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Nowcasting Rainfall

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Nowcasting Rainfall Powered By Docstoc
					Short Term Ensemble Prediction System:
STEPS




Alan Seed
Centre for Australian Weather and
Climate Research




               The Centre for Australian Weather and Climate Research
               A partnership between CSIRO and the Bureau of Meteorology
Outline

• Statistical structure of rainfall
• Modelling the errors in a nowcast
   • Temporal development
   • Radar reflectivity to rain rate conversion
   • Tracking
• Nowcast ensembles
   • Radar only nowcasts
   • Radar + NWP blending
• Products
   •   Ensembles for end users
   •   Expected rainfall – ensemble mean
   •   Probability of exceeding various thresholds
   •   Meteograms
• Products
• Developments
• Conclusions
                                                     The Centre for Australian Weather and Climate Research
                                                     A partnership between CSIRO and the Bureau of Meteorology
15-min rainfall over the UK 1000 km (15 min)




                             The Centre for Australian Weather and Climate Research
                             A partnership between CSIRO and the Bureau of Meteorology
Adelaide Radar – 250 km (10 min)




                            The Centre for Australian Weather and Climate Research
                            A partnership between CSIRO and the Bureau of Meteorology
Auckland 10 km (2 min)




          15 km x 7.5 km box, 100 m resolution
                                The Centre for Australian Weather and Climate Research
                                 A partnership between CSIRO and the Bureau of Meteorology
     Variability as a function of scale

                                        2d power spectrum

                           80
                           70
                           60
            10log(power)




                           50
                                                                                          mit vil
Modelling




                           40
                                                                                          HRRR
                           30
                           20
                           10
                            0
                                -30   -20                 -10             0
                                            10log(1/km)



             1000 km domain, eastern half of the HRRR region



                                                                The Centre for Australian Weather and Climate Research
                                                                A partnership between CSIRO and the Bureau of Meteorology
Nowcast skill as a function of scale and lead time


                                       Skill vs Lead Time

                     1
                    0.9
                    0.8
                    0.7                                                                                     500 km
                                                                                                            250 km
      Correlation




                    0.6
                                                                                                            100 km
                    0.5
                                                                                                             50 km
                    0.4
                                                                                                            20 km
                    0.3                                                                                     10 km
                    0.2
                    0.1
                     0
                          0   1   2      3        4             5              6              7
                                      Lead Time (hours)


     Widespread rain in
     Sydney                                           The Centre for Australian Weather and Climate Research
                                                          A partnership between CSIRO and the Bureau of Meteorology
Outline

• Statistical structure of rainfall
• Modelling the errors in a nowcast
   • Temporal development
   • Radar reflectivity to rain rate conversion
   • Tracking
• Nowcast ensembles
   • Radar only nowcasts
   • Radar + NWP blending
• Products
   •   Ensembles for end users
   •   Expected rainfall – ensemble mean
   •   Probability of exceeding various thresholds
   •   Meteograms
• Developments
• Conclusions

                                                  The Centre for Australian Weather and Climate Research
                                                  A partnership between CSIRO and the Bureau of Meteorology
                                   Conceptual model for rainfall

                                   • Rainfall usually has areas of higher intensity rainfall inside areas of
Temporal development of rainfall




                                     lower intensity rainfall, and we get clusters of storms and not just a
                                     random pattern of storms- variability over a wide range of scales

                                   • The lifetime of a storm increases with the size of the storm as a power
                                     law

                                   • The simplest model is a multiplicative cascade model (used to model
                                     turbulence) for the spatial scaling and a hierarchy of AR(1) models for
                                     the Lagrangian temporal evolution so as to reproduce the dynamic
                                     scaling of the field




                                                                                The Centre for Australian Weather and Climate Research
                                                                                A partnership between CSIRO and the Bureau of Meteorology
                                   Multiplicative Cascade Model for Turbulence
Temporal development of rainfall




                                                                                 Each cascade level
                                                                                 evolves in time
                                                                                 Rate of development
                                                                                 decreases with
                                                                                 increasing scale
                                                                                 Hierarchy of AR(1)
                                                                                 models used for
                                                                                 temporal development




                                                                                Lovejoy et al., 1987
                                                                                J. Geophys. Res.

