I am making a Skew T Chart in matlab and for some reason my isotherms(the diagonal lines on the plot) aren't aligned with the temperature on the x-axis. Is there a way to fix?

Question

Matthew 2023-2-14

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https://ww2.mathworks.cn/matlabcentral/answers/1912325-i-am-making-a-skew-t-chart-in-matlab-and-for-some-reason-my-isotherms-the-diagonal-lines-on-the-plot

回答： Mehmet Ceylan 2024-6-3

clear all;
close all;
[P,H,T,Td,w]=textread('OAX_sounding_corrected.dat', '%f %f %f %f %f');
fileID = fopen('OAX_sounding_corrected.dat','w'); 
formatSpec = '%f %f %f %f %f\n';
temp1 = -40:.1:50;
press1 = 1050:-50:100;
numtemp1 = numel(temp1);
numpress1 = numel(press1);
for i = 1:numtemp1
for j = 1:numpress1
a(i,j) = temp1(i)+40.*log(.001.*press1(j));
end
end
press1 = transpose(press1);
temp1 = transpose(temp1);
a = transpose(a);
figure
b = contour(temp1,press1,a,16,'k');
hold on
set(gca,'yscale','log','ydir','reverse')
set(gca,'ytick',[100:50:1050])
set(gca,'ygrid','on')
c = T-40.*log(.001.*P);
d = Td-40.*log(.001.*P);
plot(d,P,'g')
plot(c,P,'r')
xlabel("Temperature (°C)")
ylabel("Pressure (hPa)")
title("Temperature vs. Pressure")

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Answer 1

Vishwa 2023-2-27

编辑：Vishwa 2023-2-27

在 MATLAB Online 中打开

To my understanding, there is no error in the output of this MATLAB code. Contours are plotted at right locations, as visible in this figure.

To fix this, you may try the following:

Either modify your expression for a so that contours are generated with matching values of x-ticks, or
You can change the x-ticks to match the contour data points.

Here is the modified code

temp1 = -40:10:50;
press1 = 1050:-50:100;
numtemp1 = numel(temp1);
numpress1 = numel(press1);
for i = 1:numtemp1
for j = 1:numpress1
a(i,j) = temp1(i)+40.*log((1/1050).*press1(j));
end
end
press1 = transpose(press1);
temp1 = transpose(temp1);
temp2 = [-130 -120 -110 -100 -90 -80 -70 -60 -50 temp1'];
a = transpose(a);
figure
b = contour(temp1,press1,a,temp2,'k','ShowText','on');
hold on
set(gca,'yscale','log','ydir','reverse')
set(gca,'ytick',100:50:1050)
set(gca,'ygrid','on')