Extended Abstract

P2.25 MOISTURE CORRESPONDENCE BETWEEN LOWER AND UPPER TROPOSPHERE OVER
OCEANS USING AIRS OBSERVATIONS
Hengchun Ye*
C alifornia State U niversity, Los A ngeles, C A
E . J. F etzer, S . G ranger, S .-Y . L ee, E . T . O lsen , B . H . L am b rid gtsen and L . C h en
Jet P ropulsion Laboratory, C alifornia Institute of Technology, P asadena, C A.
Abstract
This study uses AIRS level 3 moisture profile data to reveal geographical correspondences of
atmospheric moisture content between lower and upper troposphere. The daily gridded AIRs
atmospheric specific humidity over world oceans between 50ºS to 50ºN are used to derive threeday
average vertical integrated moisture content for the two air columns: 1000mb-700mb and
700mb-500mb for the available three years time period. Then singular value decomposition
analysis (SVD) is performed to identify the teleconnections among grids between these two
atmospheric layers. In addition, the time series of the resulting major SVD patterns are analyzed
to reveal the dominant mode of temporal variations ranging from weekly to interannual time
scales. Results suggest that there is a good agreement in moisture variations between lower and
upper troposphere over middle-latitude and tropical oceans in general. Exceptions are found in
small areas near a landmass where moisture profile may be different from the rest of the majority
oceans.
1. INTRODUCTION
T h e A tm osp h eric I n fra red S ou n d er (A I R S )
mounted on Aqua spacecraft measures vertical
profiles of air temperature and humidity using both
microwaves and infrared irradiances (P agano et
al. 2003; L am brigtsen and L ee 2003; S u sskind et
al. 2003; Autmann et al. 2003). The AIR S’ level III
data that provide gridded values of 1° la titu d e b y
1 ° longitude for the highest tem poral resolution of
twice p er d a y b eca m e a va ila b le recently (G ra n ger
et al., 2005). This level III data were derived from
th e L evel I I V ersion 4 . 0 A I R S retrieva l a lgorith m
(F etzer et al. 2005; Ye et al. 2005). This gridded
level III data set will be very valuable for the
clim ate research com m u nity.
Corresponding author’s address: Hengchun
Ye, Department of Geography and Urban
Analysis, California State University, Los
Angeles, 1515 State University Drive, Lo
Angeles, CA 90032-8222; e-mail:
hye2@calstatela.edu
This study uses AIR S moisture profile data
to revea l geogra p h ica l corresp on d en ces of
a tm os p h e ric m ois tu re con te n t b e twe e n th e lowe r
and upper troposphere.
2. METHODOLOGY
The daily gridded AIRS atmospheric
specific hum id ity over world oceans between 50ºS
to 5 0ºN are used to derive three-day averages of
ve rtica l in te gra te d m ois tu re con te n t for th e two a ir
columns: 1000mb-500mb (1000mb, 925mb,
850mb, 700mb, 600mb, 500mb) and 500mb-
100mb (400mb, 300mb, 250mb,
200m b,1 50m b,1 00m b) for the six m onths of
January to June, 2005. The vertical integration of
wa te r va p or is b a s e d on th e followin g e qu a tion :
w =
∫
p1
p2q i
*∆p i
g
Then singular value decomposition
a n a ly s is ( S V D ) is p e rform e d to id e n tify th e
teleconnections among grids between these two
atmospheric layers. Thus the two fields analyzed
in SVD are the m oisture field below 500m b and
the m oisture field above 500m b. The tim e series

of th e re s u ltin g m a jor S V D p a tte rn s a re u s e d to
reveal the dominant mode of temporal variations
ra n gin g from d a ily to s e a s on a l tim e s ca le s .
3. RESULTS
phenom enon can be seen from daily m oisture
changes. W hile over equatorial regions of eastern
P acific between 1 50W -1 20W , u p p er trop osp heric
m oisture seem s to have a stronger seasonal
variation.
S ix m a jor p a ttern s p rod u ced b y S V D a re
analyzed. They explain about 46.8% of total
va ria n ce of th e two m ois tu re fie ld s b e low a n d
above 500m b.
The tim e series of pattern 1 shows a
stron g season a l p a ttern of va ria tion : th e va lu e
p ea ks in early F eb ru a ry a n d d ecreases gra d u a lly
for the rem aining 5 m onths (F igure 1 ). The P C 1
for both below and above 500mb match
closely.
F igu re 1 . T im e series of P C 1 for b elow 500m b
(B lue) and above 500m b (green).
This suggests that abundant moisture over
the southern hemispheric tropical ocean is
decreasing while these over the northern
h em isp h ere it is in creasin g startin g in early
February both below and above 500mb (Figure 2
and F igure 3). The correspondence between
b e low a n d a b ove 5 00m b for th is s e a s on a l p a tte rn
is very close except for a few areas. O ne of the
m ajor differences lies over 20°S in the western
S ou th P acific O cean, extend ing from east coast of
A u s tra lia to a b ou t 1 5 0W . I n th is re gion , th e
m oisture is m ore abund ant in the lower
trop os p h e re th a n th e u p p e r, th u s m ore s ign ifica n t
s e a s on a l va ria tion s of m ois tu re e xis t in th e lowe r
trop osp h ere. A sim ila r p a ttern to th is (m irror
im age) is evident in the N orth P acific O cean where
the lower atm ospheric m oisture also seem s to
have stronger seasonal variations. This m ay be
re la te d to th e fa ct th a t m ois tu re is d is ch a rge d in to
th e s e a re a s con s ta n tly th rou gh ou t th e y e a r from
land areas over upper troposphere. This
F igu re 3 . E O F of P C 1 on m oistu re ab ove 500m b .
P attern 2 shows intraseasonal variations
overlaid with a seasonal variation that peaked in
ea rly A p ril (F igu re 4 ). O n d a ily sca les, P C 2 for
lower trop osp heric (blu e) m oistu re has slightly
different values com pared to the upper
troposphere