                                                                The Centre for Australian Weather and Climate Research
                                                                A partnership between CSIRO and the Bureau of Meteorology
                                   Spectral decomposition of a rainfall field
Temporal development of rainfall




                                                         128-256-512 km     64-128-256 km                            32-64-128 km




                                           16-32-64 km     8-16-32 km        4-8-16 km                               2-4-8 km




                                                                          The Centre for Australian Weather and Climate Research
                                                                          A partnership between CSIRO and the Bureau of Meteorology
                 Radar Z-R error is coherent over scales that
                 are significant for urban hydrology
Radar measurement error
       Z - R Error




                          Radar           Gauge
                                               The Centre for Australian Weather and Climate Research
                                               A partnership between CSIRO and the Bureau of Meteorology
              Space & Time correlations of radar z-r error
              Villarini et al, WRR 45, W01404 2009
Z - R Error




                                                 The Centre for Australian Weather and Climate Research
                                                  A partnership between CSIRO and the Bureau of Meteorology
                 Errors due to observing above ground level

                                                               Correlation below WBFL

                                     0.90
                                     0.80
Sampling Error




                                     0.70
                                     0.60                                                                                            Bris rain
                       Correlation




                                     0.50                                                                                            Melb rain
                                     0.40                                                                                            Kur rain

                                     0.30                                                                                            Model

                                     0.20
                                     0.10
                                     0.00
                                         0.00   0.50   1.00   1.50      2.00       2.50       3.00        3.50        4.00
                                                                     Height (km)




                      Correlation as a function of height separation for pairs of radar
                      observations where one observation is at the base scan and the
                      other is below the wet bulb freezing level.


                                                                                          The Centre for Australian Weather and Climate Research
                                                                                          A partnership between CSIRO and the Bureau of Meteorology
                 Model of radar ZR and sampling errors
                 Observed and ensembles for 10-min rainfall
Radar measurement error
  Modelling QPE Error




                          Ensemble 1          Ensemble 2

                                                 Radar observation error model
                                                 includes Z-R and sampling
                                                 errors due to observing at a
                                                 height above the ground




                          Observation             The Centre for Australian Weather and Climate Research
                                                   A partnership between CSIRO and the Bureau of Meteorology
                      Verification of radar error model

                                                                30


                                                                20


                                                                10




                                                        power
                                                                                                                                        Model
                                                                 0
Modelling QPE Error




                                                                                                                                        Radar

                                                                -10


                                                                -20


                                                                -30
                                                                      -35     -30    -25     -20     -15      -10    -5      0
                                                                                           10log(frequency)




                         Reliability of probabilities   Power specta of observed
                                                        and perturbed fields




                                                                            The Centre for Australian Weather and Climate Research
                                                                            A partnership between CSIRO and the Bureau of Meteorology
                 Other radar observation errors are tricky, depending
                 on the situation and the QC algorithms used

       Daily rainfall accumulation for Melbourne
Radar measurement error



                                                   Beam blocking
Modelling QPE Error




                                                    Clutter




                                                        The Centre for Australian Weather and Climate Research
                                                         A partnership between CSIRO and the Bureau of Meteorology
                           Modelling the tracking error

                           • We do not have a complete description of tracking error
                           • Generating fields of U,V error components that are correlated with each
Modelling Tracking Error




                             other and in space and time is VERY tricky- at least I do not know how
                             to do it
                           • Not the most important source of error in the first 6 hours so we can
                             keep it simple
                           • Multiply the radar U,V components by a random number that has a
                             mean of 1 and some (small) variance




                                                                     The Centre for Australian Weather and Climate Research
                                                                     A partnership between CSIRO and the Bureau of Meteorology
Outline

• Statistical structure of rainfall
• Modelling the errors in a nowcast
   • Temporal development
   • Radar reflectivity to rain rate conversion
   • Tracking
• Nowcast ensembles
   • Radar only nowcasts
   • Radar + NWP blending
• Products
   •   Ensembles for end users
   •   Expected rainfall – ensemble mean
   •   Probability of exceeding various thresholds
   •   Meteograms
• Developments
• Conclusions

                                                  The Centre for Australian Weather and Climate Research
                                                  A partnership between CSIRO and the Bureau of Meteorology
         Short Term Ensemble Prediction System-
         radar only

