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17
удк 65 6.7.08:614.8.1 Leonid Dinevich [Леонид Диневич], Yossi Leshem [Ёси Лешем]
opportunities of radar tracking
way towards research of breeze
and mountain-valley air circulation influence on diurnal bird migration
Об одном случае пролета большой стаи аистов над территорией Израиля
The results of observations over the storks flight let us assume that the flock chooses the path and flight altitude instinctively, by means of vertical streams search, using their own bodies and wings, looking for minimum energy it can spend due to atmosphere conditions. It's not occasionally that the flight path of the stork is similar to the straight line only on separate parts. The path is sometimes branched and its structure is changed very rapidly under the influence of convective streams and stripes formed due to coastal breeze and mountain-valley circulation process taking place on concrete day in concrete region. One can solve the reverse task en route using the storks' flight peculiarities for the vertical streams structure determination. The structure of flight path is depends upon the structure of vertical streams movement in surface air layer.
Key words: radar ornithology, birds, bird migration, local winds, breezes, radar meteorology.
Результаты наблюдений за полетом аистов позволяют предположить, что стая выбирает маршрут и высоту полета инстинктивно путем поиска вертикальных потоков, используя для этого свои собственные тела и крылья, так чтобы минимизировать затрачиваемую энергию в зависимости от атмосферных условий. Не редко траектория полета оказывается близка к прямой линии лишь на отдельных участках. Иногда траектория оказывается разветвленной, и ее структура очень быстро меняется под воздействием конвективных потоков и течений, формируемых береговым бризом и горно-долинной циркуляцией, имеющих место в конкретный день в конкретном районе. Может быть решена обратная задача определения структуры вертикальных потоков на основе данных об особенностях полета аистов. Структура траектории полета зависит от структуры вертикальных потов в приземном слое воздуха.
Ключевые слова: радарная орнитология; птицы; миграция птиц; локальные ветры; бризы; радарная метеорология.
1. PASSAGE OF STORKS. MARCH 30, 2000
1.1 Weather conditions
Weather in Israel in this and next day was characterized by light gradient field of high pressure caused by periphery of a crest of an anticyclone with epicenter in the central Europe (fig. 1 a, b, c, d). Meteorological
Table 1. THE DATA ON TEMPERATURE OF AIR, SEAWATER,
AND WIND DIRECTION ON THREE METEOROLOGICAL STATIONS: BEIT DAGAN, HAIFA, AND ASHDOD
Station of supervision Beit Dagan Haifa Ashdod
Time of supervision 08.00; 12.00; 18.00 08.00; 12.00; 18.00 08.00; 12.00; 18.00
Temperature in C°:
Ground 17.0; 19.4; 23.7
Sea water 17.15; 17.5; 17.5 17.95; 18.15; 17.9
Difference of temperature of ground and sea water at two stations -0.15; +1.9; + 6.2 -0.95; +1.25; + 5.8
Direction of a wind in degrees 192; 275; 323
station in Beit Dagan is designated on maps by triangle, time is specified due to Greenwich (the difference with local time makes 2 hours).
Such large-scale circulating processes cannot promote the development of convection, but create favorable conditions for the maximal display of local seasonal and daily features. Due to local factors, in the surface air the convection can develop. The structure of such a convection is determined, more often, by separate ascending jets or sites of ascending air on rather small local lines of the fronts arising for the account of mountain-valley, breeze circulation above sites of underlying surface with the big gradient of reflecting factor or sharply distinguished daily radiating balance (8). Such convective processes, as a rule, do not exceed the top level of the surface air and have sharply expressed daily course in our conditions.
Let us look after what conditions in a ground layer could promote the development of convective jets this day.
In table 1 the data on temperature of ground and sea water for 8, 12 and 18 hours on three stations in Beit Dagan, Haifa, Ashdod and about the wind according to station in Beit Dagan are submitted.
Fig.1.
Date 30.03.00 Time: a) SURFACE, 08.00, Ь) SURFACE, 10.00, А Beit Dagan ^ 850 MB, 10.00, d) SURFACE, 22.00
Table 2. SONDE 1D: 1443227 RADIOSONDE OBSERVATION DATE:
30/03/2000 TIME: 10:32 GMT (12.00 local times) DATA FOR 100 METERS LEVELS
PRES. MB TIME HH:MM:SS HEIGHT METER Temperature. C° RH % DEWP C° W.D. DEG. W.S KNOTS
1055 00:00:00 0 19.2 72 14.0 280 7
1003 00:00:28 100 16.9 71 11.6 304 6
991 00:00:49 200 16.1 73 11.3 322 5
980 00:01:12 300 15.9 69 10.2 342 5
968 00:01:33 400 16.6 54 6.9 357 5
957 00:01:57 500 16.1 44 3.9 355 5
946 00:02:18 600 15.4 36 0.2 354 6
935 00:02:37 700 15.0 34 -0.8 353 8
924 00:02:58 800 15.3 24 -5.3 353 9
913 00:03:20 900 16.1 19 -7.6 351 10
902 00:03:40 1000 16.2 16 -9.3 347 11
892 00:04:02 1100 15.5 16 -10.4 343 13
881 00:04:24 1200 15.0 17 -10.2 341 15
From the table, it is visible, that seawater at 8.00 AM at station Haifa and Ashdod is warmer than ground in Beit Dagan. But already at 12.00 PM and 6.00 PM the difference of temperature between ground and sea water was changed the mark and contrasts have made, accordingly, in relation to Haifa +1.9 and + 6.2 degrees, and in relation to Ashdod +1.25 and +5.8 degrees cor-respondently. Together with that, there is sharp turn of surface wind direction. At 8.00 AM in Beit Dagan the wind blows from the land and at 12.00 PM and 6.00 PM18 hours - from the sea. For the period from 8.00AM until 6.00 PM, it has turned on 131 degree.
