AERMOD View – Processing Low Wind Speeds in AERMET
July 2017
In previous modeling tips, we’ve looked at the AERMINUTE utility and expansion of its capabilities. AERMINUTE reads raw 1-minute and 5-minute wind data logged at US-based automated weather stations (called ASOS) and calculates hourly-averaged wind speeds and directions for processing in AERMET.
One problem with standard output from ASOS is the relatively high threshold (3 knots) for identifying winds as calm. Since AERMOD cannot perform calculations in calm winds, overall data quality is degraded. AERMINUTE provides a solution to this problem by replacing calm data with its hourly averages.
Use of AERMINUTE is recommended by the USEPA for all meteorological data processing which use ASOS data as input.
On the other hand, studies have shown discrepancies between measured concentrations and those calculated by AERMOD during stable conditions with low wind speeds. To improve AERMOD’s calculations, the USEPA implemented an option in AERMET which adjusts calculations of a parameter called surface friction velocity in the presence of low wind speeds. It is called the adjusted u-star (or ADJ_U*) option.
One problem with standard output from ASOS is the relatively high threshold (3 knots) for identifying winds as calm. Since AERMOD cannot perform calculations in calm winds, overall data quality is degraded. AERMINUTE provides a solution to this problem by replacing calm data with its hourly averages.
Use of AERMINUTE is recommended by the USEPA for all meteorological data processing which use ASOS data as input.
On the other hand, studies have shown discrepancies between measured concentrations and those calculated by AERMOD during stable conditions with low wind speeds. To improve AERMOD’s calculations, the USEPA implemented an option in AERMET which adjusts calculations of a parameter called surface friction velocity in the presence of low wind speeds. It is called the adjusted u-star (or ADJ_U*) option.
Beginning with model version 16216, the USEPA recommends using ADJ_U* when processing National Weather Service surface meteorological data.
Lakes Environmental offers AERMOD-ready meteorological data from stations in the United States. When you purchase this data from Lakes, our staff meteorologists use the AERMINUTE and ADJ_U* options in accordance with regulatory recommendations. To learn more about our data services, visit our Met Data Quote Request page.
Lakes Environmental offers AERMOD-ready meteorological data from stations in the United States. When you purchase this data from Lakes, our staff meteorologists use the AERMINUTE and ADJ_U* options in accordance with regulatory recommendations. To learn more about our data services, visit our Met Data Quote Request page.
