The Hydrologic characteristics of a region are determined largely by its climate and its geological structure.
- Amount and distribution of precipitation;
- The occurrence of snow and ice;
- The effects of wind,
- Humidity on evaporation and snowmelt
Hydrology & Meterology & Weather
Hydrologic problems in which meteorology plays an important role include:
- Determination of probable maximum precipitation,
- Optimum snowmelt conditions for spillway design,
- Forecasts of precipitation and snowmelt for reservoir operation,
- Determination of probable maximum winds.
If the earth were a non-rotating sphere, a purely thermal circulation (shown in figure) would result. The equator receives more solar radiation than the higher latitudes. Equatorial air, being warmer, is lighter and tends to rise. As it rises, it is replaced by cooler air from higher latitudes.
Actual Behaviour of weather
The earth rotates from west to east .
The force that would be required to produce these changes in velocity is known as the Coriolis force. This apparent force always acts to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
- The observed pattern of the general circulation in the Northern Hemisphere is shown in figure. Unfortunately, the physical reasons for this circulation are’ only partly known. weather
- The rising equatorial air acquires an eastward component as it moves northward. At about 30o lat., it tends to subside because of cooling. The subsiding air splits into two currents, one moving southward as the northeast trade winds and the second continuing northward and eastward.
- In the polar cell, loss of heat in the lower layers results in subsidence, the subsiding air spreading southward and westward. As it moves southward the air is warmed, and at about 60o lat. it rises and returns poleward as a south westerly current aloft.
- The pressure pattern is greatly distorted by the effects of water and land masses. These effects are the results of differences in the specific heats, reflectivity, and mixing properties of water and land and of the existence of barriers to air flow.
Migratory System of Air
A cyclone is a more or less circular area of low atmospheric pressure in which the winds blow counter clockwise in the Northern Hemisphere. Tropical cyclones form at low latitudes and may develop into violent hurricanes or typhoons with winds exceeding 75 mph over areas as large as 200 mi in diameter. Extra tropical cyclones form along fronts, the boundaries between warm and cold air masses. Such cyclones are usually larger than tropical cyclones and may produce precipitation over thousands of square miles.