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Application of the AQ Rain Accumulation Product for Investigation of Rain Effects on AQ Sea Surface Salinity Measurements
Andrea Santos-Garcia1, Maria M. Jacob2, Linwood Jones1, and William Asher3
1 Central Florida Remote Sensing Lab., University of Central Florida, Orlando, FL, 2 Comisión Nacional de Actividades Espaciales, Argentina, 3Applied Physics Laboratory, University of Washington, Seattle, WA
ABSTRACT
INTRODUCTION
This paper presents results of a recent empirical investigation into the impact of rain on the Aquarius (AQ) Sea Surface Salinity (SSS) measurements. Results demonstrate that AQ SSS measurements are realistic characterizations of a transient dilution of the surface salinity, but they are NOT representative of the bulk salinity at 5 m depth given by HYCOM. We believe that, during recent rain events, careful interpretation of AQ Level-2 (L-2) data is required, and as a result, the Rain Impact Model (RIM) product has been developed. It is available to AQ science users to promote the understanding of the relationship between precipitation and the corresponding AQ SSS measurement. This paper presents the description of RIM and comparisons between RIM and AQ L-2 SSS are presented for a number of rain events along the Pacific ITCZ (Inter-tropical Convergence Zone). Results demonstrate high correlation between RIM and AQ SSS for moderate to strong rain events that occurred within a few hours of the AQ observation time. The RIM model is based on the temporal superposition of rain events (integrated rain history for the last 24 hours) using a one-dimensional stratification model and HYCOM as initialization. It estimates SSS in a quarter degree spatial resolution and integrates over the AQ IFOV (100 km) using a weighted average based on the antenna beam efficiency. Thus, the RIM predicts the modeled surface salinity that can be compared to the observed SSS as an overly to the AQ L-2 data product. In addition, the RIM provides the corresponding rain beam-fill fraction and the probability of salinity stratification. This latter parameter can be used as a “rain impact” quality flag to identify SSS that are affected by near surface stratification.
APPROACH
SUMMARY
• CFRSL has investigated the Impact of rain on the AQ Sea Surface Salinity – “Investigation of Rain Effects on Aquarius Sea
Surface Salinity Measurements” (Published at AQ Special issue JGR/Oceans)
• The Rain Impact Model (RIM) is an overlay for the AQ-L2 product that simulates the SSS under rain conditions₋ Global coverage between ±60°lat (Due to
CMORPH - Precipitation Source for RA Product)• Spatial integration over AQ IFOV
₋ Assumes circular foot print of 100 km₋ Uses 13 x 0.25° boxes weighted average based
on antenna beam efficiency
• RIMSSS (SSS estimated based on RIM) is an empirical model that estimates the SSS under rainy conditions at 0.005 meters depth.₋ Model is superposition of rain events using 1D stratification model₋ Uses HYCOM as initialization
• Other ancillary parameters provided are:₋ BF (Rain Beam Fill Fraction) represents area weighted percentage of the beam
that exceeds an IRR threshold (0.25 mm/hr)₋ PS (Probability of Salinity Stratification) is normalized delta-SSS per orbit
between RIM at 10 m and RIM at 0.05 m
32 33 34 35 3632
33
34
35
36
-2 -1 0 1-2.5
-2
-1.5
-1
-0.5
0
0.5
1AQSSS [psu]
RIM
SSS [p
su]
AQ anomaly
RIM
anom
aly
R2 = 0.77
R2 = 0.76
-2 0 2 4 6 8 10 12 1432
34
36cross correlation=0.9148/0.91936
-2 0 2 4 6 8 10 12 140
5
10
-2 0 2 4 6 8 10 12 140
10
20
-2 0 2 4 6 8 10 12 140
5
10
-2 0 2 4 6 8 10 12 140
5
-2 0 2 4 6 8 10 12 14-2
0
2x 10
-4
-2 0 2 4 6 8 10 12 140
0.5
1
-2 0 2 4 6 8 10 12 1432
34
36cross correlation=0.9148/0.91936
-2 0 2 4 6 8 10 12 140
5
10
-2 0 2 4 6 8 10 12 140
10
20
-2 0 2 4 6 8 10 12 140
5
10
-2 0 2 4 6 8 10 12 140
5
-2 0 2 4 6 8 10 12 14-0.1
0
0.1
-2 0 2 4 6 8 10 12 140
0.5
1Salin
ity
[psu
]
AQsss
●HYCOM
RIMsss
Latitude
◊ Previous HYCOM
RIM10 m- RIM0.005 m
Prob
abili
tyO
