Nested Grid Model (NGM) Archive Information
**********************************************************************************
31 MAY 2023
The NGM archive may be accessed by a ftp client or by a web browser:
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It may take a few minutes or longer for the webpage to display.
**********************************************************************************
NOTE: THE NGM ARCHIVE ENDED ON APRIL 15, 1997. USERS OF THE NGM ARCHIVE CAN NOW
ACCESS THE ETA DATA ASSIMILATION SYSTEM (EDAS) ARCHIVE AT THE FOLLOWING LOCATION:
anonymous ftp to ftp.arl.noaa.gov and change directory to /archives/edas
**********************************************************************************
NGM ARCHIVE
TD-6140
January 1991 - April 1997
Prepared for
the National Climatic Data Center (NCDC)
by
Glenn D. Rolph
NOAA Air Resources Laboratory
SSMCII, Rm. 3463
1315 East West Highway
Silver Spring, MD 20910
(301) 713-0295 x134
https://www.arl.noaa.gov
June 1997
NGM ARCHIVE
OVERVIEW
The National Weather Service's National Center for
Environmental Prediction (NCEP) runs a series of computer
analyses and forecasts operationally (Petersen and Stackpole,
1989). One of the primary operational systems is the Global Data
Assimilation System (GDAS, Kanamitsu, 1989), which uses the
spectral Medium Range Forecast model (MRF) for the forecast
(Sela, 1980). Another primary system is the Regional Analysis
and Forecast System (RAFS), which uses the Nested Grid Model
(NGM) for the forecast (Hoke et al., 1989). Output from the RAFS
covers North America. In simple terms, for each run,
observations are assimilated with "first guess" data fields
(forecasts from the previous model run), and dynamic imbalances
in the data are reduced, resulting in "analyzed" data fields.
Then the forecast is made. The analyzed data should provide a
better representation of the real atmosphere than observations
alone because of limitations in the observations. Some of these
limitations are due to measurement error or other instrument
problems, and nonuniform spatial and temporal distributions of
the observations.
At NOAA's Air Resources Laboratory (ARL), the NCEP model
data are used for air quality transport and dispersion modeling.
ARL archives both NGM and GDAS data using an ARL packing method
and both archives contain basic fields such as the u- and v-wind
components, temperature, and humidity. However, the archives
differ from each other in the number of surface fields and
vertical levels as provided by NCEP.
ORIGIN OF DATA
The enclosed 2-hourly data come from NCEP's RAFS. The data
may be referred to as NGM data because the forecast component of
the system is the NGM model. The RAFS was designed to provide
improved numerical guidance over the United States out to 48
hours. Improvements over the existing limited-area fine-mesh
model (LFM; Gerrity 1977; Newell and Deaven 1981) included
improved horizontal and vertical resolution (especially in the
lower layers) and better use of observations. Details of the
RAFS are described by Hoke, et al. (1989).
NCEP post-processing of the RAFS routinely provides NGM
forecast output at 6 hour intervals on approximately a 180 km
grid (a few fields such as precipitation are output on at 91 km)
to the NAS 9000 mainframe computer. ARL archives the NGM
forecast data at 2 hour intervals on a 180 km grid (although the
data are available to ARL at 1 hour intervals on a 91 km
operationally, due to space limitations only 2 hourly, 180 km
data are archived). The higher temporal resolution of the data
has been found to result in less transport error in an
atmospheric dispersion model (Rolph and Draxler, 1990).
ARL PROCESSING
The ARL archiving program extracts the 2 hourly, 180 km data
from the 1 hour, 91 km data onto a 33 by 28 polar stereographic
grid covering the United States, Southern Canada, and immediate
coastal waters. The ARL program runs on the NAS 9000 mainframe
and outputs the data to disk, from which it is later transferred
to tape.
DATA DESCRIPTION
The archive data file contains the data in synoptic time
sequence (GMT), without any missing records (missing data will be
represented by negative 1 and the forecast hour by negative 1).
