Optimization of Noah and Noah_MP WRF Land Surface Schemes in Snow-Melting Conditions over Complex Terrain

Abstract

The paper presents the results of high-resolution simulations performed with the WRF Model, coupled with two different land surface schemes, Noah and Noah_MP, with the aim of accurately reproducing winter season meteorological conditions in a typical Alpine valley. Accordingly, model results are compared against data collected during an intensive field campaign performed in the Adige Valley, in the eastern Italian Alps. In particular, the ability of the model in reproducing the time evolution of 2-m temperature and of incoming and outgoing shortwave and longwave radiation is examined. The validation of model results highlights that, in this context, WRF reproduces rather poorly near-surface temperature over snow-covered terrain, with an evident underestimation, during both daytime and nighttime. Furthermore it fails to capture specific atmospheric processes, such as the temporal evolution of the ground-based thermal inversion. The main cause of these errors lies in the miscalculation of the mean gridcell albedo, resulting in an inaccurate estimate of the reflected solar radiation calculated by both Noah and Noah_MP. Therefore, modifications to the initialization, to the land-use classification, and to both land surface models are performed to improve model results, by intervening in the calculation of the albedo, of the snow cover, and of the surface temperature. Qualitative and quantitative analyses show that, after these changes, a significant improvement in the comparability between model results and observations is achieved. In particular, outgoing shortwave radiation is lowered, 2-m temperature maxima increased accordingly, and ground-based thermal inversions are better captured.

Semi‐idealized simulations of wintertime flows and pollutant transport in an Alpine valley. Part II: Passive tracer tracking

“…This means that a proper initialization of the snow cover is also required at high resolution to ensure accurate air quality forecasting and to identify the most vulnerable areas. This conclusion is in line with Chow et al (2006), Tomasi et al (2017) and Lehner and Rotach (2018) who all recommend an overall improvement of the land cover initialization. Note that the present numerical set-up could be used again to quantify the tracer plume sensitivity to surface properties such as soil moisture, which is known to modulate the slope-circulation through the surface energy budget (Chow et al, 2006;Rihani et al, 2015) or land-use resolution (Schicker et al 2016).…”

“…(), Tomasi et al . () and Lehner and Rotach () who all recommend an overall improvement of the land cover initialization. Note that the present numerical set‐up could be used again to quantify the tracer plume sensitivity to surface properties such as soil moisture, which is known to modulate the slope‐circulation through the surface energy budget (Chow et al ., ; Rihani et al ., ) or land‐use resolution (Schicker et al .…”

Exchange Processes in the Atmospheric Boundary Layer Over Mountainous Terrain

“…Finally, because regional NWP models will likely adopt sub-km grid spacing in the foreseeable future, consistency will require an improved treatment of surface fields with high spatial variability and possibly a patchy spatial structure, e.g., soil moisture (which has a marked altitudinal dependence and is affected by runoff), snow cover [6], and urban land-cover [219].…”

“…The uncertainties of these parameterizations limit the accuracy of weather and climate forecasts, especially for near-surface atmospheric parameters [3][4][5][6].…”

A method to determine the characteristic time‐scales of quasi‐isotropic surface‐layer turbulence over complex terrain: A case‐study in the Adige Valley (Italian Alps)

“…; Tomasi et al. ). The complexity of these interactions and the open questions concerning atmospheric processes over mountainous terrain have been clearly highlighted in a recent paper by Serafin et al.…”