AirWare On-line Reference Manual
| Release Level | 5.3.0 beta |
| Release Date | 2007 06 |
Revision Level | 1.1 |
AERMET meteorological preprocessor
AERMET is the meteorological pre-processor for AERMOD.
Data requirements for AERMET
The minimum meteorological input data requirements using only NWS data to produce
the two meteorological files for input to AERMOD are:
- Hourly Surface Observations:
- wind speed and direction;
- ambient temperature;
- opaque sky cover; in the absence of opaque sky cover, total sky cover;
- station pressure is recommended, but not required, since it is used only to calculate the
- density of dry air; AERMET will use a default value of 1013.25 millibars (sea level
pressure) in the absence of station pressure.
- Upper Air Sounding prior to sunrise
- atmospheric pressure (millibars),
- height above ground level (meters)
- dry bulb temperature (NC),
- wind direction (degrees from north)
- wind speed (meters/second),
Preference is for the hourly Surface Observations to include more information (see below)
and twice daily upper air soundings where available.
These can also be extracted from the MM5 forecast vertically layered data.
Extended Surface observations Variables
| PRCP | = | precipitation amount (millimeters) |
| SLVP | = | sea level pressure (millibars) |
| PRES | = | station pressure (millibars) |
| CLHT | = | cloud ceiling height (kilometers) |
| TSKC | = | sky cover, total//opaque (tenths//tenths) |
| C2C3 | = | sky cover, 2//3 layers (tenths//tenths) |
| CLCn | = | sky condition//coverage, layer n = 1,2,3,4 (!!//tenths) |
| CLTn | = | cloud type//height, n=1,2,3,4 (!!//kilometers) |
| PWTH | = | present weather, liquid//frozen (no units, see codes below) |
| HZVS | = | horizontal visibility (kilometers) |
| TMPD | = | dry bulb temperature (NC) |
| TMPW | = | wet bulb temperature (NC) |
| DPTP | = | dew-point temperature (NC) |
| RHUM | = | relative humidity (percent) |
| WDIR | = | wind direction (tens of degrees from north) |
| WSPD | = | wind speed (meters/second) |
Other parameters the user can set at the interactive scenario level include:
- Roughness length, an average can be derived from (average) landuse and be made an attribute
of a model domain, see: landuse.html,
default value is: 1.0 m
- Albedo, can again be derived from landcover, but varies seasonally, see:
landuse.html,
default value is: 0.16 m
- Bowen ratio B, default value is: 4.0
The Bowen ratio is the ratio of energy fluxes from one medium to another by
sensible and latent heating respectively. It is calculated by the equation
where Qh is sensible heating and Qe is latent heating
When the magnitude of B is less than one, a greater proportion
of the available energy at the surface is passed to the atmosphere as latent
heat than as sensible heat, and the converse is true for values of B greater
than one. As Qe --> 0, B becomes unbounded making the Bowen ratio difficult
to use in formulae, especially for arid surfaces.
For Details see:
USER'S GUIDE FOR THE AERMOD
METEOROLOGICAL PREPROCESSOR (AERMET)
U.S. Environmental Protection Agency, 2004, Appendix C
http://www.epa.gov/scram001/7thconf/aermod/aermetugb.pdf
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