(i) Jet stream. A jet stream is a fast flowing wind blowing in narrow zone in the upper atmosphere. The Himalayas divide the jet stream into two parts. A westerly jet stream is placed south of the Himalayas in the winter season. An easterly jet stream is developed at about 25°N in summer. It is believed to be responsible for the sudden outbreak of Monsoons in the Northern India. This is responsible for widespread storms, thunders and rainfall over India in just 8 to 10 days.
(ii) Isotherm. Isotherm are the line drawn on a map or chart joining points with the same temperature. Isotherms are commonly used in meteorology to show the distribution of temperature at the earth’s surface or on a chart indicating constant level or constant pressure.
(iii) Dry and wet bulb thermometer. It is an instrument used to measure the relative humidity of the atmosphere. It consists of a thermometer with a bulb that is wet or moist and one that is kept dry. The relative humidity is calculated from the difference in readings of the thermometers when water evaporated from the wet bulb, decreasing its temperature. Humidity in the air is always given in percentage.
