Report: Wind Atlas Project –Work Package 5: Oct 2014 – Mar 2015
Project Report: South African Wind Atlas
Period: Apr - Sep 2015
Document Reference: CLS-CD-REP-PROJ-WASA2-2015-002 1
Document Type: Project Report
Version: 1
This document is controlled in terms of the South African Weather Services’ Quality Management System and may not be edited,
distributed or deemed obsolete without permission of the Project Manager:TQM.
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Report: Wind Atlas Project –Work Package 5: Oct 2014 – Mar 2015
Document Control
Version and Amendment Schedule
Version No.
Version Date
Authors
Description of Amendments
1
September 2015
A C Kruger & X Larsén
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Report: Wind Atlas Project –Work Package 5: Oct 2014 – Mar 2015
WASA2
Progress Report 2 (for April to September 2015)
Work Package 5 – Extreme Winds
This progress report on Work Package 5 of the Project: Wind Atlas for South Africa covers the period from
April to September 2015.
Progress according to Project Plan
Progress is tracked according to the updated Project Plan, which shows the following activities for the
2014-15 financial year:
WP25.01 Estimation and update of extreme wind estimations from measured data (SAWS)
Estimation and update of extreme wind estimations from measured data
The WASA 2 domain covers the provinces of KwaZulu-Natal, Free State and parts of the Northern Cape
(around WM11) and remaining parts of the Eastern Cape. SAWS climate stations were selected which
covered the above domain. In addition, stations were selected which were close to the border of the
domain. All 48 identified stations (listed in Progress Report 1) were audited for completeness, to ensure
at least 10 years with 90% of data up to the end of 2013.
All the identified stations were subjected to quality control, and eventually the 1:50 yr gust and 10 min
wind speed maps could be developed from the data sets. Further details, as well as the maps, were
presented in the previous progress report (CLS-CD-REP-PROJ-WASA2-2015-001 1).
WP25.02 Mesoscale modeling of extreme wind climate for 2 regions in WASA2 domain (DTU)
We use the selective dynamical downscaling method (Larsén et al. 2013) to estimate the 50-year wind
and the 50-year gust wind for the WASA II domain. For the gust estimation, the Brausseur approach is
used in connection with the mesoscale modeling (Brausseur et al. 2003, Larsén and Kruger 2014). These
methods are the same as those we used for WASA I.
Identification of the storms
The CFSR reanalysis data (1998 - 2010) (Saha et al. 2010) are used for downscaling the storm winds to a
spatial resolution of 4 km and a temporal resolution of 10 min. These CFSR data are of a spatial
resolution of about 38 km and 6 hourly. The surface winds at 10 m are used to identify the storms to be
modeled.
For each CFSR data grid point, shown in Fig. 1, the annual 10-m wind maximum for the period 1998 –
2010 was identified where the date, wind speed and direction are registered. The storm dates over all
the grid points and over all 13 years are put together and there are in total 261 storms identified. Some
of the storm lasted 1 to 2 days, some lasted 2 to 3 days and some seem to contain a series of storms in a
row.
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Report: Wind Atlas Project –Work Package 5: Oct 2014 – Mar 2015
Figure 1. Coastline around South Africa and the CFSR data grid points for WASA II domain.
Modeling the storms
The WRFV3.6 was used for modeling the identified storms. We used three one-way nested domains,
corresponding to 36 km, 12 km and 4 km horizontal resolution, respectively. Figure 2 shows the three
domains in elevation. The innermost domain corresponds to the WASA II domain.
There are 46 vertical model levels and 7 levels from surface up to about 100 m. The time steps for the
three domains are 180 s, 60 s and 20 s, respectively. We used the Lin et al scheme for the microphysics,
the RRTM scheme for the longwave and short wave radiation, the MYNN PBL and surface schemes. The
SST field was updated daily using 0.5 degree RTG analysis. The CFSR reanalysis data are used as the
initial and boundary forcing for the WRF modeling.
We use a spinning up time of 24 hours and a running period of 48 or 72 hours, depending on the length
of the storm as suggested by the dates identified from the CFSR data.
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Report: Wind Atlas Project –Work Package 5: Oct 2014 – Mar 2015
Figure 2. The three nested WRF domains in elevation.
Status and Plans
There has been delay due to the fact that the computer clusters are out of order when the work started
in July. The progress is slower than anticipated due also to that the computer cluster is overloaded with
many projects and that the model domain is a lot bigger than first estimated.
We collected long term measurements from sites spread over the WASAII domain, see Fig. 3. Ten of
them are selected to verify the quality of the storm selection. Later, these data will be used to validate
the estimate of the 50-year wind.
These 10 stations are, with numbers as indicated in the map below:
1-Noupoort, 20 years, Mostly TS – the station is exposed to some topographical features which
might influence the measurements
2-Jamestown, 20 years Mostly TS - hilly terrain, the station is exposed to some topographical
features which might influence the measurements
7. Margate, 20 years, coastal Cold fronts, well exposed at an airport
13. Durban South AWS, 21 years, coastal Cold fronts, well exposed at the old airport
15. Bolemfomtein, 20 years (I think I have it already) TS, well exposed at an airport
16. Giants Castle AWS, 19 years, mountain Cold fronts, mountains, topographical features have
an influence on the measurements
22. Ladysmith, 19 years, Mountain – coastal Not really mountainous or costal, but its not
entirely flat Should be mostly TS, well exposed at an airfield
31. Bloemhof, 20 years TS, at a large dam, exposure OK, strong thunderstorms measured there –
not sure if its entirely correct but I accepted the values.
42. Johannesburg Int WO, 22 years TS, well exposed at an airport but historically the station was
not wellm exposed during the late 1980’s.
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Report: Wind Atlas Project –Work Package 5: Oct 2014 – Mar 2015
19. Kimberley, 19 years
Figure 3. The locations of met masts, marked with numbers.
Once the modeling is finished, the annual wind maxima from the WRF outputs will be calculated and
used for the estimation of the 50-year wind. The post-processing will generalize these mesoscale winds
to the standard conditions, which are the required format for further microscale modeling using WEng.
Completion of WP25.02 and impact on WP25.03
It is anticipated that the modeling results of WP25.02 will be completed by the end of November 2015.
The delay in the completion of WP25.02 due to computer problems will not affect the remainder of the
work for WP25, of which WP25.03 is due by June 2016.
Reporting
SAWS prepared and attended the 2nd WASA 2 PIU meeting, held at SANEDI on 18 May 2015. The results
of WP25.01, i.e. the extreme wind maps from the measured data, were presented.
Financial report for SAWS
The SAWS project account number for the WASA Phase 2 project is P372. An advance payment of R42
553.21 (DKK23272.35) was paid to SAWS in October 2014.
The total budgeted amount for SAWS for the April – Sep 2015 period is DKK 17397.00. The amount of the
invoice to be issued by SAWS will be DKK 17397 (R31810.20)– 25% = R 23 857.65. It is estimated that
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Report: Wind Atlas Project –Work Package 5: Oct 2014 – Mar 2015
about 50% of the time allocated for this period has been used from March to September 2015, i.e. 10
hours = DKK 8914.46.
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