dear
i want to create dqdsst for first time by my own data. Base on different posts get_dqdsst.m is a good idea for this aim which needs sea surface temperature (Celsius), sea surface atmospheric temperature (Celsius), atmospheric density (kilogram meter-3), wind speed (meter s-1)and sea level specific humidity. I become so so grateful if you answer 2 questions of mine (if you have time):
1- is it correct to use Tair_era.nc (one output of d_ecmwf2roms.m script) as a sea surface atmospheric temperature?
2-Is follow formula good for creating sea level specific humidity:
ew = 6.1121*(1.0007+3.46e-6*Pa).*exp((17.502*Ta)./(240.97+Ta)); % in mb
q = 0.62197*(ew./(Pa-0.378*ew)); % mb -> kg/kg
which Ta is : 2 metre dewpoint temperature (c) and Pa is surface pressure (mb).
Many thanks for your attention and time, and sorry for such questions
cheers
pooran
would you please guide me that It is correct to use 2 meter dewpoint temperature (c) and surface pressure (mb) or 2 meter temperature (Tair_era.nc (c)) and mean seal level pressure (Pair_era.nc (mb)) as Ta and Pa for computing saturate specific humidity (in above formula)? Because Their calculated specific humidity were different. bulk_flux.F used Tair_era.nc and Pair_era.nc but ECMWF's supporter suggest 2 meter dewpoint temperature (c) and surface pressure (mb). http://old.ecmwf.int/research/ifsdocs/CY36r1/index.html ( at equations 7.4 and 7.5 in part IV, physical processes)
Many thanks for your help
1 – does dqdsst's relation with sst and wins speed is directly and Reverse, respectively.
2- Pair (mb),Tair (c), qsea (kg/kg), air density (kg/m3), sst (c)( which 2 first one created by d_ecmwf2roms.m and third one by first post's equation and fix value (1.29) as a air density) have benn used for computing dQdSST. it is some time less that -80 and Its mean is about -20 and. With regard that there is not any previous data in my studding region (Caspian sea) for comparing, i become appreciate if you have any recommend for me , help me.
Why don't you use COADS or ICOADS dataset? I personally don't think you need atmospheric model outputs (e.g. ERA interim) to create dqdsst. Climatology should be fine. Some use a constant dqdsst over their entire model domain.
Read the following paper to understand the concept of dqdsst.
1. Barnier, B., Siefridt, L. & Marchesiello, P. Thermal forcing for a global ocean circulation model using a three-year climatology of ECMWF analyses. J. Mar. Syst. 6, 363–380 (1995).
Dear kobashi
many thanks for your reply. I have checked those databases before but they don not have enough data in Caspian sea region because of this i was computing data from different formula and functions.
So, IS there any recommended constant value for dqdsst (especially in in Caspian sea).
I become so appreciate to get it
cheers
pooran
Dear Kobashi
i have studied mentioned article and will chose -32 as dqdsst (my studding area is located between 36N and 47N which has seasonal variation of dQdSSt). i become appreciate if you help me to understand more about it by answering follow question:
1-i found that using SST and dQdSST will help to get better model's SST. Is this process some things like data assimilation to correct model's SST base on climatological SST?
2- base on assimilating concept, it seems that it is better to use longer time interval for SST (such as daily or one for each 5 days). So, If ROMS do data assimilation, what time interval do you recommend for SST (Base on you experiment on ROMS )?
Many many thanks for any reply and time
Having dQdSST and SST does act as a nudging to that SST, but it was designed to give better heat fluxes when your SST differs from that used when computing Q.
As with other forcings, I'd go with more frequent if you have them.
So if it acts as a nudging to that SST:
1-does it required to define TCLIMATOLOGY and TCLM_NUDGING or QCORECTION is enough?
2- will this nudging do in each step or base Nudging/relaxation time scale (TNUDG)? Or TNUDG will applied whenever TCLIMATOLOGY and TCLM_NUDGING are defined?
It is a nudging with the nudging timescale set by dQdSST. It is completely separate from TCLIMATOLOGY and doesn't use that machinery at all. It only acts as a nudging because that term in the Taylor series expansion of Q about SST acts as a feedback term, making your SST more closely match that used in computing Q. TNUDG is not invoked.
The atmospheric forcing is applied at each timestep, using linear time interpolation between your forcing records.
If you think about the longwave out term in the surface heat balance, it depends on temperature in Kelvin to the 4th power. The hotter the surface, the more heat you radiate. If Q was computed using a warmer temperature than you have, it will suck heat out of your ocean too fast. The dQdSST term is there to compensate for that extra heat loss - it will be a nudging to that warmer SST.
