Fronts may differ in their types, location, or areal extent, but the following characteristics are more or less common to all of them.
Temperature:
Large differences in air temperature are recorded across a front. But the changes in temperature may be abrupt or gradual depending on the nature of the opposing air masses.
Image Source: okanagan.bc.ca/Assets/Regions/Shuswap%2BRevelstoke%2BRegion/Images2/Temperature.jpg
ADVERTISEMENTS:
Further, the width of a frontal transition zone is dependent on the temperature contrasts between the two air masses. Larger the difference in temperature, thinner the frontal zone and vice versa.
Besides, the fronts are always characterized by temperature inversion layers because of the ascent of warm air over a wedge of cold and dense air mass.
Air pressure:
Generally the isobars in an air mass are smooth curves and there are no sharp bends in them.
ADVERTISEMENTS:
But because of an abrupt change in pressure as well as pressure gradient across a front, the isobars while crossing it form a kink and always bend towards the direction of low pressure.
The wedge formed by the bending of isobars across a front always points towards the higher pressure. It is noteworthy that mostly the fronts lie in a trough of low pressure.
Winds:
As we know, wind movement is always controlled by the pressure gradient and Coriolis force. Therefore wind always blows from higher to lower pressure crossing the isobars at an acute angle.
ADVERTISEMENTS:
It is, therefore, natural that an abrupt wind shift must occur at the fronts. Southwesterly wind in a tropical air mass gives way to northwesterly wind in the polar air mass across the front. The lines of abruptly shifting winds were formerly known as wind-shift lines.
Cloud and precipitation:
Frontal activity is invariably associated with cloudiness and precipitation. Since warm air moves up along the frontal surface, it cools adiabatically which results in cloudy condensation and precipitation.
The type of clouds and precipitation falling from them depend on the slope of the front and the amount of moisture in ascending mass of air. Clouds formed on the sloping frontal surface extend for hundreds of kilometers.
It is to be remembered that clouds form in the upward moving warm air above the wedge of cold and dense polar air mass.
It is from these clouds that precipitation occurs. Sometimes local heating causes the formation of cumulus clouds in the cold sector which lie beneath the precipitation-giving warm sector clouds.