1.5 THE LAND BREEZE CHARACTERISTICS IN ISRAEL DURING THE SUMMER BY THE MM5
MODEL
S. Berkovic and Y. Feliks Department of Mathematics, Israel Institute for Biological Research P.O.B 19, Ness-Ziona, Israel
1. Introduction 2. Model Setup During the summer (mainly July and August) the The standard PSU/NCAR MM5 model version sea-land breeze circulation is the most 3.2 (Dudhia 2000) was run for 4 one-way nested prominent flow. The Persian trough is the domains starting at a resolution of 54 km over dominant synoptic system in the lower levels. At the eastern coast of the Mediterranean Sea the beginning of the night the land breeze down to 2 km for the center to the north of the develops along the coast due to sea-land Israeli coast (fig 1). 26 vertical levels were differential cooling. Later, as the katabatic wind applied, 11 levels under 2 km above the ground. arrives from the western slopes of the mountain The model initial and boundary conditions were ridges, the wind intensity increases and taken from the GEOS-1 Multi Year Assimilation becomes southeast. The mountains are 30 km Data Mediterranean subset (Da-Silva and Alpert inland in the south and approach the coast in 1996) and AVHRR sea surface temperature the north. This paper describes the land breeze (WOCE satellite Data CD-ROM, Version 1.1) and the katabatic wind along the coast in Israel data set, with a time resolution of 6 hours. The during July 1994 as obtained from MM5 model was simulations.
Rosh 69 800 700 A 59 600 Haifa 52 500 MC 400 H 300 200
Fig 1: 54, 18, 6 and 2 km MM5 modeling domains. N 24 100 On the right, the topography of the studied area and 0 locations of important points. TA(pt. 9 ) == Tel-Aviv, N( pt. 24 ) ==Netanya -100 TA Rosh ( pt. 69 ) ==Rosh-Hanikra, A( pt. 59) == Akko (Acre), Height m H( pt. 47) == Ha-Hoterim, MC == Mount Carmel
* Corresponding author address: S. Berkovic, IIBR, Ness-Ziona, Israel; e-mail: [email protected] 30km initialized at 0Z and run for 36 hours every day maximum period of 3 hours. The start time is during July 1994. The physical defined as the first time an offshore wind is parameterizations used were: Grell cumulus found after at least 4 hours of onshore wind. The scheme, MRF boundary layer scheme, Five– land breeze blows during the night, therefore we layer soil temperature model, Dudhia simple ice inspect two days. The end time is found by going microphysical scheme and Cloud-radiation backwards in time from 14Z on the next day, it is scheme. The model output was saved every the last hour at which land breeze is found, if hour. The analysis of the time series is there is an onshore wind from the end time to presented in the next section. 14Z on the next day. This definition allows the occurrence of short periods (< 3 hours) of an 3. Results onshore wind during the duration of the land The land breeze is a wind with an eastern breeze. component due to katabatic wind and differential The land breeze parameters were calculated cooling, therefore, it is defined as the component from model output of the finest domain at the of the offshore wind orthogonal to the coastline. lowest sigma level (~ 5m above the ground). The The calculated land breeze characteristics along average of the maximum intensity of the land the coast were: 1. The land breeze maximum breeze, u, v, and the wind intensity at the intensity. 2. The land breeze start, maximum maximum time, along the coastline from S to N, intensity and end times 3. Duration of the is shown in Fig. 2a. The strongest maximum land breeze, as derived from end and start land breeze intensity is 2.4 m/s south of Haifa times. around Atlit (point 44,45). The weakest The nocturnal wind is weak (< 2 m/s) and might maximum land breeze is 0.8 m/s around Haifa change from offshore to onshore wind for a (point 49).
a b 3 2.0 max 1.8 u 2 1.6 v speed 1.4 1 1.2 s
m/s 0 1.0 m/ 0.8
-1 0.6
0.4 -2 0.2 0 10203040506070 0 1020304050607080 coast points coast points Tel-Aviv Netanya Haifa Rosh-Hanikra Tel-Aviv Netanya Haifa Rosh-Hanikra
Fig 2: a. The average maximum land breeze intensity ( black), and the average u (green) ,v(red) and speed(blue) at the time of the maximum land breeze along the coastline from S to N. ( point 9 == Tel Aviv, point 25 ==Netanya, Point 52 == Haifa, point 69 == Rosh – Hanikra). b. The variance.
