Ventilated and unventilated air temperature measurements for glacier‐climate studies on a tropical high mountain site

Abstract

[1] In this paper, artificially ventilated and unventilated temperature measurements logged by high-elevation automatic weather stations (AWS) in the tropical Cordillera Blanca, Perú, are compared. Both temperatures are measured with the same sensor and radiation shield by periodic artificial ventilation. The analyzed time series range from October 1999 until May 2001. The temperature differences ÁT = T unvent. À T vent. show a persistent daily cycle with a nighttime mean value of 0.3 K and a daytime mean of 1.3 K. The daytime period of ÁT is characterized by a late morning and an early afternoon maximum and a slight secondary noon minimum. The cycle is most pronounced during the dry season, but is only slightly reduced in the wet season. It is shown that the daily cycle is mainly caused by incoming shortwave radiation and that the resulting temperature difference depends on the irradiation angle to the radiation shield. A simple radiation geometry model is proposed for the explanation of ÁT. The modeled ÁT daily cycle strongly correlates with measured monthly mean ÁT daily cycles and can be used for respective corrections. In case of snow cover, the general cycle of ÁT remains, but additional deviations are caused by reflected shortwave radiation. These deviations cannot be modeled by using simple considerations. Therefore adequately ventilated air temperature measurements on glaciers and snow-covered surfaces should be made. Natural ventilation suffices in the case of persistently high wind speeds; otherwise, artificial ventilation should be implemented whenever possible.

Air temperature variability over three glaciers in the Ortles–Cevedale (Italian Alps): effects of glacier fragmentation, comparison of calculation methods, and impacts on mass balance modeling

“…Data were periodically downloaded with a portable laptop until July 2011. Since August 2011, a satellite modem has automatically transmitted data at 3-day intervals (Abbate et al, 2013 by a ventilated screen, which is important for air temperature measurements in high-radiation and/or low-wind-speed conditions on glaciers (Georges and Kaser, 2002). Hourly mean data are stored in a Davis data logger.…”

Mass balance of a slope glacier on Kilimanjaro and its sensitivity to climate

“…The performance of these instruments has been described in association with measurements on glaciers around the world (e.g. Georges and Kaser, 2002;Oerlemans and Klok, 2002;Hardy et al, 2003;Klok et al, 2005;. Longwave radiation fluxes are also a measure of glacier (radiative) surface temperature, based on the Stefan-Boltzmann law ( .…”

“…Owing to the sub-freezing air temperatures (see below), relative humidity measurements were re-scaled to account for saturation with respect to ice rather than liquid water (cf Cullen et al, 2007a). Wind speeds (discussed further below as well) are generally high enough to guarantee sufficient (natural) ventilation of the Rotronic sensors (Georges and Kaser, 2002). Nonetheless, we explored the radiation error by comparing 2°C-binned hourly air temperature data between thermocouple and Rotronic instrument (at initially 1.75 m).…”

The footprint of Asian monsoon dynamics in the mass and energy balance of a Tibetan glacier

“…Thus, we deem this correction to be a reasonable alternative to assuming a random sensor height. Wind speed and T a /RH from AWS2 (same instruments as at AWS1) were also used to examine vertical gradients, but only for intervals when AWS1 and AWS2 sensor heights agreed within 0.2 m and when there was high enough wind speed for sufficient natural ventilation of the T a /RH sensor (Georges and Kaser, 2002; n = 1629 h for wind; n = 1340 h for T a /RH). We find no gradients in wind speed and RH, as differences are within the instrument accuracy.…”