How do I compute mean values of nine variables over Lat x lon x time?
조회 수: 5 (최근 30일)
이전 댓글 표시
I am attaching my netcdf matlab code to read the data from netcdf file. Input file netcdf is also attached. Please modify the code to compute mean values of nine meteorological variables from netcdf ERA5 hourly data. This file contains 00 and 12 GMT data. I would be highly obliged for your kind help.
I want daily average values from 00 and 12 GMT observations and also average values over lat and lon data. I have the total number of data points in input file 6961, so output file should have 3480 data points with nine variables(3481,9).
Sanchit
댓글 수: 2
Cris LaPierre
2023년 7월 19일
User has deleted their original question.
How do I compute mean values of nine variables over Lat x lon x time?
I am attaching my netcdf matlab code to read the data from netcdf file. Input file netcdf is also attached. Please modify the code to compute mean values of nine meteorological variables from netcdf ERA5 hourly data. This file contains 00 and 12 GMT data. I would be highly obliged for your kind help.
I want daily average values from 00 and 12 GMT observations and also average values over lat and lon data. I have the total number of data points in input file 6961, so output file should have 3480 data points with nine variables(3480,9).
Sanchit
답변 (1개)
Cris LaPierre
2023년 7월 19일
편집: Cris LaPierre
2023년 7월 19일
My understanding is that you want to take the mean of all the data for each day and time. This means you would lose the lat/lon and expver information.
I would take a different approach. I would turn the info into a timetable, and then use groupsummary to perform the mean by group.
unzip('matlab.zip','./');
ncfile = 'Lakhimpur_ERA5_daily_00_12_2014_2023.nc';
% Load the grouping data
lat = ncread(ncfile,'latitude');
lon = ncread(ncfile,'longitude');
expver = ncread(ncfile,'expver');
time = ncread(ncfile,'time');
time = datetime(double(time)*60*60,'ConvertFrom','epochtime','Epoch','1901-01-01');
% convert grouping data to 4x4x2x6961 arrays
[Lon,Lat,Expver,Time] = ndgrid(lon,lat,expver,time);
% Load the variables (4x4x2x6961)
var1 = ncread(ncfile,'d2m') ;
var2 = ncread(ncfile,'t2m') ;
var3 = ncread(ncfile,'e') ;
var4 = ncread(ncfile,'pev') ;
var5 = ncread(ncfile,'ssr') ;
var6 = ncread(ncfile,'ssrd') ;
var7 = ncread(ncfile,'tp') ;
d2m = var1 .* 0.00036854 + 288.2675;
d2m = d2m-273.15;
t2m = var2 .* 0.00038766 + 291.3707;
t2m = t2m - 273.15;
e = var3 .* 5.0661e-08 - 0.0030683;
pev = var4 .* 8.5836e-08 - 0.00278;
ssr = var5 .* 183.9069 + 12629668.0466;
ssrd =var6 .* 209.9315 + 14640023.0343;
tp =var7 .* 5.8624e-07 + 0.019209;
% DEWPOINTAND VAPOR PRESSURE DEFICIT EQUATIONS
% From Tetens Formula, the relation between temperature and the partial pressure of water vapor
es = 6.1078 .* exp((17.269 .* t2m) ./ (237.3+t2m));
% where,es is saturated vapor pressure in millibars and T is temperature in degrees C
% and the equation for relative humidity:
% Measure the air temperature T, in °C.
% Find out the dew point temperature Dp, in °C.
% Calculate relative humidity RH using the formula,
rh = 100 .* (exp(17.625 .* d2m ./ (243.04 + d2m)) ./ exp(17.625 .* t2m ./ (243.04 + t2m)));
% Rh=(ea/es)*100
% ea = Rh*es/100
% where, ea is the actual vapor pressure or vapor pressure at dewpoint temperature
% es is the saturation vapor pressure or vapor pressure at air temperature
% And,Vapor Pressure Deficit = es - ea at any instant in millibars
vpd = es - (rh .* es ./ 100);
% Create a timetable of all the data
Lon = Lon(:);
Lat = Lat(:);
Expver = Expver(:);
Time = Time(:);
d2m = d2m(:);
t2m = t2m(:);
e = e(:);
pev= pev(:);
ssr = ssr(:);
ssrd = ssrd(:);
tp = tp(:);
vpd = vpd(:);
rh = rh(:);
dataTbl = timetable(Time,Lon,Lat,Expver,d2m,t2m,e,pev,ssr,ssrd,tp,vpd,rh)
% Calculate the mean over latitude x longitude x time
data = groupsummary(dataTbl,["Time","Time"],["hourofday","day"],"mean",4:12)
You can then go on to process the data as you desire. See the Access Data in Tables page for help on working with table data. If you keep the results in a table, you will want to use writetable instead of writematrix.
댓글 수: 17
Cris LaPierre
2023년 7월 29일
As a technicality, in a timetable, the Time column doesn't count, so technically there are 10.
I'm not sure if you remember, but in the original data file that spawned this question, there were 12 columns, and the code you are using was written for the original data set, not your new one. You need to update the datavars input accordingly.
For reference, here is the syntax my code is using:
참고 항목
카테고리
Help Center 및 File Exchange에서 Text Data Preparation에 대해 자세히 알아보기
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!