Correlation between peak brightness temperatures and temperature at the formation height in the atmosphere. Panel (a) shows the correlation for the blue peak (k_2v) and panel (b) shows the correlation for the red peak (k_2r). The red, green, and blue contours enclose regions of 25%,50%, and 90% of the data. The orange lines indicate x = y. We normalized each column of brightness temperature to the maximum value of atmospheric temperature in that column.