Temperature profile of the Troposphere

Transcription

1 roposphere he troposphere is the lowest atmospheric layer reaching an altitude o about 20 km. Density, pressure and temperature decline with altitude. he troposphere is largely convective, which translates into a uniorm chemical composition. ritical component is H 2 O vapor rom evaporation and transpiration processes. Water vapor decreases with altitude because o condensation and cloud ormation.

2 emperature proile o the roposphere Heat transer in air: Q t k A z W mk thermalconductivity Heat transer takes place by energy transer through cross sectional area A! Vertical convective motion takes place by moving volume o air in a reversible adiabatic process (no heat exchange with surrounding environment Q=0!) his is subject to energy conservation according to the irst law o thermodynamics: du Q W Heat exchange between air packet and surrounding is: kj dq v d dv v K kg Adiabatic conditions: k air Q kj K kg dv Q 0 v d dv Speciic heat or heat capacity o an air volume element at constant volume or constant pressure.

3 For adiabatic conditions Q 0 v d dv Internal energy or speciic heat or V V const : du const : v v du d d V v or du d const : dq d Gas p J/mole K v J/mole K He Ar N O O O H 2 O vapor air Universal gas constant R = 8.31 J/mole K R v onversion: 1 mole A g

4 o derive the temperature proile along the vertical atmosphere axis as unction o altitude (z) requires dierentiating the ideal gas equation V=R or Q=0: dv V d Rd d R v v R d d d V d v d or d adiabatic dv element dv V d Reormulating the hydrostatic equation: V d d d dz V m g dz m g g dz m g dz d dz g Lapse rate deines the rate at which temperature decreases with increasing altitude z. (For the troposphere a negative value) Adiabatic lapse rate: =-9.7 K/km or dry air. z g 9.81m / s z 2

5 he adiabatic lapse rate describes the temperature change with altitude or absolutely dry air, it serves as a normalization parameter since air is never dry. increases with humidity, =1.88 KJ/km K or H 2 O vapor. An increase in humidity decreases the temperature gradient. he actual lapse rate L depends on humidity and is around 6-7 K/km! d dz V g L 6 7 K km Higher humidity increases and changes the temperature gradient that -L < -Γ or L > Γ. Flight height o 10 km, =-50 o =223K

6 d dz I the density ρ in an air volume element V is smaller than the density ρ s o surrounding environment, the buoyancy causes acceleration upward, i density o air volume is larger, element will stabilize. V smaller g L Unstable situation, convection d V larger g L dz z stable situation, no convection onvective equilibrium d dz radiation convection d d dry wet air dry m V m V V wet dry V g dz L dz g dz dz amu 3 V V m V V amu 3 m

7 louds Rising

8 loud physics and weather see next chapter

9 he stratosphere he stratosphere is the second layer o the atmosphere above the troposphere ranging rom about 20 km to 50 km altitude. he density declines in this layer rom 100 g/m 3 to 3 g/m 3, the pressure drops exponentially rom 100mb to 1mb. he temperature remains constant at the lower layer o the stratosphere and then rises with increasing altitude. At the top o the stratosphere the thin air may reach temperatures close to 0 (273 K).

10 emperature proile o Stratosphere 1/ E S S E S E E S E S E S E out S E in F F E = 255 K S = 215 K his suggests that temperature in stratosphere remains constant. his is only partially correct since ozone layer in stratosphere causes urther absorption and an increase o the stratosphere temperature up to 270K. ~20-50km altitude emperature is dominated by radiative energy balance Incoming lux must be balanced by outgoing lux. he actor is the raction o transmitted radiation.

11 hemical composition o Stratosphere emperature is low and constant or ~10 km, that region is requently called tropopause. owards higher altitude the temperature increases due to the absorption o cosmic radiation, reaching a maximum o about 0 o (273 K) at top o stratosphere. his is associated with the absorption o UV radiation by Oxygen and Ozone causing stratosphere heating in its upper layers. UV range

12 Nuclear test program deposition A total o 2057 nuclear weapon explosions since 195

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14 Bq=500 Bq

15 Mesosphere Mesosphere is the atmospheric layer above stratosphere. It is characterized by steadily decreasing density. High altitude (~80km) location or rare kind o clouds (noctilucent clouds) in polar zone, requency o occurrence seems to increase (signature or climate change, consequence o space shuttle exhaust?)

16 NL ormation requires a combination o very low temperatures, a source o water vapor, and condensation points (meteoritic dust, volcano ashes, aerosols?) NL: irst observed 1885 (two years ater the Krakatau eruption), increasing appearance o noctilucent clouds is interpreted as a consequence o a decrease in temperature at the altitude where the clouds orm parallel with an increase in water vapor by complex photochemical processes. he warming in the in the lower atmospheric layers causes the cloud layer to cool increasing the probability o ormation.

17 Mesosphere is too high to be reached by balloon or aircrat and is thereore poorly understood! New satellites such as AIM mission are launched or more detailed exploration. emperature declines towards its lowest value in the atmosphere o about =-80 o (193K). Limited absorption o the solar radiation lux and possible cooling by de-excitation o O 2 vibrational excitation modes by collision with oxygen atoms, which are in equilibrium at higher density in lower atmospheric regions. Q 2 e collision 960 rate his leads to the discussion o possible enhanced cooling with increasing O 2 budget!

18 Aerosol impact on stratosphere temperature Example: Mount inatubo eruption in June 13, 1991 causing emission o particles into higher atmosphere with direct impact on optical depth ( d) and temperature. Optical depth or 1020 nm range F F 0 F F 0 e e d d 0km; d Fv v d 99% e 9% F 0 0 d v d 0.06

19 Impact on high altitude temperature

20 Heavy metal enrichment Large numbers o meteorites are absorbed by atmosphere, they typically evaporate in the mesosphere, enriching the layer with about 0 tons/day o heavy metal containing dust! During the early phase o the planet ormation, the accretion rate was in the range o more than millions /sec rom meteors to planetesimals. FREQUENY OF IMAORS: ea-size meteoroids - 10 per hour Walnut-size - 1 per hour Graperuit-size - 1 every 10 hours Basketball-size - 1 per month 50-m rock - 1 per 100 years 1-km asteroid - 1 per 100,000 years 2-km asteroid - 1 per 500,000 years N 37 D 2.7 N: number o meteorites D: diameter o meteorites Meteorites ragment in higher atmosphere layers and the ragments evaporate in the mesosphere. Meteoritic material is enriched in heavy elements (iron meteorites) which orm dust particles in the high altitude layers.