Impact of light-absorbing particles on snow albedo darkening and associated radiative forcing over high-mountain Asia: high-resolution WRF-Chem modeling and new satellite observations

Abstract

Light-absorbing particles (LAPs), mainly dust and black carbon, can significantly impact snowmelt and regional water availability over high-mountain Asia (HMA). In this study, for the first time, online aerosol-snow interactions are enabled and a fully coupled chemistry Weather Research and Forecasting (WRF-Chem) regional model is used to simulate LAP-induced radiative forcing on snow surfaces in HMA at relatively high spatial resolution (12 km, WRF-HR) compared with previous studies. Simulated macro-and microphysical properties of the snowpack and LAP-induced snow darkening are evaluated against new spatially and temporally complete datasets of snow-covered area, grain size, and impurity-induced albedo reduction over HMA. A WRF-Chem quasi-global simulation with the same configuration as WRF-HR but a coarser spatial resolution (1 • , WRF-CR) is also used to illustrate the impact of spatial resolution on simulations of snow properties and aerosol distribution over HMA. Due to a more realistic representation of terrain slopes over HMA, the higher-resolution model (WRF-HR) shows significantly better performance in simulating snow area cover, duration of snow cover, snow albedo and snow grain size over HMA, as well as an evidently better atmospheric aerosol loading and mean LAP concentration in snow. However, the differences in albedo reduction from model and satellite retrievals is large during winter due to associated overestimation in simulated snow fraction. It is noteworthy that Himalayan snow cover has high magnitudes of LAP-induced snow albedo reduction (4 %-8 %) in pre-monsoon seasons (both from WRF-HR and satellite es-timates), which induces a snow-mediated radiative forcing of ∼ 30-50 W m −2 . As a result, the Himalayas (specifically the western Himalayas) hold the most vulnerable glaciers and mountain snowpack to the LAP-induced snow darkening effect within HMA. In summary, coarse spatial resolution and absence of snow-aerosol interactions over the Himalayan cryosphere will result in significant underestimation of aerosol effects on snow melting and regional hydroclimate.

Impact of topography on black carbon transport to the southern Tibetan Plateau during the pre-monsoon season and its climatic implication

“…The meteorological initial and lateral boundary conditions are derived from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data at 0.5 • × 0.66 • horizontal resolution and 6 h temporal intervals (ERA-Interim dataset). The modeled u and v component wind, atmospheric temperature and geopotential height over the outer domain are nudged towards the reanalysis data with a nudging timescale of 6 h following previous studies (e.g., Stauffer and Seaman, 1990;Seaman et al, 1995;Liu et al, 2012;Zhao et al, 2014;Karki et al, 2017;Hu et al, 2016Hu et al, , 2020. The spectral-nudging method is Figure 3.…”

“…In order to examine the potential impacts of the complex topography on pollutant transport across the Himalayas over the TP, this study conducts multiple experiments with the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem; Grell et al, 2005;Skamarock et al, 2008). The WRF-Chem model is selected because it includes the interaction between meteorology and aerosol and is widely used for the regional modeling of aerosol and its climatic impact (e.g., Cao et al, 2010;Zhao et al, 2010Zhao et al, , 2011Zhao et al, , 2012Zhao et al, , 2014Wu et al, 2013;Gao et al, 2014;Huang et al, 2015;Fan et al, 2015;Feng et al, 2016;Zhong et al, 2017;Sarangi et al, 2019;Liu et al, 2020). The model has also been used to investigate the aerosol transport and climatic impact over the Himalayan region (e.g., Feng et al, 2016;Cao et al, 2010;Sarangi et al, 2019).…”

Examining the atmospheric radiative and snow-darkening effects of black carbon and dust across the Rocky Mountains of the United States using WRF-Chem

“…The performance of CNT and NOCHEM in simulating several important meteorological variables is first evaluated in this study. Daily point-source measurements of minimum (T min ), maximum (T max ), and average (T av ) 2 m temperature, as well as precipitation and SWE from 418 snow telemetry (SNOTEL; Serreze et al, 1999) sites across the WUS, are used to evaluate the model performance (see black dots in Fig. 1).…”

“…The arid Rocky Mountains of the western United States (WUS) receive most of their precipitation in the form of snowfall from October through March. The resulting snowpack forms a network of natural mesoscale storage reservoirs that provide approximately 80 % of the surface water across the region during the warm season (Serreze et al, 1999;Hamlet et al, 2007). All life in the region fundamentally depends on the timed release of runoff from snowpack; humans rely on these resources for agriculture and power generation.…”

The retreival of snow properties from SLSTR/Sentinel-3 – part 2: results and validation

“…may be declining even faster than thought due to large uncertainties of how models describe the snow feedback mechanisms (Flanner et al, 2011). The uncertainties to describe the snow feedback mechanisms are largely introduced by the uncertainties of knowledge of snow properties (Hansen et al, 1984;Groot Zwaaftink et al 2011;Sarangi et al, 2019). Snow properties depend on snow age, moisture, and temperatures surrounding (LaChapelle,1969;Sokratov and Kazakov, 2012).…”