An integrated methodology to select the optimum site of an airport on an island using limited meteorological information

Transcription

1 Meteorol. Appl. 12, (2005) doi: /s An integrated methodology to select the optimum site of an airport on an island using limited meteorological information Pavlos A. Kassomenos 1, Ioannis K. Panagopoulos 2 & Athanasios Karagiannis 2 1 University of Ioannina, Department of Physics, Laboratory of Meteorology, University Campus, GR-45110, Ioannina, Greece 2 Sybilla LTD, Ypsilantou 16, GR-15122, Marousi, Athens, Greece pkassom@cc.uoi.gr Limited meteorological monitoring networks provide insufficient information for determining the suitability of a specific location for an airport runway. These data limitations are compounded by the constraints imposed by the terrain itself. Clusters of small islands (archipelagos) generally lack dense meteorological monitoring networks, while the land water distribution induces different meteorological regimes on neighbouring islands. In this paper we present an integrated methodology to study the meteorological characteristics of potential runway sites on a medium-size island in the Aegean Sea in Greece. The methodology is based on studying the three scales of motion : (i) the synoptic scale, through a synoptic classification scheme, (ii) the mesoscale circulations with the aid of a Computational Fluid Dynamics (CFD) model, and (iii) micro-scale characteristics of each potential runway site through in-situ inspections. 1. Introduction Over the last decade Greek legislation has been harmonised with relevant European Union directives that requires an Environmental Impact Assessment (EIA) to be conducted for every project undertaken in the Greek dominion. Because communication between the islands and the capital is vital for island inhabitants and visitors alike, the Greek authorities have set in motion plans to develop or reconstruct airports on most of the islands of the Aegean Sea. The Aegean archipelago consists of a large number of islands with varied land water ratios, variable sizes and diverse landscapes. The small size, as well as the varying topography, of many of the islands significantly limits the number of sites that are suitable for airport development. Another major problem is that few of the islands have adequate meteorological monitoring networks, especially with regard to wind regimes in the area around the islands. Only on large islands are there meteorological stations, but many of these are substandard and operate in non-representative areas at limited times. The reliability of their data is poor in many cases. The varied landscape of the islands (mountains, hills, steep slopes, lack of vegetation, cultivation, etc.) favours the formation of local circulation systems that may affect potential runway sites by interfering with aircraft taking-off and landing. Moreover, the Aegean Sea is affected by circulations of varying spatial scales, forming a rather complicated flow field over the whole area. In this work, we propose a novel methodology to overcome the lack of adequate and reliable meteorological information. Using the case study of the island of Chios, in the north-eastern Aegean Sea, we aim to identify the best site for a runway. The methodology consists of a three-step procedure based on the different scales of motion (synoptic, mesoscale, microscale) occurring in the general area of Chios and especially over the alternative runway sites. 2. Data and model description 2.1. The data On Chios, near the suggested airport location at Kontari, a meteorological station has been in operation since 1973 (Figure 1). It records temperature, humidity, meteorological phenomena and wind speed every 231

2 Pavlos A. Kassomenos, Ioannis K. Panagopoulos &Athanasios Karagiannis Figure 1. The island of Chios showing the four possible runway sites. 12 hours. Analysis of the meteorological data shows that the mean annual temperature is 17.3 o C, with a minimum in January/February (about 9.7 o C) and a maximum in July (about 26.4 o C). The highest temperature ever recorded was 40.6 o C in August and the lowest ( 4 o C) in January/February. The humidity is relatively high because the station is situated near the sea. The mean yearly precipitation is 530 mm, with December and January being the wettest months. The maximum precipitation recorded over 24 hours was 184 mm in September. It rains about 50 days in each year with snow being rare on Chios. Fogs appear usually during August and September and thunderstorms occur on about 15 days each year, mainly during winter. The winds are mainly northerly with a mean strength of 9 knots, increasing during high summer and winter months to knots. On about 42 days of the year the winds are stronger than Force 6 and on about five days they are exceed Force 8 (usually November March) The model In order to make a thorough study of the motion of air masses and the vertical structure of the atmosphere at 232 the possible runway locations, the CFD PHOENICS model was used. This model is based on the stationary solution of the equations of conservation, momentum, energy and mass. The model is applicable to various stability classes of the atmosphere as well as to special circulations such as sea breezes and slope winds. It solves a set of elliptic partial differential equations in a 3-D steady state environment (Launder & Spalding 1972 ; Markatos 1987). The dependent variables of the model are the wind velocity components, pressure, temperature, and turbulent kinetic energy (Panagopoulos & Markatos 1991). The modelling domain is 70 km 70 km (horizontal) and 7 km (vertical). The area was divided into uniform cells ( x = 1 km) in the horizontal plane and 40 non-uniform cells in the vertical plane. For the exact representation of the physical obstruction to the flow, a 3-D solid obstacle of the island of Chios was simulated, based on iso-height maps with 1 km 1 km resolution. In the vertical plane, the resolution was 20 m for the first six steps, 50 m for the following five steps, 100 m for the next five and variable for the remaining 24 steps.

