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