(green).
F igu re 4 . T im e series of P C 2
The m ajor activities described by this pattern are
over the eastern equatorial P acific, the equatorial
Atlantic ocean, and the southern Indian O cean
( F igu re 5 a n d F igu re 6 ) . V a ria tion of th is p a tte rn
seems to be strong over the lower troposphere in
m ost areas. H owever, in the area over the
n orth ern coa st of A u stra lia , a n d coa st of sou th ern
A frica , th e va ria tion s seem to b e m ore n oticea b le
on u p p er
troposphere.
F igu re 6. E O F of P C 2 for m oistu re above 500m b.
P a tte rn th re e s h ows a n in tra s e a s on a l
va ria tion of a b ou t 5 0 d a y s with th e s tron ge r cy cle
occu rring over F ebru ary and M arch (F igu re
7).
F igu re 7 . T im e series of P C 3
Figure 5. EOF of PC2 for moisture below 500mb.
This pattern reveals sandwiched off-phase
m ois tu re ch a n ge s ove r th e m id d le a n d trop ica l
P acific O ceans. A ctivities seem to be of sim ilar
stren gth s b etween lower a n d u p p er trop osp h ere,
except over the western equatorial ocean where
u p p er trop osp h ere h a s a stron ger va ria tion
amplitude (Figure 8 and Figure 9).

Figure 8. EOF of PC4 for moisture field below
500m b
F igu re 1 0. T im e series of P C 5
T h is p a tte rn d e s crib e s m ois tu re a ctivitie s
over isolated centers almost all concentrated in
the P acific and Indian oceans (F igure 1 1 and
F igure 1 2). The southwest-to-northeast
orientation of these centers m arks the influence of
trade winds especially over the P acific tropical
ocean.
Figure 9. EOF of PC4 for moisture field above
500m b
P attern four shows seasonal variation at
a b ou t 4 -m on th tim e s ca le with a p e a k in e a rly
M a rch a n d la te J u n e . T h is p a tte rn s h ows m ore
m oistu re va ria tion over th e u p p er trop osp h ere for
certain areas (F igure 8 and F igure 9). Three
m ajor centers are (1 ) over the eastern tropical
P acific O cean and the western coast of South
A m erica, (2) over the western Indian O cean with
two op p os ite p h a s e s b e twe e n n orth e rn a n d
equatorial areas, and (3) over the South Indian
O ce a n off th e coa s t of n orth we s te rn A u s tra lia . I n
m oisture fields below 500m b, there is an alm ost
continuous area of active moisture variation from
th e e qu a toria l I n d ia n O ce a n to th e ce n tra l P a cific
O ce a n , wh ile th is is n ot th e ca s e for th e m ois tu re
field s above 500m b.
P attern five shows moisture variation at a
tim e scale of 30 days. (F igure 1 0). The variation is
s tron ge r d u rin g th e firs t th re e m on th th a n in la te r
months.
Figure 11. EOF of PC5 for moisture field below
500mb

F igu re 1 2 . E O F of p a tte rn 5 for m ois tu re fie ld of
above 500m b
F igu re 1 4 . E O F of p a ttern six for m oistu re field
below 500mb
P a tte rn s ix s e e m s to s h ow a 1 0-d a y m ois tu re
cycle overlaid on three m onthly variations (F igure
13).
F igu re 1 5 . E O F of p a ttern six for m oistu re field
above 500m b
F igu re 1 3 . T im e series of p attern six
A ctivity ce n te rs of th is p a tte rn a ls o s h ow a
s ou th we s t-to-n orth e a s t orie n ta tion . M os t
interesting of these is a dry center over the
western coast of South A m erica for below 500mb
corre s p on d in g to a re la tive we t ce n te r a b ove
500mb (Figure 14 and figure 15).
4. CONCLUSIONS
This study analyzed connections of
m ois tu re con te n t b e twe e n th e lowe r a n d u p p e r
troposphere over global middle-latitude and
trop ica l oce a n s for th e tim e p e riod of 6 m on th in
2 005 . I t is in te re s tin g to s e e th a t th e d om in a n t
seasonal and intraseasonal variation patterns
corresp ond well between lower and u p p er
troposphere with stronger variability over the lower
trop os p h e re . A s th e va ria n ce of p a tte rn
decreases, poorer correspondence starts to show
in som e areas upper troposphere m ay have larger
variability than lower troposphere or even no
a ctivity is fou n d in th e re .
This study suggests that a universal
m oisture profile over oceans is in general a good
assu m p tion. E xcep tions occu r over certain
geogra p h ica l region s n ea r to a la n d m a ss, wh ere
m oisture profiles m ay be m od ified .

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