f Str
atific
ation
Threshold
0 50 100 15032
34
36
50 100 150 200 250 300 35032
34
36
0 50 100 150-2
-1
0
1
50 100 150 200 250 300 350-2
-1
0
1
AQsss HYCOM anomaly
0 50 100 15032
34
36
50 100 150 200 250 300 35032
34
36
0 50 100 150-2
-1
0
1
50 100 150 200 250 300 350-2
-1
0
1
AQsss
SamplesSamples
NO PRESENCE OF RAIN WITH PRESENCE OF RAIN
AQ anomaly
RIM anomaly
AQ anomaly RIM anomaly
HYCOM anomaly
• The salinity gradient (surface to 1 – 2 m depth) is time dependent and depends upon the rainfall accumulation • In our analysis we find no evidence of SSS radiometric retrievals errors due to rain
effects• The analysis of AQ SSS measurements in the presence of rain, requires careful
interpretation to account for near-surface salinity stratification • A beta version of our AQ Rain Impact Model product will be released summer
2015– We solicit constructive criticism for our AQ RIM and seek collaboration with ocean
modelers
RIM DATA ANALYSIS CONCATENATED RESULTS
RIM ANALYSIS AT DIFFERENT DEPTH
-2 0 2 4 6 8 10 12 1432
34
36cross correlation=0.9148/0.91936
-2 0 2 4 6 8 10 12 140
5
10
-2 0 2 4 6 8 10 12 140
10
20
-2 0 2 4 6 8 10 12 140
5
10
-2 0 2 4 6 8 10 12 140
5
-2 0 2 4 6 8 10 12 14-2
0
2x 10
-4-2 0 2 4 6 8 10 12 14
0
2
4
-2 0 2 4 6 8 10 12 1432
34
36cross correlation=0.9148/0.91936
-2 0 2 4 6 8 10 12 140
5
10
-2 0 2 4 6 8 10 12 140
10
20
-2 0 2 4 6 8 10 12 140
5
10
-2 0 2 4 6 8 10 12 140
5
-2 0 2 4 6 8 10 12 14-5
0
5x 10
-3-2 0 2 4 6 8 10 12 14
0
2
4
-2 0 2 4 6 8 10 12 1432
34
36cross correlation=0.9148/0.91936
-2 0 2 4 6 8 10 12 140
5
10
-2 0 2 4 6 8 10 12 140
10
20
-2 0 2 4 6 8 10 12 140
5
10
-2 0 2 4 6 8 10 12 140
5
-2 0 2 4 6 8 10 12 14-0.1
0
0.1-2 0 2 4 6 8 10 12 14
0
2
4
Salin
ity [p
su]
IRR
[mm
/h]
RA [m
m]
RA [m
m]
RA [m
m]
IRR
RA 0-6 hr
RA 6-12 hr
RA 12-18 hr
AQsss
●HYCOM
RIMsss 0.005 METERS
Latitude
RIM analysis at 1 meter depth◊ Previous HYCOM
HYCOM-RIM1METER
IRR
RA 0-6 hr
RA 6-12 hr
RA 12-18 hr
AQsss
●HYCOM
Latitude
◊ Previous HYCOM
HYCOM-RIM5 METERS
RIM analysis at 5 meters depth
IRR
RA 0-6 hr
RA 6-12 hr
RA 12-18 hr
AQsss
●HYCOM ◊ Previous HYCOM
HYCOM-RIM10 METERS
RIM analysis at 10 meters depth
Latitude
HYC
OM
-RIM
RA 18-24 hr RA 18-24 hr RA 18-24 hr
RA [m
m]
RA [m
m]
RIMsss 0.005 METERS RIMsss 0.005 METERS
COMPARISON UNDER RAIN AND NON-RAIN CONDITIONS
PROBABILITY OF STRATIFICATION
0 5 10 15 20
32.5
33
33.5
34
34.5
35
Salinity @ 0.005 m in time
Time
Salin
ity [p
su]
Stratification Performance for one single Rain Event
32 32.5 33 33.5 34 34.5 350
0.5
1
1.5
2
Model @ 0.005 m = ½ cmModel On Time
Dep
th [m
]
-20 -15 -10 -5 0 5
32.5
33
33.5
34
34.5
Superposition Model for Multiple Rain EventsDuring last 24 Hours
ToTime
Salin
ity [p
su]
Depth = 0.5 cm
HYCOM Vertical Diffusivity
Rain ImpulseFunctions
-2 0 2 4 6 8 10 12 1432
34
36
-2 0 2 4 6 8 10 12 140
5
10
-2 0 2 4 6 8 10 12 140
50
100
-2 0 2 4 6 8 10 12 140
50
100
-2 0 2 4 6 8 10 12 140
50
100
-2 0 2 4 6 8 10 12 140
50
100
-2 0 2 4 6 8 10 12 140
5
10
15
Salin
ity [p
su]
IRR
[mm
/h]
RA [m
m]
RA [m
m]
RA [m
m]
RA [m
m]
Win
dSp
eed
[m/s
]
IRR
RA 0-6 hr
RA 6-12 hr
RA 12-18 hr
RA 18-24 hr
AQsss
●HYCOM
RIMsss
Latitude
January 10th 2012 – Orbit 5 – Beam 1
◊ Previous HYCOM
-2 0 2 4 6 8 10 12 1432
34
36
-2 0 2 4 6 8 10 12 140
5
10
-2 0 2 4 6 8 10 12 140
50
100
-2 0 2 4 6 8 10 12 140
50
100
-2 0 2 4 6 8 10 12 140
50
100
-2 0 2 4 6 8 10 12 140
50
100
-2 0 2 4 6 8 10 12 140
5
10
15
Salin
ity [p
su]
IRR
[mm
/h]
RA [m
m]
RA [m
m]
RA [m
m]
RA [m
m]
Win
dSp
eed
[m/s
]
IRR
RA 0-6 hr
RA 6-12 hr
RA 12-18 hr
RA 18-24 hr
AQsss
●HYCOM
RIMsss
Latitude
February 4th 2012 – Orbit 5 – Beam 3
◊ Previous HYCOM
-2 0 2 4 6 8 10 12 1432
34
36
-2 0 2 4 6 8 10 12 140
5
10
-2 0 2 4 6 8 10 12 140
50
100
-2 0 2 4 6 8 10 12 140
50
100
-2 0 2 4 6 8 10 12 140
50
100
-2 0 2 4 6 8 10 12 140
50
100
-2 0 2 4 6 8 10 12 140
5
10
15
Salin
ity [p
su]
IRR
[mm
/h]
RA [m
m]
RA [m
m]
RA [m
m]
RA [m
m]
Win
dSp
eed
[m/s
]
IRR
RA 0-6 hr
RA 6-12 hr
RA 12-18 hr
RA 18-24 hr
AQsss
●HYCOM
RIMsss
Latitude
April 9th 2012 – Orbit 5 – Beam 2
◊ Previous HYCOM