Naslov
Climatology of bora types at Dubrovnik airport based on METAR reports

Autori
Jurković, Jadran ; Gabela Šeperić, Lada ; Baletić, Ivan ; Kos, Igor

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Skup
35th International Conference on Alpine Meteorology (ICAM)

Mjesto i datum
Riva del Garda, Italija, 02.09.2019. - 06.09.2019

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
bora, classification, METAR reports, Dubrovnik

Sažetak
Bora events have a strong impact on air traffic at Dubrovnik airport. Climatology shows that the frequency of hours with NE wind greater than 7.5 ms-1 is 10-15% during winters. Accurate forecasts of onset, severity, and duration are highly desirable. Due to lack of upstream measurements forecasters highly rely on the wind vertical profiles from mesoscale model ALADIN. Comparing it with the observed anemograms, forecasters differentiate three main bora types: standard bora, deep bora, and nocturnal gap flow. Standard bora is a typical hydraulic flow that is generally associated with bora flows. Usually, mean wind speeds are higher than 10 ms-1, with occasional gusts. Deep bora is typical for measured average wind speeds <10 ms-1, but occasionally gusts can reach 20 ms-1. Contrary to the standard bora, deep bora is characterized by a variation of wind speed and direction, which is often more than 180°. Nocturnal gap flow is steady wind during nighttime with mean speed up to 12.5 ms- 1, small variation of wind direction and absence of gusts. We developed an algorithm which will automatically classify bora types. Inputs are data of 10min wind from METAR reports. For every METAR reports, each class is estimated from thresholds for mean wind speed, occasional gusts, a variation of wind direction and time of day. Smoothing of individual class bora is applied with M of N method. At the end, time series of bora class is given in final order: deep bora, standard bora, nocturnal gap flow, unclassified bora, and no bora. Within one bora episode, several types of bora can be classified. Although empirical, this classification is useful in diagnosing the bora types. For the last 15 years, the climatology of bora types is shown with wind roses, annual and hourly distributions of wind. Comparison with previously developed classification from the model shows compatibility.

Izvorni jezik
Engleski

Znanstvena područja
Geofizika

POVEZANOST RADA