THE LAKE TEKAPO EXPERIMENT (LTEX) an Investigation of Atmosphenc Boundaiy Layer Processes in Complex Terrain

THE LAKE TEKAPO EXPERIMENT (LTEX) An Investigation of Atmosphenc Boundaiy Layer Processes in Complex Terrain

BY A. P. STURMAN, S. BRADLEY, P. DRUMMOND, K. GRANT, P. GUDIKSEN, M. KOSSMANN, H. A.

MCGOWAN, A. OLIPHANT, I. F. OWENS, S. POWELL, R. SPRONKEN-SMITH, AND P. ZAWAR-REZA

Understanding atmospheric processes operating at a range of spatial and temporal scales is paramount in explaining local wind fields and boundary layer characteristics in mountainous terrain.

he exchange of heat and momentum between boundary layer structures and winds generated the earth's surface and the overlying atmosphere within large mountain valleys and basins (Ekman Tis fundamental to local wind regimes, such as 1998; Whiteman et al. 1999, 2000; Weber and sea breezes and mountain-valley circulations. Kaufmann 1998). The Mesoscale Alpine Program in Dynamically induced effects, such as topographic Europe also examines airflow within alpine regions channeling, also result from atmosphere-terrain in- (Emeis and Rotach 1997), although it puts more teraction. Several recent studies have focused on the emphasis on precipitation. In the United States, a research program concerned with the nature of boundary layer structure and local flows in large AFFILIATIONS: STURMAN, DRUMMOND, KOSSMANN, OLIPHANT, OWENS, mountain basins has recently begun (Doran et al. SPRONKEN-SMITH, AND ZAWAR-REZA—Department of Geography, 2002). The Lake Tekapo Experiment, in New University of Canterbury, Christchurch, New Zealand; BRADLEY AND GRANT—Department of Physics, University of Auckland, Auckland, Zealand, (LTEX) is part of this international effort New Zealand; GUDIKSEN—Lawrence Livermore National Laboratory, to quantify the influences of boundary layer struc- Livermore, California; MCGOWAN AND POWELL—Department of tures and wind regimes. Geography, University of Queensland, Brisbane, Australia In LTEX, the general aim is to improve knowledge A supplement to this article is available online (DOI: 10.1175/BAMS- of the effect of the earth's surface characteristics on 84-3-Sturman) the lower atmosphere, particularly on mesoscale flow. CORRESPONDING AUTHOR: Prof. Andy Sturman, Department of Wind at this scale affects our comfort, erodes soil, Geography, University of Canterbury, Private Bag 4800, Christchurch, New Zealand provides the potential for wind power, and disperses E-mail: [email protected] dust, pollutants, and pollen. LTEX is a detailed analy- DOI: 10.1 I75/BAMS-84-3-37I sis of local and regional wind systems involving intensive field measurements and mesoscale numerical In final form 26 July 2002 ©2003 American Meteorological Society modeling. The main objective is to investigate how local wind systems are generated by terrain and ther-

