Lazar Lazić

An upgraded version of the Eta model

Upgrades implemented over a number of years in an open source version of the Eta model, posted at the CPTEC web site http://etamodel.cptec.inpe.br/, are summarized and examples of benefits are shown. The version originates from the NCEP’s Workstation Eta code posted on the NCEP web site http://www.emc.ncep.noaa.gov/mmb/wrkstn_eta, which differs from the NCEP’s latest operational Eta by having the WRF-NMM nonhydrostatic option included. Most of the upgrades made resulted from attention paid to less than satisfactory performance noted in several Eta results, and identification of the reasons for the problem. Others came from simple expectation that including a feature that is physically justified but is missing in the code should help. The most notable of the upgrades are the introduction of the so-called sloping steps, or discretized shaved cells topography; piecewise-linear finite-volume vertical advection of dynamic variables; vapor and hydrometeor loading in the hydrostatic equation, and changes aimed at refining the convection schemes available in the Eta. Several other modifications have to do with the calculation of exchange coefficients, conservation in the vertical diffusion, and diagnostic calculation of 10-m winds. Several examples showing improved performance resulting from the dynamics changes are given. One includes a case of unrealistically low temperatures in several mountain basins generated by a centered vertical advection difference scheme’s unphysical advection from below ground, removed by its replacement with a finite-volume scheme. Another is that of increased katabatic winds in the Terra Nova Bay Antarctica region. Successful forecast of the severe downslope zonda wind case in the lee of the highest peaks of the Andes is also shown, and some of the recent successful verification results of the use of the upgraded model are pointed out. The code is used at numerous places, and along with setup information it is available for outside users at the CPTEC Eta web site given above.

A real data simulation of the Adriatic bora and the impact of mountain height on bora trajectories

SummaryThis study addresses simulation of the local bora wind and its properties as reflected on typical trajectories. Trajectory calculations are implemented in the Eta Model. The Eta Model has a vertical coordinate which permits a step-like representation of mountains and quasi-horizontal coordinate surfaces, the so-called eta coordinate. A realistic real data simulation of a bora wind case in achieved using the model with a 28 km horizontal resolution and 16 layers in the vertical. Numerical experiments with different mountain heights and shapes in the bora wind region are performed. These are motivated by observational indications and theoretically based expectations that a certain intermediate mountain elevation is required for generation of downslope windstorms with bora wind properties. Three-dimensional trajectories over various mountains mimicing real mountains but differing primarily in elevation are calculated and analysed. The maximum bora wind speed is predicted as expected through three-dimensional channels in the step mountain representations. The results illustrate and are in agreement with the observational evidence that mountain barriers of the elevation of about 1000 m are a necessary requirement for the occurrence of the bora-type downslope windstorms.

Improved bora wind simulation using a nested Eta Model

SummaryThis paper reports on improvements obtained in simulations of bora wind using a nesting technique in a primitive equations model. A version of the so-called Eta Model is used for both the lower resolution as well as for the higher resolution nested run. For nesting, a technique has been developed whereby for the boundary conditions “underground” model values are used. They are obtained by horizontal interpolation of model variables inside the models eta layers. Simulations are initialized using real data. This is done in order to assess the models performance in simulating the bora wind, an important mesoscale phenomenon caused by orography. Improvements achieved by nesting are illustrated by examples of precipitation as well as a trajectories forecast.

Assessment of Air Quality in an Urban Area of Belgrade, Serbia

Mirjana Tasi a, Slavica Rajsi a, Milica Tomasevi a, Zoran Miji a, Mira Ani i a, Velibor Novakovi a, Dragan M. Markovi a, Dragan A. Markovi b, Lazar Lazi c, Mirjana Radenkovi d and Jasminka Joksi d aInstitute of Physics, Belgrade, Serbia bFaculty of Applied Ecology, Singidunum University, Belgrade, Serbia cInstitute of Meteorology, Faculty of Physics, Belgrade, Serbia dInstitute of Nuclear Science Vin a, Belgrade, Serbia

Eta model forecasts of tropical cyclones from Australian Monsoon Experiment: The model sensitivity

