Steps In MTP Post-Campaign Data Analysis

MJ Mahoney

10. Select Radiosondes to Calculate Retrieval Coefficients

This is probably the most labor intensive part of the MTP data analysis for several reasons. For example, there are often circumstances that, when the radiosonde archive is searched for soundings that are within some bias and standard deviation of a template profile identified in the previous step, very few can be found. Another problem is that while there might be soundings, they burst at too low an altitude. This is often a problem when selecting sondes for high altitude aircraft such as the ER-2, WB-57 and Geophysica, because often soundings burst near their cruise altitude in very cold conditions. To get around these limitations, we have to synthesize soundings with appropriate statistical properties. Tools for doing this are provided in the RAOBman program. There are three steps to selecting radiosondes to calculate an RC set:

open a file containing appropriate archival radiosondes,
specify appropriate filters for the selection process,
specify the sounding extension parameters,
specify the altitude range and step size for performing comparisons with the template profile,
perform the selection.

Figure 1. RAOBman Select tab

The RAOBman Select tab shown in Figure 1 is where most of the action happens in RAOBman. A RAOB file is opened using the Open RAOB button, which toggles to Close RAOB when the file is opened. Soundings for a comparison are selected using the Search button on Select tab. Before doing so, however, it is often prudent to set some selection filters, especially when dealing with very large database of soundings.

RAOBman_Filters

Figure 2. RAOBman Filters tab.

Filtering is done on the RAOBman Filters tab (shown in Figure 2) by entering information and clicking un-named check boxes on (green) or off (red). In the example above, only soundings from Edwards AFB (EDW), Miramar Naval Air Station (NKX), and Desert Rock (DRA) (see Site frame) would be selected from the open RAOB file, and only if they reached an altitude greater than 20 km (see Valid RAOB Data Needed frame, which specifies the range over which a sounding must have valid data).

Figure 3. An example of how a synthetic sounding.

Figure 3 which provides an example of a sounding from Miramar Naval Air Station in San Diego (NKX) being extended to higher altitudes. The left panel shows that the NKX2005010200 sounding burst at 23 km (yellow trace). The Miramar sounding 12 hours earlier (NKX2005010112) managed to get to 31 km (light blue trace). Since the two soundings are only 12 hours apart, and are very similar before the former sonde burst, it is safe to bet that the early bursting sonde is similar to the other at higher altitudes. Several steps are needed to extend sondes. The first is to describe how to extend it. This is done by using the triplet of numbers described in an earlier step: the lapse rate from the burst altitude to a break altitude (where the lapse rate changes), and the lapse rate from the break altitude to 50 km. How this is done is described in the next step.

RAOBman_Details

Figure 4. RAOBman Details tab.

This information is entered in the RAOB Extension frame of the RAOBman Details tab shown in Figure 4. LR1 is the lapse rate to the break altitude Zb, and LR2 is the lapse rate above the break altitude. It is also possible to add noise to the exended profile. In the Figure 4, 0.2 K/km of noise is added to LR1 and LR2, and 0.2 km of noise is added to Zb. Also seen in the RAOB Extension frame is the On checkbox. This must be checked for radiosondes to be extended while being compared to a template profile. Before soundings can be selected, one more step is necessary.

RAOBman_Export

Figure 5. RAOBman Export tab.

The Write Average Options frame of the RAOBman Export tab shown in Figure 5 has several uses. For comparing and selecting radiosondes, it specifies the minimum and maximum altitudes over which soundings are compared, as well as the altitude step size. In this example, soundings are compared from 0.5 to 50 km in 0.5 km steps. Although the highest altitude is 50 km, statistics are only collected up to the burst altitude of the template profile.

Figure 6. The RAOBman Select tab

We are now in a position to select soundings that match a particular template profile. This is illustrated in Figure 6. As shown in the list box, the Desert Rock (DRA) sounding for 20020115 at 0000UT was selected (and automatically hi-lited). The Save Ref button was clicked to use the DRA sounding as the template profile. When the Save Ref button is depressed, the following box will appear if the template profile is not in the MISSION_RAOBrange.txt file:

This illustrates one of the uses of the MISSION_RAOBrange.txt file. If the sounding was present in this file, then RAOBman would automatically enter the LR1, Zp and LR2 information into the RAOBman Details tab RAOB Extension frame. When dealing with many dozens of template profiles, this is a real convenience because after doing a few manually, there is a tendency to forget to change these values, and then everything has to be redone.

That done, the AVG and RMS text boxes were filled in with 2.0 and 3.0 K, respectively, to specify how close potential RC soundings had to be to the template profile to qualify for inclusion. In addition, the Use Bias check box was checked to enable the 2.0 K bias requirement. If it was not check, the bias would not only be ignored, it would in fact be removed. This feature is present so that when it is difficult to find enough comparable soundings, any sounding that has the "right" shape will be used, even if it has a very large bias. Finally, the RMS button is depressed to search for soundings that meet the selection criteria. In this case, 244 were found, which is a reasonable number to calculate an RC set. (100 is the absolute minimum.) The results of the radiosonde selection process are shown in Figure 7. RAOBman automatically saves the selected soundings in a file with the following fixed format:

XXXXX_YYYYMMDDHH.RAOB2

for example:

DRA___2002011500.RAOB2

in this case. Five placeholders are provided for the sounding name XXXXX to accomodate WMO Numbers when ICAO names are not available. These files are saved in the C:\MTP\RAOB\MISSION\ folder, where RCcalc will go to look for them when RCs are to be calculated.

Figure 7. The template profile (yellow) is shown in the left panel, and the selected soundings (yellow) are shown in the right panel . The average of all the selected soundings is show in white in both panels.

Sometimes when using very large archival data bases, you might end up with 500 or more soundings that meet your selection criteria. These can be reduced by reducing the AVG and RMS selection criteria, and then repeating the selection process by depressing the RMS button. (The program will remember the Save Ref template profile.) You will get a warning box:

to indicate that the file containing the previously selected soundings is about to be deleted. Normally, you would click to Yes button to continue. This is a precaution because it has been beneficial in the past!

The best strategy for selecting template profiles is to use radiosondes in the MISSION_RAOBrangeAll.RAOB2 file with an emphasis on those soundings that are closest to the aircraft flight tracks during a campaign.

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