3 Features and advantages of observational nudging are discussed in (*) below.
4 The method uses relaxation terms based on the model error at observational
5 stations, and the relaxation is such as to reduce this error.
6 Each observation has a radius of influence, a time window, and a relaxation
7 time scale determined by user-specified input. These determine where, when,
8 and how much it affects the model solution. Typical model grid points may
9 be within the radius of influence of several observations, and their
10 contributions are weighted according to the distance from the observation(s).
11 Before performing obs-nudging, you will need to generate an observation
12 input file for each WRF domain. The observation file(s) contain chronological
13 lists of the 3D positions and values of each observation, in a specific format.
14 It is critical that your observations be listed in chronological time order!
16 * Liu, Y., A. Bourgeois, T. Warner, S. Swerdlin and J. Hacker, 2005: An
17 implementation of obs-nudging-based FDDA into WRF for supporting
18 ATEC test operations. 2005 WRF user workshop. Paper 10.7.
21 How to use the obs-data converter
22 -------------------------------------
23 A utility program for converting observation data to the format required by
24 WRF has been provided (RT_fdda_reformat_obsnud.pl). The converter assumes
25 that your observation data is in standard LITTLE_R format.
27 To convert your data that is in LITTLE_R format:
29 RT_fdda_reformat_obsnud.pl yourfilename
31 where "yourfilename" is the obs-data in LITTLE_R format. The converter will
32 produce a file named yourfilename.obsnud, in the format required by the WRF
35 Note that during the conversion process:
37 1). P,T,U,V and RH fields are extracted.
39 2). U and V are assumed to be the wind components rotated to
40 the model map-projection (see 3DVAR and MM5 Little_R).
42 3). SPD, DIR and Td fields are ignored.
44 4). For upper-air data, currently WRF nudging only takes
45 those data with valid pressure records. For obs with
46 height levels (e.g. wind profilers data), users need to
47 calculate or estimate the pressure value. Inaccurate
48 estimate of pressure will lead to bad data assimilation.
51 Naming your obs-nudge input files
52 ---------------------------------
53 After you have converted your obs data file to the proper format for WRF,
54 you will need to rename it according to the naming convention for the WRF
55 domain on which the obs-nudging is to be performed. For example, for
56 observations to be used in Domain 1, use the naming convention OBS_DOMAIN101,
57 for Domain 2, OBS_DOMAIN201, etc.
59 These files must be present in your WRF run directory, along with the usual
60 WRF input and boundary files.
64 How to activate obs-nudging
65 ---------------------------
66 To activate the observational nudging option in WRF, you will need to set
67 the obs_nudge_opt flag(s) in the WRF "fdda" namelist. Note that there is
68 a unique flag for each WRF domain in which you want to activate obs-nudging.
69 To activate the print statements within the obs-nudging subroutines ERROB,
70 NUDOB, and IN4DOB, set the respective print flags obs_ipf_errob,
71 obs_ipf_nudob, and obs_ipf_in4dob to ".true." You can then easily verify that
72 you have activated observational nudging by observing text in your WRF
73 "standard out" that tell you how many obs stations are being processed at
74 given model timesteps. This information will look something like:
76 0****** CALL IN4DOB AT KTAU = 8 AND XTIME = 24.00: NSTA = 11040 ******
77 ++++++CALL ERROB AT KTAU = 8 AND INEST = 1: NSTA = 11040 ++++++
79 These lines will print out for each nest in which you have activated nudging,
80 while nudging is active on that domain.
82 Below is an example of a namelist set up to activate obs-nudging on domains
86 obs_nudge_opt = 1,1,1,0,0
88 fdda_start = 0., 0., 0., 0., 0.
89 fdda_end = 99999., 99999., 99999., 99999., 99999.
90 obs_nudge_wind = 1,1,1,1,1
91 obs_coef_wind = 6.E-4,6.E-4,6.E-4,6.E-4,6.E-4
92 obs_nudge_temp = 1,1,1,1,1
93 obs_coef_temp = 6.E-4,6.E-4,6.E-4,6.E-4,6.E-4
94 obs_nudge_mois = 1,1,1,1,1
95 obs_coef_mois = 6.E-4,6.E-4,6.E-4,6.E-4,6.E-4
96 obs_rinxy = 240.,240.,180.,180,180
98 obs_twindo = 0.6666667,0.6666667,0.6666667,0.6666667,0.6666667,
100 obs_ionf = 2, 2, 2, 2, 2,
103 obs_nobs_prt = 10, 10, 10, 10, 10,
104 obs_ipf_errob = .true.
105 obs_ipf_nudob = .true.
106 obs_ipf_in4dob = .true.
107 obs_ipf_init = .true.
109 In addition, add the following in &time_control:
111 auxinput11_interval_s = 180, 180, 180, 180, 180,
112 auxinput11_end_h = 6, 6, 6, 6, 6,