Therefore it is possible to position randomly to any point within
a data file. At each time period the surface (or single level)
data come first, followed by the data at each sigma level from
the ground up. A sigma level (Phillips, 1957) is defined as
P - Pt
sigma = --------;
Ps - Pt
where P is the reference pressure, Pt is the top model pressure
(0 mb for the NGM), and Ps is the model surface pressure along
the model terrain surface. NGM data are archived at 10 sigma
levels ranging from 0.9823 to 0.43414, or approximately 980 to
434 mb.
Tape Specifications
Data for six months are archived on a tape. NOTE: The NGM
archive ended on April 15, 1997.
TYPE 3480 1/2" Cartridge, ASCII*
LABEL Non-Labeled
RECORD FORMAT Fixed Block
RECORD LENGTH 974
BLOCK SIZE 32142
* Note that each data record is composed of a 50-character header
in ASCII, followed by the binary packed data. Therefore, an
ASCII-EBCDIC conversion on the entire data record or tape file is
not possible.
Beginning with July 1994 there are two files per month with the
first file containing data for days 1 through 15 and the second
file containing the rest of the month.
Data Grid
The data are on a 33 by 28 polar stereographic grid
(Fig. 1). In Table 1 the data grid is identified by the model
that produced the data, a grid identification number, the number
of X and Y grid points, the grid spacing ( ) which is true at the
indicated latitude, the longitude to which the Y axis is aligned,
and the pole position in grid units. The given pole position
results in the lowest left grid point to have a value of (1,1).
The NGM archive grid has an ID of #6.
Table 1. Data Grid Specifications
Model ID X Y True Align X Y
Type # Max Max Km Lat. Lon. Pole Pole
NGM 06 33 28 182.9 60N 105W 13.25 42.75
Meteorological Fields and Vertical Structure
The archived data file only contains some of the fields
normally produced by the model at NCEP. These were selected
according to what is most relevant for transport and dispersion
studies and disk space limitations. In Table 2, the fields are
identified by a description, the units, and a unique four
character identification label that is written to the header
label (see Data Grid Unpacking procedure in a later section) at
the beginning of each record. Data order in the file is given by
a two digit code. The first digit indicates if it is a surface
(or single) level variable (S) or an upper level variable (U).
The second digit indicates the order in which that variable
appears in the file. The upper level NGM data are output on the
following sigma surfaces: 0.98230, 0.94317, 0.89671, 0.84367,
0.78483, 0.72101, 0.65307, 0.58196, 0.50864, 0.43414. Table 3
gives the level number, corresponding to each data level, which
is also written to each header label. NOTE: on December 29,
1992, the surface level was changed from level 1 to level 0.
This also implies that all sigma levels were reduced by one as
well.
Table 2. Meteorological Fields for NGM Archive Data.
Field Units Label Data Order
Ice Covered Water Areas (0=no, 1=yes) ---- ICWT S1
Snow Covered Areas (0=no, 1=yes) ---- SNOW S2
Terrain Height m SHGT S3
Mean Sea Level Pressure hpa MSLP S4
Convective Precipitation m CPPT S5
Total Precipitation m TPPT S6
Exchange Coefficient at surface kg/m2/s EXCO S7
Upward Turbulent Flux of Sensible Heat W/m2 HFLX S8
Upward Turbulent Flux of Water kg/m2/s WFLX S9
Surface Pressure hpa PRSS S10
Number of Mixed Layers next to surface ----- MXLR S11
U Component of Wind wrt Grid m/s UWND U1
V Component of Wind wrt Grid m/s VWND U2
Vertical Velocity (dp/dt) hpa/s WWND U3
Specific Humidity kg/kg SPHU U4
Temperature K TEMP U5
Table 3. Description of Vertical Levels
Level Sigma
()
10 .43414
9 .50864
8 .58196
7 .65307
6 .72101
5 .78483
4 .84367
3 .89671
2 .94317
1 .98230
0 surface
Missing Data
When the NGM data are not available or there is a problem
with the ARL archiving process, missing data are written as an
array of -1. Usually the field label is as given in Table 2, but
sometimes it is defined as "NULL." No attempt at present is made
to fill in missing data with data from another source.