                1. Estimate the advection field using rainfall fields
                2. Estimate the AR(1) and cascade parameters using the
                   current observed field
                3. For each ensemble member
STEPS-nowcast




                   a) Perturb the radar analysis with the observation error
   Modelling




                      model
                   b) Perturb the advection field
                   c) Generate a conditional stochastic field for the next 90
                      minutes




                                                           The Centre for Australian Weather and Climate Research
                                                           A partnership between CSIRO and the Bureau of Meteorology
         Beijing Olympics: 1 hr forecast & observation
STEPS-nowcast




                                        The Centre for Australian Weather and Climate Research
                                        A partnership between CSIRO and the Bureau of Meteorology
                Beijing 2008 inter-comparison



                • Compared STEPS against 5 other international systems during the
                  Beijing Games
STEPS-nowcast




                                                        The Centre for Australian Weather and Climate Research
                                                        A partnership between CSIRO and the Bureau of Meteorology
            Short Term Ensemble Prediction System-
            NWP blend

            • Decompose NWP into a cascade
            • Decompose the rainfall field into a cascade
            • Use radar field to estimate stochastic model parameters
            • Calculate the skill of the NWP at each level in the
STEPS-NWP




              cascade using the correlation between NWP and radar
            • Blend each level in the radar & NWP cascades using
              weights that are a function of the forecast error at that
              scale and lead time
            • For each forecast
                • Add noise component to the deterministic blend, the
                  weight of the noise is calculated using the skill of the
                  blended forecast
                • Combine the cascade levels to form a forecast




                                                             The Centre for Australian Weather and Climate Research
                                                             A partnership between CSIRO and the Bureau of Meteorology
            Blending with NWP – calculating the weights

                y  Y  ( X   x ) T b
                ˆ
                ˆ
                y is the blended forecast
                X is the vector of forecaststo be blended, and
                b is the vector of weights
STEPS-NWP




                b   1  XY
                      XX

                 XX is the cavarianceof the forecasts
                 XY is the covarianceof forecastswith the truth


                remaining noise has variance
                var(Z )   YY - 2bT  XY  b T  XX b
                            2



                                                     The Centre for Australian Weather and Climate Research
                                                         A partnership between CSIRO and the Bureau of Meteorology
            Nowcast explained variance as a function of scale
            and lead time


                                                        Extrapolation forecast

                                   1.00
              Explained variance




                                   0.80
STEPS-NWP




                                   0.60

                                   0.40

                                   0.20

                                   0.00
                                          0   10   20   30   40    50    60   70    80     90       100      110       120
                                                                  Lead time (min)

                                                         736 Extrapolation    275 Extrapolation
                                                         100 Extrapolation    40 Extrapolation



                                                                                    The Centre for Australian Weather and Climate Research
                                                                                    A partnership between CSIRO and the Bureau of Meteorology
            NWP explained variance as a function of scale


                                                          NWP forecast

                                   1.00
                                   0.90
                                   0.80
STEPS-NWP

              Explained variance




                                   0.70
                                   0.60
                                   0.50
                                   0.40
                                   0.30
                                   0.20
                                   0.10
                                   0.00
                                          0   100   200    300      400       500          600           700           800
                                                                 Scale (km)




                                                                                    The Centre for Australian Weather and Climate Research
                                                                                    A partnership between CSIRO and the Bureau of Meteorology
        Weights for nowcast & NWP


                                             125 km scale
                                             500

                        1.20
    Blending




                        1.00
STEPS-NWP




                        0.80                                                                 Extrapolation
               Weight




                        0.60                                                                 NWP
                        0.40                                                                 Noise
                        0.20
                        0.00
                               0   100        200        300           400
                                         Lag (minutes)




                                                           The Centre for Australian Weather and Climate Research
                                                           A partnership between CSIRO and the Bureau of Meteorology
Outline

• Statistical structure of rainfall
• Modelling the errors in a nowcast
   • Radar reflectivity to rain rate conversion
   • Tracking
   • Temporal development
• Nowcast ensembles
   • Radar only nowcasts
   • Radar + NWP blending
• Products
   •   Ensembles for end users
   •   Expected rainfall – ensemble mean
   •   Probability of exceeding various thresholds
   •   Meteograms
• Developments
• Conclusions

                                                  The Centre for Australian Weather and Climate Research
                                                  A partnership between CSIRO and the Bureau of Meteorology
           Status

