Understanding monsoon controls on the energy and mass balance of Himalayan glaciers

Abstract

Abstract. The Indian and East Asian Summer Monsoons shape the melt and accumulation patterns of glaciers in High Mountain Asia in complex ways due to the interaction of persistent cloud cover, large temperature amplitudes, high atmospheric water content and high precipitation rates. While the monsoons dominate the climate of the southern and eastern regions, they progressively lose strength westward towards the Karakoram, where the influence of Westerlies is predominant. Despite the major role of the monsoon in the Himalayas, a holistic understanding of their influence on the region's glaciers is lacking because previous applications of energy- and mass-balance models have been limited to single study sites. In this study, we use a full energy- and mass-balance model and seven on-glacier automatic weather station datasets from different parts of the Himalayas to investigate how monsoon conditions influence the glacier surface energy and mass balance. In particular, we look at how debris-covered and debris-free glaciers respond differently to monsoonal conditions. The radiation budget mostly controls the melt of clean-ice glaciers, but turbulent fluxes also play an important role in modulating the melt energy on debris-covered glaciers. The sensible heat flux reduces during core monsoon, but the latent heat flux removes energy from the surface due to evaporation of liquid water. This interplay of radiative and turbulent fluxes, together with compensations between increasing and decreasing melt rates over the diurnal cycle, causes debris-covered glacier melt rates to stay almost constant over the entire ablation period through the different phases of the monsoon. Ice melt under thin debris, on the other hand, is amplified by both the dark surface albedo and the turbulent fluxes, which act as a source of energy through surface heating and condensation, especially during monsoon. Pre-monsoon snow cover can considerably delay melt onset and have a strong impact on the seasonal mass balance. Intermittent monsoon snow cover further modulates the melt rates at high elevation. Given our results, we expect the mass balance of debris-covered glaciers to react less sensitively to projected future monsoon conditions than clean-ice and dirty-ice glaciers. This work is fundamental to the understanding of the present and future Himalayan cryosphere and water budget evolution, while informing and motivating further glacier- and catchment-scale research using process-based models (Yang et al., 2017).

Controls on the relative melt rates of debris-covered glacier surfaces

“…This is reasonable for most sites considering the relevant spatial and temporal domain (debris-covered ablation area during the ablation season), although ablation-season snowfall can modulate subsequent ablation (e.g. Fugger et al 2021). This model calculates the energy balance using in situ measurements of air temperature, relative humidity, wind speed, and incoming shortwave and longwave radiation, and requires parameters for ice albedo, roughness, and emissivity.…”

11-year record of wintertime snow surface energy balance and sublimation at 4863 m a.s.l. on Chhota Shigri Glacier moraine (western Himalaya, India)

“…However, the highest multiple regression variance in combination with u (~90%) emphasise the importance of u in controlling LE/sublimation. Fugger et al (2021) also noted that the relationship between LE and meteorological variables is highly unpredictable, and u fails to explain the variability of LE at five on-glacier sites in the central and eastern Himalaya (see their Fig. A9).…”

“…To test the sensitivity of the calculated sublimation to changes in the input data, we prescribed perturbations of Tair (± 1°C), Ts (± 1°C), u (± 10%), RH (± 10%) and z0m (0.0005 m, 0.002 m, 0.003 m and 0.004 m) and re-calculated sublimation for DJFMA, 2009-2020. Similar perturbations for the meteorological variables were applied in the previous studies (Andreassen et al, 2008;Zhang et al, 2013;Steiner et al, 2018;Liu et al, 2021). For z0m, we chose higher and lower order perturbation values considering the high SD of in-situ calculated snow z0m at the AWS-G (0.001 ± 0.003 m; Azam et al, 2014a).…”

“…Wagnon et al (1999) discussed that sublimation supports the existence of high-altitude glaciers because sublimation limits Fsurface for melting by counterbalancing it through high negative LE. As the latent heat of sublimation, Ls (2.849×10 6 J kg -1 ) is 8.5 times the latent heat of fusion (3.34×10 5 J kg -1 ), the energy consumed by sublimation is 8.5 times higher than that consumed for an equal amount of melting (Liu et al, 2021). Hence, sublimation can substantially decrease the energy supply for glacier melting.…”

Cold‐Season Surface Energy Balance on East Rongbuk Glacier, Northern Slope of Mt. Qomolangma (Everest)

“…To better understand the heterogeneous response of TP's glacier to climate change, glacier surface energy balance (SEB) must be well understood since it is an effective means to physically describe the relationship between the glacier and the overlying atmosphere (W. Yang et al, 2013). Previous glacier SEB studies (Fugger et al, 2021;G. Zhang et al, 2013;S.…”