Data Grid Unpacking Procedure
NCEP typically saves their data in NCEP Office Note 84
(ON-84) format. However, here the data are stored differently
because the ARL format is a bit more compact and it can be
directly used on a variety of computing platforms with direct
access I/O.
The data array is packed and stored into one byte
characters. To preserve as much data precision as possible the
difference between the values at grid points is saved and packed
rather than the actual values. The grid is then reconstructed by
adding the differences between grid values starting with the
first value, which is stored in unpacked ASCII form in the header
record. To illustrate the process, assume that a grid of real
data, R, of dimensions i,j is given by the below example.
1,j 2,j .... i-1,j i,j
1,j-1 2,j-1 .... i-1,j-1 i,j-1
.... .... .... .... ....
1,2 2,2 .... i-1,2 i,2
1,1 2,1 .... i-1,1 i,1
The packed value, P, is then given by
Pi,j = (Ri,j - Ri-1,j) 2(7-N),
where the scaling exponent
N = ln Rmax / ln 2 .
The value of Rmax is the maximum difference between any two
adjacent grid points for the entire array. It is computed from
the differences along each i index holding j constant. The
difference at index (1,j) is computed from index (1,j-1), and at
1,1 the difference is always zero. The packed values are one byte
unsigned integers, where values from 0 to 126 represent -127 to -
1, 127 represents zero, and values of 128 to 254 represent 1 to
127. Each record length is then equal in bytes to the number of
array elements plus 50 bytes for the label information. The 50
byte label field precedes each packed data field and contains the
following ASCII data.
Field Format Description
Year I2 Greenwich date for which data valid
Month I2 "
Day I2 "
Hour I2 "
Forecast* I2 Hours forecast, zero for analysis
Level I2 Level from the surface up (see Table 3)
Grid I2 Grid identification (see Table 1)
Variable A4 Variable label (see Table 2)
Exponent I4 Scaling exponent needed for unpacking
Precision E14.7 Precision of unpacked data
Value 1,1 E14.7 Unpacked data value at grid point 1,1
*Forecast hour is -1 for missing data.
Notes
The convective and total precipitation (convective plus grid
scale) fields are accumulated from the 2- to 12-hour forecast
time. Therefore when looking at any particular forecast hour,
for example forecast hour 04, the precipitation is really a 4
hour accumulated total, and at forecast hour 12, the
precipitation is a 12 hour total.
Sample Program
In the following FORTRAN program, the unpacking subroutine
is used to read the first record. The value at grid point 1,1
from the header and the unpacked value are printed, along with
the other header values. In the program the packed data array is
in the variable QPACK and the unpacked real data array is
returned in variable QVAR. NX and NY are the number of grid
points in the horizontal and vertical directions, respectively.
NXY is just the product of NX and NY. The variable NEXP and VAR1,
are the packing exponent and value of the field at the 1,1 grid
point. These values are obtained from the header label
information.
Also attached is a sample program to determine the latitude
and longitude of any grid point on the model domain. This
program can be helpful for a user who must transform the data
into another coordinate system.