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Unauthenticated | Downloaded 09/24/21 10:23 AM UTC mal characteristics and how these winds interact with each other, as well as with synoptic airflow. Lake Tekapo, located at the northern end of a major mountain basin in the Southern Alps of New Zealand, is an ideal natural laboratory for the study of complex wind interactions. A range of dynamic and thermal effects develop when the prevailing winds interact with complicated terrain. There are extensive ranges above 2000 m throughout this alpine region, with peaks reaching 3000 m immediately west of the field area. The South Island is also a significant barrier to the westerly winds that dominate at its latitudes (41°-46°S) (Fig. 1). When these winds interact with the mountains, upstream blocking (McCauley and Sturman 1999), a downstream foehn (Lamb 1974; Brenstrum 1989), and forced and pressure-driven channeling of airflow within mountain valleys (Revell et al. 1996) can all develop. Orographic disturbance of the regional pressure field gen- erates frequent lee troughs, which significantly affect winds on the FIG. I. Map of the Lake Tekapo area showing the location of AWS sites, eastern side of the South Island vertical sounding sites, and aircraft vertical profiles. The inset shows the (McKendry et al. 1987). South Island of New Zealand, the Southern Alps, and other sites men- Lake Tekapo is located imme- tioned in the text. diately downwind of the highest of the Southern Alps (Fig. 2). Rain and snow spilling batic-katabatic winds, mountain-valley circulations, over the main divide only 15-50 km to the northwest and lake-land breeze systems, as described in earlier create a strong downwind precipitation gradient research (McGowan et al. 1995; McGowan and (Sinclair et al. 1997; Chater and Sturman 1998) Sturman 1996a). (Fig. 1). The surface varies significantly from high, This variety enables LTEX to investigate the rela- glaciated regions to broad alluvial river valleys, bare tionship between surface heat exchange, atmospheric rock, and tussock grassland at lower levels (Figs. 3 and boundary layer development, and local winds. 4). These surface characteristics and the variety of Previous researchers have investigated airflow over slope angles and orientations in the study area result flat terrain with surface discontinuities (Arritt 1987; in strong spatial and temporal differences in the heat- Doran et al. 1995; Kuwagata et al. 1994; Lewellen et al. ing and cooling of the overlying air masses and the 1996; Chen and Oke 1994), and over complex terrain thickness of the turbulent boundary layer. Thermal (Bossert 1997; Fast et al. 1996). Compared with some discontinuities form at the edges of large cold lakes previous studies, the Lake Tekapo area is considerably (such as Lake Tekapo) in several mountain basins and more complex, with significant relief and varying sur- at the edge of snow and ice at higher elevations. The face character, including the marked contrast between thermal heterogeneity in the study area results in a the lake and its surroundings (and between the South complex pattern of diurnal local flows, including ana- Island and surrounding ocean). This in turn leads to

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Unauthenticated | Downloaded 09/24/21 10:23 AM UTC FIG. 2. Satellite image of Lakes (right) Tekapo and (left) Pukaki in the central Southern Alps of New Zealand (obtained from the National Aeronautics and Space Ad- ministration).

thermally induced circulation systems of different temporal and spatial scales. Clearly the winds of this area evince several different processes interacting on a range of time- and space scales. Such interaction is common in New Zealand (McKendry et al. 1986; Sturman 1992; McGowan and Sturman 1996a; FIG. 3. Land surface classes over the Lake Tekapo area McGowan et al. 1995) and includes dynamically chan- derived from supervised classification of summer im- neled flow that penetrates complex terrain and local ages captured by the IRS-IC satellite. wind fields affected by numerous surface forcing factors. Localized wind systems, slope flows, mountain- valley winds, and lake-land breezes superimpose on more extensive foehn and mountain-plain (and land- sea) effects that link the Lake Tekapo area with other parts of the South Is- land (McGowan et al. 1995; McGowan and Sturman 1996a).

RESEARCH QUES- TIONS. The energetics of wind systems generated by both marked surface dis-

FIG. 4. View of Lake Tekapo and its surroundings from the south.

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Unauthenticated | Downloaded 09/24/21 10:23 AM UTC continuities (in this case, alpine lake breezes) and being investigated, together with the transition be- complex terrain (Chen and Oke 1994; Kuwagata et al. tween day- and nighttime regimes. The development 1994; Lu and Turco 1994) are therefore being inves- of lake-land breezes close to mountain slopes is ex- tigated. The effect of the lake and surrounding slopes pected to enhance the onset and cessation of katabatic on the development of nocturnal circulations is also winds. The effect of the heterogeneous surface on the morning inversion break up, not taken into account in existing conceptual models of convective boundary layer development in valleys (Whiteman 1982), is also being examined along with the interaction of along- and cross-valley winds. At the large scale, onset of the mountain wind in the lake basin during the evening transition may be delayed by the regional plain-mountain circulation, which often does not ease before midnight. Consequently, both the onset and cessation of the nocturnal wind field in the Tekapo area are thought to respond to a range of forcings. For example, results indicate the existence of anomalous nocturnal up- valley flows over the lake area following sunset. This may be related to the late arrival of a plain-to- mountain wind, but may also be assisted by a posi- tive land-lake temperature gradient that lasts late into the evening over the delta north of the lake. Field data FIG. 5. Interaction of topographically channeled airflow analysis and numerical modeling are being used to in the upper Godley Valley with the valley wind circulation during 14 Feb 1999. investigate the boundary layer and airflow structures associated with slope winds, mountain-valley circulations, alpine lake breezes, and plain-mountain flows.

