WAFSOPSG/5-WP/12
International Civil Aviation Organization
23/6/09
WORKING PAPER
WORLD AREA FORECAST SYSTEM OPERATIONS GROUP (WAFSOPSG)
FIFTH MEETING
Paris, France, 16 to 18 September 2009
Agenda Item 5: Operation of the WAFS
5.5: Implementation of high-resolution GRIB 2 upper wind and upper-air forecasts
IMPLEMENTATION OF HIGH RESOLUTION GRIB 2
WAFS UPPER-AIR FORECASTS
(Presented by the WAFC Provider States)
SUMMARY
This working paper presents an overview of the progress by the WAFCs
towards developing WAFS forecasts in the GRIB 2 code-form, and calls on
the WAFSOPSG to consider further how these products should be
disseminated to users.
1.
INTRODUCTION
1.1
The group will recall that, at its fourth meeting, it formulated two conclusions related to
the planned introduction of GRIB 2-coded WAFS upper-air forecasts; they called for the WAFC Provider
States to:
a)
provide two additional levels at FL 320 (275 hPa) and FL 360 (225 hPa); replace the
current thinned grid with a regular grid with a resolution of 1.25 degrees; and change
the temporal resolution from 6 to 3 hours, i.e. provide forecasts at time steps of T+6,
9, 12, 15, 18, 21, 24, 27, 30, 33, 36 hours from the analysis time; and study, in
coordination with the WAFSOPSG Member from IATA, the desirability of
improving vertical resolution below FL 300 to address the specific needs of flight
operations over polar regions. (Conclusion 4/12 refers); and
b) develop the higher resolution upper air forecasts, as specified, in time for the
WAFSOPSG/5 Meeting (Conclusion 4/13 refers); and
It will also be recalled that the group endorsed the detailed implementation plan for the transition from the
GRIB 1 to GRIB 2 code form within the WAFS (Decision 4/18 refers).
(6 pages)
116094049
WAFSOPSG/5-WP/12
-2-
1.2
This working paper outlines the progress that has been made by the WAFC Provider
States towards making GRIB 2 code-form WAFS forecasts available, and expresses some further issues
for the consideration of the group.
2.
DISCUSSION
2.1
The group will be pleased to note that, since the WAFSOPSG/4 Meeting, the two
WAFCs have worked collaboratively towards developing upper-air gridded WAFS forecasts for
wind/temperature/humidity/tropopause and icing/turbulence/CB in the WMO GRIB 2 code form, to fulfil
their obligations to the WAFSOPSG.
2.2
Traditionally, operational WAFS upper-air gridded forecasts have been in the WMO
GRIB 1 code-form, and only comprised forecasts of upper wind (including maximum), upper-air
temperature and humidity, geopotential altitude of flight levels, and flight level and temperature of
tropopause, as per Annex 3 — Meteorological Service for International Air Navigation, Chapter 3
ptrovisions. Forecasts in the GRIB 1 code-form for icing, turbulence and CB have only been available
since 2006/07 for trial and evaluation purposes on FTP servers, they have never been disseminated across
satellite distribution system for information relating to air navigation (SADIS) or international satellite
communications system (ISCS) satellite broadcasts.
2.3
It may be noted that no changes have been, or will be, made to the existing GRIB 1 data
sets available on the SADIS and ISCS services.
2.4
The development of WAFS Forecasts in the GRIB 2 code form by the two WAFCs began
in 2008 following the formulation of WAFSOPSG Conclusion 4/13. Noting the expressed wish of
Conclusion 4/12 part d), in consultation with the WAFSOPSG member from IATA, it was agreed that the
WAFCs would include additional flight level information at FL 270 (350 hPa) during the development of
the GRIB 2 data.
2.5
The specification of WAFS forecasts in the GRIB 2 code form is presented in the
appendix to this paper. This specification is also available in an abridged form within Annex 4 of the
SADIS User Guide (http://www.icao.int/anb/sadisopsg/sug/).
2.6
The group may wish to note that, by April 2009, WAFC London was in a position to
produce the requisite 1078 GRIB 2 WAFS bulletins on a daily basis for internal evaluation – i.e. they
were not distributed beyond WAFC London. These introductory data sets were uncompressed and
represented approximately 50 MB worth of data per model run – compare this with an existing GRIB 1
data set that amounts to approximately 10 MB per model run. The underlying reason for the five-fold
increase in data volume is attributable to the higher spatial and temporal resolution offered by the GRIB 2
data set, as well as the inclusion of icing/turbulence/CB forecast information. The 50 MB data volume is
in accordance with earlier expectations.
2.7
Due to the volume/size of the uncompressed GRIB 2 WAFS data sets, particularly when
compared to existing GRIB 1 data, the WAFCs recognised from an early stage that an appropriate
compression utility would need to be applied to the data set prior to transmission. Dissemination trials
conducted by the SADIS Provider State over the SADIS 2G satellite broadcast in late-April 2009 (using
uncompressed GRIB 2 WAFS data), resulted in a transmission time of 1 hour 55 minutes to send all 1078
GRIB 2 bulletins. This is a five-fold increase in the transmission time compared to an existing GRIB 1
-3-
WAFSOPSG/5-WP/12
data set across SADIS 2G at present (circa 22-25 minutes). Given that a GRIB 2 data set contains fivetimes the volume of data compared to GRIB 1, these transmission times were in line with expectations.
2.8
WAFC Washington is yet to undertake GRIB 2 data trials on the ISCS satellite broadcast.
Nevertheless, a test plan is being developed, the scope of which is expected to be presented to the
WAFSOPSG/5 Meeting in the form of a WAFC Washington information paper.
2.9
By using an appropriate compression algorithm, the WAFCs expect to achieve a
compression ratio in the region of 2:1 for the GRIB 2 WAFS grids. This will result in the net data
volume falling to around 25 MB per model run. Transmission times are similarly expected to fall to just
under 1 hour on the SADIS 2G broadcast.
2.10
At the time of writing (June 2009), WAFC London is continuing to develop a
compressed version of the GRIB 2 WAFS data. Development is expected to be completed by August
2009; whereupon further transmission tests on the SADIS 2G broadcast are expected in order to validate
the predictions shown in the paragraph 2.9 above. If conducted in time, the results of these additional
trials will be shared with the WAFSOPSG/5 Meeting.
3.
CONCLUSIONS
3.1
In accordance with the GRIB 1 to GRIB 2 transition plan endorsed by the WAFSOPSG/4
(Decision 4/18 refers), the WAFC Provider States were tasked to make available the GRIB 2 data sets on
ISCS and SADIS FTP services, in parallel with GRIB 1, by September 2009. As expressed in the WAFS
long term plan to be presented to the WAFSOPSG/5 Meeting under Agenda Item 7, the WAFCs expect to
complete this task between September 2009 and March 2010, subject to further endorsement by the
group.
3.2
The dissemination of GRIB 2 WAFS data on the ISCS and SADIS satellite broadcasts is
yet to be formally agreed. The WAFS and SADIS Operations Groups will need to consider whether the
transmission performance demonstrated by the GRIB 2 trials conducted over the satellite links are
acceptable, including compressed versus uncompressed, and the downstream implications of providing
either form of data (e.g. time taken to decompress data on end-user systems).
3.3
It should also be noted that when distributing the products over the satellite broadcasts,
there would be no way of labelling (encoding) the data as “operational” or “developmental”, and thus no
way of managing how they are interpreted or applied. Indeed, on the FTP services, the only way to
delineate the difference would be by placing them in “operational” or “developmental” sub directories – it
is not possible to encode this information into the bulletins themselves. Therefore, careful consideration
should be given to how this information is distributed beyond the WAFCs if it is to be considered (partly
or wholly) as developmental (or experimental) rather than operational.
3.4
The group may wish to agree that only the upper wind/temperature/humidity/ tropopause
forecasts in the GRIB 2 code form should be available on the ISCS and SADIS broadcasts, until such a
time that the entire complement of icing/turbulence/CB forecasts have reached a standard deemed
acceptable for flight planning applications. To achieve this, the group is invited to formulate the
following decision:
-4-
WAFSOPSG/5-WP/12
Decision 5/…. — Inclusion of WAFS forecasts in the GRIB 2
code form in the ISCS and SADIS satellite
broadcasts
That, with regard to the inclusion of WAFS forecasts in the
GRIB 2 code form in the ISCS and SADIS broadcasts, only those
for upper wind/temperature/humidity/tropopause be made
available for the time being.
Note. — The WAFS forecasts in the GRIB 2
code form for cumulonimbus clouds, icing and turbulence will be
included as soon as their quality is deemed acceptable for
operational flight planning applications by the WAFSOPSG.
4.
4.1
ACTION BY THE WAFSOPSG
The WAFSOPSG is invited to:
a) note the information contained in this working paper; and
b) decide on a draft decision for the groups consideration.