****************************************************************************
* SAMPLE PROGRAM TO UNPACK DATA ARRAY IN FIRST RECORD
****************************************************************************
* QVAR = UNPACKED REAL DATA ARRAY
* QPACK = PACKED DATA ARRAY
* NX = MAXIMUM GRID DIMENSION IN X-DIRECTION
* NY = MAXIMUM GRID DIMENSION IN Y-DIRECTION
* NXY = NX * NY
* LABEL = 50 CHARACTER ASCII HEADER, CONSISTING OF THE FOLLOWING:
* IY = YEAR FOR WHICH DATA ARE VALID
* IM = MONTH FOR WHICH DATA ARE VALID
* ID = DAY FOR WHICH DATA ARE VALID
* IHR = HOUR FOR WHICH DATA ARE VALID (GREENWICH)
* IFHR = HOURS AFTER INITIALIZATION
* LVL = LEVEL FROM THE SURFACE UP
* IG = GRID ID
* VARB = 4 CHARACTER VARIABLE LABEL
* NEXP = PACKING EXPONENT
* PREC = PRECISION OF UNPACKED DATA
* VAR1 = UNPACKED DATA VALUE AT GRID POINT (1,1)
****************************************************************************
PARAMETER ( NX=33, NY=28, NXY=NX*NY)
REAL*4 QVAR(NX,NY)
CHARACTER*1 QPACK(NXY)
CHARACTER*4 VARB
CHARACTER*50 LABEL
LREC=NXY+50
WRITE(*,*) 'ENTER NGM FILENAME'
OPEN(10,FILE=' ',ACCESS='DIRECT',RECL=LREC,FORM='UNFORMATTED')
READ(10,REC=1) LABEL,QPACK
READ(LABEL,100) IY,IM,ID,IHR,IFHR,LVL,IG,VARB,NEXP,PREC,VAR1
100 FORMAT(7I2,A4,I4,2E14.7)
CALL UNPACK(QVAR,QPACK,NX,NY,NXY,NEXP,VAR1)
WRITE(*,200) IY,IM,ID,IHR,IFHR,LVL,IG,VARB
200 FORMAT(1X,'YEAR=',I2,' MONTH=',I2,' DAY=',I2,' HOUR=',I2,
: ' FORECAST HOUR=',I2,' LEVEL=',I2,' GRID=',I2,
: ' VARIABLE=',A4)
WRITE(*,300) VAR1
300 FORMAT(1X,'FROM HEADER, QVAR(1,1)= ',F7.1)
WRITE(*,400) QVAR(1,1)
400 FORMAT(1X,'FROM UNPACKED DATA, QVAR(1,1)= ',F7.1)
STOP
END
************************************************************************
SUBROUTINE UNPACK(QVAR,QPACK,NX,NY,NXY,NEXP,VAR1)
************************************************************************
CHARACTER*1 QPACK(NXY)
REAL*4 QVAR(NX,NY)
SCALE=2.0**(7-NEXP)
INDX=0
QOLD=VAR1
DO J=1,NY
DO I=1,NX
INDX=INDX+1
QVAR(I,J)=(ICHAR(QPACK(INDX))-127.)/SCALE+QOLD
QOLD=QVAR(I,J)
END DO
QOLD=QVAR(1,J)
END DO
RETURN
END
C****************************************************************
C PROGRAM TO GIVE LAT/LON FOR ENTERED GRID POINTS
C****************************************************************
C NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
C AIR RESOURCES LABORATORY
C GLENN D. ROLPH
C****************************************************************
CALL SETNMG(90.,105.,13.25,42.75,60.,105.,182.9)
10 WRITE(6,*)'ENTER x y position to convert to lat lon'
READ(5,*)X,Y
CALL XYTOLL(X,Y,XLAT,YLON)
WRITE(6,*)'LAT,LON',XLAT,YLON
GO TO 10
STOP
END
SUBROUTINE LLTOXY (XLAT,YLON,XI,YJ)
C****************************************************************
C POLAR STEREOGRAPHIC CONVERSION OF LATITUDE AND LONGITUDE *
C Dr. A. D. Taylor NOAA/OAR/ARL *
C REVISION: 01/14/92 to allow oblique stereographic *
C projection *
C****************************************************************
C CONSTANTS BASED ON ASSUMPTION THAT RADIUS OF SPHERICAL
C EARTH IS 6371.2 KILOMETERS, AS USED BY NCEP IN ITS GRID
C MODELS.
real * 4 radpdg,drthnm,drthkm,DEARTH,POLLON,XP,YP,sclfct
real*4 cpolat,spolat,clat,slat,clon,slon,phi
real*4 x1,y1,z1,rho0,y2,r3,cosmu,sinmu
DATA RADPDG/1.745 3293E-2/ ,DRTHNM/ 6 880.35/
DATA DRTHKM/12 742.4/
DATA DEARTH,POLLON,XP,YP,SCLFCT/31.2043,260.,33.,
:33.,4.53527E-3/
data cpolat, spolat / 0.0, 1.0 /
clat = cos(radpdg * xlat)
slat = sin(radpdg * xlat)
phi = (ylon-pollon)*radpdg
clon = cos(phi)
slon = sin(phi)
x1 = clat * slon
y1 = cpolat * slat + spolat * clat * clon
z1 = spolat * slat - cpolat * clat * clon
if (1.+z1 .gt. .5e-6) then
rho0 = 1. / (1. + z1)
xi = xp + dearth * rho0 * x1
yj = yp + dearth * rho0 * y1
scale = 2. * sclfct * rho0
else
write(*,*)'LLTOXY Error:',xlat,',',ylon,' represents',
C ' point at infinity.'
