CHAPTER 2

METEROLOGICAL 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 manual are presented in sections I, II, and III as follows:

a. Section I, General Tables and Charts for Meteorological Messages. These tables and charts are used for computing general meteorological data from all types of meteorological messages.

b. Section II, Tables for Type 2 (Electronic), Ballistic Message for Surface-to-Air Trajectories. These tables include the weighting factors and the weighted quantities for density, wind, and temperature pertaining to the trajectories of air defense weapons (guns).

c. Section III, Departure Tables for Type 2 (Visual), Ballistic Message for Surface-to-Air Trajectories. These departure tables are used in determining ballistic densities for a type 2 message.

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-l 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 standard height H. R is the average radius of the earth, 6,367,650 meters.

2-4. Conversion of Wind Speed (Miles per Hour to Knots)

Chart 2-1 is used to convert wind speed in knots and miles per hour.

2-5. Pressure Conversion (Inches of Mercury to Millibars)

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

2-6. Conversion of Pressure to Percent of Standard

The conversion of surface pressure in millibars to percent of the standard mean sea level (MSL) pressure is accomplished by use of chart 2-3.

2-7. Pressure to Contact Conversion

The conversion of pressure in millibars to contact value in tenths, or vice versa, is accomplished by use of table 2-4.

2-8. Relative Humidity

Relative humidity may be determined by use of a psychrometer and psychrometer tables or by use of chart 2-4.

2-9. Table of Corrections Used to Determine Virtual Temperature for Plotting Chart ML-574( )

a. Table 2-5 provides temperature multipliers which, when multiplied by relative humidity values (i.e., 45% = 0.45, etc.) and added to the observed temperature values, yield virtual temperatures.

b. Enter the table with the observed air temperature rounded off to the nearest whole degree Celsius and the observed pressure rounded off to the nearest 50 millibars. If the observed pressure value ends with 25 or 75 (e.g., 925 or 775), round off to the lower 50-millibar value. Do not interpolate.

2-10. Conversion of Surface Density to Percent of Standard

The surface density, in grams per cubic meter and expressed as a standard surface density, may be determined from chart 2-5.

SECTION II TABLES FOR TYPE 2, BALLISTIC MESSAGE FOR SURFACE-TO-AIR TRAJECTORIES

2-11. General

Tables 2-8 through 2-14 contain the weighting factors used in obtaining a type 2 message. Some of the tables present the weighting factors directly; in others, the weighting factors are used to determine the effect of the various zone values on the line values of the meteorological message. The weighting factors used are those agreed to, on an interim basis, by the fifth meeting of the NATO Group on External Ballistics, November 1960.

2-12. Weighted Density Tables (Type 2 Message)

a. The weighted density tables give the weighted densities for the type 2 message (surface-to-air firing) and may be used to convert zone densities in grams per cubic meter to zone densities in percent of standard for that zone, and to convert zone densities to the weighted effect of these zone densities on the various line values of the meteorological message.

b. The values in the density--percent column were computed by dividing the Gm/M³ value by the zone midpoint standard density.

c. The line-zone number values were computed by multiplying the density percent values by the weighting factors shown in table 2-8. Line-zone number 21 is the product of the weighting factor (.63), line 2 of zone number 1, table 2-8 and the density--percent value. Line-zone number 32 is the product of the weighting factor (.37), line 3 of zone number 2, table 2-8 and the density--percent value.

2-13. Weighted Wind Speed Tables (Type 2 Message)

a. The weighted wind tables maybe used to convert zone winds to the weighted effect of these winds on 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 2-10. The values of line-zone number 21 are the product of zone wind speeds and the weighting factor (.50), line 2 of zone number 1, table 2-10.

2-14. Weighted Temperature Tables (Type 2 Message)

a. The weighted temperature tables may be used to convert zone temperatures in degrees Celsius to zone temperatures in percent of standard for each zone. They may also be used to convert zone temperatures to the weighted effect of temperatures on the various line values of the meteorological message.

b. The zone temperature-percent column is the quotient of the zone temperature divided by the standard zone temperature.

c. The line-zone number values are the product of the weighting factors shown in table 2-12 and the zone temperature-percent values. The line-zone number values of column 21 are the product of the weighting factor (.63), line 2 of zone number 1, table 2-12, and the zone temperature--percent values.

SECTION III DEPARTURE TABLES FOR TYPE 2 (VISUAL) BALLISTIC MESSAGE FOR SURFACE-TO-AIR TRAJECTORIES

2-15. General

The tables and charts contained in this section are used to determine the departure from mean surface density for the computation of a ballistic meteorological message (visual).