WAFSOPSG/5-WP/12
Appendix
APPENDIX
GRIB 2 WAFS product specification
WMO Header Assignment
T1
T2
A1
A2
i1i2
WAFC
London
CCCC
WAFC
Washington
CCCC
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
U
X
C, D, E, F, G,
H, I, J, K, L, M
85, 70, 60, 50, 40, 35, 30,
27, 25, 23, 20, 15, 10
EGRR
KWBC
850, 700, 600, 500, 400, 350, 300,
275, 250, 225, 200, 150, 100
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
V
X
C, D, E, F, G,
H, I, J, K, L, M
85, 70, 60, 50, 40, 35, 30,
27, 25, 23, 20, 15, 10
EGRR
KWBC
850, 700, 600, 500, 400, 350, 300,
275, 250, 225, 200, 150, 100
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
T
X
C, D, E, F, G,
H, I, J, K, L, M
85, 70, 60, 50, 40, 35, 30,
27, 25, 23, 20, 15, 10
EGRR
KWBC
850, 700, 600, 500
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
R
X
C, D, E, F, G,
H, I, J, K, L, M
85, 70, 60, 50
EGRR
KWBC
Tropopause Height
(ICAO)
n/a
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
H
X
C, D, E, F, G,
H, I, J, K, L, M
97
EGRR
KWBC
Tropopause
Temperature
n/a
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
T
X
C, D, E, F, G,
H, I, J, K, L, M
97
EGRR
KWBC
Maximum
Ucomponent Wind
n/a
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
U
X
C, D, E, F, G,
H, I, J, K, L, M
96
EGRR
KWBC
Maximum
Vcomponent Wind
n/a
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
V
X
C, D, E, F, G,
H, I, J, K, L, M
96
EGRR
KWBC
Maximum
Wind
Height (ICAO)
n/a
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
H
X
C, D, E, F, G,
H, I, J, K, L, M
96
EGRR
KWBC
Description
GRIB2 pressure levels (hPa)
GRIB2 timesteps
U-component Wind
850, 700, 600, 500, 400, 350, 300,
275, 250, 225, 200, 150, 100
V-component Wind
Temperature
Relative Humidity
WAFSOPSG/5-WP/12
A-2
Appendix
850, 700, 600, 500, 400, 350, 300,
275, 250, 225, 200, 150, 100
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
H
X
C, D, E, F, G,
H, I, J, K, L, M
85, 70, 60, 50, 40, 35, 30,
27, 25, 23, 20, 15, 10
EGRR
KWBC
Mean Icing
800, 700, 600, 500, 400, 300
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
I
X
C, D, E, F, G,
H, I, J, K, L, M
80, 70, 60, 50, 40, 30
EGRR
KWBC
Maximum Icing
800, 700, 600, 500, 400, 300
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
I
X
C, D, E, F, G,
H, I, J, K, L, M
81, 71, 61, 51, 41, 31
EGRR
KWBC
Mean
In-Cloud
Turbulence
700, 600, 500, 400, 300
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
F
X
C, D, E, F, G,
H, I, J, K, L, M
70, 60, 50, 40, 30
EGRR
KWBC
Max.
In-Cloud
Turbulence
700, 600, 500, 400, 300
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
F
X
C, D, E, F, G,
H, I, J, K, L, M
71, 61, 51, 41, 31
EGRR
KWBC
Mean CAT
400, 350, 300, 250, 200, 150
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
L
X
C, D, E, F, G,
H, I, J, K, L, M
40, 35, 30, 25, 20, 15
EGRR
KWBC
Maximum CAT
400, 350, 300, 250, 200, 150
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
L
X
C, D, E, F, G,
H, I, J, K, L, M
41, 36, 31, 26, 21, 16
EGRR
KWBC
n/a
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
B
X
C, D, E, F, G,
H, I, J, K, L, M
01
EGRR
KWBC
ICAO Height at CB
Base
n/a
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
H
X
C, D, E, F, G,
H, I, J, K, L, M
02
EGRR
KWBC
ICAO Height at CB
Top
n/a
6, 9, 12, 15, 18, 21,
24, 27, 30, 33, 36
Y
H
X
C, D, E, F, G,
H, I, J, K, L, M
03
EGRR
KWBC
Geopotential Height
of Standard levels
CB
Extent
Horizontal
Total number of GRIB 2 bulletins per model run = 1078 from each WAFC.
4 model runs (issues) per day based on 0000, 0600, 1200 and 1800 UTC synoptic data time.
Example 1: Bulletin YUXC85 EGRR is WAFC London’s u-component wind forecast at 850hPa (FL050) valid at T+6 from data time.
Example 2: Bulletin YLXM15 KWBC is WAFC Washington’s mean CAT forecast at 150hPa (FL450) valid at T+36 from data time.
— END —