3 For the initialisation of the model we used the synoptic classification scheme and we chose one representative date for each one of the synoptic categories. For each of these dates, the radiosonde data from Izmir airport in neighbouring Turkey was used. The dates chosen were in the summer, which is characterised by strong winds, local circulations and low precipitation. In the model, the latent and sensible heat fluxes are derived from the incoming solar radiation, based on the Julian day. 3. Methodology The methodology introduced here describes the flow field and the meteorological characteristics for alternative runways sites in an island situation. The methodology proposed involves the examination of the three scales of motion of the atmospheric fluid in the area. First, we examined the large-scale weather systems (synoptic) that affect the area and the weather types. Secondly, we examined the mesoscale circulations based on the topographical features of the area and the outputs of a CFD model. The model was run for each of the weather types found in the first stage of the procedure. Finally, we checked the microscale circulations at each potential runway site using the specific topographical characteristics of each area. In addition, the analysis of the existing meteorological observations is used to complement the development of the synoptic classification scheme. 4. Description of the area : alternative runway locations The island of Chios is located in the north-eastern part of the Aegean Sea. From a geographical point of view, it could be characterised as an extension of the Asia Minor continental area. In relation to the other Greek islands it is of medium-size with an area of 842 km 2.It consists of two separate landscape environments : the northern part of the island is characterised by very limited vegetation cover and tall, stony, abrupt and bare mountains ; the southern part is hilly and covered by vegetation to a varied degree. Its distance from the nearby mainland coastline varies between 7 and 40 km. On the island of Chios, four alternative locations for the development of a runway were short-listed by the relevant authorities. The alternative locations are Astifidolakos and Kontari in the central part of the island, and Nenita and Dotia in the south. The positions of the potential runway sites, as well as, the position of the single existing meteorological station are shown in Figure 1. Selecting the optimum site for an island airport 5. Meteorological analysis of the flow fields The composite flow fields in the vicinity of Chios are the combination of various scales of circulations (large, meso- and microscale) The synoptic scale A synoptic system is a large-scale weather system covering an area of about 1000 km 2. The synoptic classification usually reveals the mean synoptic systems occurring in an area. A contemporary synoptic classification was made for southern Greece by Kassomenos (2003a, 2003b), who identified the main weather systems occurring in each season of the year over Greece. Each area of course has its specific characteristics, and the local topography influences has a significant effect on the observed weather regimes. The synoptic analysis was based on the meteorological records of the Chios meteorological station. The surface and the 850 hpa levels were used to produce maps of the synoptic pressure fields over the area. The records of the nearby Izmir meteorological station were also used to validate the results of the scheme. The meteorological analysis of the 30-year meteorological records (especially winds) reveals the following facts. Owing to the Coriolis force, the northern synoptic flow passing through the Aegean Sea is turned towards the east where it then follows the coastline of the mainland. The northern synoptic flow thus becomes north-westerly along the western edge of Chios, while some of this flow permeates through the gap between Chios and the mainland. Southerly winds are also possible in the area but are less frequent. Easterly winds blowing from Asia Minor are rare in the vicinity of Chios. This flow is usually weak and dry, because the vegetation on the mainland is poor and the straits between Asia Minor and Chios (the Chios channel) are very narrow, so the air masses passing over the channel cannot take up much water vapour. By contrast, the westerly air flow is more frequent, especially during the winter months. It is combined with intense precipitation and possible thunderstorms due to the fact that it meets the geographical system of the eastern Aegean Sea islands (with a mean height of 1500 m) and it is forced to ascend. Moreover, passing over the Aegean Sea means that it absorbs significant amounts of water vapour. From the analysis presented above, we have seen that there are four significant synoptic patterns in which the prevailing wind directions are north, north-west, south and west, respectively. The quantitative analysis (of the meteorological records mentioned above) shows that NW and N winds are very frequent (more than 65% of the days each year), followed by W winds (almost 20%) and S winds (about 10%). The remaining 5% of the days are characterised 233

