2. WHAT IS TEMPERATUE
As we know that in the lower part of the atmosphere temperature generally
decreases with increasing height. All of you must know the reason, however it
occurs because as we go up in the atmosphere the density of air molecules
decrease unlike near the earth surface where the air is held by the gravity
resulting in high concentration of air and hence high pressure, the molecules
collide among themselves generating heat (high temperature). As the density
decreases so does the quantity of the air molecules which means huge gap
between the molecules allowing them to move freely without colliding much
with each other resulting in generation of less heat (low temperature). The
decrease in temperature with increase in altitude in the atmosphere is known
as vertical temperature gradient or lapse rate. The normal lapse rate is 6.5°C/km
in lower atmosphere. (Its different from adiabatic lapse rate).
But sometimes under special circumstances, this trend is reversed ie.
the temperature instead of decreasing starts increasing with altitude. This
phenomena is known as negative lapse rate or Inversion of Temperature in
meteorologically terms.
INVERSION?
7. SURFACE INVERSION
Inversion near the surface is of very short duration because the solar radiation
heats the surface during day time, warms up the pre-existing cold air near the
surface which soon disappears at night and hence the temperature inversion
also disappears. Upper air inversion lasts for longer duration because the
warming of cold air layer aloft through terrestrial radiation takes respectively
longer period of time.
Surface
Inversion
Radiation Advection
8. RADIATION INVERSION
Inversion is produced by radiation mechanism. It’s caused due to excessive
nocturnal cooling produced by outgoing terrestrial radiation. Thus, the air
coming in contact with cool ground surface also becomes cool while the air
lying above is relatively warm.
Loss of heat by terrestrial radiation is more than the insolation received during
daytime as the nights are colder and longer.
Absorbs less heat radiated by the surface in comparison to moist air
More loss of heat without any obstruction after sunset as clouds absorb and
delay the loss of heat.
No or little mixing of air and hence less transfer of heat.
Ground gets suffice amount of time to cool down.
Albedo of snow is very high, the snow covered surface heats up slowly.
At night, snow being a bad conductor of heat retards the flow of heat from
ground underneath to surface air.
Dry
Air
Clear
Sky
Calm
Air
Long
Winter
Nights
Snowy
surface
Suitable Conditions :
9.
10. ADVECTION INVERSION
Dynamically produced.
Heat is transferred by horizontal flow of fluid in atmosphere or sea where
the particles are in contact with each other.
Inversion occurs when warm air passes over cooler surface.
11. UPPER AIR INVERSION
Its of two types i) Thermal upper air inversion which is caused by presence of
ozone layer in stratosphere. It absorbs most of the UV rays radiated from the
sun increasing the temperature of the layer much higher than the layers below
and above it. This occurs only when there is no vertical movement of air only
ascent and descent of air. ii) Mechanical inversion is caused due to subsidence
of air and Turbulence & Convection mechanism.
Upper Air
Inversion
Subsidence
Convection
& Turbulence
12. SUBSIDENCE INVERSION
This type of upper-air inversion occurs in an air mass when a thick mass of air
subsides due to high pressure cell. The sinking air compresses and warms at the
dry adiabatic rate of 10°C/km. In certain cases, the subsidence continues to a
particular level where the air diverges horizontally above a lower layer of colder
air. Occurs commonly in regions of high pressure.
13. TURBULENCE & CONVECTION INVERSION
Convectional currents set up in the air near the ground are mainly responsible for
the exchange of air between upper and lower levels of the atmosphere. The
phenomena of turbulence and convection cause a thorough mixing of the
atmosphere in turbulent layers. However, the turbulent or convective mixing is
limited to a certain height beyond which it does not and cannot penetrate.
In the process of vertical mixing (convection) the air carried upward is cooled
adiabatically. Similarly the air brought downwards heated at the same adiabatic
rate. The mixing of warm and cool air produces frictional eddies which causes
instability or turbulence.
After a prolonged mixing in the atmosphere, the air at the maximum height of
turbulent penetration becomes colder than what it was before, and that at the
bottom of the turbulence layer will be warmer than what it originally was.
The transition from this cold upper part of the turbulence zone to the air above with
its temperature unaffected by adiabatic cooling comprises a temperature inversion.
In certain situations, turbulence in association with heat from the ground leads to
the formation of cumulus or cumulonimbus clouds.
Turbulence inversion may occur at a low level or it may form at very high altitudes.
In case the inversion has formed at lower levels, smoke, dust particles and other
pollutants are carried up to the inversion where they spread beneath the inversion
layer and form distinct smoke or haze lines in clear weather.
14.
15. FRONTAL INVERSION
Occurs when differing air masses converge.
The warmer air being relatively higher tends to overlie the colder and denser air in a
horizontal layer but however due to the coriolis force the boundary zone between these
contrasting air masses is sloping.
The frontal zone itself is converted into inversion layer in which the lapse rate is inverted.
16. Some of the most significant consequences of temperature inversions are the extreme
weather conditions they can sometimes create.
Freezing rain- This phenomenon develops with a temperature inversion in a cold
area because snow melts as it moves through the warm inversion layer. The
precipitation then continues to fall and passes through the cold layer of air near
the ground it becomes cooled below freezing without becoming solid. The super-
cooled drops then become ice when they land on items like cars and trees and the
result is freezing rain or an ice storm.
Intense thunderstorms and tornadoes are also associated with inversions because
of the intense energy that is released after an inversion blocks an area’s normal
convection patterns.
Smog- This is the brownish grey haze that covers many of the world’s largest cities
and is a result of dust, auto exhaust, and industrial manufacturing. This happens
because the warmer air layer accumulates over an area and prevents the normal
mixing of cooler, denser air. The air instead becomes still and over time the lack of
mixing causes pollutants to become trapped under the inversion, developing
significant amounts of smog. During inversions that last over long periods smog
can cause respiratory problems for the inhabitants of those areas
CONSEQUENCES OF INVERSION OF TEMPERATURE
