MODTRAN Up and Down IV, Moving Higher

Time to make good on the promise to progress upwards. In the first post in this series we established that Modtran sees no significant deviation from the blackbody spectrum looking down in the CO2 bands until about one kilometer altitude. Looking up, Modtran sees classical deviation from the blackbody spectrum, indicating absorption and radiation by CO2 at every altitude.

In the second post in this series we established that essentially the same is true for water, except that the altitude of first radiation in water bands looking down is four or five kilometers altitude.

In the third post in this series, we surmise that the reason Modtran can see no radiation looking down in the CO2 and water bands below their respective first altitudes, yet can see strong signals all the way to the surface looking up; is that the higher energy quantized vibrational states of the molecules at lower altitudes are transparent to lower energy radiation from above.

Where we left off at one kilometer, CO2 was just beginning to show it’s stuff looking down for the first time above the surface.

4Modtran up and down 1kmHere it is. Let’s go to five kilometers.

4Modtran up and down 5kmBig difference. Ten kilometers.

4Modtran up and down 10kmThe upwelling signal now has greater intensity that the radiation from above.

4Modtran up and down 16kmAt sixteen kilometers we are at the tropical tropopause at the beginning of the little “vertical spot” that extends to 17 kilometers. Within this kilometer, the atmosphere basically does not change temperature as you climb. Above 17 kilometers the atmosphere begins to warm with increasing altitude.

4Modtran up and down 30km

The trend beginning at one kilometer has been increasing upwelling and decreasing downwelling radiation. The really remarkable thing is that even from one meter in the first post, the temperature/intensity of the down and up looking radiation have been the same. The down and up looking values “kiss”. This trend begins to break down at 30 kilometers above, with only the 667.4 band from above stretching mightily for the kiss.


At 50 kilometers the lovers are finally separated.

What does this mean? The down and up looking values for water never match.

Up and down Water only 5km

Above is water only up and down at its heyday altitude of 5 kilometers. No hanky panky here.

We will explore the remarkable equality of up and down CO2 values in the next post.


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1 Response to MODTRAN Up and Down IV, Moving Higher

  1. Pingback: MODTRAN Up and Down V, The Kissing Conundrum | geosciencebigpicture

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