Cooperation between ARPA-SIMC and MeteoSwiss about convection-permitting
ensemble development (including KENDA)
Version 1.0 from 22.10.2012
Version 1.1 from 18.01.2013
Convection-permitting ensemble development is planned both at MeteoSwiss and in Italy. There is a
common interest on the use of KENDA to provide IC perturbations to the ensemble and to produce a
deterministic analysis for the km-scale COSMO implementation. Furthermore, the domain of both systems
will include the Alpine area and the Po Valley basin; this will facilitate the cooperation since tests will
produce results relevant for both countries. In order to ease the exchange of results and the discussion, a
web page will be set up. The tasks related to the LETKF part will be coordinated with WG1/KENDA during
the next GM to further contribute to the system development.
The main collaboration points are described below.
1. Methods to generate LBC (Lateral Boundary Condition) perturbations. (task MCH? KENDA?)
It should be investigated which is the best method to provide LBC perturbations to the convectionpermitting ensembles. EPS members are an option, but their present spatial resolution (32km) is quite low
with respect to the resolution of the COSMO runs (about 3km). Hence, COSMO-LEPS members can be
considered to provide an intermediate step. Other factors should also be considered, namely the timeliness
of the data and the possibility of using frames.
@ ARPA-SIMC.
Test two different options to provide LBC to a 2.8 km run of COSMO:
-
LBC from 1 EPS member (32km hor. res)
-
LBC from the correspondent COSMO-LEPS member (7km hor.res)
Only one run will be performed, since the impact of the resolution does not need the run of the full
ensemble. The test will be performed on few cases selected to allow different inflow-outflow conditions.
@ MCH
A master thesis will start at MCH in September. Three approaches will be tested on case studies for
providing LBC: 1) from EPS, 2) from the deterministic IFS run plus EPS perturbations and 3) from the
deterministic IFS plus perturbations from an archive of past cases (this last approach would permit to have
more ensemble members that in the EPS).
Two periods will be investigated: A summer convection period (25.7.-25.8.2012) and a winter period (to be
defined).
First, selected case studies will be looked at using ensemble simulations started from identical initial
conditions, in particular the evolution of the perturbations with time inside the COSMO domain.
2. Idealised cases with KENDA and tools development (task 1.2 MCH – task 3.4 KENDA)
Before testing KENDA in a realistic situation, idealized cases will be generated, to understand how the
system works. From an idealized model run, synthetic observations are generated, which can be in turn
assimilated by KENDA.
This requires the development of some new tools for putting synthetic or model-derived observations in
the cdfin file. The development of this tools will be proposed as part of the KENDA tasks (to be discussed at
the GM).
@ MeteoSwiss
1) Horizontal homogenous case
In this very simple setup, the temperature profile of an idealized atmosphere will be changed
through artificially generated TEMP observations from a nature run. As nature run, a stably
stratified, horizontally homogenous atmosphere at rest will be chosen. The assimilation simulations
will start from a similar atmosphere with a slightly different temperature profile and will gradually
be adapted to that of the nature simulation.
2) Alpine mountain circulation
In this semi-idealized experiment, we will simulate the daily cycle of the mountain-plain flow on a
sunny day (“Alpine pumping”) using the real Alpine topography on the target COSMO domain.
During the day, a plain-mountain flow will be induced through differential heating of the mountain
and the plain areas, which generates a pressure gradient and subsequent plain-mountain winds.
During the night, a mountain-plain flow results from the opposite mechanism as during the day.
The nature run will be produced using the best possible model using state-of-the –art physics and
ar high resolution. Artificial observations of any kind can be extracted from this simulation using
tools for generating cdfin NetCDF observation files from feedobs files (to be developed). The
assimilation simulations will use a degraded model (either physical parameterisations, or resolution
or both). A means for perturbing the ensemble members will need to be chosen (radiation
parameterization?).
This setup will also be suited for the testing of the deterministic analysis at a higher resolution.
@ ARPA-SIMC
3) Temperature inversion in the Po Valley
The nature run is perfomed by running the model without DA, producing synthetic TEMP for
inversion. Then a second run is done by assimilating the synthetic TEMP with KENDA, with LW and
SW radiation switched off in the model.
3. Ensemble size (task MCH? – task KENDA?)
The impact of the ensemble size on the assimilation will be tested. This will be studied also in dependence
of the other settings (adaptive rho, adaptive R,…) and observation density and type.
4. IC for deterministic analysis (task MCH? – task 3.5 KENDA)
The use of KENDA to produce a very high resolution analysis for the deterministic COSMO implementation
will be tested. Some open issues to be evaluated are: difference between the ensemble mean and the
deterministic analysis run, spin-up effects, suitability of the analysis for a RUC system.
It will also be studied how to improve the analysis accuracy by applying methodologies which permit to
make better use of high-resolution data (e.g. radar), like “running in place” (Kalnay …).???
5. Further development of the diagnostic tools (task 1.6 MCH – task 2.6 KENDA)
After the GM it will be planned if some further work can be done, depending on what has been already
achieved.
n. Task
1
2
3
LBC perturbations
Idealised cases
Ensemble size
Start
End
ARPA-SIMC
10 2012
06 2013
MCH
10 2012
06 2013
ARPA-SIMC
09 2012
03 2013
MCH
11 2012
03 2014
ARPA-SIMC
01 2013
12 2013
ARPA-SIMC
09 2013
09.2014
MCH
01 2013
06 2013
ARPA-SIMC
09 2012
09 2014
MCH
09 2012
09 2014
MCH
4
5
IC for deterministic analysis
Diagnostic tools