We observe similar changes in wind direction on weather maps also. At early morning time, (fig. 1a) the wind blows from land to the sea, but already at 10.00 AM, the direction has fully changed both regards ground level and 850-mbar surface (fig. 1b, c). Station Beit Dagan on a map is designated by a triangle. Time presented due to Greenwich.
Tab. 3. CONDITION OF AIR TEMPERATURE STRATIFICATION AT 10.00 AM
Height Gradient of temperature Y 0/100 m Explanations to atmosphere conditions (for convection occurrence the dry-adiabatic gradient of temperature y should be more than 0.980 per 100 meters (6).
0-100 2.3 Very unstable stratification promoting formation of convective jets
100-200 0.8 Steady stratification. In this layer, the convection should be slowed down.
200-300 0.2 Steady stratification. Here the convection should aspire to zero.
300-400 +0.7 Layer of inversion.
400-500 0.5 Steady stratification
500-600 0.7 Steady stratification.
600-700 0.4 Steady stratification
700 -1000 +1.2 Layer of inversion
In table 2, the data of radiosonde Beit Dagan from 12.00AM due to local time are submitted, and in table 3, the value of a gradient of temperature in the bottom kilometer layer of air is given according to this radiosonde. From these tables follows, that in a layer of 0-100 meters where the gradient of temperature considerably exceeds dry-adiabatic gradient of 0.980/100 meters of height, stratification of an atmosphere unstable and should conduct to creation of convection. Above this layer, the ascending stream is sharply slowed down, and at height between 300 and 400 meters the first level of inversion is situated, in a layer of 700-1000 meters - the second layer of inversion is located. Capacity of the second layer of inversion makes +1.2 °C on 300 meters of rise. On these data, the vertical currents of air at 12.00 AM could not exceed 100-150 meters, concerning the level of radiosonde launching. Thus, 150 meters of a vertical stream are achieved for the account of con-vective variation (buoyancy force) and inertia of rise in the bottom not steadi-
«h3hk0-matemathmeckhe haykh
Opportunities of radar tracking way towards research of breeze..
ly stratified layer (y = -2.30/100 m, i. e. y >> ya), and for the account of poorly steady stratification at levels between 100 and 200 meters (y = -0.80 /100 m, i. e. y < ya). Here ya - dry-adiabatic gradient equal to 0.980/100 m. The level of station from which the radiosonde was launched makes 100 meters. Hence, concerning the sea level, vertical currents of air at this time could not exceed 200-250 meters. It is completely fair to assume, that owing to the further, within day, heating of underlying surface together with mountain-valley and breeze components of process, a level of convection and height of the first level of inversion should rise essentially up to midday.
Here RH - relative humidity in %, DEWP CO - a dew point in Celsius degrees, W. D - wind direction in degrees, W. S - wind speed in meters per second.
All these parameters (table 1, 2, 3) justify breeze development in the lower underlying air during the morning and daytime in our coastal area. Thus, above the land such type of the breeze should intensify ascending stream. As specifies by E.A. Burman (2), the maximum occurrence of breezes takes place in March-April and in September-October at Mediterranean coast of Israel. On the data (4), on east coast of Mediterranean Sea the optimum conditions for development of breeze are established in April, their influence is essential in autumn as well. Influence of breeze on a daily course of air temperature is significant on distance of 15-20 kilometers from seacoast.
Absence of overcast in this day together with intensive solar heating of hills and inflow, due to a breeze, considerably cool air from the sea in valleys in the morning was promoted the active development of cellular convection and mountain-valley circulation in the ground layer of air. This process promoted the creation of convective jets above the hills amplifying in coastal zone by sea breeze.
On fig. 2, the prospective scheme of air movement in 20-30 kilometers considered coastal zone is submitted due to this day. Temperature T1 < T2 < T3. Continuous horizontal lines are the isobars. Dashed lines are the lines of equal specific volume (isobar). Arrows show direction of air movement. Actually, in figure the combined circuit of morning breeze development on sea-land border is submitted as well as the classical scheme of morning mountain-valley winds, based on theorem of circulation with reference to baroclinic atmosphere (2,3). According to this circuit in the morning and in first half of the day, the sea is colder than land. In this connection, air above the land gets warm faster than above the sea and starts to rise. Thus, more cool air leaks below from the sea to land, compensating released air masses rising above the land. If there is hill
Fig. 2. Scheme of air movement towards incorporated breeze and moun-
tain-valley process in coastal zone of Mediterranean Sea in March 30, 2000, assumed on the meteorological data. V - surfaces of equal specific air volume (isosters), P - surfaces of equal pressure (isobars),
T1, T2, T3 - temperature of the sea, land (coastal part) and hill slope.
