很多数据都以NETCDF或GRIB的格式出现，比如NCEP和ECMWF的数据基本是NETCDF的格式，读取这些数据的格式时，在linux下可以安装NETCDF库来读取，比如用fortran读取NCEP大气数据时，需要有这样一句，

call readnetcdf(ncfile, 'pres', start,count,stride,press,time)，这个‘pres’即为NCEP大气数据的关键字，那么对一个NETCDF格式的数据，如何获取这个关键字呢？这里就要用到一个很方便的工具ncdump：

ncdump -c pres.sfc.2012.nc > header.atmos

这样在header.atmos文件下将会有这样的信息：

netcdf pres.sfc.2012 {

dimensions:

lat = 73 ;

lon = 144 ;

time = UNLIMITED ; // (1464 currently)

variables:

float lat(lat) ;

lat:units = "degrees_north" ;

lat:actual_range = 90.f, -90.f ;

lat:long_name = "Latitude" ;

lat:standard_name = "latitude" ;

lat:axis = "Y" ;

float lon(lon) ;

lon:units = "degrees_east" ;

lon:long_name = "Longitude" ;

lon:actual_range = 0.f, 357.5f ;

lon:standard_name = "longitude" ;

lon:axis = "X" ;

double time(time) ;

time:units = "hours since 1-1-1 00:00:0.0" ;

time:long_name = "Time" ;

time:actual_range = 17628096., 17636874. ;

time:delta_t = "0000-00-00 06:00:00" ;

time:standard_name = "time" ;

time:axis = "T" ;

short pres(time, lat, lon) ;

pres:long_name = "4xDaily Pressure at surface" ;

pres:unpacked_valid_range = 40000.f, 115000.f ;

pres:actual_range = 49030.f, 109490.f ;

pres:units = "Pascals" ;

pres:add_offset = 367650.f ;

pres:scale_factor = 10.f ;

pres:missing_value = 32766s ;

pres:precision = -1s ;

pres:least_significant_digit = -1s ;

pres:GRIB_id = 1s ;

pres:GRIB_name = "PRES" ;

pres:var_desc = "Pressure" ;

pres:dataset = "NMC Reanalysis" ;

pres:level_desc = "Surface" ;

pres:statistic = "Individual Obs" ;

pres:parent_stat = "Other" ;

pres:valid_range = -32765s, -25265s ;

// global attributes:

:Conventions = "COARDS" ;

:title = "4x daily NMC reanalysis (2012)" ;

:history = "created 2011/12 by Hoop (netCDF2.3)" ;

:description = "Data is from NMC initialized reanalysisn",

"(4x/day).  It consists of most variables interpolated ton",

"pressure surfaces from model (sigma) surfaces." ;

:platform = "Model" ;

:references = "http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.html" ;

short pres(time, lat, lon) ; 这句中的pres即为关键字。

pres:units = "Pascals" ;  这句即为气压数据的单位：帕斯卡。

下面还有经纬度格网信息、时间信息（时间的单位是小时，time:units = "hours since 1-1-1 00:00:0.0" ），内容较多，显示不全，有兴趣的可以自己试验。

将NETCDF格式文件转化为可读文本文件：

ncdump -bc pres.sfc.2012.nc > atmos_ncep_2012.dat

但这样对于数据量大的数据比较耗时，不建议这样做，还是尽量用NETCDF的库完成NETCDF格式文件的读取。

NOTE：在当前数据目录下必须有类似动态库文件 libnetcdf.so.7！