The role of radiation penetration in the energy budget of the snowpack at Summit, Greenland

Abstract

Abstract. Measurements of the summer surface energy balance at Summit, Greenland, are presented (8 June-20 July 2007). These measurements serve as input to an energy balance model that searches for a surface temperature for which closure of all energy terms is achieved. A good agreement between observed and modelled surface temperatures was found, with an average difference of 0.45 • C and an RMSE of 0.85 • C. It turns out that penetration of shortwave radiation into the snowpack plays a small but important role in correctly simulating snow temperatures. After 42 days, snow temperatures in the first meter are 3.6-4.0 • C higher compared to a model simulation without radiation penetration. Sensitivity experiments show that these results cannot be reproduced by tuning the heat conduction process alone, by varying snow density or snow diffusivity. We compared the two-stream radiation penetration calculations with a sophisticated radiative transfer model and discuss the differences. The average diurnal cycle shows that net shortwave radiation is the largest energy source (diurnal average of +61 W m −2 ), net longwave radiation the largest energy sink (−42 W m −2 ). On average, subsurface heat flux, sensible and latent heat fluxes are the remaining, small heat sinks (−5, −5 and −7 W m −2 , respectively), although these are more important on a subdaily timescale.

Surface and snowdrift sublimation at Princess Elisabeth station, East Antarctica

“…2). The overestimation of T s , which can be noted for very low T s , was found to coincide with clear sky conditions, suggesting that during these periods either the model performs less well, or the LW in measurements are biased to lower values (Kuipers Munneke et al, 2009). However, in general, the good agreement between modelled and observed T s indicates that the model is doing well, with a mean difference ranging from 0.16 • C (AWS 16) to 1.13 • C (AWS 5) and a RMSE from 0.76 • C (AWS 6) to 1.72 • C (AWS 16).…”

“…With the goal of calculating the different components of the SEB, we use the SEB model described in detail by Van den Broeke et al (2005) (for applications see Kuipers Munneke et al, 2009;van As et al, 2005;Giesen et al, 2008 andVan den Broeke et al, 2011). Here, we only provide a very short description of the model's main steps and assumptions.…”

“…The initial T s was chosen to minimise spinup effects (see also Van Lipzig et al, 2002a). The module calculating the subsurface SW radiation penetration (Brandt and Warren, 1993) is not used in our simulations, since it has been shown that its impact upon T s both in Greenland and Antarctica is virtually inexistent (Kuipers Munneke et al, 2009;Brandt and Warren, 1993).…”

Sensitivity of a distributed temperature-radiation index melt model based on AWS observations and surface energy balance fluxes, Hurd Peninsula glaciers, Livingston Island, Antarctica

“…The temperature offset from zero degrees is made to allow for melting at depths below the surface skin layer that T s is representing. Sub-surface melting at sub-zero T s can occur because of the ability of short-wave radiation to penetrate into the snow cover, where the thermal conductivity is low (Koh and Jordan, 1995;Kuipers et al, 2009). We consider that the surface is refreezing and cooling when A turns negative, and to be heated to resume to melt conditions when A is positive and T s < −0.5 • C. Thus, G balances A during non-melting conditions.…”

Near-surface climate and surface energy budget of Larsen C ice shelf, Antarctic Peninsula

“…Before the AWS data can be used as input for the SEB model, some corrections to the raw data are necessary. Many of these corrections have been described before in detail by Van den Broeke et al (2004);Kuipers Munneke et al (2009);Giesen et al (2009). First of all, the shortwave fluxes are corrected for sensor tilt using the tilt sensors of the AWS.…”