stop
end if
RETURN
ENTRY XYTOLL (XI,YJ,XLAT,YLON)
x1 = (xi - xp) / dearth
y1 = (yj - yp) / dearth
rho0 = .5 * (1. + x1 * x1 + y1 * y1 )
z1 = 1. - rho0
SCALE = 2. * SCLFCT * rho0
slat = cpolat * y1 + spolat * z1
y2 = cpolat * z1 - spolat * y1
clat = sqrt( x1 * x1 + y2 * y2)
xlat = atan2( slat , clat ) /radpdg
if (clat.ge..5e-6) then
clon = -y2/clat
slon = x1/clat
YLON = AMOD(POLLON+180.+ATAN2(slon,clon)/RADPDG,360.)-180.
else
clon = 1.
slon = 0.
ylon = 0.
end if
RETURN
ENTRY UVG2N(UG,VG,UE,VN)
C****************************************************************
C Converts grid wind components (ug,vg) into North-South *
C components (vn,ue) for the location of the last point *
C transformed by lltoxy or xytoll. *
C****************************************************************
if (abs(xlat).le.89.) then
r3 = sqrt(clat*clat+slat*slat)
cosmu = - clon * (r3 + slat * spolat) + clat * cpolat
sinmu = - slon * (r3 * spolat + slat)
r3 = sqrt (cosmu*cosmu + sinmu*sinmu)
vn = (vg*cosmu + ug*sinmu)/r3
ue = (ug*cosmu - vg*sinmu)/r3
else
C****************************************************************
C In the regions around the North or South Pole, component *
C winds have to be redefined. The standard adopted here for*
C sites within one degree of the poles is that winds are *
C assigned directions according to the meridian from which *
C they are blowing; 0 or 360 (North) for winds from the *
C Greenwich meridian, 90 (East) for winds from the 90W *
C meridian, etc. Thus, VN is the component in the direction*
C of Greenwich and UE is the component in the direction of *
C 90W. For the South polar region, replace 90W in the above*
C with 90E. *
C****************************************************************
cosmu = cos(radpdg * pollon)
sinmu = sin(radpdg * pollon)
if (slat.lt.0.) then
cosmu = - cosmu
sinmu = - sinmu
end if
ue = ug * cosmu + vg * sinmu
vn = vg * cosmu - ug * sinmu
end if
RETURN
ENTRY UVN2G(UE,VN,UG,VG)
C****************************************************************
C Converts North-South wind components (vn,ue) into grid *
C components (ug,vg) for the location of the last point *
C transformed by lltoxy or xytoll. *
C****************************************************************
if (abs(xlat).le.89.) then
r3 = sqrt(clat*clat+slat*slat)
cosmu = - clon * (r3 + slat * spolat) + clat * cpolat
sinmu = - slon * (r3 * spolat + slat)
r3 = sqrt (cosmu*cosmu + sinmu*sinmu)
vg = (vn*cosmu - ue*sinmu)/r3
ug = (ue*cosmu + vn*sinmu)/r3
else
C****************************************************************
C In the regions around the North or South Pole, component *
C winds have to be redefined. The standard adopted here for*
C sites within one degree of the poles is that winds are *
C assigned directions according to the meridian from which *
C they are blowing; 0 or 360 (North) for winds from the *
C Greenwich meridian, 90 (East) for winds from the 90W *
C meridian, etc. Thus, VN is the component in the direction*
C of Greenwich and UE is the component in the direction of *
C 90W. For the South polar region, replace 90W in the above*
C with 90E. *
C****************************************************************
cosmu = cos(radpdg * pollon)
sinmu = sin(radpdg * pollon)
if (slat.lt.0.) then
cosmu = - cosmu
sinmu = - sinmu
end if
ug = ue * cosmu - vn * sinmu
vg = vn * cosmu + ue * sinmu
end if
RETURN
ENTRY SCALER(SIZENM)
C****************************************************************
C returns the size of a grid cell in nautical miles at the point*
C last referenced *
C****************************************************************
SIZENM=SCALE
RETURN
ENTRY SETNMC
C****************************************************************
C restores grid settings to standard NMC grid: North Polar *
C Stereographic, oriented with 80W longitude vertical in the *
C sense of North up, tangent point (North Pole) sited at 33,33, *
C and scaled 281km at 60N. *
C****************************************************************
DEARTH=31.2043
POLLON=260.