            • QPE and STEPS-nowcast running on LINUX workstations in
              operational mode
            • STEPS-NWP (radar + NWP blend) running on a super computer
            • 16 radars with QPE, 15 QPF domains
            • Generating 1000 products (100 Mbytes) per hour
Products




            • Up to 100 clients inside the Bureau being served with products on a
              busy day
            • QPE live to the public for capital city radars
            • Planning to go live to the public with QPF in May 2011




                                                   The Centre for Australian Weather and Climate Research
                                                    A partnership between CSIRO and the Bureau of Meteorology
           Rainfall Estimates




           • Melbourne, Sydney, Brisbane, Adelaide
           • 30, 60, 120 min, since 9 AM, daily accumulations blended
Products




             with rain gauges and updated every 30 min
           • 10 min accumulations radar only with real-time gauge
             adjustments and updated every 6 or 10 minutes



                                                   The Centre for Australian Weather and Climate Research
                                                    A partnership between CSIRO and the Bureau of Meteorology
           Rainfall Forecasts: 0 – 90 minutes




           60 min accumulation    Probability of rain > 50 mm Forecast time series at a point
                                                              with uncertainty shown
Products




             •   4 major cities, 1 km & 6 min resolution, 250 km domain
             •   3 Regional forecasts, 2 km & 10 min resolution, 500 km domain
             •   30 member ensemble updated every 6,10 minutes
             •   30, 60, 90 min accumulations of ensemble mean (expected rain)
             •   Probability that rain accumulation will exceed 1,2,5,10,20,50 mm in
                 next 60 minutes
                                                         The Centre for Australian Weather and Climate Research
                                                          A partnership between CSIRO and the Bureau of Meteorology
           Rainfall forecasts: 1 – 6 hours




    Probability of rain > 1 mm for 2 & 3 hour lead     Rainfall intensity forecast,
    times, Melbourne                                   150 min lead time, Brisbane
           • Melbourne, Sydney, Brisbane – 500 km domain, 2 km & 10 min
Products




             resolution
           • 30 member ensemble updated every hour
           • 10-min forecasts of rainfall intensity out to 6 hours
           • Probability products for hourly accumulations for next 6 hours

                                                     The Centre for Australian Weather and Climate Research
                                                     A partnership between CSIRO and the Bureau of Meteorology
Example from east Victoria – NWP




                                   The Centre for Australian Weather and Climate Research
                                   A partnership between CSIRO and the Bureau of Meteorology
 Example from east Victoria- STEPS




Ensemble member 1
                                 The Centre for Australian Weather and Climate Research
                                 A partnership between CSIRO and the Bureau of Meteorology
Met Service Canada: Point Mode




  Paul Joe, 2010
                           The Centre for Australian Weather and Climate Research
                           A partnership between CSIRO and the Bureau of Meteorology
Met Service Canada: Point-Time Mode




                                                                          Paul Joe, 2010
  PDF of rainrates at a point for all time lagged nowcasts
                                              The Centre for Australian Weather and Climate Research
                                              A partnership between CSIRO and the Bureau of Meteorology
 Met Service Canada: POP for a validtime and
 rainrate threshold




Paul Joe, 2010




                                                     exceeding threshold
      Rainrate threshold is 1 mm/h; number of hits Centre for Australian Weather and Climate/Research
                                                The
      number of samples (60)                     A partnership between CSIRO and the Bureau of Meteorology
 Probability




Probability of 60 min accum > 5 mm
                                     The Centre for Australian Weather and Climate Research
                                     A partnership between CSIRO and the Bureau of Meteorology
Outline

• Statistical structure of rainfall
• Modelling the errors in a nowcast
   • Radar reflectivity to rain rate conversion
   • Tracking
   • Temporal development
• Nowcast ensembles
   • Radar only nowcasts
   • Radar + NWP blending
• Products
   •   Ensembles for end users
   •   Expected rainfall – ensemble mean
   •   Probability of exceeding various thresholds
   •   Meteograms
• Developments
• Conclusions

                                                  The Centre for Australian Weather and Climate Research
                                                  A partnership between CSIRO and the Bureau of Meteorology
               Qualitative severe weather warning



