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I want to analyze the decadal variation of surface specific humidity over the western North Pacific(130-150E, 10-20N) 
in late summer (Aug-Sep-Oct-Nov) by the satellite data. I downloaded the monthly GSSTFM.3 (http://disc.gsfc.nasa.gov/daac-bin/DataHoldingsMEASURES.pl) and HOAPS
(Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data) 3.2 last week. The mannual of HOAPS3.2 says: "On climatological scale the near surface specific humidity, qa is highly correlated with the total columnar water
vapour (Liu, 1986). Since the water vapour content can be reliably derived from SSM/I brightness temperatures this
relationship could be used to derive qa using the retrieved water vapour as a proxy. Although this method provides a
reasonable estimate on the global monthly and climatological scale, it is not suitable to derive values of qa on
regional scale or for individual scenes. This is especially the case when the planetary boundary layer is decoupled
from the upper troposphere (Schlüssel, 1989)." So, I think the surface specific humidity of HOPAS3.2 is not suitable to be used to analyze the decadal variation of
surface specific humidity over the western North Pacific. Therefore, I wonder if the surface specific humidity of GSSTM.3 can be used to analyze the decadal variation of surface
specific humidity over regional scale.

 

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3 Comments

  1. Thank you very much for your kind consideration in using our GSSTF3 specific humidity product. 
     
    Actually, both HOAPS3.2 and GSSTF3 have happened to use the same algorithm of retrieving specific 
    humidity originally developed by Bentamy et al. (2003), where the potential effect/impact by the
    SSM/I precipitable water of the planetary boundary layer (e.g., the lowest 500-m layer) was
    genuinely considered. Your concern would have been legitimate, otherwise. The content in your
    quote (“The manual of HOAPS3.2 says:...”) has kind of surprised me a little bit, as one of the
    data providers in this field. In any case, I suggest you might want to retrieve the document
    (see link below) that I think should be up-to-date: http://www.cmsaf.eu/EN/Documentation/Documentation/PUM/pdf/SAF_CM_DWD_PUM_HOAPS_1_1.pdf?__blob=publicationFile Therefore, I believe and suggest that you should feel free to use either HOAPS3.2 (0.5 x 0.5 degree)
    or GSSTF3 (0.25 x 0.25 degree) (or even some other proper products) for your study as long as their
    data spatial resolutions properly fit into your region-of-interest scale, plus that, of course,
    the data length should be reasonably long. You might also take a look at our other available
    GSSTF product, i.e., GSSTF2c, but with a more coarse spatial resolution (1 x 1 degree) and using a
    different algorithm for the specific humidity retrieval. In closing, I would also like to recommend one fine related paper for your info. A paper by
    Prytherch et al. (2014) objectively conducting a comparison of the SSM/I-derived global marine
    surface-specific humidity datasets (including the GSSTF products, HOAPS3.2, and others), which
    should be worthy of your attention. Thanks.

     

    References:
    
    Bentamy A., K B. Katsaros, M. Alberto, W. M. Drennan, E. B. Forde, and H. Roquet, 2003: Satellite 
    Estimates of wind speed and latent heat flux over the global oceans, J. Climate, 16, 637-656. Prytherch, J., E. C. Kent, S. Fangohr, and D. I. Berry (2014), A comparison of SSM/I-derived
    global marine surface-specific humidity datasets, Int. J. Climatol., doi:10.1002/joc.4150. Shie C-L. 2011. Science background for the reprocessing and Goddard satellite-based surface
    turbulent fluxes (GSSTF2c) data set for global water and energy cycle research. Science Document
    for the Distributed GSSTF2c via Goddard Earth Sciences (GES) Data and Information Services Center
    (DISC), 19 pp. http://disc.sci.gsfc.nasa.gov/measures/documentation/Science_of_the_data.GSSTF2c.pdf Shie C-L. 2012. Science background for the reprocessing and Goddard satellite-based surface
    turbulent fluxes (GSSTF3) data set for global water and energy cycle research. Science Document
    for the Distributed GSSTF3 via Goddard Earth Sciences (GES) Data and Information Services Center
    (DISC), 21 pp. http://disc.sci.gsfc.nasa.gov/measures/documentation/Science_of_the_data.GSSTF3.pdf
     

     

  2. Regarding the quote from the HOAPS manual:  your quote, i.e., one paragraph from the ATBD, was kind of one piece of "literature review" addressing a pioneer and famous (yet very old) method by Liu (1986), while the next and following paragraphs in the ATBD addressed the method really being applied in HOAPS3.2.

  3. Hello Jim, I've just "discovered" this.  Should have felt a bit "guilty" for a belated finding, I guess.  (wink)   In any case, many thanks for thoughtfully including this user request (concern), along with my replies, into the forum.