Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Climatological characterisation of the Ora delGarda wind in the Alps

L. Giovannini1, L. Laiti1, D. Zardi1, M. de Franceschi1,2

dino.zardi@ing.unitn.it

1Atmospheric Physics Group, Department of Civil, Environmental and MechanicalEngineering, University of Trento, Trento, Italy

2Major Seminary, Diocese of Bolzano-Bressanone, Bressanone, Italy

Kranjska Gora, 4 June 2013

32nd International Conference on Alpine Meteorology 2013

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Study area

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Dataset

I Two surface weather stations

I 10-year period (2003-2012)

I April-September

I Hourly average wind speed(WS) and direction (WD)

I Maximum hourly wind gust(sampled every 10 s)

I Global solar radiationI Air temperature

I Hourly observations of lake water temperature at 10 m depth2010-2012 at RIV

I Daily values of WS and WD at 850 hPa from NCEP reanalysis(1200 UTC)

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Criteria for selection of lake breeze days

I Global solar radiation until noon >30% of the maximum radiation inthe same time period for that month

I WD reverses from offshore to onshore at sunrise ± 2 h

I WD becomes offshore or WS <1 m s−1 after sunset

I WD is offshore or WS <1 m s−1 for most of the hours betweenmidnight and sunrise

I 135◦N<WD<255◦N for at least 3 h consecutively and at the sametime WS>2 m s−1

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Frequency of lake breeze days on the lake’s shore

The lake breeze at RIV occurs in 68% of the days analysed.

Higher frequencies in the central months of the period:

I April: 57%

I May: 71%

I June: 71%

I July: 75%

I August: 72%

I September: 63%

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Lake breeze intensity on the lake’s shore

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Timing of the lake breeze on the lake’s shore

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Monthly variations on the lake’s shore: onset

I Progressive delay in the onset from April to September

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Monthly variations on the lake’s shore: cessation

I Later cessation in May-July

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Frequency of lake breeze days in the Adige Valley

Lake breeze days at GAR:

I WD = 240◦N ± 30◦N and at the same time WS > 2 m s−1 for atleast 1 h between the onset time at RIV and 2 hours after thecessation time

⇓

The lake breeze breaks up at GAR in 89% of the days in which itdevelops at RIV.

High frequencies in all months:

I April: 88%

I May: 85%

I June: 88%

I July: 92%

I August: 88%

I September: 91%

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Lake breeze breakup intensity in the Adige Valley

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Timing of the lake breeze breakup into the Adige Valley

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Onset-breakup timing

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Monthly variations in the Adige Valley: onset

I As at RIV, progressive delay of the onset from April to September

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Monthly variations in the Adige Valley: cessation

I Earlier cessation in August and September

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Influence of the lake’s temperature

cf. Telisman Prtenjak and Grisogono (2007) Theor. Appl Climatol.

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Influence on air temperature

The arrival of the lake breeze front is marked by a temperature drop atthe lake’s shore

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Influence on air temperature

The temperature drop tends to be smaller and smaller from April toSeptember

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Influence of the synoptic windData were divided into 6 classes based on WS and WD at 850 hPa:

I Onshore (On): 135◦≤ WD ≤ 255◦

I Onshore Strong (OnStr): 135◦≤ WD ≤ 255◦and WS ≥ 4 m s−1

I Offshore (Off): WD ≤ 75◦or WD ≥ 315◦

I Offshore Strong (OffStr): WD≤75◦or WD≥315◦and WS>4 m s−1

I Parallel East (E): 75◦< WD < 135◦

I Parallel West (W): 255◦< WD < 315◦

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Influence of the synoptic wind on the lake’s shore

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Influence of the synoptic wind in the Adige Valley

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

Study area Dataset Ora del Garda statistics Lake’s temperature Air temperature Synoptic wind Conclusions

Conclusions

I Very regular circulation, marking significantly local climaticconditions:

I High wind intensities at both stations and significant temperaturedrop at the passage of the front

I Monthly variations:I Later onset from April to SeptemberI Stronger intensities in spring at GAR

I No clear relationship between water/air temperature contrasts andthe lake breeze strength

I Influence of the synoptic wind:I Synoptic wind influences the timing and the stregth of the lake breezeI Opposite effects on lake breeze strength between RIV and GAR

Giovannini, Laiti, Zardi, de Franceschi Climatological characterisation of the Ora del Garda wind in the Alps

THANKS FOR YOUR KIND ATTENTION!