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Variability of soil moisture and its relationship with surface albedo and soil thermal diffusivity at Astronomical Observatory, Thiruvananthapuram, south Kerala


Continuous observation data collected over the year 2008 at Astronomical Observatory, Thiruvananthapuram in south Kerala (76°59′E longitude and 8°30′N latitude) are used to study the diurnal, monthly and seasonal soil moisture variations. The effect of rainfall on diurnal and seasonal soil moisture is discussed. We have investigated relationships of soil moisture with surface albedo and soil thermal diffusivity. The diurnal variation of surface albedo appears as a U-shaped curve on sunny days. Surface albedo decreases with the increase of solar elevation angle, and it tends to be a constant when solar elevation angle is greater than 40°. So the daily average surface albedo was calculated using the data when solar elevation angle is greater than 40°. The results indicate that the mean daily surface albedo decreases with increases in soil moisture content, showing a typical exponential relation between the surface albedo and the soil moisture. Soil thermal diffusivity increases firstly and then decreases with the increase of soil moisture.

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α :

Surface albedo

S u :

Reflected solar radiation (W/m2)

S d :

Total downward solar radiation (W/m2)

T :

Soil temperature (°C)

k :

Soil thermal diffusivity (m2s−1)

t :

Time (s)

A :

Amplitude of the soil thermal wave at any depth (°C)

A 0 :

Amplitude of thermal wave at the surface (°C)

z :

Soil depth (m)

ω :

Angular velocity of earth’s rotation (rad/s)

θ :

Solar elevation angle (degree)

Ws :

Average soil moisture (%)

η :

Volumetric moisture content (m3m−3)


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Correspondence to M. S. Roxy.

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Roxy, M.S., Sumithranand, V.B. & Renuka, G. Variability of soil moisture and its relationship with surface albedo and soil thermal diffusivity at Astronomical Observatory, Thiruvananthapuram, south Kerala. J Earth Syst Sci 119, 507–517 (2010).

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  • Soil moisture
  • rainfall
  • surface albedo
  • solar elevation angle
  • thermal diffusivity
  • atmospheric sciences
  • meteorology
  • geophysics