Arrows specify direction of air stream.
near the coast its slope focused to the sun, gets warm faster than valley. As a result, there is lowering of surfaces of equal specific volume (isostere), as derivates isobar-isostere air circulation rising on slopes and flowing from height in opposite compensation stream. Thus, the convective jets can appear above the hills. The compensation top stream can be directed aside opposite to the surface wind (as shown in fig. 2). More often, it is distributed, for the account of more powerful general geostrophic wind in the top part of jet, in one established direction. Such process was quite characteristic for our case. The data of the given radiosonde according to which at the level of more than 200 m, the stream is rather steadily directed from the part of sea (see tab. 2) testify to it. At night, the circulation gets return direction.
1.2. Radar-tracking surveys over flight of the large stork flock
On fig. 3, 4, 5 the «lines» of radio echo from the storks, received with the help of radar at wave band of 10 cm at 9.56 AM, 10.21 AM and 14 21 AM are submitted.
The variability of structure of these «lines» in rather close time interval, from 9.56AM until 10.21 AM can attract someone's attention.
Actually, «line» represented the set of many considerably direct pieces united in constantly varied branchy «line».
General time of radar-tracking surveys over the flock has made 5 hours, from 9.30AM up to 14.30 PM. The maximal length of «line» exceeded 100 km.
At 7.30 AM the radar on 50 km scanning marked strong negative refraction towards sea direction that proves the presence of temperature inversion in the lower surface air that should collapse with morning warming up. At 9.00 AM the negative refraction has stopped. In refraction zone the detection of radio echo from birds at small height is very complicated because of the raised reflection from ground clutter.
The first radio echo from groups of storks was found out at 8.00 AM in sector of 210-240 degrees on distance of 30-40 km from Latrun in Kiryat Gat vicinity. This zone is located on distance of 10-20 km from the sea in a shoreline, which height above sea level does not exceed 100 m. Further from the sea, the sharp increase of relief begins. According to (2) in similar zones the breeze front and mountain-valley circulation effect should be displayed most actively. At the initial moment of survey, the radio echo from storks looked as separate, chaotically located, slowly moving dots occupying the area of 10 km of distance and 20 km on azimuth. Fluctuation of the reflected signals on oscilloscope was characteristic for fluctuation of radio echo from bird groups, the period of fluctuation of amplitude maximum made some seconds. The characteristic attribute was the moving of dots that proved the obtained points were radio echo from birds. Radar-tracking reflectivity from these points on both channels reached 30 dB on distance of 25 km (nuo = 1.9 x 10-11 cm1 ). Here size of radar-tracking reflectivity n = 1001 • nR2/Q, where n - radar reflectivity in dB, R-dis-tance to the target in cm, Q - radar constant in cm3.
In our case n = 30 dB, R = 25 km, CA10 = 3,3 x 1026 cm3. Probably, similar points of radio echo were formed on the greater distance from station, however it was not possible to observe them because of curvature of the ground and, accordingly, small height of flight. The radio echo height from bird groups did not exceed 100 m from ground level (the height is determined with the help of radar). For the period of half an hour, the points of bird's radio echo have generated a faltering line, which was quickly extended in both sides (to the south and north). It justifies that storks take-off approximately in one time from various sites of the ground, grouped and occupied some position in the space, re-
«h3hk0-matemathmeckhe haykh
Opportunities of radar tracking way towards research of breeze..
minding a line. At 9.00 AM, the separate points have taken the form of the branchy line, which southern end was on distance of 50 km and northern has come nearer to radar. Radar reflectivity of the line end on distance of 50 km to the south made 18db on both channels (%i0 = 7.6 * 10-11 cm1). The height of the line part on distance of 30 km from Latrun made 250 m above sea level according to radar. The southern end of the line managed to be seen only at some antenna angles (0-0.2) on scanning of 50 km. Calculation of the height of distant radio echo point, in view of curvature of the ground, shows, that the maximal height of flight of flock in this place made 200-250 meters concerning to sea level. In view of size of radar-tracking reflectivity the maximal range of detection regards these birds by station MRL-5 in Latrun (270 m above sea level) could make more than 80 km, however they should fly at height not below 500 m above sea level.
The radio echo line was well visible on both channels. Difference was made only with its width, which corresponded to width of the directional diagram on both channels. On X = 3.2 it did not exceed 200 m on distance of 25 km, on X = 10 cm - 600 m accordingly.