How does dynamic channeling interact with thermal effects in this area? The dominant westerly synoptic flow over the South Island is commonly channeled into a northerly wind in the narrow northern section of the study area (Fig. 1). Figure 5 shows a developing valley wind in the Godley Valley north of Lake Tekapo (Fig. 1) interacting with down-valley-forced channeling of the gradient wind on 14 February 1999. The prevailing northwesterly flow upwind of the South- ern Alps was evident from the wind profiles for Hokitika. Channeling of gradient westerly to northwesterly flow in the Tekapo area is frequently associated with a prevailing 500-hPa westerly geostrophic flow. The role of surface energy exchanges in coupling

FIG. 6. (a) Typical daytime cloud development along the foothills on the eastern side of the Tekapo basin, during clear summertime conditions on 20 Jan 1996 [Advanced Very High Resolution Radiometer (AVHRR) image provided by Landcare Research], and (b) a waterfall cloud along the Two Thumb Range resulting from air descending into the basin, viewed from the northern end of Lake Tekapo (sodar in fore- ground).

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Unauthenticated | Downloaded 09/24/21 10:23 AM UTC this down-valley foehn with local thermally induced air contaminants (see McGowan et al. 1996), as well winds is currently under investigation (McGowan as aviation weather forecasting in complex terrain. et al. 2002). Of particular interest is the interaction of the How is the valley/basin circulation affected by larger-scale down-valley-channeled foehn with the combined wind systems? The basin atmosphere is not a closed valley-wind-lake-breeze circulation. This thermally system. Heat and moisture may be transported into generated system often undercuts the foehn north of and out of alpine basins by larger-scale thermally in- the lake unless it is flushed from the whole basin by duced circulations. The convergence of low-level the strong foehn, which regularly attains velocities in winds around the coast of the South Island is clearly excess of 30 m s_1 ahead of an approaching cold front apparent during weak gradient synoptic situations. (McGowan and Sturman 1996a). The convergence of The depth of onshore flow is seen to be typically of the thermally induced winds and the foehn in the the order of 1000 m or less, developing before mid- Godley Valley is often characterized by dust devils, day and often continuing through to midnight. Both with plumes of dust clearly defining the microfront. the sea-breeze and mountain-plain circulation appear Sometimes the combined lake-breeze-valley-wind to draw air toward the center of the South island. circulation continues in the vicinity of the lake, while The penetration of air into the Tekapo area from farther south, increased mechanical turbulence and the eastern plains is accompanied by cloud devel- thermal convection associated with dry outwash opment along the eastern side of the foothills, which surfaces allows the foehn to descend to the surface. is dissipated as the air descends into the basin The strength of the prevailing gradient flow and (Fig. 6a). The easterly flow frequently enters the lake associated channeling also influences the nocturnal basin in late afternoon through two saddles in the wind field and the onset, duration, and cessation of Two Thumb Range (Fig. 1), and is often character- katabatic flows and the mountain wind. Improved ized by stratus streaming into the basin as a "water- understanding of these processes will have direct fall" cloud (Fig. 6b). The sequence of surface wind application to the study of the dispersion of dust and field maps in Fig. 7 illustrates the interaction of the

FIG. 7. The near-surface wind field around Lake Tekapo at (left to right) 0100, 1300, 1600, and 2100 NZST on 12 Feb 1999.

