Similar to ISA which has been defined for aircraft and instruments another definition has been made for high level flights and spacecraft testing. Although most of the definitions are same there are some variations between JSA and ISA. In JSA air is considered to be dry and mean sea level its temperature is +15 degrees centigrade just like that of ISA. The mean sea level pressure continues to remain 1013.25 hecta pascals. Air density at sea level is 1225 grams per meter cube. The acceleration due to gravity is 9.80665…

# Category: Aviation Meteorology

Understanding Aviation aspects of Meteorology is essential for safe Flight Operations. In this section, we would teach you Aviation Meteorology for DGCA Examinations.

## ISA Lapse Rate

As defined by ISA, the Mean Sea Level temperature is +15 degrees centigrade. The temperature decreases at a constant rate of 1.98 degrees Celsius per 1000 feet, or by 0.65 degrees Celsius per 100 meters. The temperature continues to reduce down to minus 56.5 degrees Celsius at 11 kilometres above the earth’s surface. This is where we find the tropopause in ISA, where the temperature no longer decreases with altitude. From this point onwards we have the tropopause. In tropopause, ISA assumes the temperature would remain constant at minus 56.5…

## International Standard Atmosphere

Most of our flying and our weather is contained within the first two layers of the atmosphere, namely the troposphere and the stratosphere. Within these two layers we have many properties which are important to us like density, pressure and temperature. It is essential to construct a model atmosphere for calibration of instruments and aircraft testing. This model atmosphere is known as the International Standard Atmosphere shortened as ISO or ISA. This model extends to 32 kilometres. ISA assumes that at Mean Sea Level, air is totally dry, the temperature…