At 9.30 AM, the radio echo of flock looked like a dashed line with length about 100 km, extended from the south to north. To determine the groundspeed from this parameter was not possible as occurrence of new sites of line within whole flight route occurred not only due to moving of all the birds from south to north, but also due to their rise from various areas of the ground. Groundspeed was determined for moving, separate, and stable in time sites of radio echo line. It has made about 40 km/hour. Separate points of radio echo at 2.00 PM could be seen in the north at reduction of the aerial up to angle of 0.2 on the distance of 80 km, i.e. the given groups of birds flied at height that was not less than 500 m above sea level. Taking into account the narrow diagram of the aerial (0.50 for X = 3.2 cm and 1.50 for X = 10 cm), simultaneous survey over the whole line of radio echo from flock at one aerial elevation angle is not possible. For restoration of radio echo line in zone near to radar, the surveys were conducted at large angles with the appropriate registration of line sites. Taking into account that at 12.00 AM birds flew by in a zone of direct visibility from the radar location, the opportunity was presented to estimate some parameters of their flight in visual mode. In immediate proximity from radar, in the visibility range without binocular, in the period between 12.00 AM and 01.00 PM the large bird flocks have flown by at height (by visual definition) of 200-300 meters, concerning radar height. The rough number of birds in each group made up
to 200 individuals. Their flight was accompanied rather long (up to 2-3 mines) soaring without wing beats above one place, thus they gradually rose, concentrated in more compact groups, and then being extended in a line, fast moved further to the north up to new place of soaring and grouping.
2. massive diurnal flight of large predatory bird, honey buzzard, on 10th and 11th of september 2001
2.1. Weather conditions
Weather in Israel in these days was characterized by light gradient of a high pressure (fig. 6a, b, c, d). In figures the fragments of surface weather maps for day and night time of September 10 and 11, 2001 are presented. Beit Dagan meteorological station is designated by a triangle. Thus, on 10th and 11th of September in the afternoon one can see above sea are the formation of regular anticyclone which center has moved aside to the land by night of September, 10 and was completely washed away by September, 11 was completely washed away. As a result, on 10th and 11th of September in the afternoon the atmosphere circulation in the bottom ground air layer and breeze circulation, form surface wind directed from the sea to land. Above the land, this air, coming from the sea, gets warm and rises upwards, forming convective jets, and on occasion, mesofronts. Radio echo of mesofronts was not visible these days, though already almost at the end of day on September, 10 it is possible to observe formation of weak cloudy layer extended in the same direction in which the strips of birds radio echo are focused (fig. 8). Thickness of this layer made 500 m, its top border was at height of 1km and it was much better seen on wave band of 10 cm (12 db at distance of 25 km for X = 10 cm and less than 6 db at the same distance for X = 3 cm). Nevertheless, that reflectivity from this layer on X = 3 cm was sufficient for formation of radio echo on the radar screen, means that reflections were formed not only due to the big temperature gradient, but also due to hy-drometeors. A nature of these hydrometeors formation is a question of separate discussion. Here pertinently to note the following. In a number of situations, the mesofronts of such type are registered quite well by radar (fig. 7). As an example of such mesofronts the photo of radar screen from 06.08.01 is submitted.
In a photo made from the radar screen on August 6, 2001 at 7,23 PM on wave band of 10cm, the radio echo of mesofront, generated due to the pro-
cesses occurred in surface layer on sea-land border is clearly visible. This echo represents rather narrow trip extended from the north to south. The limited scale of photo (25 km) does not give full imagination about all length and evolution of mesofront radio echo in time aspect, however due to journal records it makes about 35 km and was generated on distance of 40 kilometers from the radar, namely near the coastline. Up to the moment of photo registration, it was displaced on 20-25 km. (All other white stains on this and other photos from the radar screen are the reflections from hills). The top border of radio echo was equal to 2,5 kilometers that is much lower than a zero isotherm for this season. Thus, in accordance to radar journal records, the radio echo of this surface mesofront is well visible on wave band of 10 cm (n = 10-9 cm-1 or ~ 30 dBZ) and very poorly visible on wave band of 3 cm (~ 0dBZ). It is necessary to notice, that numerous surveys of such type radio echo in this coastal zone have shown the following. More often radar-tracking reflectivity from them is much more on wave band of 10 cm, however, the cases when radar-tracking reflectivity on various sites of such radio echo for both wave bands is shown on any other business are not rare. For example, one site is better visible on wave band of 10 cm, and other - on wave band of 3 cm. This phenomenon demands additional researches. It is possible to assume, that it is connected to condensation processes on separate sites of such a mesofront. In a result, there, where the condensation processes contribute to radio echo, the reflectivity on wave band of 3cm is more than on 10 cm and, on the contrary, on sites where the radio echo is formed only due to high values of temperature gradient, it has higher value on wave band of 10 cm. The wave band of 3 cm in radars like MRL-5 starts «to see» the signal reflected from hydrome-teors which sizes exceed 100 micron (1). Such size hydrometeors form dense enough clouds that could be seen visually. Actually, the radio echo presented on figure 7, was not visible, there were no clouds as well. It proves that the radio echo from some area of atmosphere was generated not due to hydrometeors, and was connected to reflection from area with the big gradient of temperature (7).