XP=33.
YP=33.
SCLFCT=4.53527E-3
cpolat = 0.0
spolat = 1.0
RETURN
ENTRY SETNMG(tnplat,tnplon,tnpx,tnpy,reflat,reflon,GRIDSZ)
C***************************************************************
C Sets grid settings to specification. Tnp is the "tangent *
C point" for the oblique stereographic projection; tnplat and *
C tnplon specify the latitude and longitude, resp, of the *
C tangent point, while tnpx and tnpy specify the grid *
C coordinates x and y of the tangent point. Reflat and reflon *
C specify the latitude and longitude of the scale reference *
C point, while gridsz is the size in kilometers of a grid cell *
C at that point. The meridian through the tangent point is *
C assumed vertical in the sense of North up, unless the tangent*
C point is the North or South pole, in which case the trulon *
C longitude is vertical in the sense of North up. *
C setnmc is equivalent to setnmg(90.,80.,33.,33.,60.,0.,281.) *
C****************************************************************
xp = tnpx
yp = tnpy
cpolat = cos(radpdg * tnplat)
spolat = sin(radpdg * tnplat)
POLLON=AMOD( AMOD(tnplon,360.) + 540. , 360.)
z1 = spolat * sin(radpdg * reflat) -
1 cpolat*cos(radpdg*reflat)*cos(radpdg*(reflon-pollon))
dearth = drthkm * .5 * (1. + z1) / gridsz
SCLFCT = DEARTH / DRTHNM
RETURN
end
REFERENCES
Gerrity, J., 1977: The LFM model - 1976: A documentation. NOAA
Tech. Memo. NWS NMC 60, 68 pp.
Hoke, J.E., N. A. Phillips, G.J. DiMego, J.J. Tuccillo, and J.G.
Sela, 1989: The Regional Analysis and Forecast System of the
National Meteorological Center, Weather and Forecasting, 4 (323-
334).
Kanamitsu, M., 1989: Description of the NMC Global Data
Assimilation and Forecast System, Weather and Forecasting, 4(335-342).
Newell, J.E. and D.G. Deaven, 1981: The LFM-II Model - 1980. NOAA
Tech. Memo. NWS NMC 66, U.S. Department of Commerce, Washington,
D.C., 20 pp.
Petersen, R.A. and J.D. Stackpole, 1989: Overview of the NMC
Production Suite, Weather and Forecasting, 4 (313-322).
Phillips, N.A., 1957: A Coordinate System Having Some Special
Advantages for Numerical Forecasting. J. Meteor., 14 (184-185).
Rolph, G.D. and R.R. Draxler, 1990: Sensitivity of Three-
Dimensional Trajectories to the Spatial and Temporal Densities of
the Wind Field, Journal of Applied Meteorology, 29 (1043-1054).
Sela, J.G., 1980: Spectral modeling at the National
Meteorological Center, Mon. Wea. Rev., 108 (1279-1292).
******************************************************************
DATA AVAILABILITY -- January - April 15, 1997
NOTE: THIS IS THE END OF THE NGM ARL ARCHIVE.
