lat=ncread('sst.mnmean.nc','lat'); %for reading the lat variable from .nc file
lon=ncread('sst.mnmean.nc','lon');
sst=ncread('sst.mnmean.nc','sst');
id1=find(lat>30&lat<60); %find function finds the index in lats where the value lies between 30 and 60
id2=find(lon>150&lon<240);
lat1=lat(id1); %lat1 stores those lat values from id1, in which the specific indices are saved
lon1=lon(id2);
sst1=nanmean(sst(id2,id1,:),3); % sst accepts the indices from id1 and id2 and mean takes the mean alone the third dimension
contourf(lon1,lat1,sst1','linecolor','none') %contour plot of the required plot.
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