DIRECT TROPOSPHERIC OZONE RETRIEVALS 

FROM  

SATELLITE ULTRAVIOLET RADIANCES

Alexander D. Frolov, University of Maryland

 

Robert D. Hudson, University of Maryland

 

Anne M. Thompson. NASA/Goddard Space Flight Center

OUTLINE

  INTRODUCTION 

BASIC CONCEPT 

NEW ALGORITHM 

RESULTS

INTRODUCTIONNADIR LOOKING SATELLITE INSTRUMENTS MEASURE THE TOTAL COLUMN OZONE AMOUNT, I.E. TROPOSPHERE + STRATOSPHERE

 WE MUST REMOVE THE STRATOSPHERIC CONTRIBUTION IN ORDER TO GET THE TROPOSPHERIC CONTRIBUTION

 PIONEERING WORK BY FISHMAN AND LARSEN (1978) USED LIMB SCANNING INSTRUMENT (SAGE) TO MEASURE THE STRATOSPHERIC CONTRIBUTION - RESIDUAL TECHNIQUE. THE RESULTING TROPOSPHERIC DATA WERE MONTHLY AVERAGES.

HUDSON ET. AL. (1995) AND HUDSON AND THOMPSON (1998) REFINED THIS TECHNIQUE BY INTRODUCING CORRECTIONS FOR THE EFFICIENCY WITH WHICH NADIR INSTRUMENTS SEE TROPOSPHERIC OZONE.

 DATA BASED ON THIS TECHNIQUE IS ARCHIVED AT http://metosrv2 .umd.edu/~tropo. 1979-1992, Nimbus-7 TOMS, -20 to +20 LATITUDE, 15 DAY AVERAGES. 1996-PRESENT, EP TOMS, -30 to +20 LATITUDE, DAILY AND 9 DAY AVERAGES.

 THE NEW ALGORITHM WHICH DERIVES TROPOSPHERIC COLUMN OZONE DIRECTLY FROM THE NADIR RADIANCES, ON A DAILY BASIS.

 

  

BASIS FOR THE ALGORITHM (1)

$ IF ONE EXAMINES A TOMS IMAGE (MARCH 1990) THEN ONE SEES THREE DISTINCT REGIMES SEPARATED BY THE UPPER TROPOSPHERE SUB-TROPICAL AND POLAR FRONTS.

 $ THESE FRONTS ARE ASSOCIATED WITH THE JET STREAMS $ THESE FRONTS SHOW UP AS SHARP GRADIENTS IN THE

GEOPOTENTIAL HEIGHT FIELDS AND POTENTIAL VORTICITY FIELDS. $ THERE IS A STRONG CORRELATION BETWEEN THE SHARP GRADIENTS IN THE TOTAL OZONE FIELD AND THE METEOROLOGICAL FIELDS. $ WITHIN EACH REGIME THE TOTAL OZONE DISTRIBUTION IS STRONGLY PEAKED WITH A HALF WIDTH OF ABOUT 10 DU. $ THE MEAN VALUE WITHIN EACH REGIME SHOWS LITTLE VARIATION OVER A MONTH BUT DOES HAVE A SEASONAL DEPENDENCE

   

BASIS FOR THE ALGORITHM (2) 

$ TOMS IMAGE FOR JULY 1999 DOES NOT SHOW GOOD AGREEMENT BETWEEN THE SHARP GRADIENTS IN THE GEOPOTENIAL HEIGHT FIELD AND THE

TOTAL OZONE FIELD FOR THE SUBTROPICAL FRONT.  $ THIS IS BECAUSE OF ADDITIONAL TROPOSPHERIC OZONE FROM POLLUTION

EVENTS.  $ AS 90% OF THE TOTAL OZONE IS WITHIN THE STRATOSPHERE, WE ASSUME

THAT IT IS THE STRATOSPHERIC DISTRIBUTION THAT HAS THE NARROW DISTRIBUTION. $ THE OZONE PROFILES WITHIN A REGIME HAVE A NARROW DISTRIBUTION

AS A FUNCTION OF ALTITUDE. $ HENCE FOR ANY MONTH THE CLIMATOLOGICAL STRATOSPHERIC PROFILE

SHAPE CAN BE ASSUMED TO BE CONSTANT. $ WE CAN NOW CALCULATE A SET OF LOOK-UP TABLES THAT ASSUME A CONSTANT STRATOSPHERIC PROFILE, BUT VARYING TROPOSPHERIC PROFILES (THE REVERSE OF THE CURRENT TOMS ALGORITHM)    

SUMMARY OF THE ALGORITHM  

ASSUMES A FIXED STRATOSPHERIC PROFILE AND A VARIABLE TROPOSPHERIC PROFILE

STRATOSPHERIC PROFILE DERIVED FROM CLIMATOLOGY. 

TROPOSPHERIC PROFILES CAN ALSO BE BASED ON CLIMATOLOGY. FOR THE RESULTS PRESENTED, WE USED PROFILES CORRESPONDING TO A CONSTANT OZONE MIXING RATIO 

SET OF LOOKUP TABLES CALCULATED USING THE TOMRAD CODE  

ULTRAVIOLET ALBEDOS OBTAINED FROM EP-TOMS, LEVEL-2 DATA SET 

IN THIS TALK WE LIMIT THE ANALYSIS WITHIN THE TROPICAL REGIME, HOWEVER ALGORITHM CAN BE APPLIED TO ANY REGIME.

PROCEDURE $ USE ONLY PIXELS WHOSE REFLECTIVITY IS LESS THAN 20%.

REFLECTIVITY OBTAINED FROM THE MEASURED ALBEDO AT 360 NM.

 

$ THIS AVOIDS PROBLEMS WITH CLOUDS IN THE FIELD OF VIEW, AND WITH LARGE AEROSOL CONCENTRATIONS.

 

$ SELECT TOTAL OZONE DATA FROM THE LEVEL-2 DATA SET FOR THE TROPICAL REGIME, AND DETERMINE THE MOST LIKELY STRATOSPHERIC MEAN COLUMN OZONE AMOUNT.

$ USE TWO WAVELENGTHS (B PAIR) TO DETERMINE THE COLUMN OZONE AT EACH OF THE SELECTED PIXELS.

$ GRID DATA ON A 1.0 X 1.25 DEGREE LATITUDE-LONGITUDE GRID.

ERROR ANALYSIS

We have assumed that the stratospheric column ozone has a fixed and stable monthly value. An error of +1 DU in the stratospheric column ozone will introduce a bias error of -1.15 DU in the retrieved tropospheric column ozone. The standard deviation of the ozone distribution shown for July, 1999 is 10 DU, this translates into an error of 11 DU in the retrieved tropospheric ozone. There is a third error due to our choice of tropospheric profile. To check this we have compared the retrieved tropospheric ozone values with ozonesonde data from Huntsville.

FILM NOTES  

$ WHITE AREA REPRESENTS THOSE PIXELS WHICH ARE NORTH OF THE SUB-TROPICAL FRONT.

 

$ BLACK PIXELS REPRESENT EITHER NO DATA IN THE TOMS RECORD, OR REFLECTIVITIES GREATER THAN 20%

CONCLUSION

  WE HAVE DEVELOPED A PYHSICAL ALGORITHM WHICH

RETRIEVES COLUMN TROPOSPHERIC OZONE AMOUNTS FROM BACKSCATTERED ULTRAVIOLET RADIANCES.

  COMPARISON OF THESE DATA WITH OZONE SONDE

MEASUREMENTS ARE IN GOOD AGREEMENT.