J2.2 Assessment of the Sensitivity to the Thermal Roughness Length in Noah and Noah-MP Land Surface Model Using WRF in an Arid Region

Tuesday, 8 January 2019: 10:45 AM
North 127ABC (Phoenix Convention Center - West and North Buildings)
Michael Weston, Khalifa Univ., Abu Dhabi, United Arab Emirates; and M. Temimi and V. K. Valappil

Fog is an atmospheric surface level phenomenon that depends on complex interactions that determine surface air temperature and moisture content. Atmospheric models are known to underestimate land surface temperature and, by association, 2 m air temperature over dry arid regions during the day due to the treatment of the thermal roughness length also known as roughness length of heat. The thermal roughness length can be controlled by the Zilitinkevich parameter, known as Czil, which is a tunable parameter within the models.
We run three different scenarios with the WRF model to test the impact of the Czil parameter on the simulations using two land surface models: the Noah and Noah-MP models. In this study we tested a modified version of the Noah-MP model in which Czil parameter, and therefore the thermal roughness length varies depending on the land cover and vegetation height. However, WRF adds some complexity by assigning soil types within the desert the land cover class which has an effect on diagnosing 2 m air temperature. We changed the soil types in order to verify their effect on temperature and fog formation.
Our model domain is over the United Arab Emirates (UAE) where the major land cover type is desert. We tested the Noah model with Czil=0.1 and the Noah-MP model with Czil=0.5 over desert. We verified the results of 2 m air temperature against stations in the UAE and we compare fog patch frequency to satellite data from the Seviri instrument. We found that loamy sand soil type produced excess fog patches in the model and this decreased when the soil type was changed to sand.
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