DOWNSCALING OF ERA40 FOR THE WIND FIELD IN A COMPLEX TERRAIN

This study deals with the optima] strategy for setting up the ALADIN model for the purpose of dynamic downscaling of ERA40 over the Alpine region. The mesoscale model wind field is compared with MAP-SOP reanalysis data and with wind observations at eleven Slovenian stations. As expected, there is an improvement in the conventional statistics at a 10-km grid as compared to the 40-km analyses. However, the differences between the mesoscale model scores at various domains can be greater than the difference between the MAP-SOP reanalyses and a particular mesoscale simulation

HIGH-RESOLUTION WIND CLIMATOLOGY FOR SLOVENIA: A SPATIO-TEMPORAL VERIFICATION

An NWP model AI.AD1N is applied for dynamical downscaling of ERA40. The purpose is to deduce the wind climatology of Slovenia at horizontal scales around ten kilometers and finer. Verification against MAP-SOP reanalyses indicates that the downscaling has been successful. However, MAP-SOP reanalysis data produce wind roses closer to the observations and contain more energy in the subdiurnal range. On the other hand, a 10-km ALADIN overestimates the amount of energy in longer than diurnal periods

PREDICTABILITY OF A STRONG PRECIPITATION EVENT; A CASE STUDY AND AN INVESTIGATION OF MODEL SENSITIVITY

For a convective event, simulated rainfall intensity is compared to the observations at a minute-time-scale. Temporal intermittency and peak intensities are found to be similar to the rain-gauge data, when the model is forced with analysis at the lateral boundaries. Predictability of the same event, estimated on the basis of several simulations starting on different initial large-scale analysis and with forecast lateral boundary conditions, is found to be very low, meaning that accurate predictions of this and similar events at 36 — 48 hour ranges are unlikely

Utjecaj advekcije i rada sila na mahovitost bure

Local wind changes within the flow of the Adriatic Bora are investigated in the case of 8 December 2001 that was simulated with the WRF/ARW model in a 333 m horizontal resolution and with all relevant model variables archived during a 3 h time interval with 1 s temporal resolution. Along a selected cross section, two locations of strong gusts in the lee of a Dinaric mountain ridge are found - the upper one on the slope and the other over the sea close to the coastline; in between the wind is considerably weaker. About 16 to 18 gusts developed in the 3 h interval at both locations with an average period of approximately 8.5 min. The advective transport of kinetic energy (KE), the work of the unbalanced part of the pressure gradient force and the diffusion and dissipation of KE cause the local change ΔKE, and their quasi-periodic fluctuations lead to gusts and lulls. The results of the numerical simulation enable an estimation of the contributions of advection, the work of forces and of turbulence and dissipation effects. Advective contributions to local changes are more or less in the phase with ΔKE and ahead of the phase of KE, while the contributions of work are generally smaller and in the opposite phase: so in general the advection and the work effects oppose each other. The advection and the work effects are not spatially homogeneous, i.e. they cease and even change their sign between the two locations of the strongest gusts and so there is no continuous displacement of KE from the upper to the lower location by either of the two effects: their contributions interchange with each other down the slope.Lokalne promjene vjetra u buri istražene su u slučaju od 8. prosinca 2001. koji je bio simuliran WRF/ARF modelom s horizontalnom rezolucijom od 333 m i sa svim relevantnim modelskim varijablama arhiviranim tijekom 3-satnog vremenskog intervala s vremenskom rezolucijom od 1 s. Duž odabranog presjeka paralelnog s burom nađene su dvije lokacije u navjetrini Dinarida s jakim udarima – jedna na obronku planine i druga iznad mora blizu obale, dok je između njih vjetar znatno slabiji. U promatranom trosatnom intervalu razvilo se oko 16 do 18 udara vjetra s prosječnim periodom od približno 8,5 minuta. Advektivni transport kinetičke energije (KE), rad neuravnoteženog dijela sile gradijenta tlaka te difuzija i disipacija KE uzrokuju lokalnu promjenu ΔKE, i njihove kvazi-periodičke fluktuacije vode do pojave udara i zatišja. Rezultati numeričke simu- lacije omogućavaju procjenu doprinosa advekcije, rada sila te učinaka turbulencije i di- sipacije. Advekcijski doprinosi lokalnim promjenama su više ili manje u fazi s ΔKE i ispred faze KE, a doprinosi rada su općenito manji i u suprotnoj fazi. To znači da advekcija i rad općenito djeluju suprotno. Učinci advekcije i rada nisu prostorno homogeni, tj. oni prestaju ili čak mijenjaju predznak između dvije lokacije najjačih udara. Stoga nema kontinuiranog pomaka KE od više prema nižoj lokaciji koji bi bio uzrokovan bilo kojim od ova dva učinka: njihovi se doprinosi međusobno izmjenjuju niz obronak