Understanding the local valley wind regimes in the Hindu-Kush Karakoram Himalaya is vital for future predictions of the glacio-hydro-meteorological system. Here the Weather Research and Forecasting model is employed at a resolution of 1 km to investigate the forces driving the local valley wind regime in a river basin in the Nepalese Himalaya, during July 2013 and January 2014. Comparing with observations shows that the model represents the diurnal cycle of the winds well, with strong daytime up-valley winds and weak nighttime winds in both months. A momentum budget analysis of the model output shows that in the summer run the physical drivers of the near-surface valley wind also have a clear diurnal cycle, and are dominated by the pressure gradient, advection, and turbulent vertical mixing, as well as a nonphysical numerical diffusion term. By contrast, the drivers in the winter run have a less consistent diurnal cycle. In both months, the pressure gradient, advection, numerical diffusion, and Coriolis terms dominate up to 5,000 m above the ground. The drivers are extremely variable over the valley, and also influenced by the presence of glaciers. When glaciers are removed from the model in the summer run, the wind continues further up the valley, indicating how the local valley winds might respond to future glacier shrinkage. The spatial variability of the drivers over both months is consistent with the complex topography in the basin, which must therefore be well represented in weather and regional climate models to generate accurate outputs. Plain Language SummaryThe rain and snow in Himalayan valleys, and the formation and melting of glaciers, are affected by the wind in the valleys. Exactly what drives this wind is not fully understood. Around the world, wind in valleys generally travels up the valley, and up the sides of mountains, during the day. This is due to the sun heating different areas by different amounts, creating areas of low and high air pressure. Here we use a computer simulation to determine whether the difference in pressure is the main cause of the acceleration of the wind in a valley in the Himalayas, or whether there are other forces which also affect the wind. We compare the simulation to measurements taken in the valley. We find that the pressure difference is the main process affecting the acceleration of the wind. However, the winds in the valley are also driven by the effects of turbulence and affected by the shape of the valley. The forces are consistent over the month, accelerating the wind in the morning and decelerating the wind in the afternoon every day.
Peruvian glaciers are important contributors to dry season runoff for agriculture and hydropower, but they are at risk of disappearing due to climate change. We applied a physically based, energy balance melt model at five on‐glacier sites within the Peruvian Cordilleras Blanca and Vilcanota. Net shortwave radiation dominates the energy balance, and despite this flux being higher in the dry season, melt rates are lower due to losses from net longwave radiation and the latent heat flux. The sensible heat flux is a relatively small contributor to melt energy. At three of the sites the wet season snowpack was discontinuous, forming and melting within a daily to weekly timescale, and resulting in highly variable melt rates closely related to precipitation dynamics. Cold air temperatures due to a strong La Niña year at Shallap Glacier (Cordillera Blanca) resulted in a continuous wet season snowpack, significantly reducing wet season ablation. Sublimation was most important at the highest site in the accumulation zone of the Quelccaya Ice Cap (Cordillera Vilcanota), accounting for 81% of ablation, compared to 2%–4% for the other sites. Air temperature and precipitation inputs were perturbed to investigate the climate sensitivity of the five glaciers. At the lower sites warmer air temperatures resulted in a switch from snowfall to rain, so that ablation was increased via the decrease in albedo and increase in net shortwave radiation. At the top of Quelccaya Ice Cap warming caused melting to replace sublimation so that ablation increased nonlinearly with air temperature.
Many of the glaciers in the Nepalese Himalaya are partially covered in a layer of loose rock known as debris cover. In the Dudh Koshi River Basin, Nepal, approximately 25% of glaciers are debris‐covered. Debris‐covered glaciers have been shown to have a substantial impact on near‐surface meteorological variables and the surface energy balance, in comparison to clean‐ice glaciers. The Weather Research and Forecasting (WRF) model is often used for high‐resolution weather and climate modelling, however representation of debris‐covered glaciers is not included in the standard land cover and soil categories. Here we include a simple representation of thick debris‐covered glaciers in the WRF model, and investigate the impact on the near‐surface atmosphere over the Dudh Koshi River Basin for July 2013. Inclusion of this new category is found to improve the model representation of near‐surface temperature and relative humidity, in comparison with a simulation using the default category of clean‐ice glaciers, when compared to observations. The addition of the new debris‐cover category in the model warms the near‐surface air over the debris‐covered portion of the glacier, and the wind continues further up the valley, compared to the simulation using clean‐ice. This has consequent effects on water vapour and column‐integrated total water path, over both the portions of the glacier with and without debris cover. Correctly simulating meteorological variables such as these is vital for accurate precipitation forecasts over glacierized regions, and therefore estimating future glacier melt and river runoff in the Himalaya. These results highlight the need for debris cover to be included in high‐resolution regional climate models over debris‐covered glaciers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.