Once having generated on sea-land border, such mesofront is slowly displaced from the sea aside the land, sometimes on 30-40 km (2). On the basis of the carried out survey, the spatial orientation of such front, concerning coastline, together with radar-tracking reflectivity on its various sites under influence of a relief and mountain-valley circulation can vary, at times taking the form of curved line. Most frequently, the breeze front and processes proceed-
Fig. 6 (a, b).
Fragments of surface weather maps, September 10, 2001. c) 18.00 h; d) 00.00 h.
Fig. 6 (c, d).
Fragments of surface weather maps, September 11, 2001 c) 12.00 h; d) 00.00 h.
Fig. 7.
The breeze mesofront radio echo stretched from the north to south parallel to coastline.
ing on it remain not visible for radar or create the radio echo on separate and the most active sites. As already it was mentioned above, on September 10 only after 5.00 PM (look at figure 8), the processes of condensation and formation of weak clouds have begun in northern part of breeze mesofront, due to amplification of convection and auxiliary factors (probably increased moisture content). The radio echo strip from the birds has practically coincided with a line of breeze mesofront. The level of zero isotherm, according to Beit Dagan radiosonde was little bit above 1700 meters that could promote the formation of fine drops here. Further, this cloud did not develop because of instability energy absence at these levels and low relative humidity (according to a radiosonde at 1800m, air relative humidity did not exceed 28 %).
In such figure the narrow southern strip stands for birds, northern part of this radio echo transforms in one from weak overcast. As it was already shown in section 1.1, such circulating processes in conditions of Israel within this year period could not promote development of rain clouds without additional energy of large-scale circulating formations. However, they could create favorable conditions for the maximal display of regional seasonal and daily features of convective jets formation. In late autumn, in winter and in early spring the same conditions influence on sludging ability, aggravating or, on occasion, weaken-
Fig. 8. Birds radioecho transformed in his northern part in one from weak
clouds, I = 3 cm.
ing the large-scale circulating processes, including fronts. We can observe how the birds of passage use these local atmospheric processes.
For this purpose, we need to add the data on synoptic situation with some additional parameters of atmospheric condition in considered days.
In table 4, the data on surface air and seawater temperature are presented from observations at 8.00 AM, 12.00 AM, and 6.00PM on 10th and 11th of September according to Haifa and Ashdod stations.
From the table, it is visible, that on 10th of September the seawater at 8.00 AM at Haifa and Ashdod stations is warmer than surface air at the appropriate ground meteorological stations. Thus, already at 12.00 AM and 6.00 PM the difference between temperature of surface air and seawater water was changed with the mark and contrasts have made, accordingly, in Haifa +2.7 and + 4.9 degrees, in Ashdod +0.9 and +2.1 degrees. On September 11 - in Haifa - +2.9 and +4.5 degrees and in Ashdod - +1.3 and +3.1 degrees correspondingly. As it is stated in 1.1, such ratio of temperatures results in formation of breeze circulation that leads to convective jets development.
In tables 5 and 6, the data of Beit Dagan radiosonde from 12.00 AM (local time) taken on 10th and 11th of September are submitted. In table 7, the value of temperature gradient in the bottom layer of air is given according to this radiosonde.
Table 4. THE DATA ON AIR AND SEAWATER TEMPERATURE
FROM HAIFA AND ASHDOD METEOROLOGICAL STATIONS, 10th AND 11th OF SEPTEMBER 2001
September, 10 September, 10 September, 11 September, 11
Station of survey Haifa Ashdod Haifa Ashdod
Time of survey 08.00; 12.00; 18.00 08.00; 12.00; 18.00 08.00; 12.00; 18.00 08.00; 12.00; 18.00
Temperature in C°:
Air 26.4; 30.9; 31.4 26.6; 29.9; 29.4 26.3; 30.5; 30.2 26.7; 29.6; 29.6
Seawater 28.7; 28.2; 26.5 29.5; 29.0; 27.3 28.3; 27.6; 25.7 29.4; 28.3; 26.5
Difference of temperature of air and seawater -2.3; +2.7; +4.9 -2.9; +0.9; +2.1 -2.0; +2.9; +4.5 -2.7; +1.3; +3.1
Here RH - air relative humidity air in %, DEWP C0 - dew point in Celsius degrees, W. D - wind direction in degrees, W. S - wind speed in meters per second.
