1.5 THE LAND BREEZE CHARACTERISTICS IN ISRAEL DURING THE SUMMER BY THE MM5 MODEL

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1. THE LAND BREEZE CHARACTERISTICS IN ISRAEL DURING THE SUMMER BY THE MM MODEL S. Berkovic and Y. Feliks Department of Mathematics, Israel Institute for Biological Research P.O.B 19, Ness-Ziona, Israel 1.

At the beginning of the night the land breeze develops along the coast due to sea-land differential cooling.

1 1. THE LAND BREEZE CHARACTERISTICS IN ISRAEL DURING THE SUMMER BY THE MM MODEL S. Berkovic and Y. Feliks Department of Mathematics, Israel Institute for Biological Research P.O.B 19, Ness-Ziona, Israel 1. Introduction During the summer (mainly July and August) the sea-land breeze circulation is the most prominent flow. The Persian trough is the dominant synoptic system in the lower levels. At the beginning of the night the land breeze develops along the coast due to sea-land differential cooling. Later, as the katabatic wind arrives from the western slopes of the mountain ridges, the wind intensity increases and becomes southeast. The mountains are 3 km inland in the south and approach the coast in the north. This paper describes the land breeze and the katabatic wind along the coast in Israel during July 1994 as obtained from MM simulations. 2. Model Setup The standard PSU/NCAR MM model version 3.2 (Dudhia 2) was run for 4 one-way nested domains starting at a resolution of 4 km over the eastern coast of the Mediterranean Sea down to 2 km for the center to the north of the Israeli coast (fig 1). 26 vertical levels were applied, 11 levels under 2 km above the ground. The model initial and boundary conditions were taken from the GEOS-1 Multi Year Assimilation Data Mediterranean subset (Da-Silva and Alpert 1996) and AVHRR sea surface temperature (WOCE satellite Data CD-ROM, Version 1.1) data set, with a time resolution of 6 hours. The model was Rosh 69 8 Fig 1: 4, 18, 6 and 2 km MM modeling domains. On the right, the topography of the studied area and locations of important points. TA(pt. 9 ) == Tel-Aviv, N( pt. 24 ) ==Netanya Rosh ( pt. 69 ) ==Rosh-Hanikra, A( pt. 9) == Akko (Acre), H( pt. 47) == Ha-Hoterim, MC == Mount Carmel * Corresponding author address: S. Berkovic, IIBR, Ness-Ziona, Israel; berkovic@iibr.gov.il A 9 Haifa 2 MC H N 24 TA 3km Height m

2 initialized at Z and run for 36 hours every day during July The physical parameterizations used were: Grell cumulus scheme, MRF boundary layer scheme, Five layer soil temperature model, Dudhia simple ice microphysical scheme and Cloud-radiation scheme. The model output was saved every hour. The analysis of the time series is presented in the next section. 3. Results The land breeze is a wind with an eastern component due to katabatic wind and differential cooling, therefore, it is defined as the component of the offshore wind orthogonal to the coastline. The calculated land breeze characteristics along the coast were: 1. The land breeze imum intensity. 2. The land breeze start, imum intensity and end times 3. Duration of the land breeze, as derived from end and start times. The nocturnal wind is weak (< 2 m/s) and might change from offshore to onshore wind for a imum period of 3 hours. The start time is defined as the first time an offshore wind is found after at least 4 hours of onshore wind. The land breeze blows during the night, therefore we inspect two days. The end time is found by going backwards in time from 14Z on the next day, it is the last hour at which land breeze is found, if there is an onshore wind from the end time to 14Z on the next day. This definition allows the occurrence of short periods (< 3 hours) of an onshore wind during the duration of the land breeze. The land breeze parameters were calculated from model output of the finest domain at the lowest sigma level (~ m above the ground). The average of the imum intensity of the land breeze, u, v, and the wind intensity at the imum time, along the coastline from S to N, is shown in Fig. 2a. The strongest imum land breeze intensity is 2.4 m/s south of Haifa around Atlit (point 44,4). The weakest imum land breeze is.8 m/s around Haifa (point 49). m/s a m/s u v speed b Tel-Aviv Netanya Haifa Rosh-Hanikra Fig 2: a. The average imum land breeze intensity ( black), and the average u (green),v(red) and speed(blue) at the time of the imum land breeze along the coastline from S to N. ( point 9 == Tel Aviv, point ==Netanya, Point 2 == Haifa, point 69 == Rosh Hanikra). b. The variance.