SummaryThe Australian Monsoon Experiment (AMEX) (10 January through 15 February 1987) has resulted in the first ever quality mesoscale data set in the Australian tropics. This provides the first observational confirmation of previous hypotheses, modelling experiments and refinement of the parametrization of convective processes. During the AMEX a large area of convective activity off northwestern Australia accompanied four tropical cyclones onset:Connie, Irma, Damien andJason. As already reported by the author, the Eta Model of the University of Belgrade and the National Meteorological Centre, Washington (UB/NMC), successfully predicted the development, structure, associated precipitation and tracks of these cyclones.Using again the AMEX tropical cyclone cases, in the present study the sensitivity of the Eta Model is examined with respect to the initial and boundary conditions, the vertical coordinate and orography, the location of the initial vortex, the surface fluxes of heat and moisture, the sea surface temperature and the Betts-Miller convection parametrization scheme.Also, some available forecasts of the AMEX tropical cyclones were intercompared. These included the forecasts obtained by the Eta Model, the T106 global (then) operational European Centre for Medium-range Weather Forecasts (ECMWF) model, the ECMWF T106 limited area model and the Florida State University (FSU) limited area model. A review of the intercomparison results suggests that the Eta Model is highly competitive with the other sophisticated models, both in terms of quality and the computational effort required.

“Non-cancellation” instability in horizontal advection schemes for momentum equations

SummaryThe minimum subsystem of the linearized finite-difference shallow water equations was found within which the instability first noticed with the ECMWF energy and enstrophy conserving scheme (Hollingsworth and Kallberg 1979; Hollingsworth et al. 1983) still occurs. This subsystem consists of the Coriolis and the advection terms.In real data runs with the HIBU (Hydrometeorological Institute and Belgrade University) model no instability was encountered. A possible explanation for this is proposed.ZusammenfassungIn der vorliegenden Arbeit wird für ein “seichtes Wasser”-Modell ein miminales Subsystem von linearisierten endlichen Differenzengleichungen abgeleitet, das zu Instabilitäten fähig ist, wie sie erstmals im Konservierungsschema für Vorticity und Enstrophie des ECMWF-Modells auftraten. Dieses Subsystem schließt den Coriolis- und Advektionsterm ein.Bei Modellrechnungen mit einem realen Datenmaterial des HIBO-Modells (Modell des Jugoslawischen Hydrometeorologischen Instituts gemeinsam mit der Universität Belgrad) treten derartige Instabilitäten nicht auf. Es ist dies auf ein unterschiedliches numerisches Integrationsverfahren zurückzuführen.

Eta model forecasts of tropical cyclones from Australian Monsoon Experiment: Dynamical adjustment of initial conditions

SummaryThe University of Belgrade/National Meteorological Centre, Washington (UB/NMC) limited area Eta Model predicted the development, structure, associated precipitation and tracks of the Australian Monsoon Experiment (AMEX) (10 January through 15 February 1987) tropical cyclonesConnie, Irma, Damien andJason. The initial positions and intensities of the tropical cyclone vortices from the global European Centre for Medium-Range Weather Forecasts (ECMWF) analyses, which are used as initial data, do not quite agree with the observations. These disagreements produce additional erros in predicting the tropical cyclone tracks.To improve the initial position of the vortex, the flow is split into the small and the large scale motions, and during the first two hours of the integration, the small-scale part is forced in small steps towards its observed position. The adjustment is performaed with the reduced model dynamics (adjustment processes only) and no physics.With the adjustment during the first two hours of the integration, the model successfully adjusts to the new position of the initial vortex. After the completion of the adjustment stage, the model runs normally, i.e., without any modification. The tracks of the 48-h forecasts with the adjusted initial vortices are parallel to the tracks obtained in the control forecasts without the adjustment. However, e.g., the mean absolute error of the positions during 48-h forecast of the tropical cycloneConnie was reduced from 174 km in the control case to 129 km in the case with adjustment of the position.The latent heat, the thermal energy, the kinetic energy and the total energy of the extracted small scale vortices are calculated every three hours of the integration time. These small-scale energies obtained in the 48-h control forecast are compared to those of the rund with the initial vortex adjustment to monitor the “spin up” of the model.

Some Characteristic Air Back Trajectories For High PM10 And PM2.5 Concentration Episodes in Belgrade

A pilot study was performed to assess the concentration level of ambient suspended particulate matter PM10 and PM2.5 in the Belgrade urban area. This study has shown theoretical and experimental evidence of pollutants for characteristic measurements when maximum PM concentrations occurred. For this study, 60‐h air‐back trajectories are calculated. When the air masses were coming from the SW direction, the contribution from the complex of coal‐fired power plants was evident.