Military

CHAPTER 2

METEOROLOGICAL TABLES AND CHARTS

SECTION I.

GENERAL TABLES AND CHARTS FOR METEOROLOGICAL MESSAGES

2-1. Description of Tables and Charts

The tables and charts in this chapter are presented in sections I and II as follows:

a. Section I, General Tables and Charts for Meteorological Messages. These tables and charts are used in computing data for visual ballistic and computer meteorological messages.

b. Section II, Tables for Type 3 Ballistic Messages for Surface-to-Surface Trajectories. These tables include the weighting factors and the weighted quantities for density, winds, and temperatures pertaining to all artillery weapons firing at terrestrial targets.

2-2. Zone Structure of Atmosphere

For convenience in computing, reporting, and applying corrections, the standard atmosphere is further identified by dividing it into zones for standard heights. The zones for the various meteorological messages are illustrated in figure 2-1.

2-3. Horizontal Distance Tables

a. Horizontal distance tables (table 2-1) are computed for the standard heights of the zone structure as shown in figure 2-1 and for a curved Earth surface according to the following formula:

b. In this formula, D is the arc distance of the Earth's surface in meters and q is the elevation angle to a balloon at a standard height H. R is the average radius of the Earth, 6,367,650 meters.

2-4. Pressure Conversion (Inches of Mercury to Millibars)

The millibars of pressure for a certain number of inches of mercury may be determined from chart 2-1.

2-5. Conversion of Pressure to Percent of Standard

The conversion of surface pressure in millibars to percent of the standard mean sea level pressure is accomplished by use of chart 2-2.

2-6. Virtual Temperature Tables

The virtual temperature tables (table 2-2) are computed for an assumed station pressure of 990 millibars (mb), this being approximately the average station pressure for most areas of the United States. These tables, without correction for pressure differences, are appropriate for all artillery applications. Computations for the tables were made using table 72 (Virtual Temperature Increment of Saturated Air), Smithsonian Meteorological Tables, Sixth Edition 1951 and the Relative Humidity-Psychrometric Tables, US Department of Commerce, Weather Bureau 1953.

SECTION II.

TABLES FOR TYPE 3 BALLISTIC MESSAGES FOR SUFACE-TO-SURFACE TRAJECTORIES

2-7. General

The tables and charts in this section contain the weighting factors and the weighted quantities for density, winds, and temperatures pertaining to all artillery weapons firing surface-to-surface.

2-8. Surface Temperature, Percent of Standard

The conversion of surface temperature to percent of standard surface temperature is accomplished by use of chart 2-3.

2-9. Mean Surface Density

The percent of standard mean surface density for a particular height in meters may be determined from chart 2-4.

2-10. Weighted Wind Speed Tables (Type 3 Message)

a. The weighted wind speed tables may be, used to convert zone winds to the weighted effect of these winds on the various line values of the meteorological message.

b. The Line-Zone Number values are the product of zone wind values and the weighting factor values shown in table 2-9. The values of Line-Zone Number 21 are the product of zone wind speeds and the weighting factor (.20), line 2 of Zone Number 1, table 2-9.



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