MEAN ZONAL WINDS
Experimenting with Seasonal Predictions for High Altitude Balloon Flights
Ralph Wallio, WRPK   W0RPK  at  netINS.net


Experienced planners of Amateur Radio high altitude balloon missions routinely use winds aloft forecasts and observations to predict ground tracks and landing areas. The prediction process and original software was developed in the late 1980's by Bill Brown, WB8ELK, and most recently available as Balloon Track for Windows by Rick von Glahn, NKKZ (see http://www.eoss.org/wbaltrak/index.html). Predictions for specific missions are typically created only a few days before they fly with an average ≈12-mile accuracy (see Touchdown Prediction entries at the bottom of http://showcase.netins.net/web/wallio/ARHABrecords.htm).

Seasonal planning for high altitude missions may also be possible but it has not been as widely discussed or utilized. Planners could consider methods discussed below to understand how flight track characteristics change month-to-month through the year. They could then consider these changes as they plan for flights several months in advance. Planners already have a good handle on ascent rates, descent rates and burst altitudes. The only missing link is a long-term view of winds aloft.

This discussion experiments with a long term view of winds aloft available in
National Center for Atmospheric Research (NCAR) Technical Note 366, Global Atmospheric Circulation Statistics, 1000-1 mb, by William J. Randel (see http://www.ucar.edu/communications/technotes/technotes301-400.shtml for ordering information). It contains 256 pages of interesting discussion of methods and graphics but we only need the last few pages that contain tables of wind speeds across 12 months, surface to 157,000ft, latitudes 85dS to 85dN.

This technical note discusses the concept of Mean Zonal Winds (MZW) and how they vary month-to-month. Daily data from 12 years, 1979-1990, has been used to develop mean wind speed values at 1-1000mb heights (157,000-0ft) in 5 degree increments of latitude for all 12 months of the year. Statistical deviations from mean values are given for daily and interannual periods (2-10 years). Data for Mean Zonal Temperatures is also available.

Given these MZW values, this experimental process involves six steps:

1) Format MZW values via EXCEL into a table compatible with Balloon Track for Windows (BTW).
2) Run BTW and export track prediction output in CSV format (Comma Separated Variables).
3) Import BTW CSV output to EXCEL and standardize data format.
4) Graph downrange distance vs. altitude and consolidate results.
5) Construct charts containing 12 months of MZW downrange tracks
6) Compare MZW based predictions with results from actual missions.


STEP-1: Preparing MZW values for BTW

NCAR/TN-366 provides individual MZW tables for each month of the year that contain values for 35 latitudes (north and south in 5 degree increments) and 17 altitudes, 1000-1mb (0-157,000ft). Wind speeds are given in meters/second (m/s) which can be converted to knots (KTS = m/s x 1.9426), miles per hour (MPH = m/s x 2.237) or kilometers per hour (KPH = m/s x 3.6)
.

Wind direction is given only as westerly or easterly, e.g., there is no attempt to predict precise wind directions. In the Northern Hemisphere during the winter, winds at all levels are out of the west (270 degrees). During the summer, lower level winds are out of the west (270 degrees) while higher level winds are out of the east (090 degrees). In the tables easterly winds are indicated with negative speed values, e.g., -10m/s.

From these extensive tables I have extracted wind speed values for 40N latitude. U.S. Standard Atmosphere, 1976 (available from NTIS) is used to convert heights given in millibars to meters and feet ASL.