From these tables follows, that in a layer from the surface up to 100 meters (above radiosonde point), where the gradient of temperature (3.80/100 m on September, 10 and 3.80/100 m on September, 11) is exceeded considerably the dry-adiabatic gradient of 0.980/100 meters of height, the atmospheric stratification is strongly unstable and should conduct to convection creation. Above this layer the air temperature stratification is remain poorly unstable and indifferent up to height of 500 m on September 10 and up to height of 700 m on September 11(above radiosonde point). On these data, the vertical currents of air at 12.00 AM on 10th and 11th of September can reach 500 and 700 m accordingly, concerning the level of radiosonde point that is equal to 100 m above sea level. Hence, concerning the sea level, the top layer of convection in these days could reach 600 and 800 m correspondingly. The actual height of birds' flight due to radar-tracking measurements (concerning a level of station) on September 10 at 1.00 PM made 700-800 m and 800-900 m at 2.00 PM on September 11. It is
Tab. 5 SONDE ID: 2466164 RADIOSONDE OBSERVATIONS
Date: 10/09/2001, Time: 10:31 GMT (12:31), DATA FOR 100 meters LEVELS
PRES. mb TIME HH: HEIGHT, TEMP. RH DEWP W.D W.S
MM:SS m C° % C° Deg Knots
1008 00:00:00 0 30.6 52 19.6 318 11
997 00:00:21 100 26.8 64 19.3 316 14
986 00:00:40 200 25.7 68 19.3 315 16
974 00:01:00 300 25.0 71 19.3 319 16
963 00:01:23 400 23.8 74 18.9 328 14
952 00:01:43 500 22.9 78 18.8 337 11
942 00:01:59 600 22.4 75 17.6 348 8
931 00:02:16 700 22.6 68 16.5 3 6
920 00:02:35 800 21.7 68 15.6 31 5
910 00:02:52 900 21.5 66 14.8 53 5
899 00:03:10 1000 20.7 66 14.1 71 6
possible to assume that heating of underlying surface has strengthened unstable making atmospheres for the period between measurements of temperature by radiosonde and time of radar-tracking measurement of bird flights' height. This time difference exceeded one hour. It is necessary to note that the direction of birds' flight practically coincided with steady northwest wind direction from the sea on 10th and 11th of September. Only at height of convection top level, this direction changed to northeast.
Thus, on September 10 in layer from surface up to height of convection top level the wind direction is within 315-348 degrees. At height of 700 m, this is equal to 3 degrees, being displaced by every 100 m more to the east (800 m - 31 degree, 900 m - 53 degrees, 1000 m - 71 degree, 1100 m - 86 degrees, 1200 m - 97 degrees, 1300 m - 109 degrees and so on). Very similar picture is observed on September 11.
This factor also specifies that in the bottom surface layer the local factors together with breeze and mountain-valley circulation influence the wind direction.
Tab. 6. SONDE ID: 2480357 RADIOSONDE OBSERVATIONS
Date: 11/09/2001 Time: 10:35 GMT (12:35) DATA FOR 100 meters LEVELS
PRES. TIME HH: HEIGHT, Temperature. RH, DEWP, W.D W.S
mb MM:SS m C° % C° Deg Knots
1008 00:00:00 0 29.3 46 16.5 325 8
996 00:00:16 100 25.8 52 14.9 322 9
985 00:00:35 200 24.6 55 150 319 11
974 00:00:52 300 23.7 67 14.5 316 12
963 00:01:04 400 22.7 58 14.1 317 12
952 00:01:21 500 21.6 61 13.8 317 12
941 00:01:38 600 20.6 66 13.9 319 12
930 00:01:56 700 19.6 69 13.7 326 11
919 00:02:17 800 19.1 70 13.6 333 9
909 00:02:35 900 18.1 73 13.1 333 7
898 00:02:53 1000
2.2. Radar-tracking surveys
According to visual surveys of ornithologists on September
9, 10 and 11 in territory of Israel the big number of birds of passage, Honey Buzzard, stopped for the night roosting.
The first radioechoes from groups of birds on wave band of 10 cm were found out at 9.10 AM in sector of 250-360 degrees on distance of 80-85 km from Latrun, on September 10 and 11. This zone is located on distance of 1020 km from the sea in a shore which height above sea level does not exceed 100 m. Further, deep from the sea into the land increase of a relief begins.
On September 10, at the initial moment of survey, radio echo from birds looked as separate, chaotically located, several slowly moving dots and one strip with length about 5 km (at 10.00 AM the length of this strip already exceeded 30 km). The height of radio echo was about 700 meters.
On September 11, already at the first detection, the radio echo looked as several strips extended from the north to south, with length of 8-15 km every-
Table 7. CONDITION OF AIR TEMPERATURE STRATIFICATION
UP TO 12.00 AM.
Height, m Temperature gradient Y 0/100 m September 10 September 11 Explanations to atmosphere condition (for convection occurrence the dry-adiabatic gradient of temperature y should be more than 0.980 per 100 m (6)
0-100 3.8 3.8 Strongly unstable stratification
100 -200 1.1 1.2 Unstable staratification
200 -300 0.7 0.9 Poorly steady stratification
300-400 1.2 1.0 Unstable stratification
400-500 0.9 1.1 Indiffierent stratification - 10.09 Unstable stratification -11.09
500-600 0.5 1.0 Steady srtatification - 10.09 Indifferent stratification - 11.09
600-700 -0.2 1.0 Inversion layer - 10.09 Indifferent stratification - 11.09
700-800 0.9 0.5 Indifferent stratification -10.09 Steady stratification - 11.09
800-900 0.2 1.0 Steady stratification - 10.09
Indifferent stratification - 11.09
one. The height of bird flights, according to radar made 800 m. Fluctuation of the reflected signals on oscilloscope was characteristic for fluctuation of radio echo from bird groups. The period of fluctuation of maximum of radio echo amplitude, as well as in the case with storks, made some seconds. A characteristic attribute of that dots of radio echo are reflections from birds, there was nothing but the moving. Radar-tracking reflectivity from these dots on both channels reached 25 dB on distance of 25 km (September 10, n^o = 19 x 10-11 cm1), 18 dB on distance of 43 km (1.2 x 1011 cm1), 6 dB on distance of 82 km (2.8 x 10-12 cm1). On September 11, the reflectivity were equal to 8 db on the maximal distance of 82 km (5.8 x 1011 cm1) and 18 dB on distance of 27 km (4.5 x 1012 cm1).
