Plot air temperature data on pressure levels (Hovmöller diagram).

Hi, i need to plot air temperature at certain pressure levels. For reference a netcdf sample file is attached.

I want the data to be plotted for a certain latitude suppose (55) and a certain Longitude range suppose (60-90), and pressure levels suppose (1-17). In this case the X-axis will denote the Longitude range while Y-axis will show the pressure levels.

Any help will be appreciated.

[jonas]

I'm new to CDF data sets and how to deal with them in MATLAB. I wrote a script to extract data and plot, but the resulting figure makes no sense to me (see attachment), so perhaps I did something wrong. What is the unit of the variable t?

[khan]

Sir, i think what you did is right, can you please share the procedure so i can see the steps and use. This data is Air temperature anomalies with unit of Kelvin. Thank You for helping

[jonas]

Done! Didn't want to post an answer before it was correct. Happy to help.

Answer 1

[jonas]

Here you go! Note that you specify the latitude and range of longitudes as the indices of their respective vectors, and not in units of degrees. You can easily try other types of plots (like controuf) or change the colormap.

ncid = netcdf.open('amj_w.nc','NOWRITE')
ncdisp('amj_w.nc');
lon = ncread('amj_w.nc','longitude');
lat = ncread('amj_w.nc','latitude');
p = ncread('amj_w.nc','level');
T = ncread('amj_w.nc','t');
lat_const=50; %the latitude as the index in the lat vector
range=1:100; %specify the lon range as index... 
T=permute(T,[3 1 2]);
surf(lon(range),p,T(:,range,lat_const),'edgecolor','none');
cb=colorbar;
cb.Label.String='Temperature / K';
xlabel('longitude / degrees east')
ylabel('pressure / millibars')
set(gca,'XLim',[lon(min(range)) lon(max(range))])
view([0 90])
box on
title(['Latitude: ',num2str(lat(lat_const)),' degrees'])
set(gca,'layer','top')
colormap(parula)

[khan]

Thank You Sir, Nice and easy steps much clear. Respect and Regards

[jonas]

Happy to help! Note that there was an error in the original answer (changing the latitude did not have any effect) that I have now fixed.

[Tanziha Mahjabin]

Hi,

I have weakly average of SST (6X340X245) . i was trying to write the code in the same way. But don't know what is going wrong here. I have attached a sample data.

for i=1:length(TIMEw)

h=figure;

lat_const=-38.45; %the latitude as the index in the lat vector

range=246:340; %specify the lon range as index...

surf(lon(range),lat(lat_const),SSTw(i,range,lat_const),'edgecolor','none');

end

[jonas]

Hi,

You have to explain briefly what you want to plot.

One problem in your code is that you are trying to use a decimal number "lat_const" as an intex lat(lat_const)

Start by this code (plots the data for 1 point in time on a spatial grid) and then explain what you want to do:

load matlab.mat
SSTw = permute(SSTw,[2,3,1]);
h = surf(lon,lat,SSTw(:,:,1))
set(h,'edgecolor','none')
view([0 90])
colorbar

[Tanziha Mahjabin]

Thank you for your reply. This one i did removing the decimal part for lat_const and using repmat afterwards. It worked .

But if I want to have longitude on x axis and Time on y axis , in that case what should i do? (I want to generate something like the attached figure, but for sst)

I tried something like this, but something went wrong:

[lon2,TIMEw2] = meshgrid(lon,TIMEw);

[nT nJ nI ]=size(SSTw);

sstw=reshape(SSTw,nI*nJ,nT);

sstw=sstw';

figure;

surf(lon2, TIMEw2,sstw,'FaceColor', 'interp', 'EdgeColor', 'flat')

view([0 90])

caxis([15,19])

colormap jet

colorbar

xlabel('Longitude ')

ylabel('Time (mm/dd/yy) ')

set(gca,'TickDir','out')

set(gca(),'yticklabel',datestr(TIMEw,'mm/dd/yy '))

[jonas]

Still a bit confused what it is that you want to plot. Plotting longitude (x), time (y) and your data (z) is easy:

t = datetime(datevec(TIMEw))
long = lon(:,1);
[G,T] = meshgrid(long,t);
lat_const = 1;
data = SSTw(:,:,lat_const)
surf(G, T,data,'FaceColor', 'interp', 'EdgeColor', 'flat')
view([0 90])

but then you just plotting for a single latitude, interpolating between the values you can also see here:

figure(2)
scatter3(G(:),T(:),data(:),[],data(:),'filled')

In the figure you attached it seems they have data for many more points in time, which is why they get a nicer looking graph (unless I am misunderstanding something).

[Tanziha Mahjabin]

I found my problem. when i was plotting lon vs time, i was not having latitude constant.

It works fine now. Thank you

[jonas]

Great, no problem! I recommend using the datetime class instead of the old buggy datenum

Answer 2

[kafhi bachrudin]

hello sir i have a question how to find latitude constant ?