1 . Atmosphere

atmosphere defn

the atm of earth is a an envelope of homogeneous mixture of gas called air

atm thickness

approx 480 km

80% of atm is within 16km

composition of dry air

78.08% Nitrogen 21.95% oxygen 1% other gases ( 0.93% argon , 0.004% co2) ozone is 0.00007%

N2 02 ration by volume & by weight

By volume 4 1 by weight 3 1

Homosphere vs heterosphere

Homosphere upto 80km nearly uniform composition well mixed

Heterosphere above 80km gases seperated by molecular weight composition varies

Variable gases

gases like water vapour , carbon monoxide , sulpher dioxide , nitrogen dioxide vary in amount frrom place to place

Greenhouse gases and effect

water vapour , CO2 , O3 , Methane , are transparent to solar radiation short wave but partially absorb long wave terrestrial radiation and re radiate it. this keeps earth warmer

Water Vapour

rapidly decreases with height

warm air can hold greater amount of water vapour

between 23N/S air can hold upto 4% WV by volume

Ozone

froms in upper atm

Max O3 concentration 20-25km

O3 found between 10-50km

vertical distribution of airmass

6-10-35 ; half - ¾ - full

thermal structure of the atm

solar radiation heats the earth, the earth in turn heats the atm by conduction , convextion , radiation & release of latent heat by condensation of water vapour

Heat flow from earths surface

sensible heat & latent heat

sensible heat 23%

latent heat 77

Atm layers and temp trend

Troposphere ; temp falls mostly wx preesent here tropopause 8-18km

Stratosphere ; temp rises in the upper part

Mesosphere ; temp generally falls

thermosphere ; temp generally rises 80 - 85km

Troposphere

lowest portion of atm
surface to 16-18km at eqtr 8-10km at poles

higher height at eqtr due to rising hot air convection currents

temp falls at 6.5 deg/km cecius lapse rate

contains 75% of atm mass & 99% of wv and aerosols

lower tropospher - surface to 2.1km

mid - 2.1 to 7.6

higher - 7.6 to tropopause

tropopause

marks the bdry btwn troposphere and stratosphere

lapse rate reduces to approx 1-2 deg celcius/km

temp at eqtr -75 c

temp at poles -45 c

at lower height in winters than summer

warmer the surface higher the tropopause

breaks or folds in tropopause

2 regions where tropopause abruptly changes height called breaks or folds

at 40 & 60 degree latitudes

break @ 40deg more prominent

jet streams occur at this breaks

stratosphere

initially isothermal (8-10 km above tropopause)

temp then increases slowly & towards the top sharply

inversion due absorbtion of UV by ozone

very dry and stable region

Nacreous clouds

mesosphere

50-80km from stratopause

lack of solar radiation absorbtion + weak vertical mixing → temp falls with height

noctilucent clouds

mesopause - temp stop falling , coldest region , temp at 80km is -100 c

Thermosphere

mesopause to exopshere

temp increase with height

ionosphere overlapping ionised region that extends across parts of mesosphere , thermosphere , higher atm

imp for radio wave propgn

Exosphere

outermost layer extending upto 10000km

hight temp particles but far apart hence no very little heat present

ISA

a standard avg atm specified for various purpose like design and testing of ac

ISA specs

air = dry

temp 15 c msl

px 1013.25 hpa

density 1225 g/m3

accln 9.8m/s2

lapse rate = upto 11km (36k ft) 6.5 c/km

temp = 11 - 20k (65k ft) = -56.5 c isothermal constant

temp 20 - 30 km - rises at 1 c / km with temp -44.5 deg c at 32 km (104k ft )

isa deviation formulae

actual temp - isa temp

JSA jet std atm

isa values are satisfactory for ac operating below 30k ft but not above

for space flight s , ac testing , very high alt flying & engine manufacturing additional specific values are required . jsa was introduced to meet these req

JSA specs

msl temp is 15 c

2 degree celcius lapse rate per 1000ft

No tropopause

total atm thickness

480km

80% of atm within

16km

N2 O2 by volume by weight

4 1 3 1

supplementary o2 is reqd above

10000ft

homosphere upto

80km

max WV (tropics )

4% by volume

saturated air RH

100%

ozone max concentration

20-25km

ozone range

10-50km

sensible heat

23%

latent heat

77%

troposphere height at equator

16-18km

troposphere height at poles

8-10km

lapse rate til 11km

6.5 degree celcius/km

WV + aaerosols in troposphere

99%

atm mass in troposphere

75%

tropopause temp at equator

-70 to -75 degree celcius

tropopause temp at poles

-40 to -45 degree celcius

stratosphere upto

50km

ozone layer height

25 km

mesosphere range

50-80km

mesopause temp

-100 degree celcius

ionospher region

overlaps upper layers , its bdry varies

exosphere upto

10,000 km

T S M T E

troposphere

stratosphere

mesosphere

thermosphere

exosphere

polar tropopause & tropical tropopause

polar tropopause @ 300hpa

tropical tropopause @ 100hpa

temp at 80km

173 kelvin or -100 degree celcius mesopause

green house gases

W C O M

water vapor

co2

o3

methane

stratosphere extends upto

50km from earths surface

30-32 km above tropopause at equator

mother of pearl clouds ( nacreous clouds occur in )

stratosphere

noctilucent clouds occur in

mesosphere

by volume proportion of CO2 in the atm is

0.03% ( actual current value is 0.042)

half of the atm mass is contained below

20,000 FT ( FL180 = 500hpa )

tropical tropopause extends from equator to lat 35-40 . over india it is at ?

16 - 16.5km

tropical tropopause lies at 100hPa level approx 16-16.5 km

it is the tropopause over india in most of the summer

most of the water vapor in atm is confined upto

30,000 ft

heat transfer in the atm is max due to

latent heat ( evaporation , condensation , sublimation ) = 77%

in ISA atm tropopause occur at a height of

11km 3600ft

Na Stra

nacreous clouds stratosphere

Kelvin to celcius

K = c + 273