Chapter 2: general circulation in the tropics

Question 1

general circulation:

Answer 1

mean movement of air (planetary) over the globe or part of the globe. (large scale mean movement of air on a planetary scale) which is described by the distribution of pressure and wind

Question 2

driving force of general circulation:

Answer 2

latitudinal imbalance of energy (radiation)/heat

Question 3

how is the surplus energy transported?

Answer 3

by latent and sensible heat

Question 4

surface provides energy to the atmosphere in 2 ways

Answer 4

• Sensible heat (20%) - transport of heat due to differences of temperature (no phase change)
• latent heat (80%: nearly 1/2 occurs in tropical ocean through convection): occurs due to condensation of water vapor to liquid

Question 5

Bowen ratio

Answer 5

used to describe the type of heat transfer from the surface (ß). it is the ratio of sensible heat flux (Q_H) to the latent heat flux (Q_E) from the surface to the atmosphere.

ß=Q_H/Q_E

Question 6

ß=Q_H/Q_E (more-less-negative)

Answer 6

• more -> Q_H>Q_E ->
  
  • Ex: ß= 5 (semi arid)
• less -> Q_E>Q_H ->
  
  • Ex: ß= 0.5 (Forest)
  • Ex: ß= 0.2 (Irrigated grass)
  • Ex: ß= 0.1 (Ocean)
• ß<0
  
  • atmospher is warmer than the surface

Question 7

General circulation of the atmosphere (PARTS)

Answer 7

• Meridional (N-S and ht)
• Zonal (E-W and ht)

Question 8

what is the unicellular meridional circulation

Answer 8

non rotating (two cells)

Question 9

rotating meridional circulation:

Answer 9

• hadley cell
• farel cell
• polar cell

results in low at the equator, high at 30 degrees, low at 60 degrees (Subpolar low), polar high

Question 10

tropopause acts as

Answer 10

a lid to turn rising air at the equator to earth (poles) when the earth is stationary.

Question 11

when you add rotation what would happen?

Answer 11

when you add rotation (real case) with angular velocity the corriolis effect will shift winds in easterly direction in NH (southerlies will become westerlies) and (northerlies will become easterlies)

Question 12

when you add rotation (real case) with angular velocity the corriolis effect will shift winds in easterly direction in NH (southerlies will become westerlies) and (northerlies will become easterlies) the winds will rise frim the equator and break down due to

Answer 12

conservation of angular momentum and corriolis effect

Question 13

the singular meridional cell (stationary) will

Answer 13

breakdown to 3 due to sinking motion (high pressure will form at 30 degrees. poleward branch will rise at 60 degrees and make another cell towards the equator and towards the pole).

Question 14

what is the difference between the cells

Answer 14

hadley cell and polar cell are direct (hot air rise and cold air sink) while the farel cell is indirect (hot air sink and cold air rise)

Question 15

difference between direct cell and indirect cell

Answer 15

• direct cell (hot air rises, cold air sinks)
  
  • KE to PE
• Indirect cell (cold air rises, hot air sinks)
  
  • PE to KE

Question 16

the hadley cell is a meridional circulation with

Answer 16

• an ascending branch over the extreme low latitude
• sinking branch over the subtropics

Question 17

the ascending branch of the hadley circulation charactaristics:

Answer 17

• the associated with the zone of maximum solar heating which migrates with season
• if the earth surface was uniform (land and water) the mean position of the ascending branch would be above the equator (5^oN)
• the mean position of the ascending branch of the hadly cell is 5^o N and varies between 5^o s & 15^oN
• in each hemisphere the hadly cell is strongest in winter
• carries heat from surface to troposhere to the higher latitudes (polewards)

Question 18

Zonal Circulation driving force:

Answer 18

(ES and ht)

the differential heating of level and water (uneven distribution of land and water and their differential heating capacity)

three zonal circulation cells exist in the tropics

Question 19

the zonal circulation cells in the tropics:

Answer 19

• over the pacific (walker circulation)
• over the atlantic
• over the indian ocean

Question 20

walker circulation is associated with

Answer 20

el nino

Question 21

elnino:

Answer 21

appearance of warm water in the eastern tropical pacific (pacific has large equatorial extent compared to other basins)

Question 22

the position of rising branch and sinking branch depends on

Answer 22

heat

the position will give precipitation in regions, when el nino occure these areas will have draught

Question 23

reason of formation of subtropical high:

Answer 23

• sinking branch of the hadly cell and the farell cell
• sinking occurs because of radiation cooling and conservation of angular momentum and convergence

Question 24

reason of convergence of poleward moving air:

Answer 24

the spherical shape of the earth (using the stereographic projection of the earth)

Question 25

what is the result of the curvature of the earth:

Answer 25

notice the confluence of meridions from equator towards poles. if you take a parcel moving from equator to pole the parcel will converge (poleward moving air must converge)

Question 26

the fractional rate of change in area with time due to curvature effect and the resultant confluence of the meridions

Answer 26

(1/A)(dA/dt) = (-v/R_e)tan(theta)

R_e: radius of the earth

theta: latitude
v: meridional velocity

Question 27

meridional velocity +ve and -ve

Answer 27

>0 –> S –> N (equator to pole)

<0 –> N–> S

Question 28

when air moving polewards

Answer 28

v>0 –> (1/A)(dA/dt) <0 (convergence)

Question 29

v>0 –> (1/A)(dA/dt) <0 (convergence)

thus

Answer 29

the mass convergence (upper air) of cold air moving poleward in the upper branch of the hadley cell promotes subsidence and help to establish the persistent belt of high pressure in the subtopics