4 Pavlos A. Kassomenos, Ioannis K. Panagopoulos &Athanasios Karagiannis either by easterly winds or calm conditions. We examined each synoptic weather type at two wind speeds (8 and 13 m/s) as described below, which led to eight meteorological scenarios (four weather types for each of two wind speeds). These wind speeds refer to the mean synoptic wind at the level of 850 hpa (e.g m). To initialise the model, a radiosonde from the meteorological station at Izmir was used for each case. It must be noted that civil aviation regulations allow small aeroplanes to fly when wind speeds are below 15 knots (e.g. 7.5 m/s) and large aeroplanes when wind speeds are below 25 knots (e.g m/s). For this reason we have chosen the wind speeds of 8 and 13 m/s The mesoscale regime The dominance of the N S flow field in the area of Chios leads to the channelling of the synoptic flow in the area between the island and the coast of Asia Minor. The direction of such a circulation is perpendicular to the coast and could create problems to the landing taking off procedure on those runways with a N S orientation. The strong northerly winds limit the development of mesoscale circulations such as sea breezes. By contrast, calm conditions favour the development of such circulations. The existing water area between eastern Chios and the coast of Asia Minor (although of variable extent) is not large enough to allow the development of a strong sea breeze cell that would penetrate into the interior of the island. Owing to their proximity to the coast, two out of the four proposed runways (Kontari and Astifidolakos) may be affected by sea breezes. In the southern and northern part of the island, where the existing water area between the island and the mainland increases, development of stronger sea breeze cells may occur. The physical characteristics of the island (mountains, hills, abrupt slopes, and vegetation distribution, etc.), favour the formation of slope winds and intense turbulence phenomena which must be taken into account when selecting the appropriate location for the runway. The ground cover, which in many cases is bare (especially in the central and north part of the island), favours the development of these kinds of circulations and the intensifying of the sea breeze cells. A bare soil favours the formation of intense thermal flows in the form of sea/land breezes and up/downslope winds, due to the intense heating of the soil during the day and intense cooling during the night (warm period of the year). It must be noted that soils with significant vegetation cover contain significant amounts of humidity and thus one part of the incoming solar radiation is spent to evaporate the humidity (i.e. latent heat). So the available energy is not enough to establish intense mesoscale circulations (Triantafyllou & Kassomenos 2002). 234 In order to simulate the mesoscale circulations, we used the CFD model PHOENICS, which was executed for the eight different scenarios identified in the synoptic analysis. Since the alternative runways could be grouped into (i) the central runways (Astifidolakos and Kontari) and (ii) the southern runways (Nenita and Dotia), the mesoscale model was run only for two domains : the central Chios domain and the southern domain. Central Chios The meteorological fields computed by the model showed that, when the synoptic wind is coming from the north or northwest, the topographical features in the area of Astifidolakos and Kontari do not affect significantly the wind flow, which remained from the same directions in the enlarged area of the two runways. Specifically, the winds are parallel to the potential runways of Astifidolakos and Kontari when the synoptic flow is from the north or form a 45 o angle when the winds are from the north-west. The same was found when the wind flow comes from the south (i.e. the wind blows parallel to the runways). When the synoptic flow is from the west the winds are perpendicular to the runways. Figure 2 presents a typical wind flow regime during northern synoptic wind of 8 m/s speed at 500 m height above sea level. In the same context, Figure 3 presents similar flow for wind direction perpendicular to the two runways at 200 m height above sea level with speed about 13 m/s. The vertical components of the wind play a significant role in the safety of the flights, since strong wind-shear is dangerous during the landing taking off procedure. Figure 4 shows a weak wind shear near the ground (e.g. 200 m above sea level) in Kontari, while in Astifidolakos the wind shear was negligible. This refers to the scenario of a NW synoptic wind (8 m/s). When the synoptic wind was coming from the south (13 m/s) the characteristics of the wind shear remained the same over Astifidolakos, but over Kontari a shallow wind shear was detected (Figure 5). South Chios The orientation of the two potential runways of southern Chios is SW NE. If we examine the flow fields around the sites when the synoptic wind was coming from the NW (8 m/s), we see that the winds are almost perpendicular to the runways (Figure 6). The winds are not so strong in Nenita, but in Dotia are stronger. In the case of westerly synoptic winds, the flow is somewhat perpendicular to the runways (at an angle of about 50 o ). The same was also detected when the synoptic flow was from the north (at an angle of about 45 o ). These regimes may cause problems to the landing taking off procedure of the airplanes.