Mean Zonal Winds (meters/second) at 40N Latitude

MILLIBARS

METERS

FEET

JAN

FEB

MAR

APR

MAY

JUN

JUL

AUG

SEP

OCT

NOV

DEC

1000

100

328

1

1

1

1

1

1

1

0

0

0

1

1

850

1450

4757

6

5

5

4

4

3

2

2

2

4

5

6

700

3000

9843

11

10

9

8

7

6

4

4

5

8

10

10

500

5550

18210

18

17

16

14

12

11

8

8

11

14

17

18

400

7200

23623

22

21

20

18

16

14

11

10

14

18

21

22

300

9200

30185

27

26

25

22

20

19

15

14

18

22

26

27

250

10400

34122

29

28

27

24

22

21

17

16

21

24

28

29

200

11800

38716

30

29

27

24

23

23

19

18

23

26

30

30

150

13600

44622

30

28

26

22

20

21

17

16

21

24

28

29

100

16200

53152

25

23

21

17

14

12

8

8

13

18

22

24

70

18500

60699

18

16

14

11

7

4

1

2

7

11

16

17

50

20600

67589

13

11

9

7

2

0

-4

-2

3

8

12

13

30

23900

78416

10

6

5

4

0

-4

-8

-6

0

7

11

10

10

31200

102367

14

7

8

11

2

-8

-14

-10

1

12

20

19

5

36000

118116

21

12

16

16

1

-11

-18

-13

1

18

30

30

2

42800

140427

32

23

28

20

0

-17

-24

-16

4

28

47

47

1

48000

157488

41

32

34

19

-6

-26

-34

-22

4

34

57

59

Charting Altitude (feet ASL) vs. Wind Speed (mph) data from this table yields interesting results:

MZW values of interest are then entered into an EXCEL spreadsheet that takes care of unit conversion, wind direction and formatting. In this example MZW values from July 40dN are manually transferred as input to the conversion form:

(EXCEL spreadsheet is available from W0RPK at netINS.net)

Output from the input/conversion form is then copied into a second sheet of the same workbook and then saved from that sheet in CSV format to an appropriately named file, e.g., MZW_July_40N.CSV. The result looks like this when opened with a text viewer like NotePad:



STEP-2: Run BTW and export track prediction output

The CSV file prepared in Step-1 is opened by Balloon Track for Windows (BTW) which is then set up for ascent rate, descent rate and burst altitude (via SET UP and FLIGHT DATA tabs). Using 1000ft/min, 1500ft/min and 100,000ft respectively, BTW looks like this when also set up for launch coordinates of 0 degrees latitude and longitude.

BTW then exports output in CSV format to an appropriately named file, e.g., MZW_JULY_40N_BTW.CSV, (using FILE then EXPORT then COMMA DELIMITED).


STEP-3: Import BTW CSV output to EXCEL and standardize data format

The BTW CSV file is opened as an EXCEL spreadsheet for clean-up, conversion and graphing in a standardized format. A great circle navigation formula is used to calculate distance downrange from launch coordinates (GEOFUNC.XLA, an EXCEL function add-in which performs trigonometric calculations for plane and spherical geometry and a number of other related calculations is available at
http://nmml.afsc.noaa.gov/Software/ExcelGeoFunctions/excelgeofunc.htm).



STEP-4: Graph downrange distance vs. altitude and consolidate results

EXCEL is used to develop an X-Y scatter/line chart which plots Distance Downrange (X) vs. Altitude (Y). Note that in this case for July, lower level winds push the balloon and payload to the east (some direction northeast through southeast in actual flights) and then upper level winds push them back to the west until burst at 100,000ft.

This chart predicts a single track caused by a 1000ft/min ascent through Mean Zonal Winds but we could add another track for a 500ft/min ascent rate. The result would bracket the vast majority of flights that ascend in the range 500-1000ft/min. To add the second track we back up to STEP-2 and run BTW using 500ft/min and continue through STEPS 3-4. We then consolidate the two tracks into a single EXCEL chart.


Note that track characteristics are similar but distances are longer when ascent rate is slower. Descent track is exactly the same (1500ft/min was used in both cases) but starts further east in the case of a slower 500ft/min ascent.


STEP-5: Construct charts containing 12 months of MZW tracks

Steps 1-4 can be used to create downrange track data for all 12 months and then EXCEL can be used to combine all 12 tracks into two charts (two charts rather than one because track overlap on a single chart is visually confusing). I have used 90,000ft burst altitudes for all 12 downrange tracks.





Note that track distances for winter months are substantially longer than for summer months (peaking in December and January). Easterly winds during summer months cause the characteristic "loop" (peaking in July and August).


STEP-6: Compare MZW based predictions with results from actual flights

Finally (sez the reader), we can compare seasonal MZW downrange track predictions with results from actual flights. Most amateur high altitude missions include GPS receivers and periodically make position reports via digital downlink telemetry radio channels. These position reports include precise time stamp, latitude, longitude and altitude data fields. Telemetry collected at ground stations is often available for post-flight analysis by others.

I am in the process of collecting telemetry data files from as many flights as are available. Data is structured into a standard EXCEL format and organizing by month-of-the-year. An EXCEL downrange track chart is created for each flight and then consolidated with MZW predicted tracks into monthly charts and tables that follow. In the tables, ASCENT is average rate for entire ascent in feet/minute; DESCENT is approximate descent rate in feet/minute at sea level; and RECORDS is the number of GPS data records available in the data file. Brief comments are added for what appear to be unpredicted or extraordinary situations.

MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

EOSS-46

14Jan01

Colorado

40dN

92,748

unk

unk

622

No GPS time stamps

Upper level easterlies are not predicted by MZW. Ascent rate of EOSS-46 can not be determined due to lack of time stamps but it appears to be significantly higher than 1000ft/min. Descent rate appears to be close to 1500ft/min (sea level) as used for MZW tracks.


MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

EOSS-47

25Feb01

Colorado

40dN

93,811

1045

~1300

129

na

HABET-L24

06Feb99

Iowa

42dN

60,438

1480

~600

1067

Slow descent under small balloon

KNSP-99A

06Feb99

Kansas

39dN

114,399

912

~1000

173

na

Upper level easterlies reversing track of KNSP-99A are not predicted by MZW. It is interesting that winds above 105,000ft veer back to the west (this does not happen during summer months).


MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

EOSS-25

17Mar96

Colorado

38dN

96,119

1141

~1000

240

Floater and altitude hold

EOSS-39

12Mar00

Colorado

39dN

97,504

1223

~800

87

Data starts at 42505ft ascending

NSBG-01

25Mar00

Kansas

38dN

98,284

1111

~400

252

na



MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

EOSS-26

06Apr96

Colorado

38dN

83,634

839

~500

226

na

EOSS-40

16Apr00

Colorado

40dN

97,995

unk

~1000

126

Data starts at 35,579ft ascending

EOSS-48

01Apr01

Colorado

40dN

90,045

905

~1000

140

na

EOSS-49

21Apr01

Colorado

40dN

88,056

687

unk

143

Data stops at 12,240ft descending

EOSS-50

21Apr01

Colorado

40dN

103,984

501

unk

215

Data stops at 91,051ft descending

KNSP-99C

18Apr99

Kansas

38dN

86,546

698

~800

282

na

NSTAR01A

14Apr01

Nebraska

41dN

60,321

1172

~1700

135

na



MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

BEAR-1

27May00

Alberta

53dN

104,211

455

~900

254

Edmonton, Alberta, Canada

NSTAR-01B

19May01

Nebraska

41dN

95,384

1046

~1000

265

na

TVNSP-01C

12May01

Idaho

43dN

67,012

808

unk

336

Altitude hold during descent

Note that BEAR-1 flew at 54dN latitude and therefore should not be compared to MZW tracks that are for 40dN latitude. The match of NSTAR-01B and 1000ft/min MZW tracks is very close.


MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

BOR-0106A

07Jun01

Montana

45dN

45,341

392

~1100

445

na

BOR-0106B

30Jun01

Montana

45dN

85,994

unk

unk

400

Data anomalies

EOSS-41

18Jun00

Colorado

39dN

94,204

unk

unk

160

No GPS time stamps

HABET-L27

17Jun99

Iowa

41dN

87,146

1191

unk

632

Data stops at 35,865ft descending

KNSP-98B

06Jun98

Kansas

39dN

90,562

730

~950

279

na

KNSP-99E

20Jun99

Kansas

38dN

109,217

724

~700

344

na

NSBG1-3

30Jun01

Kansas

38dN

78,247

964

unk

131

Data stops at 60,751ft descending

NSTAR-01C

24Jun01

Nebraska

41dN

83,625

1099

~1000

196

na

NSTAR-01D

30Jun01

Kansas

38dN

91,365

986

~1150

208

na

TVNSP-01D

30Jun01

Kansas

38dN

83,099

446

~1000

293

na

During June we see several examples of upper level easterlies as predicted by MZW but we also see a very wide range of track distances, almost 10:1 (BOR0106A:NSTAR01C).

MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

ANSR-2

28Jul01

Arizona

35dN

85,742

401

unk

349

16,818ft ascend to 14,206ft descend

EOSS-24

30Jul95

Colorado

39dN

96,141

1081

400

257

na

HABET-L49

26Jul01

Iowa

42dN

85,970

1266

na

160

Descent via small balloon

KNSP-97B

12Jul97

Kansas

39dN

79,457

313

unk

126

7,398ft ascend to 26,836ft descend

KNSP-99F

10Jul99

Kansas

37dN

51,659

550

~750

257

na



MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

BEAR-2

05Aug00

Alberta

53dN

99,482

714

~1150

165

Edmonton, Alberta, Canada

EOSS-51

25Aug01

Colorado

39dN

91,458

1178

~1000

207

na

KNSP-98C

08Aug98

Kansas

38dN

78,354

770

~700

118

na

TRAVELER1

04Aug01

Kansas

38dN

90,139

1291

unk

50

na

TVNSP-01F

12Aug01

Idaho

42dN

85,439

919

unk

93

Data stops at 32,982ft descending



MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

HABET-L28

23Sep99

Iowa

41dN

84,935

914

unk

852

Data stops at 37,321ft descending

NSTAR-01E

01Sep01

Nebraska

41dN

54,380

879

~900

414

na

TVNSP-01G

29Sep01

Idaho

43dN

44,113

800

~600

299

na



MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

ANSR-3

14Oct01

Arizona

32dN

98,581

642

~1150

103

na

EOSS-52

20Oct01

Colorado

39dN

92,224

1198

unk

212

na

HABET-L21

10Oct98

Iowa

42dN

93,072

1232

~750

2235

na

KNSP-98D

10Oct98

Kansas

39dN

88,822

622

~800

158

na

KNSP-98E

25Oct98

Kansas

38dN

90,279

650

unk

88

Data stops at 53,357ft descending

NSTAR-00A

07Oct00

Nebraska

40dN

83,675

972

~1400

200

na



MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

EOSS-37

14Nov98

Colorado

40dN

79,950

926

unk

55

Data stops at 37,165ft descending

EOSS-45

19Nov00

Colorado

40dN

90,573

unk

unk

421

No GPS time stamps

HABET-L44

15Nov00

Iowa

42dN

59,999

1326

~500

1436

na

HABET-L52

15Nov01

Iowa

41dN

90,078

1126

~600

1985

na

KNSP-98F

22Nov98

Kansas

38dN

86,635

581

~900

290

na

NSTAR-00B

04Nov00

Nebraska

41dN

74,242

1029

~1200

189

na



MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

ANSR-4

01Dec01

Arizona

32dN

90,226

1159

~1200

50

Data starts at12,058ft ascending

EOSS-53

01Dec01

Colorado

39dN

94,755

1065

~1000

236

na




Step-6 compresses movement to a flat 2D chart that could hide interesting track characteristics. Early experiments with 3D charts have produced this comparison. I have found visualization of these 3D charts to be difficult, e.g., my old and tired eyes don't always see the three dimensions correctly. Given only one track, I have found it helps to also draw 2D tracks for latitude-longitude, altitude-latitude and altitude-longitude as guides for visualizing the 3D track. I am experimenting with similar aids for multiple track charts.



This experiment is producing mixed results. During some months most actual tracks are reasonably predicted by Mean Zonal Winds. During other months there is a very wide range of tracks well beyond predicted bounds. A few actual tracks are almost exactly as predicted while others have very different characteristics than predicted. Regardless, we can see track characteristics change month-to-month and season-to-season so we can understand how a summer flight will differ from a winter flight.


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