DQRID : D050725.12
Start DateStart TimeEnd DateEnd Time
02/01/2005070005/06/20050000
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Subject:
PYE/MWR/M1 - Reprocessed: Revised Retrieval Coefficients
DataStreams:pyemwrtipM1.a1, pyemwrlosM1.b1
Description:
IN THE BEGINNING (June 1992), the retrieval coefficients used to derive the precipitable 
water vapor (PWV) and liquid water path (LWP) from the MWR brightness temperatures were 
based on the Liebe and Layton (1987) water vapor and oxygen absorption model and the Grant 
(1957) liquid water absorption model.

Following the SHEBA experience, revised retrievals based on the more recent Rosenkranz 
(1998) water vapor and oxygen absorption models and the Liebe (1991) liquid water absorption 
model were developed. The Rosenkranz water vapor absorption model resulted a 2 percent 
increase in PWV relative to the earlier Liebe and Layton model.	The Liebe liquid water 
absorption model decreased the LWP by 10% relative to the Grant model. However, the 
increased oxygen absorption caused a 0.02-0.03 mm (20-30 g/m2) reduction in LWP, which was 
particularly significant for low LWP conditions (i.e. thin clouds encountered at SHEBA).

Recently, it has been shown (Liljegren, Boukabara, Cady-Pereira, and Clough, TGARS v. 43, 
pp 1102-1108, 2005) that the half-width of the 22 GHz water vapor line from the HITRAN 
compilation, which is 5 percent smaller than the Liebe and Dillon (1969) half-width used in 
Rosenkranz (1998), provided a better fit to the microwave brightness temperature 
measurements at 5 frequencies in the range 22-30 GHz, and yielded more accurate retrievals. 
Accordingly, revised MWR retrieval coefficients have been developed using MONORTM, which 
utilizes the HITRAN compilation for its spectroscopic parameters.  These new retrievals 
provide 3 percent less PWV and 2.6 percent greater LWP than the previous retrievals based on 
Rosenkranz (1998).

At Point Reyes, the original coefficients implemented in March 2005 were based on a 
version of the Rosenkranz model that had been modified to use the HITRAN half-width at 22 GHz 
and to be consistent with the water vapor continuum in MONORTM.  These retrievals yielded 
nearly identical results to the MONORTM retrievals.

The MONORTM-based retrieval coefficients became active at PYE.M1 20050506.

Note: The PYE.M1 MWRLOS data for 20050201-20050506 have been reprocessed
to apply the MONORTM-based retrievals for all time. The reprocessed data
were archived in April 2007.  The TIP data have not been reprocessed.
Suggestions: 
Retrieve the reprocessed data for use in your analysis.
Measurements:pyemwrtipM1.a1:
  • Total liquid water along zenith path using tip-derived brightness temperatures(liqtip)
  • Total water vapor along zenith path using tip-derived brightness temperatures(vaptip)
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pyemwrlosM1.b1:
  • Averaged total liquid water along LOS path(liq)
  • Total water vapor along LOS path(vap)
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