Jahresbericht 08 - PMOD/WRC

Julian Gröbner and Stefan Wacker
We describe a method to determine the effective
boundary layer temperature from concurrent measurements
of two pyrgeometer. Measurements from
four sites in Switzerland (Davos, Payerne, Locarno-
Monti and Jungfraujoch) were analyzed. The measurements
at Davos, Payerne and Locarno-Monti show a
stable inversion layer during the night and the transition
to a convective state during daylight. These sites
also show distinct diurnal and seasonal patterns of the
atmospheric boundary layer temperature with respect
to surface temperature. At Payerne, the measurements
were additionally validated with temperature measurements
from a meteorological tower.
We derive the atmospheric boundary layer (ABL) temperature
from concurrent measurements of two pyrgeometers
measuring over two wavelength ranges: One standard pyrgeometer
sensitive to the 3 µm to 50 µm wavelength range
and one modified pyrgeometer sensitive only in the atmospheric
window, i.e. from 8 µm to 14 µm. By combining
the two measurements we retrieve the effective
temperature of the saturated atmospheric water vapor from
the radiation emitted by the atmosphere in the wavelength
range 3 µm to 8 µm and 14 µm to 50 µm at four sites in
Switzerland: Davos, Payerne, Locarno-Monti and
Jungfraujoch. The radiation in this wavelength range is
emitted from the layers of the atmosphere closest to the
Earth’s surface which form the atmospheric boundary layer.
The temperature derived from these measurements can be
considered as an effective temperature of the saturated atmospheric
water vapor, which depends directly on the
profiles of humidity and temperature.
The atmospheric boundary layer temperature measurements
obtained from the pyrgeometers were compared to
air temperature measurements obtained from a meteorological
tower at 10 m and 30 m at the Payerne BSRN site.
The measurements clearly show the stable inversion layer
during the night with atmospheric temperatures larger than
at the surface, followed by the transition to a convective
boundary layer during daylight due to solar heating (see
Fig. 1). Measurements from Davos and Locarno-Monti
confirm the observations obtained at Payerne. The measurements
also reveal the seasonal variability of the atmospheric
boundary layer: during night, the temperature
difference between the ground and the atmospheric
boundary layer is more pronounced in winter than in summer
due to the enhanced cooling of the snow-covered surface
(see Fig. 2). Indeed, the short and reduced solar
heating in winter is not capable of breaking up the strong
inversion during daytime.
Our observations of the atmospheric boundary layer temperature
using infrared radiation emission of saturated
water vapor are a crucial parameter for the parametrization
of atmospheric longwave radiation models and can be
used to improve cloud cover algorithms using longwave
radiation measurements from standard pyrgeometers.
Temperature difference to surface (2 m) /K
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Day September 2007
Figure 1. Air temperature from pyrgeometer measurements
(red curve), 30 m (blue) and 10 m (green) temperature from the tower
relative to synoptic temperature at Payerne.
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Scientific Research Activities 27
Retrieving the Effective Boundary Layer Temperature from Pyrgeometer Measurements
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Figure 2. Diurnal course of ABL temperature derived from pyrgeometer
measurements for summer (top) and winter (bottom) at Davos. Mean and
standard deviation are highlighted in red and black, respectively.