The influence of the coastline curvature is seen intensity and broadens the variance of the wind by the varying contribution of the u and v direction. horizontal wind components (u –from W to E, v – The average start, maximum and end times of from S to N). The contribution of u increases at the land breeze are shown in fig 3a. The land the northern points (55-70) where the coastline breeze starts at 19-23Z. North of Rosh Hanikra is straight and goes from south to north. (points 68-80) the start time is earlier: 19-20Z, The variance of the parameters ( Fig 2.b) probably as a result of the proximity of steep changes significantly along the coast probably mountains to the coast. The latest start time is as a result of the topography. In areas of 23Z around the Carmel area where steep complex terrain: Haifa, Akko (Acre) and Rosh mountain and curved coastline meet. The Hanikra (points 52 59 68) the highest variance average land breeze maximum time is 01-03Z, ~1 m/s was found. In areas of flat terrain and from Rosh-Hanikra and further north it is earlier: straight coastline: from Tel-Aviv to Netanya 23-01Z. The average end time is 05-06Z, from (points 10-24) the smallest variance 0.3-0.5 m/s Rosh-Hanikra and further north it is earlier: 04- was found. McPherson 1970 explained the 05Z. The variance (Fig3b) of the start time is 2- asymmetric flow above a rectangular bay as a 2.5 hours. The variance of the maximum time is result of Coriolis and the pressure gradient 1.5-2.5 hours. The variance of the end time is ~ forces counter acting on one side of the bay and 1 hour from Tel-Aviv to Ha-Hotrim, south of the co–acting on the other side. Gilliam et al 2004 Carmel (point 47), around Acre it increases to pointed out the special flow where the coastline 1.5 hour and further north from Rosh-Hanikra it has cusps. Furthermore, the katabatic wind adds increases to 1.5-2.5 hours. to the curvature effect, it strengthens the wind’s
ave start max end var start max end start max 30 8.5 end 8.0 29 7.5 28 7.0 6.5 27 start 6.0 max 26 5.5 end 5.0 25 4.5
24 urs 4.0 GMT
ho 3.5 23 3.0 22 2.5 2.0 21 1.5 20 1.0 0.5 19 0.0 0 1020304050607080 0 1020304050607080 coast points coast points Tel-Aviv Netanya Haifa Rosh-Hanikra Tel-Aviv Netanya Haifa Rosh-Hanikra
Fig 3: a. The average start, maximum intensity and end times of the land breeze along the coastline from S to N. b. The variance. The Carmel area is a singular point as a result of time is narrower than the distribution of the start its unique topography and needs further study. and the maximum time. At all the points, the The greatest variance of start and end times was most frequent hours of the start (21-23Z), found there, which indicates a different flow. maximum (03-04Z) and end times (04-05Z) The duration of the land breeze is 7-10 hours agree within 1 hour. The average values of the and its variance is 2-4 hours. maximum time are 1-2 hours earlier than the Further statistical information is gained most frequent hours of the maximum time. The from the histograms of the start, maximum and average and the most frequent hours of the start end times of the land breeze at the following and end times are the same. coast points: Tel-Aviv (point 9), Netanya (point 24), Haifa bay (point 55) and Rosh-Hanikra (point 69) (Fig 4). The distribution of the end
Netanya pt 9 Tel-Aviv pt 24 start_t max_t end_t 45 45 45 45 start_t 45 max_t 45 end_t 40 40 40 40 40 40 35 35 35 35 35 35
30 30 30 30 30 30
% 25 25 25 %
25 25 25
s t s 20 20 20 20 20 20 ent ven
e 15 15 15 ev 15 15 15 10 10 10 10 10 10
5 5 5 5 5 5
0 0 0 0 0 0 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35
GMT hours GMT hours Haifa bay Rosh-Hanikra pt 55 start_t max_t end_t 35 35 35 40 40 40 30 30 30 35 35 35
25 25 25 30 30 30
25 25 25 20 20 20 % %
s 20 20 20
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ent 15 15 15 v en e 15 15 15
ev 10 10 10 10 10 10 5 5 5 5 5 5 0 0 0 0 0 0 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 15 20 25 30 35 152025303540 GMT hours GMT hours
Fig4: start, maximum intensity and end time histograms of the land breeze at the coast points : Tel-Aviv, Netanya, Haifa bay and Rosh-Hanikra. Summary The start, maximum intensity and end times of References the land breeze along the coast were Da-Silva A. and Alpert P., 1996: Documentation of the multi-year GEOS-1 assimilation data calculated. It starts earlier in the northern part of subset for the Northern Africa, the the coast probably as a result of the proximity of Mediterranean and the Middle East, NASA/Goddard Space Flight Center, Data the mountains to the coast. The distribution of Assimilation Office Note 96-05 24pp. start and maximum times is broader than the Dudhia J., Gill D., Guo Y. and Manning K., 2000: end time distribution. The average maximum PSU/NCAR Mesoscale modeling system tutorial intensity of the land breeze is about 2 m/s at a class notes and Users guide height of 5 m above the ground. The Israeli Gilliam R. C., Raman S. and Niyogi D. T. S., coastline is straight except near Haifa (in the 2004: Observational and numerical study of the influence of large-scale flow direction and north) where the coastline curves sharply to coastline shape on sea-breeze evolution. form the bay and there the Carmel Mountain Boundary-Layer Meteorology 111:275-300. reaches the coast. In this region the land breeze McPherson R. D., 1970: A numerical study on has a different behavior and the maximum land the effect of a coastal irregularity on the sea breeze. J Appl. Meteor. 9,767-777. breeze intensity is found there.