Climate
of intertropical zone
Radiation conditions
" Low seasonal contrasts in radiation flux at
the upper limit of the atmosphere
 Low seasonal day-length changes
 Low solar angle changes
 The increased radiat ion intensity during S
hemisphere summer is compensat ed by the
difference of seasons length
" Cloudiness modifies radiant energy flux in
large extent
RC - intertropical zone 2
Total solar radiation - January
RC - intertropical zone 3
Total solar radiation - July
RC - intertropical zone 4
Pressure systems
and atmospheric circulation
" Semi permanent steering pressure syst ems:
 Oceanic anticyclones
 Intertropical low pressure trough
 Intertropical convergence zone (IT CZ)
" Seasonal range of trough motion is larger than that of ITCZ
 Above ABL trade winds penetrate even 1000 km closer to the
equator
 This is the case e.g. in N Africa and S Asia in the first month of
summer monsoon
" Seasonal steering pressure syst ems near both
tropics:
 Wintertime highs (=anticyclones) over continents
 summertime lows (=cyclones) over continents
RC - intertropical zone 5
Seasonal position of ITCZ
RC - intertropical zone 6
Air temperature
" Weak seasonal variations:
 Along the equator, in oceanic conditions and in all-yer-
around humid climate: (SRT<2 K)
" Nocturnal T drop is limited by atmospheric infrared radiation
(cloudiness and high water vapour content)
" TMAX ograniczona przez ciepło utajone parowania
 Observed increase with latitude and in drier climate
" Limited spatial variation
 Except of areas neighbouring with cold oceanic waters
(strong cool sea breeze within a limited coastal range)
RC - intertropical zone 7
Air temperature (& )
" Strong T decrease with altitude (around 0,6 -0,7 K/100 m)
 Exception  trade inversion area above ABL
 The highest mountains situated above perennial snow line (4500-
6000 m a.s.l.)
" Vertical landscape setting:
 Tierra caliente (0-800 m a.s.l.)
" Rain forest, tropical agriculture (bananas, sugar, cocoa& )
 Tierra templada (800-1800 m a.s.l.)
" Most populated zone, coffee, corn, wheat
 Tierra fria (1800-3600 m a.s.l.)
" Up to the tree line; hardy crops  barley, potatoes
 Tierra helada (3600-4500 m a.s.l.)
" Cold, barren, grass; sheep grazing
 Tierra nevada (above 4500 m a.s.l.)
" Up to snow line, perennial snow, glaciers
RC - intertropical zone 8
Air temperature (& )
" Urban heat island (UHI)
 Typicaly weaker than in higher latitudes
 More distinct in dry season
 In dry conditions might be changed into  cool
island e.g. Alice Springs, Australia, is cooler
than the ambient area about 1K because of
 oasis effect where latent heat consumption for
evaporation is increased
RC - intertropical zone 9
T  annual average
RC - intertropical zone 10
T - January
RC - intertropical zone 11
T - July
RC - intertropical zone 12
T - April
RC - intertropical zone 13
T - October
RC - intertropical zone 14
Water vapour pressure - January
RC - intertropical zone 15
Water vapour pressure - July
RC - intertropical zone 16
Origin of atmospheric precipitation
" Convective precipitation
" Precipitation in cyclonic
disturbances/sytems
" Orographic precipitation
Lack of frontal precipitation at the contact of
differant air masses
RC - intertropical zone 17
Convective precipitation
" Individual convective cells cover area 10 -300 km2
" They may be organized as e.g. breeze f ront, linear
disturbance or squall line (MCS, MCC)
" Relatively low cloud base, usually 500 -800 m a.s.l.
" High position of 0 C isothermal surf ace due to high T and
humidity  as the result even intense precipitation might
form without Bergeron -Findeisen mechanism
" In case of convective clouds developed into the upper
troposphere the role of B-F mechanism is still important 
so large hailstones may be f ormed
" Precipitation inversion occurs at relatively low altitude:
 The more humid air mass is, the lower inversion is oserved; e.g.
in W Colombia or at W slopes of Mt. Kameroun the largest
precipitation totals are observed below e few hudred meters a.s.l.
RC - intertropical zone 18
Precipitation in cyclonic
disturbances/sytems
" = precipitation in areas with organized circulation around
a cyclone or within a trough; still convective clouds
involved
" Formed over ocean (e.g. eastern waves) or land (e.g.
squall lines)
" Encouriging condition is: large area of conditional
instability  in such a case the source area of humid air
has great extent
" consequently large volume of water vapour is
incorporated (sucked in) into the forming clouds
" Large volume of water is condensed which effects in
high precipitation intensity
RC - intertropical zone 19
Sezonowość opadów atmosferycznych
" Wilgotne tropiki (1):
 1a:
 1b:
" Klimaty z porą suchą (2):
 2a:
 2b:
 2c:
 2d:
 2e:
" Klimaty suche (3)
RC - intertropical zone 20
Dobowy rytm opadów -
uwarunkowania
" Ogrzewanie podłoża przez insolację
" Ruch frontu bryzowego (w strefie
wybrzeży)
" Konwergencja bryz
" Wiatr dolinny w terenach górski ch
" Interferencja cyrkulacji lokalnej z
synoptyczną
" Nocne ochładzanie wierzchołków chmur
konwekcyjnych
RC - intertropical zone 21
Dobowy rytm opadów
główne kategorie
" Maksimum popołudniowe
 Uwarunkowane ogrzewaniem podłoża i intensyfikacją konwekcji
 W głębi lądu  popołudniowe burze
 W strefie wybrzeża związane z awansem frontu bryzowego
" Maksimum wczesnym rankiem (ok. h 6), minimum po
południu
 Przyczyną zwiększone nocne wychładzanie otoczenia komórek
konwekcyjnych przez wypromieniowanie; wzrost kontrastu
termicznego (dolne partie chmur wyraz
nie cieplejsze od
otoczenia, stąd wzrost intensywności konwekcji)
 Wychładzanie powierzchni wierzchołków chmur przez nocne
wypromieniowanie prowadzi do dalszej intensyfikacji konwekcji
 Charakterystyczne dla obszarów oceanicznych niskich SzG
RC - intertropical zone 22