Chapter 1: Characteristics of tropical regions Flashcards
tropical weather is influenced by
- its geography
- its control over weather systems
- movement and development
factors that effect the development and movement of weather in tropics
- the districution of land and water (sea)
- land and sea breeze
- local scale
- durinal scale
- monsoon
- large scale
- seasonal
- land and sea breeze
- the effect of mountain chains on the motion of weather systems
- moonsoon
- hemalaian mountains deflect monsoon wind to keep it in Asia
- moonsoon
tropical geography:
- less land in tropics than at higher latitudes (36 % of the earths land mass is in tropics)
- generate monsoon flows of the tropical zones
- provides the moisture that drives the tropical heat engine (moisture releases latent heat)
- in tropics more land to the north than to the south of the equator
- brings more rain to the north of the equator due to the formation of heat low over the land
- the tropical zone has a dissproportionality large amount of high land (more mountain ranges) ex: himalayas, SE asian mountains
- guid and block the movement of weather systems
Major differences between tropics and midlatitude
- corriolis parameter is small in the tropics
- weather systems in tropics are dominated by convection and the effects of water vapor and latent heating (in mid latitude dominated by waves)
because of convection the planetary boundary layer is much deeper in tropics - tropopause is much higher and cooler in the tropics
- sea level pressure exhibits durinal and semi diurinal cycle due to gravitaional and thermal tides in the atmosphere
implications of corriolis parameter being small in the tropics
- winds cannot be assumed geostrophic or quasigeostrophic
- the relationship (dynamic link) between divergence/ convergence & vorticity tendency is much weaker than in higher latitudes
- circulations are much larger (in tropics circulation penetrates more into the land)
what is the corriolis parameter
f= 2(omega) sin (theta)
omega= 7.292 x 10-5 s-1
theta = latitude
planetary boundary layer
1 km layer near the surface that is influenced by turbulences. if turbulences and convection is more the height will increase (tropics)
tropopause height in the equator and near the poles
13 km
8 km
Horizontal momentum equation (simplified) in vector form:
Horizontal momentum equation (simplified) in vector form: (explain the terms)
if you apply the scale analysis to Horizontal momentum equation
you will see a balance between PGF and corriolis terms. The terms on the RHS are larger. If the ratio between the PGF and corriolis force will determine if the acceleration term can be neglected
in the tropic corriolis force is almost
zero
Breakdown of geostrophic approximation
(A) acceleration (inertial)
(B) Pressure gradient force ( required for air to move from one place to another)
(C) corriolis force (change with latitude)
The rossby number
(R0) ratio of the inertial force (term A) to the corriolis force (Term C)
Express the Rossby number
R0 may be
- <<0
- In extratropics and higher latitudes R0 almost 0.1 (SYNOPTIC SCALE)
- corriolis force is large
- inertial forces are unimportant
- balance between PGF and Corriolis ofrce (Geostrophic balance)
- >>1
- In tropics R>0.1 (SYNOPTIC SCALE)
- corriolis force is small
- coriois force is unimportant
- balance between inertial force (acceleration) and pressure gradient force (cyclostrophic balance)
- almost 1
- occure in mesoscale systems (hurricanes, tornadoes) in tropics and extra tropics
- Corriolis force and inertial force are of the same order
- No term can be neglected
- gradient wind balance
geostrophic approximation validation
- in tropics (NOT VALID)
- in high latitudes (VALID)
when wind is geostrophic it follows
isobars (you will be able to measure wind from isobars)
isobaric analysis is important in
extra tropics
we cannot use isobaric analysis in tropics due to
- lack of simple wind pressure relationship (geostrophic wind relationship)
- pressure gradients are week in tropics
instead of isobaric analysis ……………. is used in the tropics
stream line analysis and isotach analysis
in tropics we analyse …………
in extratropics we analyse …………
wind
pressure
the two most important levels for tropical wind analysis
- the gradient wind level
- the lowest level at which frictional force is not important
- just above the PBL
- almost at 850 hpa
- the 200 hPa level
stream lines
lines that are parallel to the wind
common features in streamline analysis
- Asymptotes
- cusps
- neutral point (col)
- Influent and outflow
- cyclone and anticyclone
asymptotes
streamlines form with other streamlines
- diffluent
- confliunt
cusps
intermediate between a wave and a developing closed circulation
(when you see a cusp expect circulation to form)
neutral point (col)
occure at intersection of two asymptotes of opposite sign ( one confliuent one difluent)
in the tropics the wind is
ageostrophic which gives rise to convergence and divergence (plays a prominant role in tropics than midlatitude)
Divergence and convergence patterns can be infered from
cloud patterns on a sattelite image
a distinct cloud feature on a satellite image indicate
a convergent asymptote at low levels
a divergent asymptote at higher levels
a large cloud free area indicates
a divergent asymptote at low levels
a convergent asymptote at high levels
sunglint on the visible image indicate
(reflection from the surface of the ocean)
- light winds
- can help locate
- ridge axes
- neutral points
absolute vorticity
(ع+f)
the synoptic scale vorticity equation can be written as:
d/dt(ع+f)= -(ع+f) -/.v
when del . v is
+ve then divergence then (ع+f) decreases
-ve then convergence then (ع+f) increases
charactaristics of absolute vorticity in the tropics:
- the absolute vorticity is week (small) in tropics beceause f is small
- a given amount of conv and div will have a much smaller effect on abs vort in tropics than in mid lat
- strong anticyclones are not common in tropics
atmospheric tides:
the large amplitude, durinal and semi durinal variation of sea level pressure due to solar heating (not due to gravitational force)
solar heating excites
three pressure oscillations having periods 24 hrs, 12 hrs, 8 hrs
all of which differ in horizontal and vertical structure
the 12 hr (semi durinal) oscillation:
- the largest amplitude occur at the surface at a range of 1 to 2 mb
- the amplitude decreases with height and is less than 0.5 mb at the tropopause
- the pressure maximum occur at 10 and 22 and the pressure minimum occur at 04 and 16
explain how the tidal range varies
- greater near the equator and decreases polewards
- greater overland than over water