3 The influence of the coastline curvature is seen by the varying contribution of the u and v horizontal wind components (u from W to E, v from S to N). The contribution of u increases at the northern points (-7) where the coastline is straight and goes from south to north. The variance of the parameters ( Fig 2.b) changes significantly along the coast probably as a result of the topography. In areas of complex terrain: Haifa, Akko (Acre) and Rosh Hanikra (points ) the highest variance ~1 m/s was found. In areas of flat terrain and straight coastline: from Tel-Aviv to Netanya (points 1-24) the smallest variance.3-. m/s was found. McPherson 197 explained the asymmetric flow above a rectangular bay as a result of Coriolis and the pressure gradient forces counter acting on one side of the bay and co acting on the other side. Gilliam et al 24 pointed out the special flow where the coastline has cusps. Furthermore, the katabatic wind adds to the curvature effect, it strengthens the wind s intensity and broadens the variance of the wind direction. The average start, imum and end times of the land breeze are shown in fig 3a. The land breeze starts at 19-23Z. North of Rosh Hanikra (points 68-8) the start time is earlier: 19-2Z, probably as a result of the proximity of steep mountains to the coast. The latest start time is 23Z around the Carmel area where steep mountain and curved coastline meet. The average land breeze imum time is 1-3Z, from Rosh-Hanikra and further north it is earlier: 23-1Z. The average end time is -6Z, from Rosh-Hanikra and further north it is earlier: 4- Z. The variance (Fig3b) of the start time is 2-2. hours. The variance of the imum time is hours. The variance of the end time is ~ 1 hour from Tel-Aviv to Ha-Hotrim, south of the Carmel (point 47), around Acre it increases to 1. hour and further north from Rosh-Hanikra it increases to hours. GMT ave start end start end urs ho var start end start end Fig 3: a. The average start, imum intensity and end times of the land breeze along the coastline from S to N. b. The variance.

4 The Carmel area is a singular point as a result of its unique topography and needs further study. The greatest variance of start and end times was found there, which indicates a different flow. The duration of the land breeze is 7-1 hours and its variance is 2-4 hours. Further statistical information is gained from the histograms of the start, imum and end times of the land breeze at the following : Tel-Aviv (point 9), Netanya (point 24), Haifa bay (point ) and Rosh-Hanikra (point 69) (Fig 4). The distribution of the end time is narrower than the distribution of the start and the imum time. At all the points, the most frequent hours of the start (21-23Z), imum (3-4Z) and end times (4-Z) agree within 1 hour. The average values of the imum time are 1-2 hours earlier than the most frequent hours of the imum time. The average and the most frequent hours of the start and end times are the same. Tel-Aviv pt _t 4 end_t 4 Netanya pt 24 4 _t 4 end_t pt 2 3 Haifa bay _t 2 3 end_t 2 3 Rosh-Hanikra Fig4: start, imum intensity and end time histograms of the land breeze at the : Tel-Aviv, Netanya, Haifa bay and Rosh-Hanikra.

5 Summary The start, imum intensity and end times of the land breeze along the coast were calculated. It starts earlier in the northern part of the coast probably as a result of the proximity of the mountains to the coast. The distribution of start and imum times is broader than the end time distribution. The average imum intensity of the land breeze is about 2 m/s at a height of m above the ground. The Israeli coastline is straight except near Haifa (in the north) where the coastline curves sharply to form the bay and there the Carmel Mountain reaches the coast. In this region the land breeze has a different behavior and the imum land breeze intensity is found there. References Da-Silva A. and Alpert P., 1996: Documentation of the multi-year GEOS-1 assimilation data subset for the Northern Africa, the Mediterranean and the Middle East, NASA/Goddard Space Flight Center, Data Assimilation Office Note 96-24pp. Dudhia J., Gill D., Guo Y. and Manning K., 2: PSU/NCAR Mesoscale modeling system tutorial class notes and Users guide Gilliam R. C., Raman S. and Niyogi D. T. S., 24: Observational and numerical study of the influence of large-scale flow direction and coastline shape on sea-breeze evolution. Boundary-Layer Meteorology 111:27-3. McPherson R. D., 197: A numerical study on the effect of a coastal irregularity on the sea breeze. J Appl. Meteor. 9,

1 INTRODUCTION. Figure 2: Synoptical situation at the beginning of the simulation: 5th January 1999 at 12UTC.

1 INTRODUCTION. Figure 2: Synoptical situation at the beginning of the simulation: 5th January 1999 at 12UTC. 2.2 NOCTURNAL CIRCULATIONS UNDER WEAK PRESSURE GRADIENTS IN THE ISLAND OF MALLORCA J. Cuxart and M.A. Jiménez Universitat de les Illes Balears, Spain 1 INTRODUCTION To study the local nocturnal circulations