improving real time observation and nowcasting rdt - saws rsmc
TRANSCRIPT
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E de Coning, M Gijben, B Maseko and L van Hemert
Nowcasting and Very Short Range Forecasting
Improving real time
observation and nowcasting –
RDT
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Introduction
• Satellite Application
Facilities (SAFs) are
centres for processing
satellite data
• The Nowcasting SAF
started in February
1997 aiming to produce
the software to deal
with the Nowcasting
and Very Short Range
Forecasting using the
characteristics of the
MSG SEVIRI data and
the NOAA and EPS
AVHRR data
(EUMETSAT
Satellites).
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Nowcasting SAF products website
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Cloud Mask
Cloud type
Cloud top temperature and
height
Precipitation Clouds
Convective Rainfall Rate
Precipitation with microphysics
TPW
Layer PW
RDT
Stability indices
High Resolution wind
Satellite Image interpretation
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Nowcasting SAF products in SA
• These products are operationally available in Europe,
but have not been operationally implemented and/or
extensively tested over regions in Africa.
• WRC Funded project in SA: Using MSG and the
local version of the UK Met Off Unified Model data as
NWP input to the algorithms
• Project started in 2013 and will end in 2015
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Aim of the WRC project
• To provide forecasters, aviation meteorologists
and hydrologists information about the
development, life cycle and dissipation of convection
in regions where radar systems do not provide
coverage (in between radars over South Africa) or no
radars systems are available (most of South Africa’s
neighbouring countries).
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Rapidly Developing Thunderstorms - background
• The Rapid Developing Thunderstorm (RDT) combines
a cloud tracker and an algorithm to discriminate
convective and non-convective cloud objects.
• The cloud objects defined by the RDT are cloud towers
with a significant vertical extension (namely at least
6°C colder than the warmest pixels in its
surroundings)
• The major benefit of an automatic tool like the RDT is
the object and tracking approach.
Improved identification of convective cloud by the RDT product
Y. Guillou, F. Autones, S. Sénési 6
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• The objectives of RDT are twofold:
• The identification, monitoring and tracking of
intense convective system clouds
• The detection of rapidly developing convective
cells
• There are 3 stages in the process:
• Detection
• Tracking
• Discrimination
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RDT= Detection + Tracking
Phase 1: detection
– towers identification, based upon 10.8 m channel
– Adaptative threshold (reflectivity!)
– Tracking is done using consecutive images
Slide courtesy: Jean-Marc Moisselin
Météo-France, Toulouse
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Phase 2: The discrimination method makes use of discrimination
parameters calculated from MSG channels: IR 10.8, IR8.7, IR
12.0, WV 6.2 and WV 7.3 with NWP
• Two kinds of such discrimination parameters are considered:
• spatial characteristics
• temporal characteristics
• Discrimination is done using cloud top cooling rate and
expansion rate
• The discrimination scheme is a mix between empirical rules and
statistical models tuned on a learning database
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• Phase of development is determined by:
• History (last few time steps)
• Temperature trend (cooling/warming)
• Vertical extent
• Expansion
• Convective or Non-Convective storm activity
• Mature: top temperature < -40°C for at least 45min
• Mature transition: crossing top temperature –40°C
• Cold transition: crossing top temperature –35°C or base of cloud tower –
25°C
• Warm2 transition: crossing top temperature –25°C or base of cloud tower
–15°C
• Warm1 transition: crossing top temperature –15°C or base of cloud tower
–5°C
• Warm : top temperature > -15° and base of cloud tower > –5°C,
preceding Warm1 crossing
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Discrimination of convective systems
The picture above displays all RDT
detected cells. This picture points out
the detection and tracking efficiency of
RDT.
The next image displays convective
objects only. The ratio between no
convective and convective objects is
about 100.
Convective mask (from NWP)
identifies stable, neutral/unclear
and unstable areas to remove
stable regions from being
processed, thus reducing
processing time and reducing
false alarms.
Slide courtesy: Jean-Marc Moisselin
Météo-France, Toulouse
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RDT uses….
• Mainly (and non-optional) satellite channel is IR10.8 μm (used
for detection, tracking and discrimination).
• Additionally WV6.2, WV7.3, IR8.7 and IR12.0 μm channels can
be used for convective discrimination.
• Other SAF-NWC products allow to establish a cloud mask (to
operate RDT detection only on cloudy areas) and to describe
RDT attributes (pressure and temperature at the cloud top,
cloud type, Convective Rain Rate)
• NWP data can be used as instability masks, improving the
detection of warm systems by RDT.
• Lightning data, if available in real time, greatly contribute to the
discrimination of convective systems.
