Ground heat flux determination based on near-surface soil hydro-thermodynamics

Abstract. Independent measurements of radiation, sensible and latent heat fluxes and the ground heat flux are used to describe the annual cycle of the surface energy budget at a high-arctic permafrost site on Svalbard. During summer, the net short-wave radiation is the dominant energy source, while well developed turbulent processes and the heat flux in the ground lead to a cooling of the surface. About 15% of the net radiation is consumed by the seasonal thawing of the active layer in July and August. The Bowen ratio is found to vary between 0.25 and 2, depending on water content of the uppermost soil layer. During the polar night in winter, the net long-wave radiation is the dominant energy loss channel for the surface, which is mainly compensated by the sensible heat flux and, to a lesser extent, by the ground heat flux, which originates from the refreezing of the active layer. The average annual sensible heat flux of −6.9 Wm−2 is composed of strong positive fluxes in July and August, while negative fluxes dominate during the rest of the year. With 6.8 Wm−2, the latent heat flux more or less compensates the sensible heat flux in the annual average. Strong evaporation occurs during the snow melt period and particularly during the snow-free period in summer and fall. When the ground is covered by snow, latent heat fluxes through sublimation of snow are recorded, but are insignificant for the average surface energy budget. The near-surface atmospheric stratification is found to be predominantly unstable to neutral, when the ground is snow-free, and stable to neutral for snow-covered ground. Due to long-lasting near-surface inversions in winter, an average temperature difference of approximately 3 K exists between the air temperature at 10 m height and the surface temperature of the snow. As such comprehensive data sets are sparse for the Arctic, they are of great value to improve process understanding and support modeling efforts on the present-day and future arctic climate and permafrost conditions.

Download Full-text

Application of harmonic analysis to ground heat flux determination by creating an artificial fundamental period

Meteorologische Zeitschrift ◽

10.1127/metz/2019/0968 ◽

2019 ◽

Vol 28 (6) ◽

pp. 471-486

Author(s):

Hans-Dieter Wizemann ◽

Volker Wulfmeyer ◽

Thilo Streck

Keyword(s):

Heat Flux ◽

Harmonic Analysis ◽

Fundamental Period ◽

Ground Heat Flux ◽

Flux Determination

Download Full-text

The annual surface energy budget of a high-arctic permafrost site on Svalbard, Norway

The Cryosphere Discussions ◽

10.5194/tcd-3-631-2009 ◽

2009 ◽

Vol 3 (2) ◽

pp. 631-680 ◽

Cited By ~ 1

Author(s):

S. Westermann ◽

J. Lüers ◽

M. Langer ◽

K. Piel ◽

J. Boike

Keyword(s):

Heat Flux ◽

Surface Energy ◽

Latent Heat ◽

Energy Budget ◽

Sensible Heat Flux ◽

Surface Energy Budget ◽

Wave Radiation ◽

Sensible Heat ◽

Near Surface ◽

Ground Heat Flux

Abstract. Independent measurements of radiation, sensible and latent heat fluxes and the ground heat flux are used to describe the annual cycle of the surface energy budget at a high-arctic permafrost site on Svalbard. During summer, the net short-wave radiation is the dominant energy source, while well developed turbulent processes and the heat flux in the ground lead to a cooling of the surface. About 15% of the net radiation is consumed by the seasonal thawing of the active layer in July and August. The Bowen ratio is found to vary between 0.25 and 2, depending on water content of the uppermost soil layer. During the polar night in winter, the net long-wave radiation is the dominant energy loss channel for the surface, which is mainly compensated by the sensible heat flux and, to a lesser extent, by the ground heat flux, which originates from the refreezing of the active layer. The average annual sensible heat flux of −6.9 Wm−2 is composed of strong positive fluxes in July and August, while negative fluxes dominate during the rest of the year. With 6.8 Wm−2, the latent heat flux more or less compensates the sensible heat flux in the annual average. Strong evaporation occurs during the snow melt period and particularly during the snow-free period in summer and fall. When the ground is covered by snow, latent heat fluxes through sublimation of snow are recorded, but are insignificant for the average surface energy budget. The near-surface atmospheric stratification is found to be predominantly unstable to neutral, when the ground is snow-free, and stable to neutral for snow-covered ground. Due to long-lasting near-surface inversions in winter, an average temperature difference of approximately 3 K exists between the air temperature at 10 m height and the surface temperature of the snow.

Download Full-text

Nonlinear controls on evapotranspiration in arctic coastal wetlands

Biogeosciences ◽

10.5194/bg-8-3375-2011 ◽

2011 ◽

Vol 8 (11) ◽

pp. 3375-3389 ◽

Cited By ~ 69

Author(s):

A. K. Liljedahl ◽

L. D. Hinzman ◽

Y. Harazono ◽

D. Zona ◽

C. E. Tweedie ◽

...

Keyword(s):

Heat Flux ◽

Vapor Pressure ◽

Coastal Wetlands ◽

Surface Resistance ◽

Surface Soil ◽

Surface Soil Moisture ◽

Near Surface ◽

Limited Ability ◽

Bulk Surface ◽

Evapotranspiration Rate

Abstract. Projected increases in air temperature and precipitation due to climate change in Arctic wetlands could dramatically affect ecosystem function. As a consequence, it is important to define controls on evapotranspiration, the major pathway of water loss from these systems. We quantified the multi-year controls on midday Arctic coastal wetland evapotranspiration, measured with the eddy covariance method at two vegetated, drained thaw lake basins near Barrow, Alaska. Variations in near-surface soil moisture and atmospheric vapor pressure deficits were found to have nonlinear effects on midday evapotranspiration rates. Vapor pressure deficits (VPD) near 0.3 kPa appeared to be an important hydrological threshold, allowing latent heat flux to persistently exceed sensible heat flux. Dry (compared to wet) soils increased bulk surface resistance (water-limited). Wet soils favored ground heat flux and therefore limited the energy available to sensible and latent heat flux (energy-limited). Thus, midday evapotranspiration was suppressed from both dry and wet soils but through different mechanisms. We also found that wet soils (ponding excluded) combined with large VPD, resulted in an increased bulk surface resistance and therefore suppressing evapotranspiration below its potential rate (Priestley-Taylor α < 1.26). This was likely caused by the limited ability of mosses to transfer moisture during large atmospheric demands. Ultimately, in addition to net radiation, the various controlling factors on midday evapotranspiration (i.e., near-surface soil moisture, atmospheric vapor pressure, and the limited ability of saturated mosses to transfer water during high VPD) resulted in an average evapotranspiration rate of up to 75% of the potential evapotranspiration rate. These multiple limitations on midday evapotranspiration rates have the potential to moderate interannual variation of total evapotranspiration and reduce excessive water loss in a warmer climate. Combined with the prevailing maritime winds and projected increases in precipitation, these curbing mechanisms will likely prevent extensive future soil drying and hence maintain the presence of coastal wetlands.

Download Full-text