Transcript The EXIM (Extrapolated Imagery) products Alexander Jann ZAMG, Vienna, Austria NWCSAF User Workshop, 24-26 February 2015, AEMET HQ, Madrid, Spain Goal of EXIM Provide  forecast satellite.

The EXIM (Extrapolated Imagery)
products
Alexander Jann
ZAMG, Vienna, Austria
NWCSAF User Workshop, 24-26 February 2015, AEMET HQ, Madrid, Spain
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Goal of EXIM
Provide
 forecast satellite images
 forecast NWCSAF products
• through kinematic extrapolation
• for lead times ≤ 1 hour
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Heritage (MFG IR, +2h)
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Forecast Cloud Type 12/12/2008, 11.00 + 15min
Forecast Cloud Type 12/12/2008, 11.00 + 30min
Forecast Cloud Type 12/12/2008, 11.00 + 45min
Forecast Cloud Type 12/12/2008, 11.00 + 60min
Outline of the algorithm
 Interpolate (irregularly distributed) HrW product down
to pixel level
 Apply the vector field on every pixel n times (n results
from user’s specifications plus the limitation of max. + 1
hour)
 Construct the predicted image / NWCSAF product by
putting pixels at their predicted positions
 Fill gaps through nearest-neighbour or average
interpolation
 Other post-processing, e.g. applying land-sea mask or
writing NODATA at the edge of the image
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Assumptions...
…that might be worth some discussion:
 We take every piece of HrW information that we can get,
i.e. we eventually mix HrW vectors from those channels
which the user selected in the HrW configuration file.
 We make predictions at multiples of slot intervals, i.e.
for MSG in nominal mode: +15, +30, +45 and +60. Thus,
we “have” images / products earlier than without EXIM,
yet we don’t produce imagery for times where we have
no actual satellite images.
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Input fields we already tried
 SEVIRI: WV6.2, WV7.3, IR8.7, IR9.7, IR10.8,
IR12.0, IR13.4 (yes, VIS0.6-IR3.9 work technically just as well but there are
doubts whether we should enable their forecasting in the first version)
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Cma
CT
CTTH_HEIGHT, CTTH_PRE
PC_PR1 and PCPh_PC
CRR and CRPh_CRR
SPhR_BL, ML, HL, KI, LI, SHW, TPW
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Output files we envisage
 One file per channel / product per forecast date
 Mimicking output format for analysis output as perfect
as possible. Ideally, EXIM products can be
distinguished from their analysis counterparts only
through the filename and the directory where they are
dumped
 “DATABUF” for satellite imagery, netCDF for products
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Output files we envisage (2)
 Relevant quality flags shall be extrapolated as well and
be included in the forecast netCDF
 The EXIM-specific quality flag (“actually extrapolated”
vs. “achieved through post-processing / gap-filling”,
applicable to both SEVIRI and product forecasts, hence
one per forecast date) is dumped as DATABUF
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Validation
The SAFNWC PRT defines EXIM’s threshold accuracy as:
on average better than persistence forecast
Target accuracy is:
always better than persistence forecast
Hence, the validation approach is quite obvious:
Compare the EXIM forecast with what was actually
observed 15, 30,… minutes later and verify that the
displacement actually did anything positive on the skill
score (we use Peirce’s [abbr. PSS] and, for the CT product,
its multicategorical variant, “R” “verification”
”multi.cont”)
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Validation
The following slides show PSS time series
 Extracted every 2 hours
 Over ~3.5 months (Sep 14 – Jan 15)
 from ZAMG’s operational NWCSAF v2013+ suite,
meaning in particular
 the HrW default model configuration file was used
 3-hourly NWP data, ECMWF, 1 degree resolution
 European area
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Geographical coverage
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SEVIRI
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NWCSAF PRODUCTS
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Conclusions - SEVIRI
Release of EXIM certainly OK for
 IR
 WV
Perhaps it would be OK even for the entire
spectrum, but the lack of modelling the solar
radiation impact for 0.6 – 3.9 means: Risk!
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Conclusions – NWCSAF products
Release of EXIM certainly OK for
 CMa
 CT
 CTTH
 CRR
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Conclusions – NWCSAF products
Big question-mark on PC with its pronounced
dependence on illumination conditions (recommended
to users only during high-summer season?).
For PCPh and CRPh, stringent validation difficult
(uncertainties about areas where one can have 100%
confidence). Statistics nevertheless indicate that there
is value in the extrapolation (and things should
improve with the 24h products announced by AeMet).
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Conclusions – SPhR (future TqPh)
SPhR and extrapolation with the atmospheric flow do
not seem to go well together:
 For the stability indices sub-group, this could have
been expected.
 For the moisture parameter subgroup, we have
evidence that - to a large degree - the task is to
predict the outcome of temporal NWP interpolation,
at least for NWP intervals ≥ 3 hours
→ Leave it in the portfolio for those who wish to
experiment with 1-hr NWP (actually recommended by
SPhR developers)??
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Future developments
Until v1.0:
 Consolidate the software (in particular working on the new
netCDF output format)
 Incorporating User WS outcome that can be accommodated
fairly quickly
 Continue validation
Afterwards:
 Incorporating User WS outcome that is rather challenging to be
implemented
 Take new NWCSAF/GEO products on board (we are always “day2”)
 MTG
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