5 Selecting the optimum site for an island airport Figure 2. The wind flow over central Chios at a height of 500 m above ground (scenario with northerly wind, 8 m/s). Figure 3. The wind flow over central Chios at a height of 200 m above ground (scenario with westerly wind, 13 m/s). Figure 7 shows the mesoscale flow over Dotia and Nenita when the synoptic flow was from the south (13 m/s) at 200 m above sea level. It can be observed that the air flow is at an angle of about 45 o to the runways. As in central Chios, we also examined the vertical component of the wind. It was found that in Dotia the wind shear is stronger compared with Nenita (Figure 8), when the synoptic wind was blowing from northerly or southerly directions (Figure 9) The microscale circulations In this section the micro-meteorological characteristics of each position are analysed using in-situ inspections 235

6 Pavlos A. Kassomenos, Ioannis K. Panagopoulos &Athanasios Karagiannis Figure 4. The vertical wind component over central Chios at a height of 200 m above ground (scenario with NW winds, 8 m/s). Figure 5. The vertical wind component over central Chios at a height of 200 m above ground (scenario with southerly winds, 8 m/s). and questionnaires completed by both the authorities and local residents. Kontari The orientation of the runway is north south. The possible sea breeze/land breeze circulations are perpendicular to the runway and consequently may 236 affect the landing taking off procedure. In the previous section we noted why we do not expect intense circulations of this kind in this location, due to the relatively narrow stretch of sea between the island and the mainland (8 km). The development of shallow anabatic/katabatic flows in the area is possible due to the hilly area to the west of the runway, which becomes mountainous further away.

7 Selecting the optimum site for an island airport Figure 6. The wind flow over south Chios at a height of 200 m above ground (scenario with NW winds, 8 m/s). Figure 7. The wind flow over south Chios at a height of 200 m above ground (scenario with southerly winds, 13 m/s). The topography is responsible for the development of slope winds, perpendicular to the runway, which may affect the landing taking off procedure. The frequency of such phenomena is not significant: they occur during summer, but their intensity diminishes at other times of the year. Thunderstorms and other turbulence phenomena occur during the cold periods of the year with a frequency of 1 3 days per month. Fogs are very rare. From the meteorological analysis of the available data, winds perpendicular to the runway with a magnitude higher than 15 knots occur on about 4% of the days each year, while winds with a magnitude higher than 25 knots occur on about 2% of the days each year. Astifidolakos Astifidolakos is located in central-east Chios and has a N S runway orientation. The location is well known 237

8 Pavlos A. Kassomenos, Ioannis K. Panagopoulos &Athanasios Karagiannis Figure 8. The vertical wind component over south Chios at a height of 200 m above ground (scenario with northerly winds, 8 m/s). Figure 9. The vertical wind component over south Chios at a height of 200 m above ground (scenario with westerly winds, 8 m/s). for its unusual microclimatic conditions, especially for the high frequency of fogs. The area of Astifidolakos comprises a small plateau with a mean height of 300 m above sea level close to the east coast (the channel between Chios and the mainland coast is about 20 km across), while in the west there is a mountainous area reaching 800 m height. The area is affected by a sea breeze cell which is perpendicular to 238 the runway and is, of course, more intense than that of Kontari due to the greater extent of the water area. At the east end of the site there is a cliff, which may cause turbulent effects. There is a high slope leading upto the mountainous area to the west of the site, resulting in intense slope winds perpendicular to the runway. The altitude alone, as well as the characteristics of the terrain (the area is open from