Month/Year Date Time Missing data
JAN 97 None
FEB 97 None
MAR 97 09 00Z initialization*
12 12Z initialization*
APR 97 04 02-12Z Missing
16-30 Missing
_______________________________________________________________
* Initialization means that the 0 hour data were written instead
of the 12 hour forecast data. In these cases, a few of the
surface (or single) level fields may be filled with 0's. The NGM
does not compute these fields at the initialization hour, which
is why the 02- to 12-hour forecast fields are normally archived.
DATA AVAILABILITY -- July - December, 1996
Month/Year Date Time Missing data
JUL 96 None
AUG 96 None
SEP 96 06 14-22Z All data missing
07 00Z initialization*
OCT96 10 12Z initialization*
NOV 96 None
DEC 96 None
_________________________________________________________________
* Initialization means that the 0 hour data were written instead
of the 12 hour forecast data. In these cases, a few of the
surface (or single) level fields may be filled with 0's. The NGM
does not compute these fields at the initialization hour, which
is why the 02- to 12-hour forecast fields are normally archived.
DATA AVAILABILITY -- January - June, 1996
Month/Year Date Time Missing data
JAN 96 None
FEB 96 None
MAR 96 None
APR 96 None
MAY 96 None
JUN 96 4 00Z initialization*
_________________________________________________________________
* Initialization means that the 0 hour data were written instead
of the 12 hour forecast data. In these cases, a few of the
surface (or single) level fields may be filled with 0's. The NGM
does not compute these fields at the initialization hour, which
is why the 02- to 12-hour forecast fields are normally archived.
DATA AVAILABILITY -- July - December, 1995
Month/Year Date Time Missing data
JUL 95 None
AUG 95 11 12Z Initialization*
SEP 95 None
OCT 95 None
NOV 95 None
DEC 95 None
_________________________________________________________________
* Initialization means that the 0 hour data were written instead
of the 12 hour forecast data. In these cases, a few of the
surface (or single) level fields may be filled with 0's. The NGM
does not compute these fields at the initialization hour, which
is why the 02- to 12-hour forecast fields are normally archived.
DATA AVAILABILITY -- January - June, 1995
Month/Year Date Time Missing data
JAN 95 26 14-22Z All data missing
27 00Z initialization*
FEB 95 None
MAR 95 None
APR 95 None
MAY 95 27 00Z initialization*
JUN 95 24 00Z initialization*
_________________________________________________________________
* Initialization means that the 0 hour data were written instead
of the 12 hour forecast data. In these cases, a few of the
surface (or single) level fields may be filled with 0's. The NGM
does not compute these fields at the initialization hour, which
is why the 02- to 12-hour forecast fields are normally archived.
DATA AVAILABILITY -- July - December, 1994
Month/Year Date Time Missing data
JUL 94 28 00Z Initialization*
AUG 94 None
SEP 94 None
OCT 94 None
NOV 94 16 00Z Initialization*
DEC 94 21 12Z Initialization*
_________________________________________________________________
* Initialization means that the 0 hour data were written instead
of the 12 hour forecast data. In these cases, a few of the
surface (or single) level fields may be filled with 0's. The NGM
does not compute these fields at the initialization hour, which
is why the 02- to 12-hour forecast fields are normally archived.
DATA AVAILABILITY -- January - June, 1994
Month/Year Date Time Missing data
JAN 94 17 14-22Z All data missing
18 00Z initialization*
FEB 94 None
MAR 94 None
APR 94 None
MAY 94 None
JUN 94 None
_________________________________________________________________
* Initialization means that the 0 hour data were written instead
of the 12 hour forecast data. In these cases, a few of the
surface (or single) level fields may be filled with 0's. The NGM
does not compute these fields at the initialization hour, which
is why the 02- to 12-hour forecast fields are normally archived.
DATA AVAILABILITY -- July - December, 1993
Month/Year Date Time Missing data
JUL 93 None
AUG 93 None
SEP 93 None
OCT 93 None
NOV 93 None
DEC 93 None
_________________________________________________________________
* Initialization means that the 0 hour data were written instead
of the 12 hour forecast data. In these cases, a few of the
surface (or single) level fields may be filled with 0's. The NGM
does not compute these fields at the initialization hour, which
is why the 02- to 12-hour forecast fields are normally archived.