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Unauthenticated | Downloaded 09/24/21 10:23 AM UTC various thermally generated airflow components on several hours after sunset, interacting with the devel- 12 February 1999. The nocturnal situation at 0100 oping nocturnal wind field, as seen at 2100 NZST New Zealand standard time (NZST) was replaced by (Fig. 7). Heat budget analysis described in the local slope winds, lake breezes, and the valley wind Web supplement (http://dx.doi.org/IO.! 175/BAMS- by 1300 NZST during the day (Fig. 7). The larger- 84-3-Sturman) shows that this inflow significantly scale plain-to-mountain flow entered the southern cools the lake basin boundary layer, undoubtedly part of the area by 1600 NZST, eliminating the influencing the development of the nocturnal wind localized flows there. This flow often continues for field. Such interactions have been described else- where by Kimura and Kuwagata (1993), de Wekker et al. (1998), and Whiteman et al. (2000). Field data FIELD MEASUREMENTS (see sidebar titled "Field Measurements") and model simulations (see sidebar titled "Modeling") are being The field phase of LTEX involved deployment of a network of automatic weather stations (AWSs) used to examine this process and assess the relative providing measurements of air and soil tempera- significance of the elevated heat source provided by ture, atmospheric humidity, wind speed and the mountains and the land-sea temperature differ- direction, precipitation, and solar radiation. ence at the coastline. Already, the model results Ground level energy balance measurement illustrate clearly that both local- and regional-scale equipment has also been deployed, using both thermally forced flows have a pronounced influence eddy correlation and Bowen ratio methods. on the wind regime of Lake Tekapo. During weak Sounding systems were used to obtain measurements of the wind and thermodynamic structure synoptic pressure gradients, locally generated up- of the atmospheric boundary layer. These include Doppler sodar, pilot balloons, and radiosondes, as well as instrumented tethered balloons and kites. An instrument package was also developed and mounted on a light aircraft to measure tempera- It is often difficult to apply models to mountain- ture, pressure, humidity, and remotely sensed ous terrain (Fast 1995; Fast et al. 1996). The ground surface temperatures. The distribution of Regional Atmospheric Modelling System (RAMS) sites around Lake Tekapo (Fig. I) was chosen on from Colorado State University (Pielke et al. the basis of previous observations and logistical 1992) is being used to simulate characteristic considerations. airflow patterns observed during selected case Routine surface meteorological data and heat studies. The complicated structures that have flux measurements were collected over most of been observed within the Lake Tekapo area the period between October 1997 and March provide a useful assessment of the ability of 1999, normally as hourly averages and totals. current mesoscale models to simulate the During two special field campaigns, the frequency influence of both thermal and dynamic effects on of AWS data collection was increased to 10 min the airflow in such complex terrain. The field intervals, and some additional AWS sites were measurements are adequate for both initializing established. These campaigns lasted for a period model runs and assessing the validity of model of I month during both November-December output. 1997 and January-February 1999. Special 1-2-day The RAMS has been used to perform idealized observation periods (SOP) occurred during these two- and three-dimensional numerical experi- campaigns when various profiling systems were ments to examine the circulation patterns that deployed. The 1997 field campaign took place can develop exclusively from terrain heating at during an El Nino, resulting in a very high inci- local and regional scales (as observed on dence of westerly foehn winds. The 1999 field 12 February 1999). The three-dimensional simula- campaign was carried out during a La Nina, which tions are configured with four two-way interacting caused a higher frequency of settled anticyclonic grids, having horizontal resolutions of 9.6, 2.4, 0.8, conditions associated with weak easterly ambient and 0.27 km respectively. The coarsest grid covers winds. the whole of South Island and the finest grid Meteorological data are also available from the covers the area around Lake Tekapo, with national surface synoptic network as well as AWSs adequate computational nodes spanning the lake operated by other agencies, such as the rural fire to simulate lake-breeze effects. RAMS uses a weather network. Radiosonde and rawinsonde sigma (terrain following) coordinate system, and ascents were made at Invercargill, Hokitika (wind for this study 12 sigma levels were placed in the only), and Paraparaumu (on the North Island) lowest 1000 m in all grids to adequately resolve (see Fig. I inset). the vertical structure of the boundary layer.

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Unauthenticated | Downloaded 09/24/21 10:23 AM UTC slope and up-valley winds dominate the flow in the ambient atmospheric stability, and the effect of asso- area during the day until early afternoon. From that ciated cloud cover on daytime heating and nocturnal time onward, the simulations show that air from out- cooling of the air. The prevailing synoptic-scale wind side starts to intrude into the basin through Burke enhances, counteracts, or deflects local- or regional- Pass and gaps in the Two Thumb Range situated east scale airflow. Ambient atmospheric stability and cloud of the lake, eventually totally cover influence the degree to dominating the flow in the area which synoptic-scale and (Fig. 8). boundary layer winds are Selected two- and three- coupled. This relationship is be- dimensional simulations sup- ing investigated using both port the conclusion that these short-term case studies and winds are generated by a com- longer-term analysis of the in- bination of the plain-to-plateau teraction of flows at the differ- (Mannouji 1982) and sea-breeze ent scales. effects, producing a Canterbury Plains breeze (CPB). The air can SOME INITIAL RESULTS. either pour into the mountain Surface heat and moisture fluxes basin over the ranges (de Wekker control atmospheric boundary et al. 1998) or enter through layer heating and, subsequently, gaps and passes in the foothills the wind field. The nature of this (Doran and Zhong 2000). The relationship can be inferred CPB's analog, albeit at a larger from surface measurements de- horizontal scale, has been stud- rived from the AWS network ied observationally and numeri- and surface energy balance sys- cally by Bossert and Cotton tems. Figure 9 illustrates this re- (1994a,b) for the case of the lationship for a site south of Rocky Mountains, and Bossert Lake Tekapo (the AWS just (1997) for the case of Mexico southwest of Tekapo village in City, Mexico. The primary forc- Fig. 1) on 12 February 1999, one ing for the CPB is the horizon- of the special observation days. tal temperature difference be- The near-surface wind observa- tween the air over the basin and tions (Fig. 9a) show that noctur- FIG. 8. Wind vectors at 26 M above that outside, at the same level. ground level for 1300 NZST from a nal mountain winds from a Numerical experiments show RAMS simulation of clear summer- northerly direction prevailed that the sea breeze over the Can- time conditions showing the intru- until about 0800 NZST. South- terbury Plains prevents heating sion of the Canterbury Plains breeze erly up-valley flow developed af- of the boundary layer air outside through Burke Pass and Tekapo ter about 0900 NZST, with wind the basin, thereby strengthening Saddle, which eventually over- speeds increasing from 2 to whelms the locally generated up- the horizontal temperature dif- about 4 m s"1 by 1300 NZST. valley and lake-breeze circulations. ferential across the foothills re- The wind direction was initially sulting in a 10% increase in the south-southwest, but between intensity of the CPB. At a more local scale, the simu- 1300 and 1400 NZST the wind became southeasterly lations show that once the CPB flows into the lake as air from the east coast plain started to flow through area, the cold air pool created by the cold surface of Burke Pass (829 m above sea level) into the basin. This Lake Tekapo may prevent the grounding of the re- pass is the lowest point in the surrounding mountain gional-scale inflow in some areas. ranges and is located about 18-20 km east-southeast of the observation site. The cold, moist inflow from What effect does synoptic weather have on smaller-scale outside the basin results from differential heating of processes? A relationship is frequently observed be- the air masses inside and outside of the basin, reached tween the synoptic and local wind fields in complex a maximum wind speed of 12 m s-1, and continued terrain (Weber and Kaufmann 1998; Whiteman and until about 2000 NZST, when winds started to turn Doran 1993). The synoptic weather pattern influences westerly and specific humidity began to decrease the direction and strength of the overlying airflow, again.

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Unauthenticated | Downloaded 09/24/21 10:23 AM UTC modeling, in spite of early doubts about application to such complex terrain. Although most work so far has involved case study data, longer-term data will also be used to examine particular aspects of the research problem. For example, analysis of the seasonality of thermal and dynamic effects and their interaction is required to fully understand the boundary layer structures observed. In addition to the research currently under way, fur- ther work includes

• developing a method for estimating spatial and temporal variation in surface energy balances over complex terrain and links to atmospheric boundary layer development (this will include examin- ing seasonal and synoptic controls on surface radiation and energy budgets across the area); • evaluating the relationship between boundary layer development and heat fluxes using data from the special observation periods; • analyzing synoptic links with the local wind field in the Lake Tekapo region, including a case study investigation of both channeling and thermally induced effects; and • identifying characteristic airflow patterns in complex terrain using statistical analysis of data collected around Lake Tekapo during both 1997 and 1999, and an earlier project conducted in 1992-93 (the influence of synoptic weather systems on observed characteristic patterns will be an important focus).

ACKNOWLEDGMENTS. This research is being conducted with the generous support of Marsden Fund Grant UOC602, awarded by the Royal Society of New Zealand. The continuing encouragement and support of the Univer- sity of Canterbury and the Department of Geography is also FIG. 9. Measurements of (a) wind speed (line) and di- much appreciated. The modeling work was undertaken as rection (dots), (b) air temperature (red line) and spe- part of a collaborative program with scientists at the Pa- cific humidity (blue line), and (c) surface energy budget components determined using the Bowen ratio cific Northwest National Laboratory, Richland, Washing- method near the surface southwest of Tekapo Village ton, including Drs. David Whiteman, Jerome Fast, Shiyuan on 12 Feb 1999. Here, Q* is net radiation; QH and QE Zhong, and Chris Doran, who have provided significant are vertical turbulent sensible and latent heat fluxes, assistance during visits of members of our research group. respectively; and QG is ground heat flux. Marney Brosnan, John Thyne, Graham Furniss, and James Guard provided significant field assistance, while Gary CONCLUSIONS. The first major phase of this re- Smith and Walter Gallagher contributed with preparation search project, the field data collection, has been com- of field equipment. We are also grateful for the assistance pleted. Data analysis is currently well under way with of the staff of Air Safaris at Tekapo Airport and for per- several key topics under intensive study, including the mission granted by several high country farmers for the interaction of wind systems of varying scales, the role installation of equipment on their properties. Permission of the lake in the local wind regime, the interaction from the Civil Aviation Authority to fly our balloon and of thermal and dynamic forcing, and derivation of kite systems in the field area was also much appreciated. heat budget components for the valley atmosphere. We are also indebted to David Whiteman for his careful Progress has also been achieved with the numerical critical review of the manuscript.

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Unauthenticated | Downloaded 09/24/21 10:23 AM UTC Kuwagata, T., J. Kondo, and M. Sumioka, 1994: Thermal REFERENCES effect of the sea breeze on the structure of the bound- Arritt, R. W., 1987: The effect of water surface tempera- ary layer and the heat budget over land. Bound. -Layer ture on lake breezes and thermal internal boundary Meteor., 67, 119-144. layers. Bound.-Layer. Meteor., 40, 101-125. Lamb, P. J., 1974: The nor'wester's advance across the Bossert, J. E., 1997: An investigation of flow regimes Canterbury Plains, New Zealand. N. Z. J. Sci., 17, affecting the Mexico City region. /. Appl. Meteor., 36, 375-380. 119-140. Lewellen, D. C., W. S. Lewellen, and S. Yoh, 1996: Influ- , and W. R. Cotton, 1994a: Regional-scale flows in ence of Bowen ratio on boundary-layer cloud struc- mountainous terrain. Part I: A numerical and obser- ture. /. Atmos. Sci., 53, 175-187. vational comparison. Mon. Wea. Rev., 122, 1449- Lu, R., and R. P. Turco, 1994: Air pollutant transport in 1471. a coastal environment. Part I: Two-dimensional , and , 1994b: Regional-scale flows in mountain- simulations of sea-breeze and mountain effects. /. ous terrain. Part II: Simplified numerical experi- Atmos. Sci., 51, 2285-2308. ments. Mon. Wea. Rev., 122, 1472-1489. Mannouji, N., 1982: A numerical experiment on the Brenstrum, E., 1989: Canterbury's damaging nor'wester. mountain and valley winds. /. Meteor. Soc. Japan, 60, N. Z. Geogr., 1, 110-111. 1085-1105. Chater, A. M., and A. P. Sturman, 1998: Atmospheric McCauley, M. P., and A. P. Sturman, 1999: A study of conditions influencing the orographic spillover of orographic blocking and barrier wind development westerly rainfall into the Waimakariri catchment, upstream of the Southern Alps, New Zealand. Southern Alps, New Zealand. Int. J. Climatol., 18,77- Meteor. Atmos. Phys., 70, 121-131. 92. McGowan, H. A., and A. P. Sturman, 1996a: Interact- Chen, J. M., and T. R. Oke, 1994: Mixed layer heat ad- ing multi-scale wind systems within an alpine basin, vection and entrainment during the sea breeze. Lake Tekapo, New Zealand. Meteor. Atmos. Phys., 58, Bound.-Layer Meteor., 68, 139-158. 165-177. de Wekker, S. F. J., S. Zhong, J. D. Fast, and C. D. , and , 1996b: Regional and local scale char- Whiteman, 1998: A numerical study of the thermally acteristics of foehn wind events over the South driven plain-to-basin wind over idealized basin to- Island of New Zealand. Meteor. Atmos. Phys., 58, pographies. /. Appl. Meteor., 37, 606-622. 151-164. Doran, J. C., and S. Zhong, 2000: Thermally driven gap , I. F. Owens, and A. P. Sturman, 1995: Thermal and winds into the Mexico City basin. /. Appl Meteor., dynamic characteristics of alpine lake breezes, Lake 39, 1330-1340. Tekapo, New Zealand. Bound.-Layer Meteor., 76, 3- , W. J. Shaw, and J. M. Hubbe, 1995: Boundary layer 24. characteristics over areas of inhomogeneous surface , A. P. Sturman, and I. F. Owens, 1996: Foehn en- fluxes. J. Appl Meteor., 34, 559-571. hancement of aeolian dust transportation and depo- , J. D. Fast, and J. Horel, 2002: The VTMX cam- sition within the alpine environment. Lake Tekapo, paign. Bull Amer. Meteor. Soc., 83, 1233-1247. New Zealand. Geomorphology, 15, 135-146. Ekman, R. M., 1998: Observation and numerical simu- , , M. Kossmann, and P. Zawar-Reza, 2002: lation of winds within a broad forested valley. /. Appl Observations of foehn onset in the Southern Alps, Meteor., 37, 206-219. New Zealand. Meteor. Atmos. Phys., 79, 215-230. Emeis, S., and M. Rotach, 1997: Working group on plan- McKendry, I. G., A. P. Sturman, and I. F. Owens, 1986: etary boundary layer (WG-PBL). Mesoscale Alpine A study of interacting multi-scale wind systems, Can- Programme Newsletter, No. 6, Schweizerische terbury Plains, New Zealand. Meteor. Atmos. Phys., Meteorologische Anstalt, Zurich, Switzerland, 10-18. 35, 242-252. Fast, J. D., 1995: Mesoscale modeling in areas of highly , , and , 1987: The Canterbury Plains north- complex terrain. J. Appl Meteor., 34, 2762-2782. easterly. Wea. Climate, 7, 61-74. , S. Zhong, and C. D. Whiteman, 1996: Boundary Pielke, R. A., and Coauthors, 1992: A comprehensive layer evolution within a canyonland basin. Part II: meteorological modeling system—RAMS. Meteor. Numerical simulations of nocturnal flows and heat Atmos. Phys., 49, 69-91. budgets. J. Appl Meteor., 35, 2162-2178. Revell, M. J., D. Purnell, and M. K. Lauren, 1996: Kimura, F., and T. Kuwagata, 1993: Thermally induced Requirements for large-eddy simulation of surface wind passing from plain to basin over a mountain wind gusts in a mountain valley. Bound.-Layer range. J. Appl Meteor., 32, 1538-1547. Meteor., 80, 333-353.

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