Fabien Maussion

Precipitation Seasonality and Variability over the Tibetan Plateau as Resolved by the High Asia Reanalysis

AbstractBecause of the scarcity of meteorological observations, the precipitation climate on the Tibetan Plateau and surrounding regions (TP) has been insufficiently documented so far. In this study, the characteristics and basic features of precipitation on the TP during an 11-yr period (2001–11) are described on monthly-to-annual time scales. For this purpose, a new high-resolution atmospheric dataset is analyzed, the High Asia Reanalysis (HAR), generated by dynamical downscaling of global analysis data using the Weather Research and Forecasting (WRF) model. The HAR precipitation data at 30- and 10-km resolutions are compared with both rain gauge observations and satellite-based precipitation estimates from the Tropical Rainfall Measurement Mission (TRMM). It is found that the HAR reproduces previously reported spatial patterns and seasonality of precipitation and that the high-resolution data add value regarding snowfall retrieval, precipitation frequency, and orographic precipitation. It is demonstrat...

Evaluation of a Coupled Snow and Energy Balance Model for Zhadang Glacier, Tibetan Plateau, Using Glaciological Measurements and Time-Lapse Photography

Abstract We present a new open-source, collaborative “COupled Snowpack and Ice surface energy and MAss balance model” (COSIMA) that is evaluated for Zhadang glacier, Tibetan Plateau. The model is calibrated, run, and validated based on in situ measurements and atmospheric model data from the High Asia Refined analysis (HAR) over the period April 2009 to June 2012. Results for the model runs forced by both in situ measurements and HAR agree well with observations of various atmospheric, glaciological, surface, and subsurface parameters on the glacier. A time-lapse camera system next to the glacier provides a 3-year image time series of the mean transient snow line altitude and the snow cover pattern, which is used for the spatial and temporal validation of the model. The model output corresponds very well to the observed temporal and spatial snow cover variability. The model is then run for a 10-year period of October 2001 to September 2011 forced with HAR data. In general, the radiation components dominate the overall energy turnover (65%), followed by the turbulent fluxes (31%). The generally dry atmosphere on the Tibetan Plateau causes sublimation to be responsible for 26% of the total mass loss. A proportion of 11% of the surface and subsurface melt refreezes within the snowpack.

MODIS Derived Equilibrium Line Altitude Estimates for Purogangri Ice Cap, Tibetan Plateau, and their Relation to Climatic Predictors (2001–2012)

Abstract The variation of the equilibrium line altitude can be used as an indicator for glacier mass balance variability. Snow lines at the end of the ablation period are suitable proxies for the annual equilibrium line altitude on glaciers. We investigate snow lines at Purogangri ice cap on the central Plateau in order to study the interannual variability of glacier mass balance. Datasets of the daily Moderate Resolution Imaging Spectroradiometer snow product MOD10A1 were used to infer transient snow line variability during 2001–2012 and to derive regional‐scale, annual equilibrium line altitude. The Moderate Resolution Imaging Spectroradiometer snow albedo embedded within the snow product was compared with high‐resolution Landsat imagery. An albedo threshold was established to differentiate between ice and snow and the 13th percentile of the altitudes of snow‐covered pixels was chosen to represent the snow line altitude. The second maximum of the snow line altitudes in the ablation period was taken as a proxy for the annual equilibrium line altitude. A linear correlation analysis was carried out (1) between interannual variability of the equilibrium line altitude at Purogangri ice cap and various climate elements derived from the High Asia Reanalysis, and (2) between interannual variability of the equilibrium line altitude and the circulation indices North Atlantic Oscillation and Indian Summer Monsoon. Results suggest that air temperature and meridional wind speed above ground in July, as well as the lower tropospheric zonal wind in June and August play a crucial role in the development of the annual equilibrium line altitude.

Limited influence of climate change mitigation on short-term glacier mass loss

Glacier mass loss is a key contributor to sea-level change1,2, slope instability in high-mountain regions3,4 and the changing seasonality and volume of river flow5–7. Understanding the causes, mechanisms and time scales of glacier change is therefore paramount to identifying successful strategies for mitigation and adaptation. Here, we use temperature and precipitation fields from the Coupled Model Intercomparison Project Phase 5 output to force a glacier evolution model, quantifying mass responses to future climatic change. We find that contemporary glacier mass is in disequilibrium with the current climate, and 36 ± 8% mass loss is already committed in response to past greenhouse gas emissions. Consequently, mitigating future emissions will have only very limited influence on glacier mass change in the twenty-first century. No significant differences between 1.5 and 2 K warming scenarios are detectable in the sea-level contribution of glaciers accumulated within the twenty-first century. In the long-term, however, mitigation will exert strong control, suggesting that ambitious measures are necessary for the long-term preservation of glaciers.Glaciers outside Greenland and Antarctica have been rapidly losing mass. Contemporary ice declines are shown to be a response to past greenhouse gas emissions, with present mitigation efforts unlikely to be beneficial in preventing future short-term ice loss.

MODIS-derived interannual variability of the equilibrium-line altitude across the Tibetan Plateau

Abstract. Using the Moderate Resolution Imaging Spectroradiometer (MODIS) Level 1 radiance Swath Data (MOD02QKM) with a spatial resolution of 250 m, we derive snowlines during July–September 2001–12 for several mountain ranges distributed across the Tibetan Plateau (TP). Radiance bands 1 and 2 are projected to the study area and processed automatically. The discrimination between snow and ice is done using a k-mean cluster analysis and the snowlines are delineated based on a fixed percentile of the snow-cover altitude. The highest transient snowline altitude is then taken as a proxy for the equilibrium-line altitude (ELA). In the absence of measured glaciological, meteorological or hydrological data, our ELA time series enable better understanding of atmosphere-cryosphere couplings on the TP. Interannual ELA variability is linked to local and remote climate indices using a correlation analysis. Southerly flow and higher temperatures are linked with a higher ELA in most regions. Eastern and Trans-Himalayan sites show positive correlations between winter temperatures and ELA. As winter temperatures are substantially below zero, this suggests an enhancement of winter sublimation as opposed to a reduction in accumulation. It appears that large-scale atmospheric forcing has varying and sometimes opposite influences on the annual ELA in different regions on the TP.

Prominent Midlatitude Circulation Signature in High Asia's Surface Climate During Monsoon

Author(s): Molg, T; Maussion, F; Collier, E; Chiang, JCH; Scherer, D | Abstract: