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Long-term global GW activity in lower
and middle atmosphere from
CHAMP, GRACE and COSMIC radio
occultation data between
2001 and 2010.
Pablo Llamedo Soria
Universidad Austral, Buenos Aires, Argentina
Introduction
Gravity Waves
GWs play an important role driving the general
atmospheric circulation.
GWs drag in general circulation models (GCM) has
been usually treated with parameterizations.
A limitation of the development and validation of
these representations has been the lack of
observational constraints on waves.
GPS Radio Occultation
description
α
GPS
LEO
Δφ
α(a)
refractivity
Temperature
GPS Radio Occultation
characteristics
GPS RO technique provides global, all-weather,
high vertical resolution T profiles in the troposphere and
stratosphere.
Many observed wave properties are related to the
instrumental sensitivities to certain portions of the wave
spectrum or to the operational heights (J. Alexander,
JGR98, Kuo et al, GRL05; Wu et al, JASTP06; Preusse et
al, JGR08).
GPS RO, as all satellite limb viewing techniques have a
good vertical resolution and a coarse horizontal
resolution (typically 1 km against 100 km).
GPS Radio Occultation
limitation
Line of sight (LOS) dependance
Well resolved
Bad resolved
GPS Radio Occultation
Large Ep can only be found when both conditions are met:
high activity and favorable angle.
Low Ep values may be true or may be due to inappropriate
observational geometry.
limitation
GPS Radio Occultation
Data Set
Combined GPS RO T retrievals from CHAMP, GRACE
and COSMIC missions.
200 daily RO between 2001-2006 (CHAMP-GRACE)
1800 daily RO from 2006 (CHAMP-GRACE-COSMIC)
GPS RO coverage exhibits irregular patterns.
Due to their relatively sparse sampling, only monthly or
longer processes could be studied
Number of RO. Cell= 5ºx5º. June 2004
Number of RO. Cell= 5ºx5º. June 2010
12
50
10
8
6
40
30
4
20
2
10
Data Processing
Introduction
Linear GW theory predicts a constant Ek/Ep ratio.
The total energy of the atmospheric system is studied from T
perturbations alone [Tsuda et. al., 2000].
1
EP = 2 (z – z )
2
1
∫
z2
z1
g 2 T’ 2
dz
N TB
The extraction of T’ and TB is crucial in any GW analysis.
To measured the contributions of GWs only, is important to
extract the planetary waves contributions from the T profiles
Data Processing
Filtering Planetary waves
Profiles are binned within each day in a latitude band
(for example 15S-15N at equator).
Irregular GPS measurements are gridded in longitude.
Dominant horizontal wave numbers are isolated using
a fitting function (non linear least-squares) for each altitude.
4
TH’ ( lon, z0) =
∑ A sin s( lon + φ )
i
s
s=1
This large scale TH’(lon0 , z) variation is then subtracted from
each T profiles removing the planetary waves contribution.
Data Processing
Filtering procedure
by averaging T profiles binned
into lat-lon-time cells.
z
T
TB
by applying a high-pass filter to
each individual profiles.
T
T’=T - TB
by a polynomial fitting functions.
Overestimate Ep
(tropopause problems).
Fail to separate planetary
waves and GWs
Limitations
Data Processing
Filtering procedure
After remove the planetary wave contribution we apply a high-pass non recursive
filter to each individual profiles. Then Ep is calculated.
Complete
Method
[Schmidt et. at., 2008]
z
LRT
T
z
LRT
Separate
Method
T
LRT
LRT
T’=T - TB
Data Processing
Filtering procedure
Double Filtering
40
T
TB
Altitude [km]
Tc’=T’ - B
T’=T - TB
30
B
20
LRT
10
190
210
230
250
-6
0
Temperature [K]
6
-6
0
6
Data Processing
Filtering procedure
We create syntethic data to compare differents filtering procedures
[de la Torre, ASR2010].
104 syntethic T profiles at each 2.5º latitude intervals.
(T’/T)2 was calculated using differents procedures and compared
with the reference value.
3.5
Relative Variance
3
2.5
2
1.5
1
0.5
0
-80
-60
-40
-20
0
Latitude
20
40
60
80
Data Processing
EP =
1
2 (z2 – z1)
z2
∫
z
1
Filtering procedure
g
N
2
T’
TB
2
dz
(individual profiles)
Z1=5km
J/kg
Z2=35km
10
8
6
Complete Filtering Procedure
4
2
0
Double Filtering Procedure
Ep vs time
Results
-80<lon<-60
number of profiles
Ep [J/kg]
8
-40<lat<-30 monthly mean
6
4
2
6
12
2001
6
2002
12
6
12
2003
6
12
2004
6
2005
12
6
12
2006
6
12
2007
6
2008
12
6
2009
12
6
2010
6
12
2001
6
2002
12
6
12
2003
6
12
2004
6
2005
12
6
12
2006
6
12
2007
6
2008
12
6
2009
12
6
2010
60
50
40
30
20
10
-10<lat<10
Ep [J/kg]
-30<lat<-40
40<lat<30
6
2006
12
6
2007
12
6
2008
12
6
2009
12
2010
6
Climatology
Results
2007
Climatology
Results
2008
Climatology
Results
2009
Climatology
Jan 2008
Jun 2008
Results
Summary
From synthetic data, the results obtained with the
double filtering method indicate a considerable
improvement respect to previous filtering techniques.
GW activity is strong in the tropics and winter
hemispheres and weak in summer hemispheres.
Future work (with more data)
Bin the profiles in latitude-longitude-time-LOS bins
Remove low Ep values (threshold??).