EAS 308, Meeting 20

Compare actual and RAMS-TTC predicted average climb rates

Now, we move to the second test of the RAMS predictions: compare the actual and RAMS-predicted average climb rates. The RAMS predictions are connected to the TTC algorithm through the CBL depth vs climb rate algorithm described in the OSTIV manuscript:

Again, followingOlofsson and Olsson7, the mean rate of climb w(m/s) is given by

w = 0.75 x (h/1000) x W/200 x (1 - TADV/2) x 20/FF (B-2)

where h is the depth of the CBL in m AGL, Wis as in Equation (B-1),TADV is the temperature advection at 1000 m in C/h (cold air advection enhances lift and vice versa) and FF is the wind speed at 1000 m AGL in knots; if ff < 20, ff = 20 (large wind speeds reduce lift rates and vice versa). The leading constant in Equation (B-2) used by Olofsson and Olsson was 1 after guidance from WMO TN1588. But, this value produced TTC task speeds significantly larger than actual speeds (111 vs 98 km/h) for the 52 OCGP flight records from the OLC for 2004, 2005 and 2006. The constant 0.75 was determined using 27 flight records from two top pilots at OCGP as depicted in Figure 4:

Using this value in Equation (B-2) produced TTC task speeds and actual speeds much closer (99 vs 101 kph). Thus, the magnitude of the lift rate, has a significant affect on predicted speeds.

Our task is to determine the average predicted climb rate for the forecast regions through which the tasks were flow. Here’s the procedure:

  1. Simultaneously displaying on your PC screen the flight track in SeeYou and in TTC. To open a flight track in SeeYou, go to “Open” and browse to the file of your first place finisher in the Standard Class and click on it (but, note the hieroglyphic name, which will be used to open the file in TTC). To open the file in TTC you must first load in the *.rams file for your contest day then click on “Flight, IGC” and browse to the location of the file. You will only see the file with the hieroglyphic, click on it.

Here is an image of the region names valid for the *.rams file you just opened:

You can see the flight trace and region numbers simultaneously in TTC. The region numbers are at the bottom left-hand corner near the latitude and longitude values (location of the pointer on the flight trace).

  1. Now, determine the times (EST) the pilot flew in the forecast regions. By placing your cursor on the flight-trace in SeeYou, you will see the time at that point (make sure it’s in EST, check the UTC offset in Tools, Options, General). Now, carefully follow the trace writing in an Excel spread sheet the region number and the time the pilot entered and exited the region.
  2. Now, in TTC, turn off the flight trace (Flight, Close flight) and task. If a task remains after turning off the flight trace close the task (Task, Close task). TTC now displays only the RAMS meteorological predictions.
  3. Adjust your TTC scales to a maximum altitude of 5 km and time starting at 06EST.
  4. Put your cursor in the first forecast region and the expected climb rate profile will be displayed. The values are for every half-our centered on the half hour. For example, my first place pilot Baud Litt flew in Region 809 from 1217 to 1242EST. So the nearest climb rate value would be the 1230EST value of 1.1 m/s (you must add the decimal place to the TTC-displayed value).
  5. Then, put your cursor in the next region in which the pilot flew. In my case it was Region 800 between 1242 and 1256EST. The nearest climb rate value would be the 13EST value, 1.2 m/s.
  6. The next region in which Baud flew was Region 802 between 1256 and 1310EST. So, the nearest climb rate value would be at 13EST, 1.1 m/s.
  7. I continue this procedure all the way around the track to where it started.
  8. I average all the values to get the average predicted climb rate for the flight: 1.2 m/s.

Following instruction in Mtg. 19, I determine the average actual climb rate of Baud Litt’s flight using SeeYou and enter the value, 2.1 m/s, next to the predicted value on my Excel spread sheet.

A major discrepancy between the actual and predicted climb rates has resulted, 2.1 vs 1.2 m/s. Let’s investigate the values for the terms in Equation B-2 to see if we can explain the discrepancy. The actual and predicted CBL depths I reportedin Mtg. 19 notes had an excellent agreement at 13EST of about 2.2km AGL. Using this value in Fig. 4 gives a mean climb rate of about 1.7 m/s, a value substantially closer to the 2.1 value. But, the predicted wind speeds were almost 30 knts. Thus, wind speed term in Eq. B-2 reduced the 1.7 m/s value significantly.

Looking at the actual and predicted barogram trace for Baud’s flight reveals more information on the discrepancy.:

The red and black line is the actual altitude excursions of Litt’s flight. Woops, first, there is a display error caused by a timing error in the *.rams file:

ZCZC

gggg800

GG800Region, Mi 14.10.2006

UTC T Td Steig Basis-Top Wind

hh:mm [C] [C] [m/s] [m] - [m] [deg/kt]

04:00 7 -6 286 30

04:30 6 -6 284 29

05:00 6 -6 282 28

05:30 6 -6 278 27

06:00 6 -6 275 26

06:30 6 -6 273 26

07:00 6 -6 272 27

07:30 7 -6 272 28

08:00 8 -6 273 29

08:30 9 -6 0.7 1400 275 30

09:00 10 -6 0.9 1800 277 31

09:30 11 -6 0.9 2000 277 29

10:00 12 -6 1.0 2100 277 28

10:30 12 -6 1.1 2200 278 28

11:00 13 -6 1.2 2200 278 27

11:30 13 -7 1.2 2300 278 26

12:00 13 -7 1.2 2300 278 25

12:30 13 -7 1.2 2300 278 24

13:00 13 -7 1.3 2200 278 24

13:30 13 -7 1.1 2200 278 24

14:00 13 -7 0.8 2200 278 24

14:30 13 -7 0.4 2100 278 25

15:00 13 -7 278 25

15:30 13 -7 279 26

16:00 12 -7 280 26

NNNN

It appears the RAMS file is still on MST, that is, what you see above as 0400 is really 0600EST and1600 is really 1800EST. The meteorological values do not change, just the times change.

So, I called Steve Saleeby (13 Nov 06) and he fixed the time in the Rams2TopTask.exe that produces the *.rams file from the RAMS.GEM file, the file that contains all the RAMS meteorological predictions. I will rerun the *.ram files for your contest days and e-mail them to you.

Note, this time error will not affect your predicted CBL depth values in Assignment 13.

Another timing error has occurred. In the above barogram display (time-height diagram), the CBL depth is correct but the flight trace is two hours too early. So, slide over theflight trace two hours, and you see Litt, indeed, flew during the strongest time of the day. But, notice he flew 200 to 300 m higher than the predicted CBL depth. This is another reason his climb rates wee larger than those predicted by RAMS-TTC. There is a strong dependence of climb rates and CBL-depth in eq, B-2.

On 14 November after Meeting 20, I called Olivier Liechti and reported that TTC apparently was on MST not EST; a remnant of the earlier development for Colorado. He said this diagnosis was true and he will make a fix to TTC so it will recognize the time zone of the *.igc file. I will get the new TTC during my visit with Olivier over the Thanksgiving Break. This will allow us to complete the final test of the RAMS-TTC system for the R4N flights: compare actual and predicted task speeds.

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