Daily cycle of the surface energy balance in Antarctica and the influence of clouds

Abstract

We present the summertime daily cycle of the Antarctic surface energy balance (SEB) and its sensitivity to cloud cover. We use data of automatic weather stations (AWS) located in four major Antarctic climate zones: the coastal ice shelf, the coastal and interior katabatic wind zone and the interior plateau. Absorbed short wave radiation drives the daily cycle of the SEB, in spite of the high surface albedo (0.84-0.88). The dominant heat sink is the cooling by long wave radiation, but this flux is distributed more evenly throughout the day so that a pronounced daily cycle in net all-wave radiation remains with all-sky night-time heat losses of 20-30 W m −2 and noontime heat gains of 30-40 W m −2 . During the night, heat is re-supplied to the snow surface by the sensible heat flux, especially in the katabatic wind zone, and the sub-surface heat flux. Daytime radiative energy excess is removed from the surface by sublimation (except at the high plateau) and sub-surface heat transport. Daytime convection occurs at all sites around solar noon but is generally weak. Spatial differences in the SEB are largely controlled by differences in cloud cover. Clouds are associated with higher surface temperatures and near-surface wind speeds. This especially limits nocturnal cooling, so that the strongest daytime convection is found during overcast conditions on the interior plateau.

Improving satellite-retrieved surface radiative fluxes in polar regions using a smart sampling approach

“…In addition, the complete SEB contains turbulent fluxes as well, which can play an important role in energy exchanges between surface and atmosphere (Curry et al, 2000;Van Den Broeke et al, 2006;de Boer et al, 2014) and in mass-related processes such as sublimation (Thiery et al, 2012), in addition to the radiative fluxes considered here. Since turbulent fluxes cannot be retrieved from CloudSat and CALIPSO observations, these are not included in the present study.…”

“…Different components of the local SEB can be retrieved by specialized equipment such as radiometers and spectrometers (Ohmura et al, 1998), which have led to the deploy-K. Van Tricht et al: Improving satellite-retrieved surface radiative fluxes ment of numerous automatic weather station (AWS) networks across both the Arctic and the Antarctic (Steffen and Box, 2001;van den Broeke, 2004;van den Broeke et al, 2008;Ahlstrøm et al, 2008;Lazzara et al, 2012). However, despite the increasing number of AWSs, the distribution of these ground-based observations of energy components remains strongly irregular with numerous extensive unobserved areas, hindering an accurate assessment of the complete polar energy budget.…”

Near-surface thermal stratification during summer at Summit, Greenland, and its relation to MODIS-derived surface temperatures

“…Miller et al, 2013;Berkelhammer et al, 2016) and Antarctica (e.g. van van den Broeke et al, 2006;Kuipers Munneke et al, 2012). At our study site in particular at Summit, Greenland, Miller et al (2013) inversions over two years at but consider the 2 m air temperature to be the base of these inversions, and they did not investigate 100 the surface processes beneath 2 m height.…”

Evaluation of cloud effects on air temperature estimation using MODIS LST based on ground measurements over the Tibetan Plateau

“…Rather than the visually observed percentage of cloud cover in the sky, the CI used here represents the optical thickness of clouds (Van Den Broeke et al, 2006).…”