Meteorological preferences

PREFERENCES PANEL
Meteorological tab

CHECKBOXES

Geopotential heights in full meters only - The geopotential height on upper-level charts are commonly plotted in decameters (dam). When this box is checked, contour labels and upper plot models will appear in full meters. When it is unchecked, the labels and plot models will switch to conventional shortening typically used by meteorologists (see table below). The default setting is unchecked. Conventional shortening is as follows: 100 to 500 mb, undreds, tens, and units of decameters are displayed; 501 to 1000 mb, hundreds, tens, and units of meters are displayed.

Round synoptic reports to nearest 3 hours when importing - You have two options when importing synoptic (SYNOP) data — you can either round the reports to the nearest 3 hours (making maximum use of off-hour data) or use no rounding (ensuring sampling of the atmosphere at an exact moment). It is generally best to use no rounding when possible.

View NEXRAD RCM rather than RAREP radar data - This prevents two different radar formats from being mixed when you use Data > Radar > Echoes. Check this box whenever you use NEXRAD RCM data (such as that transmitted over EMWIN). If you use the old SD RAREP code, uncheck this box.

Round AIREP reports within __ mb of a standard level - Forecasters like to see AIREP reports on upper-air charts, but AIREPs are rarely at an exact standard constant-pressure level. When this box is checked, it allows AIREPs within a certain range of the active pressure level to be included on the map. Usually 25 mb is a good value. When it is unchecked, no AIREPs will be used unless they are at the exact pressure level that's active.
Display highs and lows when plotting ASUS1 frontal bulletin - This should usually be left unchecked. When you produce a pressure analysis, Digital Atmosphere will automatically plot highs and lows. When you use , it will plot its own sets of highs and lows, which clashes with Digital Atmosphere's depiction. Since the ASUS1's fields are coarser and may differ from the isopleth fields, you should generally leave this unchecked unless you have no surface data and want to see the ASUS1 output of highs and lows.
Display pressure values when plotting frontal bulletins.
Winter depiction: extend contours over nonprecipitating areas.
Convert ALSTG to SLP for analysis (advanced users only).

FOUS DATA LEVEL

Whenever you plot model (ETA/NGM) data, the temperature and moisture variables are determined according to this setting. Normally the first button (T1/R1) is selected to give you surface data, but by choosing another button you can plot or analyze temperature or moisture aloft (calculating derived values such as dewpoint should be done with caution, though, since T3 is not the same level as R2). Here are the meanings of the different levels.

Level Equivalent
  T1    Surface
T3    About 100 mb above the surface (1 km)
T5    About 215 mb above the surface (2 km)
R1    Surface to about 35 mb above the surface (lowest 1000 ft)
R2    About 35 mb above the surface to 500 mb
  R3    500 mb to the tropopause

CAPE MIXED LAYER DEPTH

Calculates the depth of the layer to use when performing mixed layer stability.

MISCELLANEOUS QUANTITIES

Lowest possible METAR pressure - The METAR surface observation code format only allows the tens, units, and tenths place to be encoded, which means that Digital Atmosphere has to determine whether the final millibar value is 9xx.x or 10xx.x. The default value for lowest METAR pressure is 960 mb, which means that if a value such as 584 is found, Digital Atmosphere will assume it is 1058.4 mb, not 958.4 mb. Normally there is no need to change this, but if you're looking at exceptionally low pressure areas and the sea level pressure contours aren't plotting correctly, you'll want to decrease this value. Likewise, if you're looking at very high pressure and the sea level pressure contours aren't plotting correctly, you'll want to increase this value.

Earth's rotation constant - Specifies the earth's rotation in radians per second, which is normally set at 0.000007292. Naturally, there is no need to change this unless you want to tinker and see the results. The earth's rotation constant is used in the Coriolis parameter equations, which are used for geostrophic wind calculations and calculation of absolute vorticity. Hitting reset replaces any entered value with the Earth's rotation constant.

Gravity constant - Specifies the gravity acceleration, which is normally set at 9.806 m/s-2. There's no need to change this unless you want to tinker and see the results. Gravity is only used in the calculation of geostrophic wind based solely on height contours. Hitting the reset button replaces any entered value with the Earth's gravity constant.