HIRLAM 1D model tool B.H. Sass December 2005

Overview 1) Introduction 1) Introduction 2) History of 1D-model(s) 2) History of 1D-model(s) 3) Basics of the HIRLAM 1D-model tool 3) Basics of the HIRLAM 1D-model tool 4) Which cases have been studied ? 4) Which cases have been studied ? 5) Comment regarding future strategy for 5) Comment regarding future strategy for using a common 1D-tool using a common 1D-tool

Why use a 1D-model ? Advantages: 1) Allows for a simplified investigation of the role of physics in a complex 3D model 2) Adequate for understanding the individual physical processes. 3) Ideal for a systematic development of physical parameterizations from well defined experiments using specified forcing, observations or possibly associated analytical solutions.

Why use a 1D-model (2) Disadvantages:1) There is a not a complete mutual interaction between the physics and the dynamics in a 1D-model 2) -Requires in practice some maintenance and development to be sufficiently optimal in a project of collaboration. - In order to ensure that experiments with different schemes can be compared with confidence it is important that input and output preparation is the same for researchers studying the same case !

HIRLAM-1D history  There is a long tradition in the meteorological communi- ties of using 1D-models for testing model physics. Most HIRLAM people working on physics have used a 1D- model to some extent during their work.  Use of a 1D-model for physics goes long back, almost to the start of HIRLAM history. A 1D-model is used more and more in recent years: Example: At KNMI a workshop was arranged in 1998 with the purpose of testing competing turbulence schemes in specific tests for the planetary layer (cloud free PBL, stratocumulus PBL and shallow cumulus PBL )

Basic principles of HIRLAM 1D model (1)  Resemble the full model as far as possible apart the inherent limitations of the 1D model.  The same physics code will be used apart from special routines extracting diagnostic information or providing specified forcing in physics (e.g.surface fluxes)  The code contains a ”1D-dynamics” containing pressure gradient and coriolis term and advective terms. The latter are prescribed. These terms are needed in order to simulate realistic atmospheric cases. Frictional forces are included and come from the turbulence scheme and the surface friction.

Basic principles of HIRLAM 1D-model (2) Why is 1D-dynamics needed for physics tests and why is it desirable to describe dynamical advective forcing :  One reason is the need to study wind profiles in the PBL. With the inclusion of coriolis pressure gradient and frictional effects it is possible to establish Ekman profiles in the PBL and to carry out diagnostic studies on the effect of changes in the turbulence scheme, e.g. the effect of mixing length formulation.

Why is 1D-dynamics and forcing needed ?  The BOMEX case is a good example to show why some dynamical forcing is needed, in this case some subsidence. It is to achieve a quasi- steady state representative of shallow cumulus convection in the trade wind regime. –The plot below illustates that cumulus clouds are indeed subgrid ones since the shown model domain of the LES simulation from the BOMEX home page (P.Siebesma, 1997) is only few (6) km.in extent

The 1D-model basics (1)  Only recently (2005) a sort of reference 1D-model has been decided upon. This model has been managed by Javier Calvo (INM). The model is based on a previous model development by B. H. Sass (DMI). FACTS  The amount of software involved is quite small compared with the IFS system ! (a small 1D dynamics library and a physics library)  A script (bourne shell) takes care of compilation (Makefiles used) and execution.

The 1D model basics (2)  The total namelist information is short compared with the complete list of IFS/ALADIN  An experiment associated with a well documented case has some integer number ’NDATSET’  The following sequence of events take place: 1)Read namelist information 2)Read data inputfile information 3)Prepare datafile information to produce actual initial state of a model run (e.g. vertical interpolation) 4)The model then runs subject to the given namelist information, and to the dynamics forcing (if any), and for some cases a special forcing, e.g. prescribed surface fluxes.

The 1D-model basics (3)  Experiments have also been run with more complicated dynamical forcing as a function of time, determined from prescribed mathematical forcing for different variables, e.g. oscilations. OUTPUT OUTPUT  Many ASCII files are produced automatically containing vertical profiles of different parameters, e.g flux profiles or tendencies due to some processes. –  It is possible to make time means of the vertical profiles.

The 1D model basics (4) Many other types of relevant output has been studied in 1D- HIRLAM  Time series (other basic type of ASCII files)  Moisture budgets  Frequency spectra of precipitation and clouds PLOTTING is done via a script making graphics based on gnu-plot (alternative software for plotting have been used by HIRLAM people as well)

Data sets studied in the past (1) 1)Neutral and convective ’dry’ PBL (Ayotte et al., 1996) 2)ASTEX stratocumulus case 3)BOMEX shallow cumulus case 4)’Leipzig’ case (near neutral shear driven PBL) 5)’GABLS’ stable PBL case (not yet in ’standard’ setup) 6)EUROCS diurnal cycle of cumulus over land 7)EUROCS stratocumulus case 8)Two EUROCS cases of deep convection (not yet in standard setup)

Data sets studied in the past (2) 9) Cost 722 cases of fog simulations (not yet in standard setup) 10) Many test simulations of idealized situations for various purposes.

Example of results with 1D-HIRLAM (1)

Examples of results with 1D-HIRLAM (2) A HIRLAM 1D-simulation of vertical cloud profile of BOMEX (left) and time series of max. cloud cover of EUROCS shallow cumulus over land (right)

Recommendations for the future. 1)The importance of a common 1D-model setup for experimentation in larger projects (especially as regards data-files, preparation of input and output) should not be underestimated. 2)The establishment of a common data base for 1D-tests seems a natural step in the collaboration between HIRLAM/ALADIN/MF if a common 1D-setup for experiments will be made and supported !