RAPID DEVELOPMENT THUNDERSTORM (RDT)
J.-M. Moisselin1, P. Brovelli1, F. Autonès1
Météo-France, Nowcasting Department
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RDT–PGE 11
Detection
+
Discrimination
Cloud Products
SAF/NWC NWP indicesFoudre
Brightness
temperature
BUFR/HDF5
Rapidly Developing Thunderstorms Product v2012
Slide courtesy: Jean-Marc Moisselin
Météo-France, Toulouse
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RDT: Examples from case studies comparing to radar data
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Case 1: 09 November 2012
1130 UTC 1130 UTC
Slide courtesy Bathobile Maseko
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Case 2: 17 October 2012
1615 UTC1615 UTC
Slide courtesy Bathobile Maseko
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RDT: Examples from case studies comparing to TRMM
rainfall data
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Case 3: 28 December 2013
120012001200
ZIMBABWE
Slide courtesy Bathobile Maseko
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Case 3: 28 December 201312001200 1200
Slide courtesy Bathobile Maseko
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RDT: Recent (v2013) examples
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Case 1: 10 October 2014
Slide courtesy Bathobile Maseko
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Case 2: 11 October 2014
Slide courtesy Bathobile Maseko
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Case 3: 5 June 2014
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Case 3: Compared to radar at
1630 UTC
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Case 4: 20 September 2014 –Afternoon thunderstorms and hail in JhB
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Case 5: 10 August 2014
from 1200 to 1445 UTC
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Case 6: 28 Sep 2014
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Radar 1045 UTC
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Case 7: 6 Oct 2014
0600-1100 UTC - Namibia
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Case 8: Yesterday
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Hail/tornado?
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Validation of RDT by the developers (in France)
• “RDT provides an accurate depiction of convective
phenomena, from triggering phase to mature
stage.
• The RDT object allows pointing out some areas of
interest of a satellite image.
• It provides relevant information on triggering and
development clouds and on mature systems.
• The subjective evaluation confirmed the
usefulness of the RDT with moderate lightning
activity.
• Thanks to these good results the status of RDT
has been set up to “operational” by EUMETSAT in
2012.”
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Validation of RDT by Hungarian Weather Service (v2009)
• It detects the majority of the mature phase convective
clouds.
• The small and/or warm cells are often missed
• Better performance in „pure’ convective situation than
in frontal situation. Sometimes a huge part of a front
is detected as convective.
• We have verified RDT without the optional lightning
input. If we used lightning as input, we would get
better results.
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Validation of RDT in SA
• 24 Lightning detection sensors over SA domain which measures
CLOUD-GROUND
Advantages:
• Complete coverage of SA
• 90% or more of Cloud-to-ground (CG) lightning strokes can be
detected.
Disadvantages:
• Only CG lightning detected – Intra-cloud lightning (IC) not detected.
This can negatively impact on the evaluations since some lightning is
not observed.
• Lightning occurs in all thunderstorms, not just rapidly developing
thunderstorms. This can negatively impact the statistics unless one
distinguishes between the intensities of the strokes.
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Slide courtesy Morne Gijben
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Validation methodology
• Used Mature and growing phase storms
(Most CG lightning)
• Considered lightning intensities (similar to
developers of RDT)
• Lightning intensities defined as:
• Low: >3 strokes (1 flash x 3)
• Moderate: >15 strokes (5 flashes x 3)
• Severe: >60 strokes (15 flashes x 3)
Slide courtesy Morne Gijben
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Results for 10 cases over SA
Slide courtesy Morne Gijben
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Slide courtesy Morne Gijben
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Slide courtesy Morne Gijben
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0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
TIME (UTC)
Hanssen-Kuipers Discriminant - Average of 10 Cases
3 Strokes 15 Strokes 60 Strokes
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Validation results
• Statistics show:
• Fair amount of lightning occurs inside the RDT
polygons.
• POD, POFD and HKD are good
• FAR are too high – due to grid-box-based validation
methods. Object orientated methodology is better to
use. This is future work.
• Visual and statistical evaluations show that RDT
polygons correctly identify the storms which
produce lightning.
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Slide courtesy Morne Gijben
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Validation – future plans
• We are looking into improving our evaluation
methodology by using an object-orientated
evaluation technique on both the RDT polygons
and lightning.
• Include lightning data as input into RDT
• Test the 2013 version of NowSAF software
(operational)
• The NOWSAF products are also updated regularly,
so we can look forward to even better products in
the future.
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Slide courtesy Morne Gijben
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Back to 16 October 2014…
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WIND
ARROWS
INDICATE
DIRECION AND
SPEED OF
MOVEMENT –
NOWCASTING!
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Tornado time +- 0900 to 1000 UTC
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Conclusion
• For the initial work, the v2012 of the software was used, the
latest version of the software (v2013) is now operational in SA.
Improvements in the software algorithms will possibly have even
better validation results
• RDT showed very promising results to be used in addition to
other observations such as radar and lightning detection in SA,
where these are available
• In regions without radar systems and/or lightning detection
networks, these satellite and NWP products will certainly benefit
nowcasting procedures.
• RDT - Images for SADC and SA regions on RSMC for past 2
hours
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RDT Summary and Future work
• The RDT can provide useful information on the
development and phase of the intense parts of
thunderstorms over data sparse regions such as
Africa.
• If we upgrade to UM on 4 or 1.5 km we will also see
improvement to RDT (Sfc Press/925 hPa included)
• Nowcasting applications in South Africa – to
complement the radar data (where available)
• Nowcasting applications in southern Africa – where
very few radar systems are operationally available
• Validation against lightning data over SA domain
showed promising results. Methodology will be
improved with time.
• Nowcasting on direction/speed of identified storms! 45