As well as in case of survey over the storks flock, it is possible, that similar dots of radio echo were formed on the greater distance from station, however to observe them it was not possible because of earth's curvature and, accordingly, height of flight was insufficient for radar-tracking detection. In figures 9, 10, 11, 12, and 13 the evolution of radio echo strips from birds in time
and in space on 10 and 11 of September is submitted. Thus, as against the case of survey over storks, the part of figures is received by photographing the radar screen (11), and a part with the help of the computer-aided system (12, 13), allowing summarizing a signal from birds at all heights.
Let us consider these figures.
In figure 9, four pictures, from which two photos of the radar screen on wave band of 10cm and two, appropriate to these photos on time are the listing of computer processing results of a radar-tracking signal. Time of the appropriate figures and photos differs a little, as technologically to extract information by photographing the radar screen and with the help of the computer cannot be made simultaneously. Photos are executed at one elevation angle of the aerial (0.50), computer shooting is executed at all angles of possible birds detection. Time exposure of the radar screen is 10 sec and time of computer shooting and data processing is 2-3 minutes. In both figures, radio echo strips from birds on a background of reflections from local subjects (hills, constructions, planes etc.) are clearly visible. Nevertheless, the structure of radio echo from birds is much better visible on listings. Therefore, for example, on figure 9 central and southern part of birds radio echo are visible quite well, while in their photo it is not present. In computer figure, some strips from birds are visible good, while in the appropriate photo only one strip is visible well. Besides, in the same figure the lines of three planes, two in the south and one in the west are precisely visible. The radio echo from planes represents with dashed line. Moreover, the more speed of the plane, the far from each other dotted lines are situated. On distance between dashed lines, knowing the speed of aerial rotation, it is possible with sufficient speed to define the speed of the plane and to calculate the moment and time of crossing the line of the plane with birds. Having such operative information it is always possible to warn the pilots about possible crossing of the plane with the large birds flock. It is necessary to pay attention that in figure 9 the radio echo line from birds in northern part has coincided with zone of weak clouds formation. It is well visible both in photo and on computer printing. As it was already marked, this circumstance shows the presence of connection between the choices of flight line by the birds with areas of the most active convection.
On figure 10, on a background of reflections from ground clutter and other targets, computer printings of birds' radio echo are presented. They illustrate real picture regards two wave bands towards September 11 at 10.42 AM and September 10 at 3.09 PM. From the submitted figures, it is visible, that at com-
физико-математические науки
Opportunities of radar tracking way towards research of breeze..
puter shootings the radio echo structure from diurnal birds is visible better on wave band of 3 cm, than on 10 cm. It is confirm, that wider diagram of the aerial on wave band of 10 cm increases the areas of radio echo from all targets including ground clutter and birds. Strips of radio echo from birds on wave band of 10cm are wider and better visible, however thus they on many sites merge with ones from ground clutter. At the same time, it is necessary to bear in mind, that such conclusion is fair only for a radar-location of the large birds migrating in the afternoon. Small birds, namely they mainly fly at night as it was shown in (5), are better registered on wave band of 10 cm as this channel has higher potential.
Let us look at figures 11 and 12.
In figures, the evolution of radio echo from Honey Buzzard is presented towards space and time on September 10 according to the data received with the help of photographing of radar screen on wave band of 10 cm and according to computer processing of radar-tracking signals. In figure 13, the similar computer data for September 11 are submitted.
Spatial and time evolution of radio echo strips from birds confirms its dependence from circulation processes that develop in region. In our real case, its dependence from breeze and mountain-valley processes is especially visible. In such figures the pictures of the beginning and end of flights are not submitted, however even for given time (4 hours for September 10 and 5 hours for September 11), the strips of radio echo focused from the north to the south, were displaced from initial position more than to 20-25 km eastward. In all ground layers from surface level up to the top border of radio echo from birds as it was shown in 2.1, the wind direction steadily coincides with a direction of flight. Drift of the line to the west in this case can only be explained only by displacement of maximal convection from coastal line deep into land that can be in turn explained by movement of breeze front and conditions of mountain-valley circulation. General moving speed of maximal convection line has made roughly 5-5.5 km/h on September 10 and 4-4.5 km/h on September 11.
