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The Available NCEP Reanalyses
Wesley EbisuzakiClimate Prediction Center
National Centers for Environmental PredictionNWS/NOAA
Maryland, [email protected]
Topics
Introduction R1, R2, NARR, CFSR Grib 1 and 2 and various utilities Getting the data by Nomads Will try to cover these topics from a user
perspective. Some overlap with NOMADS and GrADS presentations.
Download links
http://www.cpc.noaa.gov/products/wesley/ams2010_sc.html
Documentation package includes a pdf version. The pdf has more details and covers more material.
Are Reanalyses Truth?
Convenient Run through quality control programs Consistent (ex. winds, temperature,
heights) Almost every variable that you would
ever want Better than interpolation of observations
But
Need observations Some regions are poorly observed Some levels are poorly observed
Some fields depend on the model physics Clear sky radiation is pretty good Clouds and other moist process are bad BL is somewhere in between
Reanalysis Errors
Best for winds, temperature and heights Observations, consistency relationships Near surface more dependent on BL physics
Humidity Fewer observations, model physics important
Other fields More model physics dependent
Not all observations are equal
Sondes and aircraft data are good quality Surface pressure is good quality Surface winds, temperatures, humidities
Hard to assimilate, elevation, representativeness Satellite data
Retrievals=old, Radiances=new Hard to get a consistent record with historical
data A concern for trend analyses
Analysis Uncertainties Factors to Consider
Observation density Sensitivity to model parameterizations Dependent on lesser quality observations Model and data assimilation system
Are Observations Truth?
Data assimilation could fit the observations exactly but produce a worse forecast!
Error by equipment manufacturer Representativeness error
Observation in an air parcel is not the same as average value in the grid cell
Finally a plotspread from an ensemble of opn analyses and reanalyses
simple way to get a error estimate
Averaged over a year
Monthly Means
Analysis Uncertainties
Not simple Uncertainty for a day: synoptic and data Averaged over a year: data Monthly/seasonal means have smaller
uncertainties than daily field, biases
NCEP Reanalyses
NCEP/NCAR Reanalysis (R1, CDAS) Mid 1990s, 1947-present, 2.5 degree grid, global
NCEP/DOE Reanalyses (R2) Late 1990s, 1979-present, 2.5 degree grid,
global North American Regional Reanalysis (NARR)
Early 2000's, 1979-present, 32 km grid Climate Forecast System Reanalysis (CFSR)
2010, 1979-present, 0.5 degree grid, global
Others Reanalyses
ECMWF: ERA-15, ERA-40, ERA-interim
JMA, CRIEPI: JRA-25/JCDAS
NASA/GSFC: MERRA
ERSL (different approach)
Check for robust signal
Support of NCEP Reanalyses
1) Journal articles (BAMS)2) Web: NCEP, NCAR, ERSL, NCDC3) Questions to provider of data4) NCDC, NCAR, ERSL will forward tough
questions to NCEP5) At NCEP: R1, R2, NARR: [email protected] CFSR: to be determined
Nuts and Bolts: data formats
Data formats: grib1, grib2
grib is a WMO standard and national meteorological centers use WMO standards for day-to-day operations
Reanalyses run at highest resolution possible Large portion of supercomputer, massive tape storage grib files are smaller than netcdf
Netcdf NCAR and ERSL often translate into netcdf and
redistribute the NCEP reanalyses
My grib1 toolbox
wgrib: inventory, get values, database tool GrADS: plots, some computations copygb: convert to different grid
Calculations often easier on lat-lon grid Save space
ggrib and lcgrib: subset of lat-lon, lambert-conformal grids, faster than copygb Save space
C/fortran programs: ieee -> grib
My grib2 tool box
wgrib2: inventory, contents, database, encode
GrADS: plots and some computations copygb2: convert to a different grid,
computations are often easier on lat-lon grid cnvgrib: convert between grib1 and grib2 ggrib and lcgrib functionality in wgrib2 wgrib2: ieee -> grib2
grib2 to grib1: cnvgrib
grib2 is new, many people use cnvgrib to convert from grib2 to grib1
Long term solution? NO! NCO dropped support for cnvgrib (5
years) New variables in grib2 are not in grib1 grib2 files are compressed, easier to use New features in grib1 utilities?
