Download Problem Set 1

Problem Set 1
1.1
State Buys-Ballot law and illustrate it by showing the positions of low and high pressures in the
free atmosphere (~ above 850 hPa) and near the surface (~ below 850 hPa).
1.2
(i) What is the monsoon system over India? (Answer this question describing the locations of
high and low pressures over land and ocean, and regions of heavy and low rainfall. The
southwest monsoon over India originates from the southern Indian Ocean and the prevailing
winds during summer bring moisture to the Indian subcontinent. Discuss from thermodynamical
point, the importance of the land and sea temperature contrast for the monsoon system, which
may affect evaporation over sea to produce tangible variations in the rainfall over the Indian
subcontinent.
(ii) Where are the mean sea level high and low pressure centres located on the globe during
summer and winter seasons? Justify your answer if you notice differences in their distribution in
the northern and southern hemisphere.
(iii) Depict the barotropic and baroclinic structure of atmosphere or ocean graphically. Draw the
orientation of isobars and isothermal for such atmospheres.
(iv) Describe the low level convergence forced by a mid-tropospheric heat source. Which
system will form above this zone of low-level convergence in the upper troposphere: a
convergent or a divergent centre? Distinguish such thermally forced systems from those formed
dynamically as atmosphere is always in motion.
1.3
(i) Describe in your own words and illustrate with figures: (a) Circulation around a low pressure
centre and high pressure centre; (b) Thermal wind, backing and veering of geostrophic wind
with height. (c) An isothermal and adiabatic atmospheric/oceanic layer.
(ii) (a) Why does temperature decrease with height in the troposphere. (b) Heating by solar
radiation and advection of warm or cold air are the two mechanisms that may lead to instability
of an otherwise stable atmospheric column. Discuss their importance in atmospheric stability
and state conditions when dry and moist air masses rise up in the atmosphere.
1.4
Sketch the Hadley, Ferrel and Polar cells and comment on the thermally direct and indirect cells
in the context to atmospheric general circulation.
1.5
Calculate the direction and wind speed between a high pressure 1025 hPa located at 40o N and a
low pressure 980 hPa located at 60o N. Both these system are at the mean sea level and lie on
the same meridian. [Hint: use the balance between the Coriolis and the pressure gradient force;
take density of air =1.2 kgm-3 and 1o latitude measures 110 km.]
1.6
Discuss the implications of conservation of potential vorticity. How is vorticity generated in air
mass columns of constant and changing heights? Could deflection of isobars southward be
explained from conservation of potential vorticity after monsoon air current crosses the Arabian
Sea and flows over the Deccan Plateau? (Hint: Base your argument on the height differences
experienced by the south-westerly moist air current)
1.7
How does Ekman flow engender in the atmosphere and ocean? Is it a geostrophic flow? Also
comment on the Ekman transport, Ekman pumping and suction.
1.8
Does Ekman flow originate only in the open sea or could it be generated by the action of wind in
the shallow coastal ocean waters?
1.9
(i) The term thermohaline is widely used in oceanography. Mechanical stirring drives
Thermohaline circulation which transports heat, mass, freshwater and other properties in
meridional and zonal directions in the ocean. The mechanical stirring of the ocean at the surface
is maintained by external sources. What are the external sources of mechanical stirring?
(ii) What are the time scales of the thermohaline circulation?
1.10 (i) As an application of the thermal wind to ocean, how will the magnitude of the ocean current
vary with depth if isopycnal slope upward on the left while looking downstream to current?
(ii) Strong winds in the Arabian Sea achieve jet speeds (12-18ms-1) which drive the Somali
current in the Arabian Sea. This wind-driven current originates off the Somalia coast and flows
northeastward. Comment, if this current could trigger upwelling of cold water from bottom
layers; if yes, then justify your answer.
(iii) Deep ocean waters mostly form in the North Atlantic Ocean. What could be the possible
reasons for the truth of this statement?
(iv) Wind driven circulations in the ocean are generally called the gyres. Which are the possible
1 regions in the world oceans where such gyres are present and dominate the global ocean current
system. What is the orientation of the global ocean circulation in general?
1.11
Illustrate the warm and cold core eddies in the ocean. What kind of circulation you can be
depicted around such eddies using the principle “light on the right. Also comment on the
relative position of the thermocline below a warm core eddy and a cold core eddy.
1.12
Could you interpret the following figures (a) – (e)?
F2
+
V2
F3
+
V1
F1
(b)
(a)
pe
ro
nt
e
s
i
θ + δθ
Cold wind
δp
ise
ntr
op
e
δ p is the pressure difference
from North
North↑
30000 gpm
θ
35000 gpm
(c)
45000 gpm
+A
Isobaric surface
B
+
60000 gpm
60000 gpm
45000 gpm
35000 gpm
30000 gpm
(e)
(d)
2