Due to radar-tracking data, the maximal radio echo line length was 100km for the period of survey. However, it is possible, that its actual length was more because of ground curvature and low birds airspeed. Because of this, the radar was not able to register the continuation of these lines. In some cases the radar detected up to 4 parallel lines of birds radio echo, each of which was focused from the north to south and was of some tens kilometers length.
а
в
Fig. 9
Comparative radioecho of migratory birds, obtained by photo registration of radar screen (b, d) and computer radar-tracking system (a, c), Septembr 10.
с
d
( ni)f Л I
5 or 4 чa
а, в) 14.06 - 14.32 с, d) 17.35 - 17.39
Fig. 10
Comparison of migratory birds' radioecho obtained by computer radar-tracking system on two wave bands (3 and 10 cm) a) 11 September, 10.42, l
физико-математические науки
Opportunities of radar tracking way towards research of breeze..
Fig. 11 (a,b,c,d,e,g) Evolution of radioecho from migratory bird Honey Buzzard in space and time (according to photo registration data, September 10, 2001), l
Fig. 12 (a,b,c,d,e,g). Evolution of radioecho from Honey Buzzards in space and time (according to the data of computer radar-tracking system, September 10, 2001), l
Fig. 13 (a,b,c,d,e,g). Evolution of radioecho from Honey Buzzards in space and
time (according to the data of computer radar-tracking system, September 11, 2001), l.
3. discussion of survey results
The most interesting fact is that the beginning of grouping and bird's tale-off in all three cases of survey has fallen to morning time when con-vective streams in ground layer of atmosphere were not generated yet. In the same time, the basic part of flight has fallen to the period of advanced convection.
This circumstance enables to assume, that birds do not choose weather and do not wait for formation of the convection for their seasonal flights, they use optimum structure of streams, that under influence of those or other weather processes are formed in flight region. The spectrum of weather conditions at which birds make the flights, is very wide. For this reason the seasonal «schedule» of flights is stable enough.
Conditions of weather influence, mainly, only the range of flight in time unit. If weather conditions are accompanied by presence of convective jets, birds spend less energy on flight and can move on the greater distance per time unit, otherwise this distance is decreases, due to weariness of wings.
Results of the given survey allow making the assumption, that the flock instinctively, by method of search for vertical jets with the help of own bodies and wings, has chosen a way and height of flight on which meteorological conditions in atmosphere have allowed it to spend a minimum of energy. Not casually, the line of flock flight only on separate sites is close to a direct line. As to all line, it in some cases branched and its structure quickly varies in time. In a way the convective jets acted as well as the strips formed under influence of coastal breeze and it mountain-valley circulating process during these days in this region. On these lines, it is possible to solve a feedback task, using characteristics of bird flight for definition of vertical movements structure in atmosphere.
The structure of birds' flight line depends on structure of vertical movements in surface air.
It is necessary to mention, that the computerized radar-tracking complex allows registering and giving the operative information on presence and character of massive flight lines with high reliability.
REFERENCES
1. Abshaev, I, Burtsev, I, Vaksenburg, C and Shevela, G. 1980. Manual
on application of radars MRL-4, MRL-5, MRL-6 in anti-hail system.
Leningrad, Hydrometeoizdat.
2. Burman, E. 1969. Local winds. Leningrad, Hydrometeoizdat, pp. 11113.
3. Bjerkness, V. 1900. Das dynamische Prinzip der Zirkulations bewegungen in der Atmosphare. Met. Zs.
4. Vitvitski, G. 1960. Climates of foreign Asia. Geographgis., Moscow.
5. Dinevich, L., Leshem, Y., Kapitannikov, A. and Shupiatcky, A. 2000. Use of the MRL-5 Radar for Birds Migration Studies, «Scientific Cooperation Israel-the CIS and Baltic States».
6. Dinevich, L., Leshem, Y., Sikora, O. 2001. Radar Observations Analysis of Season Bird Migration in Israel at Night, «Scientific Israel-Technological Advantages», ISSN: 1565-1533, VOL. 3.
7. Chernikov, A., 1979. Radar-tracking reflections from the clear sky.
8. Khrgian, A., 1978. Physics of atmosphere, Leningrad, Hydrometeoiz-dat.
ОБ АВТОРАХ
Леонид Абрамович Диневич, профессор, научный сотрудник Тель-Авивского университета (г. Тель-Авив, Израиль), доктор физико-математических наук. Лауреат гос. премии СССР в области науки и техники за 1985 год. E-mail: [email protected]. Yossi Leshem - профессор, заведующий отделом орнитологии Тель Авивского университета, лауреат премии государства Израиль в области экологии. Телефон 03-6406010. E-mail: yleshem@post. tau.ac.il.
Leonid Abramovich Dinevich, a professor in the Tel Aviv University (Tel Aviv, Israel), Doctor of Physical and Mathematical Sciences. Winner of the state prize of the USSR in the field of science and technology in 1985. E-mail: [email protected].
Yossi Leshem - Professor, Head of the Department of Ornithology Tel Aviv University, winner of the State of Israel on the environment.