               • THESPA
                 • Calculates the probability of a TITAN cell passing over a point in the next
                   60 minutes based on the current velocity and cell size and a climatological
                   TITAN tracking error
                 • Being developed for aviation applications and use in TIFS
Developments




               • TIFS
                 •   Operational in most Regional Forecast Centres                                    25 km

                 •   Automatic version for aviation is operational
                 •   Revising the software architecture
                 •   Graphical and automated text editing feature development




                                                             The Centre for Australian Weather and Climate Research
                                                             A partnership between CSIRO and the Bureau of Meteorology
Development: Closing the gap between NWP &
nowcasts

• Strategic Radar Enhancement Project
   • $48 M project over 7 years, 8 people for three years in CAWCR
   • 4 new radars
   • Radar data assimilation in ACCESS
      • Roll out of a new radar data quality control system for ~50 radars
      • Characterise radar errors for use in data assimilation (and QPE)
      • Assimilate radar data (LH nudging, Doppler radial winds, reflectivity) into high res
        (~2 km) NWP meso-scale models over capital cities


• Seamless rainfall prediction
   • Integrate rainfall forecasts from 0 – 10 days lead time into a seamless
     forecast
   • Use STEPS to blend the forecasts from the various models
   • Develop a portal for convenient access to the rainfall forecasts


                                                    The Centre for Australian Weather and Climate Research
                                                     A partnership between CSIRO and the Bureau of Meteorology
                                              Seamless rainfall forecasts



                                               • Rainfall portal                     ACCESS-G
Cross-cutting programs: ESM, CWD, OEB, NMOC




                                                                                     AGREPS-G
                                                                         3-10 day    ECMWF EPS                               2 x daily
                                                                                                             40-100
                                                 • Data source           forecasts   PME/GOCF                km
                                                   transparent to user               GFE
                                                                                     TIGGE?
                                                 • Aggregation                       ACCESS-A
                                                                                     ACCESS-C                                                        Down-
                                                                          1-2 day                                            2-4 x
                                                 • Disaggregation        forecasts
                                                                                     AGREPS-R
                                                                                     ECMWF EPS
                                                                                                             5-25
                                                                                                             km              daily
                                                                                                                                                     scaled
                                                                                                                                                     and
                                                                                     PME/GOCF                                                        blended
                                               • New science                         GFE                                                             using
                                                                                                                                                     STEPS
                                                 • STEPS                 1-24 hour   ACCESS-A
                                                                                                             2-10            4-8 x
                                                                         forecasts   ACCESS-C
                                                   downscaling                                               km              daily
                                                                                     GFE

                                                 • Blending strategy
                                                                          1-6 hour   ACCESS-C                                hourly
                                                                                                             1-2
                                                 • Verification (esp.    forecasts   STEPS-NWP
                                                                                                             km
                                                   transition periods)
                                                                         10-90 min
                                                                                     STEPS-nowcast           1 km            every 10
                                                                         nowcasts                                            min


                                                                                        The Centre for Australian Weather and Climate Research
                                                                                         A partnership between CSIRO and the Bureau of Meteorology
               Issues



               • Limited capacity in the Regional Forecast Centres Head Office support
                 branches to deploy and learn new nowcasting systems, busy with the
                 Next Generation Forecast and Warning System – slows the adoption of
                 new algorithms
Developments




               • Focus has been on improving the service adoption of existing
                 nowcasting science through
                  • Delivering the products through a range of platforms – 3drapic, Google
                    maps, web pages
                  • Using formats that are carefully designed and that conform to formal geo-
                    spatial standards (eg CF compliant netCDF)
                  • Serving the data on a range of platforms (ftp, SOAP, directories)
                  • Formalising the use of QPE&F products in the forecast process
                  • Training


                                                             The Centre for Australian Weather and Climate Research
                                                              A partnership between CSIRO and the Bureau of Meteorology
Conclusions

• Nowcasting rainfall is an uncertain business
• Have incomplete description of the error structure of QPE and QPF
• Have enough of a description to make useful stochastic ensemble
  models
• There is still a lot of work to do to make the stochastic models include
  more meteorological knowledge
• There is even more work to do to help the end-users make full use of
  the ensemble members in their decision support systems




                                            The Centre for Australian Weather and Climate Research
                                            A partnership between CSIRO and the Bureau of Meteorology

				
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