Short Grib1 Inventories-sh-3.00$ wgrib -s narr.t09z.awip32.merged1:0:d=09102809:MSLET:MSL:anl:NAve=02:166602:d=09102809:PRMSL:MSL:anl:NAve=03:333204:d=09102809:PRES:hybrid lev 1:anl:NAve=0..-s is the short inventorycolumn 1 = message (record) numbercolumn 2 = byte location starting from 0column 3 = analysis time or initial time of the forecastcolumn 4 = variable namecolumn 5 = level/layercolumn 6 = timing information,
anl=analysis, acc=accumulation, ave=averagecolumn 7 = number of fields used to make an ave/acc
Short Grib2 Inventories
--sh-3.00$ wgrib2 pgblnl.gdas.2007010100.grb2 -s1:4:d=2007010100:HGT:1 mb:anl:2:16552:d=2007010100:TMP:1 mb:anl:3:22064:d=2007010100:RH:1 mb:anl:..column 1: message or message.submessage numbercolumn 2: the byte location of the grib messagecolumn 3: the analysis or start of forecast time,
use -T to see the minutes and secondscolumn 4: variable namecolumn 5: levelcolumn 6 = timing information, anl=analysis, acc=accumulation, ave=average, fcst = forecast
Names
HGT = geopotential height (m)TMP = temperature (K)UGRD = zonal wind (m/s)VGRD = meridional wind (m/s)
see NCEP tables on web (see pdf file)or use -v option in wgrib/wgrib2
Grid information: grib
grib1/grib2 support many different grids
internally grib stores data in different orders,8 in grib1, 16 in grib2up to software to figure it out
wgrib -Vwgrib2 -grid
Values at specified locations
Grib1: understand the grid R1, R2: WE:NS storage NARR: WE:SN storage Global – easy to figure out the lat-lon of
points NARR – need file with the lat-lon of the points
rr-fixed.grb is with other course files
On your own
Values at specified locations
Grib2: harder to understand and easier to use 16 storage orders (3 in common use) wgrib2 convert data to WE:SN order by
default Can use old way to pick up data (i.e. get n-th
point) Can use wgrib2 to get the data (-lon option) See documentation for wgrib2 examples
Winds and other vectors
Winds have two orientations
North can point to the north pole (earth relative)
North can point to the north grid point (grid relative)
Non-staggered grid: (ix,iy) -> (ix,iy+1)
NARR Output Grid
Winds and other vectors
NCEP convention is grid relative
Lat-lon, Gaussian, Mercator is not an issue
Lambert-conformal, polar stereographic an issue
NARR is earth relative (anti-NCEP convention)
Good for new users
Bad for users of other NCEP regional products
GrADS and grib
Widely used, open source, visualization + more
Data model GrADS x,y,z,t and ensemble
Grib time is more complicated forecast verification time Start of forecast time (or analysis time) average from 6-12 hours into the forecast Monthly average of one of the above
Need to map grib times into GrADS time
Making plots with GrADS: grib1
Analyses grib2ctl.pl grib_file >ctl_file
gribmap -0 -i ctl_file(run grads)
Forecastsgrib2ctl.pl -verf grib_file >ctl_filegribmap -i ctl_file(run grads)
Making plots with GrADS: grib2Analysesg2ctl.pl -0 grib_file >ctl_file
gribmap -0 -i ctl_file (run grads)
Forecasts g2ctl.pl grib_file >ctl_file
gribmap -i ctl_file (run grads)
Unified options, -b option is working
More GrADS
See Jennifer's presentations
Getting data the Nomads way
On-line is easiest way – if downloading time ok
Big jobs: spend more time optimizing the transfer and reduce the amount of data transferred
Small jobs: ease of use is important, ex. plots, OpeNDAP (lat-lon grid, text output).
Downloading Methods
Partial http downloading:download the fields that you wantselect by field/time/leveldata is compressed (grib2) or packed
(grib1)efficient for the server (support many
clients)easy to script (not point and click)example in the documentation packagegood for large downloads
Downloading Methods
g2subset (grib-filter):download the fields that you wantselect by field/time/levelselect an optional regional subsetgrib2 onlypoint and click to learn or a few filesmoderately easy to scriptexample in the documentation packagemore server resources, less data
transferred
Downloading MethodsOPeNDAP:
standard protocol (text based)select field/time/level/regiondata is read by the serverinterpolated to a lat-lon grid if neededsent to the client by a standard protocol
advantages: supported by softwareeasy to use .. can even use a browser
disadvantages: server overheaddata may not be compressed
Downloading Methods
Plots: Part of the development nomads at
NCEP Point and click Designed for casual use of the data Not designed to do everything Research: download and do own
plots For some people, this all that they need
Downloading Methods
Full File: Can use browser, etc to download full file
from http server, get the directory listing and right click.
Easy
Good to get a sample file to help plan the download.
Typical Nomads front page
Summary
Reanalyses are not truth Observations are not truth Tools for grib1 and grib2 Introduction to Nomads Save time in downloading data
Select fields that you will need Can alway get other fields later
Select access method