Cloud effects on surface energy and mass balance in the ablation area of Brewster Glacier, New Zealand

Abstract

Abstract. The effect of clouds on glacier surface energy balance (SEB) has received increased attention in the last decade, but how clouds interact with other meteorological forcing to influence surface mass balance (SMB) is not as well understood. This paper resolves the SEB and SMB at a site in the ablation zone of Brewster Glacier over a 22-month period, using high-quality radiation data to carefully evaluate SEB terms and define clear-sky and overcast conditions. A fundamental change in glacier SEB in cloudy conditions was driven by increased effective sky emissivity and surface vapour pressure, rather than a minimal change in air temperature and wind speed. During overcast conditions, positive net long-wave radiation and latent heat fluxes allowed melt to be maintained through a much greater length of time compared to clear-sky conditions, and led to similar melt in each sky condition. The sensitivity of SMB to changes in air temperature was greatly enhanced in overcast compared to clear-sky conditions due to more frequent melt and changes in precipitation phase that created a strong albedo feedback. During the spring and autumn seasons, the sensitivity during overcast conditions was strongest. To capture these processes, future attempts to explore glacier-climate interactions should aim to resolve the effects of atmospheric moisture (vapour, cloud, and precipitation) on melt as well as accumulation, through enhanced statistical or physically based methods.

Comparison of the meteorology and surface energy fluxes of debris-free and debris-covered glaciers in the southeastern Tibetan Plateau

“…Such radiation compensation has been also recorded in many temperate glaciated regions (e.g. Conway and Cullen, 2016). In addition, the decreased H sen was to some extent balanced by the increased H lat release by water condensation in the overcast conditions.…”

The Influence of Weather Systems in Controlling Mass Balance in the Southern Alps of New Zealand

“…Given that the T weather type is an important control on both snowfall and ablation (Figure ), closer scrutiny of how it lowers air temperature and affects the altitude of the rain/snow threshold during different seasons is warranted. The latter directly controls glacier‐wide accumulation and the associated glacier albedo feedback that is critical to the surface energy balance (Conway & Cullen, ; Cullen & Conway, ). The same seasonal analysis should also be applied to the TNW weather type, as it also plays a dominant role in controlling snowfall and ablation (Figure ).…”

“…Modeling surface temperature correctly is important as it determines all surface fluxes except incoming shortwave and longwave radiation and affects the proportion of energy available for ablation, which is one of the two critical mass balance terms used in this study. The model was also found to successfully reproduce large ablation and snowfall events (Conway & Cullen, ), with the uncertainty in accumulated surface mass balance over the 22‐month period (2010–2012) well within measurement and parameter error uncertainty defined using a series of Monte Carlo simulations. The uncertainty in modeled ablation during the two discrete summer periods in 2007/2008 and 2008/2009 was less than the ±10% reported by Conway and Cullen () for 2010–2012.…”

“…One of the main challenges in assessing how weather systems influence glacier behavior has been the lack of observational data from high‐elevation sites in the Southern Alps. However, high‐quality meteorological and glaciological observations from Brewster Glacier (e.g., Conway & Cullen, ; Cullen et al, ; Cullen & Conway, ) enable us for the first time to assess how weather systems influence both ablation and solid precipitation (snowfall) over different seasons of a mass balance year. This is achieved by running a physically based mass balance model over four summers and two winters to resolve daily ablation and snowfall, which are then compared to Kidson weather types.…”

The Role of Atmospheric Rivers for Extreme Ablation and Snowfall Events in the Southern Alps of New Zealand

“…Direct mass balance monitoring has been carried out at Brewster Glacier since 2004 and has been recently consolidated by Cullen et al (), making it the longest complete record of its kind in New Zealand. Brewster Glacier has also been the site of extensive surface mass and energy balance modeling (e.g., Anderson et al, ; Conway & Cullen, , ; Conway et al, ; Cullen & Conway, ; Gillett & Cullen, ). Brewster Glacier is one of 50 “index glaciers” in the Southern Alps monitored as part of the end‐of‐summer snowline survey program that was established in 1977 (Chinn et al, ; Willsman et al, ).…”