB∼15 TW, with all except geomagnetism supporting as high as ∼20 TW. These values provide a tighter constraint on core heat flux relative to previous work. Our work describes the seismic properties consistent with a TBL, and supports a long‐lived basal mantle molten layer through much of Earth's history.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- The DOI is not currently available.