9 the N and S), is responsible in general for stronger winds compared to the site at Kontari. (c) Selecting the optimum site for an island airport the two sea-breeze cells, one from the bay of Kalamoti and the other from the Aegean Sea. The flows in combination with the altitude may create fogs and possibly thunderstorms with a frequency higher than at other potential sites during all seasons. Nenita This site is located in the south of the island. The direction of the runway is NE SW and is designed to be lie in a shallow canyon surrounded by hills with heights between 100 and 200 m. At the edge of the canyon, the hilly area becomes higher reaching 400 m. The position of the runway inside the canyon may induce intense channelling effects, while the anabatic/katabatic flows near the walls of the canyon and the nearby hills may induce local circulations responsible for the appearance of turbulent phenomena and fogs. At heights above 300 m, wind shears occur due to the topographic characteristics of the area. The position of the airstrip would seem to be affected by three shallow sea-breeze cells, two of them (from Megalos Limnionas NE, and the Aegean Sea SE, respectively) with 45 o angles to the runway, and the third parallel to the runway coming from the bay of Kalamoti. At this location, the channel between Chios and the mainland coast is about 15 km for the first two cells and greater for the third. The interaction of the three seabreeze cells leads to turbulence and fogs because of the differential water vapour content and vertical extent of the three air masses. This runway may be affected by a larger number of thunderstorms owing to the local topography. Dotia Dotia is located on the south edge of the island. The direction of the runway is SW NE, lying inside a canyon with walls m in height. This position is affected by a rather complicated flow field, due to: (a) (b) the prevailing edge effects of the large-scale flow around the south side of the island. In this area, the two parts of the divided synoptic flow, i.e. the more intense and humid NW and the NE flow, interact leading to the creation of fogs and turbulent phenomena; the channelling of the flow inside the canyon, as well as, the slope winds near the walls of the canyon and the nearby hilly areas in their vicinity (heights up to 500 m). It must be noted that the slope of the walls of the canyon and the hills is significant. Therefore, the anabatic/katabatic flow is expected to be intense. This is a significant disadvantage for this site, since the direction of the flow is perpendicular to the runway; and The sea channel between southern Chios and the mainland coast is greater than 30 km, leading to the formation of rather intense sea-breeze cells with directions that may be perpendicular to the runway if the sea breeze comes from the bay of Kalamoti, or at a45 o angle if the sea breeze comes from Aegean Sea. The interaction of these two cells creates a complicated flow field. This may also induce intense turbulence phenomena, as well as fogs, reduced visibility, and mists that render the position more problematic than the other potential runway sites. Dotia is expected to experience more frequent thunderstorms, fogs, turbulence, rains and other intense weather phenomena than the other potential runway sites on the island. 6. Conclusions In this work we examined four alternative locations for the siting of a runway on the island of Chios. We followed a three-stage methodology to study the problem at three scales of motion. First, we studied the synoptic weather regimes based on meteorological records not only from Chios, but also from the Turkish station of Izmir, and we distinguished four different weather types. Then we examined the mesoscale circulations using the CFD model PHOENICS for each of the synoptic scenarios. Finally, the microscale circulations were examined through in-situ inspections and questionnaires. The optimum site, from a meteorological point of view, is the location of Kontari, followed by Astifidolakos, Nenita and Dotia. The Kontari site was less affected by adverse meteorological phenomena (fogs, wind shears, local thunderstorms, etc.) compared with the other sites. It must be noted that although meteorological factors are significant, they are not the factors to be taken in to account. Other significant factors in the decisionmaking process include access to the site, the existing road network and relevant facilities, the proximity to a town (especially the capital of the island), and air and noise pollution. Acknowledgements This work was partly funded by the Greek Civil Aviation Service. The authors would also like to thank the Prefecture of Chios for the valuable help and information that was made available during the course of this work. References Kassomenos, P. (2003a) Anatomy of the synoptic conditions occurring over southern Greece during the second half 239

10 Pavlos A. Kassomenos, Ioannis K. Panagopoulos &Athanasios Karagiannis of 20th century. Part I. Summer and winter. Theor. Appl. Climatol. 75 (1 2): Kassomenos, P. (2003b) Anatomy of the synoptic conditions occurring over southern Greece during the second half of 20th century. Part II. Spring and autumn. Theor. Appl. Climatol. 75 (1 2) : Launder, B. E. &Spalding. D. B. (1972) Mathematical Models of Turbulence, London: Academic Press. Markatos, N. C. ((1987)) Computer simulation in techniques for turbulent flows. Encyclopedia of Fluid Mechanics Vol. 6 : Complex Flow Phenomena and Modeling, Houston : GULF Publishing Company. Panagopoulos, G. & Markatos, N. C. (1991) A method of assessing the contribution of various pollution sources through mathematical modelling. Paper presented at the International Conference on Environmental Pollution, Lisbon, April Triantafyllou, A. & Kassomenos, P. (2002) Aspects of atmospheric flow and dispersion of air pollutants in a mountainous basin, Science of the Total Environment 297: