Simulating heat transport of harmonic temperature signals in the Earth's shallow subsurface: Lower-boundary sensitivities

We assess the sensitivity of a subsurface thermodynamic model to the depth of its lower-boundary condition. Analytic solutions to the one-dimensional thermal diffusion equation demonstrate that boundary conditions imposed at shallow depths (2-20 m) corrupt the amplitudes and phases of propagating temperature signals. The presented solutions are for: 1) a homogeneous infinite half-space driven by a harmonic surface-temperature boundary condition, and 2) a homogeneous slab with a harmonic surface-temperature boundary condition and zero-flux lower-boundary condition. Differences between the amplitudes and phases of the two solutions range from 0 to almost 100%, depending on depth, frequency and subsurface thermophysical properties. The implications of our results are straightforward: the corruption of subsurface temperatures can affect model assessments of soil microbial activity, vegetation changes, freeze-thaw cycles, and hydrologic dynamics. It is uncertain, however, whether the reported effects will have large enough impacts on land-atmosphere fluxes of water and energy to affect atmospheric simulations

Characterizing Land–Atmosphere Coupling and the Implications for Subsurface Thermodynamics

The objective of this work is to develop a Simple Land-Interface Model (SLIM) that captures the seasonal and interannual behavior of land–atmosphere coupling, as well as the subsequent subsurface temperature evolution. The model employs the one-dimensional thermal diffusion equation driven by a surface flux boundary condition. While the underlying physics is straightforward, the SLIM framework allows a qualitative understanding of the first-order controls that govern the seasonal coupling between the land and atmosphere by implicitly representing the dominant processes at the land surface. The model is used to perform a suite of experiments that demonstrate how changes in surface air temperature and coupling conditions control subsurface temperature evolution. The work presented here suggests that a collective approach employing both complex and simple models, when joined with analyses of observational data, has the potential to increase understanding of land–atmosphere coupling and the subsequent evolution of subsurface temperatures

Technically assisted rehabilitation

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively

Combining airborne thermal infrared images and radium isotopes to study submarine groundwater discharge along the French Mediterranean coastline

The French Mediterranean coastline, which includes karstic springs discharging into coastal seas and coastal lagoons. Study focus We investigated submarine groundwater discharge (SGD), an important vector for many chemical elements that may impact the quality of the coastal environment. First, we acquired airborne thermal infrared (TIR) images to detect terrestrial groundwater inputs. Then we report in situ data (salinity; temperature; radium isotopes). We use these data i) to confirm the presence of groundwater discharge and to characterize the different systems, and ii) to quantify SGD fluxes and estimate the residence time of the water bodies. New hydrological insights for the region Few studies have been conducted on SGD along the French Mediterranean coastline. The terrestrial groundwater spring inputs in La Palme and Salses-Leucate coastal lagoons are in the range (0.04–0.11) m 3 s −1 , ≤ 2% of the local river inputs. In comparison, total SGD estimates to La Palme lagoon (0.56–1.7 m 3 s −1 ) suggest that the recirculation of lagoon water through the sediment is two orders of magnitude greater than the terrestrial groundwater inputs. At the Calanque of Port-Miou, the terrestrial groundwater flux to the coastal seas was between 0.6 and 1.2 m 3 s −1 in July 2009. This study demonstrates the application of airborne TIR remote sensing for detecting surficial groundwater springs, and the inability of the method to detect deeper, submerged springs

Recent changes in nitrate and dissolved organic carbon export from the upper Kuparuk River, North Slope, Alaska

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): G04S60, doi:10.1029/2006JG000371.Export of nitrate and dissolved organic carbon (DOC) from the upper Kuparuk River between the late 1970s and early 2000s was evaluated using long-term ecological research (LTER) data in combination with solute flux and catchment hydrology models. The USGS Load Estimator (LOADEST) was used to calculate June–August export from 1978 forward. LOADEST was then coupled with a catchment-based land surface model (CLSM) to estimate total annual export from 1991 to 2001. Simulations using the LOADEST/CLSM combination indicate that annual nitrate export from the upper Kuparuk River increased by ~5 fold and annual DOC export decreased by about one half from 1991 to 2001. The decrease in DOC export was focused in May and was primarily attributed to a decrease in river discharge. In contrast, increased nitrate export was evident from May to September and was primarily attributed to increased nitrate concentrations. Increased nitrate concentrations are evident across a wide range of discharge conditions, indicating that higher values do not simply reflect lower discharge in recent years but a significant shift to higher concentration per unit discharge. Nitrate concentrations remained elevated after 2001. However, extraordinarily low discharge during June 2004 and June–August 2005 outweighed the influence of higher concentrations in determining export during these years. The mechanism responsible for the recent increase in nitrate concentrations is uncertain but may relate to changes in soils and vegetation associated with regional warming. While changes in nitrate and DOC export from arctic rivers reflect changes in terrestrial ecosystems, they also have significant implications for Arctic Ocean ecosystems.This work was supported by the Arctic System Science Program of the National Science Foundation (OPP- 0436118) and by NSF funding for the Arctic LTER through a series of grants from 1987 to present

Seasonal Forecast of St. Louis Encephalitis Virus Transmission, Florida

Disease transmission forecasts can help minimize human and domestic animal health risks by indicating where disease control and prevention efforts should be focused. For disease systems in which weather-related variables affect pathogen proliferation, dispersal, or transmission, the potential for disease forecasting exists. We present a seasonal forecast of St. Louis encephalitis virus transmission in Indian River County, Florida. We derive an empirical relationship between modeled land surface wetness and levels of SLEV transmission in humans. We then use these data to forecast SLEV transmission with a seasonal lead. Forecast skill is demonstrated, and a real-time seasonal forecast of epidemic SLEV transmission is presented. This study demonstrates how weather and climate forecast skill verification analyses may be applied to test the predictability of an empirical disease forecast model

Effects of bottom boundary placement on subsurface heat storage: Implications for climate model simulations

A one-dimensional soil model is used to estimate the influence of the position of the bottom boundary condition on heat storage calculations in land-surface components of General Circulation Models (GCMs). It is shown that shallow boundary conditions reduce the capacity of the global continental subsurface to store heat by as much as 1.0 x 10²³ Joules during a 110-year simulation with a 10 m bottom boundary. The calculations are relevant for GCM projections that employ land-surface components with shallow bottom boundary conditions, typically ranging between 3 to 10 m. These shallow boundary conditions preclude a large amount of heat from being stored in the terrestrial subsurface, possibly allocating heat to other parts of the simulated climate system. The results show that climate models of any complexity should consider the potential for subsurface heat storage whenever choosing a bottom boundary condition in simulations of future climate change

Drought-Induced Amplification of Saint Louis encephalitis virus, Florida

We used a dynamic hydrology model to simulate water table depth (WTD) and quantify the relationship between Saint Louis encephalitis virus (SLEV) transmission and hydrologic conditions in Indian River County, Florida, from 1986 through 1991, a period with an SLEV epidemic. Virus transmission followed periods of modeled drought (specifically low WTDs 12 to 17 weeks before virus transmission, followed by a rising of the water table 1 to 2 weeks before virus transmission). Further evidence from collections of Culex nigripalpus (the major mosquito vector of SLEV in Florida) suggests that during extended spring droughts vector mosquitoes and nestling, juvenile, and adult wild birds congregate in selected refuges, facilitating epizootic amplification of SLEV. When the drought ends and habitat availability increases, the SLEV-infected Cx. nigripalpus and wild birds disperse, initiating an SLEV transmission cycle. These findings demonstrate a mechanism by which drought facilitates the amplification of SLEV and its subsequent transmission to humans