1. Assimilation of radar data - research plan
Marián Jurašek
Slovak Hydrometeorological Institute

2. ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003
Introduction
in June 2003 prepared proposal of workplan for research of radar data assimilation for ALADIN
radar data - essential for mesoscale assimilation
available radar data:
reflectivity
instantaneous rainrate
cumulated rainfall
doppler wind , wind shear, turbulence
vertical wind profile
quantities from multiple polarisation measurements
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003

3. ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003
Which radar data?
each has advantages and disadvantages
not all available on all radar sites
reflectivity seems to be available on most European sites
not common form of data:
“PPI” images
volume data
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003

4. ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003
The philosophy
learning from satellites
remote sensing process is complex and nonlinear
we should assimilate quantity close to measured (reflectivity instead of rainrate)
derived quantities contain hardly correctable errors coming from mixture of real data, model field and empirical assumptions about the atmosphere
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003

5. ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003
The philosophy (2)
observation operator must simulate the reflectivity for each radar
development of system for radar data against model data monitoring
biases and big errors cannot be handled by 3D/4D-Var
software for detection and removal of corrupted data
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003

6. ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003
The philosophy (3)
study of space- and time structure of biases between simulated and observed data for bias correction
each radar processed independently
thinning of too dense data consistently with the resolution of the analyses
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003

7. ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003
The philosophy (4)
very accurate modelling of physical process of observation
precisely interpolating / averaging model variables along the radar beam path
physical part of observation operator should be prepared by radar specialists
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003

8. ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003
Which model?
reflectivity is sensitive to cloud properties
simulation depends on clouds representation in model (subgrid-scale diagnostic cloud in large-scale physics or detailed prognostic mesoscale microphysics)
problem: we must work on both ALADIN and AROME model
advantage: we will be prepared for ARPEGE (resp. IFS)
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003

9. ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003
Which model? (2)
observation operator need not to know how the fields are calculated  should be developed relatively independent from model physics
we need only interface with each model physics to get field for reflectivity simulation
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003

10. ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003
Things To Do
get samples of very good quality radar reflectivity data
get idea of fields needed to simulate reflectivity
literature study
study of existing radar simulation models (DWD/HIRLAM)
get simple (to start with) reflectivity simulation formulae
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003

11. ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003
Things To Do (2)
specify observation operator by:
list of necessary model fields for interpolation
list of necessary information about observation for screening and minimisation
obs. operator should access to the radar data by radar beam rather that by gridded pixels like for imagery - processing volume radar data
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003

12. ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003
Things To Do (3)
carefully specify the technical implementation of previous things
parallelization
minimise the disturbance for others developers
universal structure compatible with next similar obs. operator (= with slanted interpolation path)
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003

13. ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003
Things To Do (4)
implement radar data into the ODB processing
radar data only loaded to the model
check CPU and memory costs
implement direct interpolation of model fields
extracting grided fields from physics (or historical files)
interpolation/average to the radar beam path
beam feeling problem
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003

14. ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003
Things To Do (5)
convert model field to the reflectivity, compute and store difference with observation
storing differences in ODB
computation of the Jo in screening run
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003

15. ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003
Things To Do (6)
study monitoring statistics
design bias correction, screening, thinning and quality control
implementation to the screening part or to the preprocessing program
crucial for success of reflectivity assimilation
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003

16. ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003
Things To Do (7)
code tangent linear and adjoint of obs. Operator
functional 3DVar minimisation
check speed and quality
simulate one radar pixel
check correction of atmospheric field by 3DVar
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003

17. ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003
Things To Do (8)
study the impact of reflectivity assimilation to forecast
for ALADIN and AROME
for different situations (front, strong convection)
for different resolutions (10 km, 2.5 km)
check spin up
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003

18. ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003
Things To Do (9)
run several cycles of data assimilation to see the cumulative and beneficial effect
background should be closer to the radar
retune preprocessing and analysis parameters
improve obs. operator
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003

19. Thank You for your attention!
ALADIN/RC LACE Data assimilation miniworkshop Budapest, October 2003