DATA AVAILABILITY -- January - June, 1993
Month/Year Date Time Missing data
JAN 93 08 00Z Initialization*
FEB 93 17 00Z Data missing only this hour
MAR 93 08 12Z Initialization*
APR 93 None
MAY 93 None
JUN 93 None
_________________________________________________________________
* Initialization means that the 0 hour data were written instead
of the 12 hour forecast data. In these cases, a few of the
surface (or single) level fields may be filled with 0's. The NGM
does not compute these fields at the initialization hour, which
is why the 02- to 12-hour forecast fields are normally archived.
DATA AVAILABILITY -- July - December, 1992
Month/Year Date Time Missing data
JUL 92 None
AUG 92 None
SEP 92 None
OCT 92 None
NOV 92 01 14-22Z All data missing
02 00Z initialization*
DEC 92 None
_________________________________________________________________
* Initialization means that the 0 hour data were written instead
of the 12 hour forecast data. In these cases, a few of the
surface (or single) level fields may be filled with 0's. The NGM
does not compute these fields at the initialization hour, which
is why the 02- to 12-hour forecast fields are normally archived.
NOTE: on December 29, 1992, the surface level was changed from
level 1 to level 0. This also implies that all sigma levels were
reduced by one as well.
DATA AVAILABILITY -- January - June, 1992
Month/Year Date/Time Missing data or comments
JAN 92 01/01Z - 17/11Z Odd hours written instead of
even hours (1,3,5...)
17/12Z Initialization*
FEB 92 None
MAR 92 04/02Z - 04/12Z Missing data
26/14Z - 27/22Z Missing data
28/00Z Initialization*
28/14Z - 28/22Z Missing data
29/00Z Initialization*
29/14Z - 29/22Z Missing data
30/00Z Initialization*
APR 92 None
MAY 92 None
JUN 92 None
_________________________________________________________________
* Initialization means that the 0 hour data were written instead
of the 12 hour forecast data. In these cases, a few of the
surface (or single) level fields may be filled with 0's. The NGM
does not compute these fields at the initialization hour, which
is why the 02- to 12-hour forecast fields are normally archived.
DATA AVAILABILITY -- July - December, 1991
Month/Year Date Time Missing data
JUL 91 03 12Z initialization*
04 12Z initialization*
06 12Z initialization*
07 12Z initialization*
AUG 91 17 00Z initialization*
18 00Z initialization*
SEP 91 None
OCT 91 25 12Z all data
29 00Z all data
NOV 91 26 12Z initialization*
DEC 91 02 12Z initialization*
04 12Z initialization*
_________________________________________________________________
* Initialization means that the 0 hour data were written instead
of the 12 hour forecast data. In these cases, a few of the
surface (or single) level fields may be filled with 0's. The NGM
does not compute these fields at the initialization hour, which
is why the 02- to 12-hour forecast fields are normally archived.
Note: During 1991 the odd hour (01,03,...11) convective and total
precipitation fields were inadvertently added to the even hour
(02,04,...12) precipitation fields. Therefore, to estimate the
correct accumulated precipitation one should divide the
convective and total precipitation by 2. This error was
corrected on January 1, 1992.
DATA AVAILABILITY -- January - June, 1991
Month/Year Date Time Missing data
JAN 91 None
FEB 91 None
MAR 91 None
APR 91 04 12Z initialization*
05 00Z initialization*
22 12Z all data
23 00Z initialization*
24 00Z initialization*
MAY 91 07 12Z all data
08 00Z initialization*
23 12Z all data
JUN 91 None
_________________________________________________________________
* Initialization means that the 0 hour data were written instead
of the 12 hour forecast data. In these cases, a few of the
surface (or single) level fields may be filled with 0's. The NGM
does not compute these fields at the initialization hour, which
is why the 02- to 12-hour forecast fields are normally archived.
Note: During 1991 the odd hour (01,03,...11) convective and total
precipitation fields were inadvertently added to the even hour
(02,04,...12) precipitation fields. Therefore, to estimate the
correct accumulated precipitation one should divide the
convective and total precipitation by 2. This error was
corrected on January 1, 1992.