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  • View in gallery

    Wind rose plots of 1-Hz (2D sonic anemometers) and 10-Hz (3D sonic anemometers) time series data indicating the presence of an end vortex at one of the street ends for a half-hour period on IOP 6 [0900–0930 central daylight time (CDT) 16 Jul 2003]. Measurements were obtained during the Joint Urban 2003 field experiment.

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    Plan view of the Park Avenue street canyon showing approximate building heights and sonic anemometer and tethersonde wind vane locations used to identify the end vortices. The figure is not to scale.

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    Instrument locations relative to building walls at the eastern side of the Park Avenue street canyon. Sonic anemometers were placed on tripod stands near 2 m AGL. Tethersonde wind vanes were placed on each side of the street at heights near 1, 5, 10, 20, 30, and 40 m. The overhang sonic anemometers were placed on booms that were attached to building roof edges and extended toward the street. The overhang sonic anemometers on the Sonic building were near 47 m AGL, and the one on 101 Park Avenue was at 45 m AGL. The figure is not to scale.

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    Instrument locations relative to building walls at the western side of the Park Avenue street canyon. Sonic anemometers were placed on tripod stands about 2 m AGL. The figure is not to scale.

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    Probability distribution of the angle of attack for the 3D DSTL7 sonic anemometer for upper-level wind direction between 150° and 170°. Angle of attack for ∼76% of the data was within ±40°.

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    Histogram showing the prevailing wind conditions for the IOPs during the Joint Urban 2003 experiment. These measurements were made at 250 m AGL by the PNNL sodar.

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    Wind roses for the near-surface sonic anemometers at the Park Avenue–Broadway Avenue intersection, possibly revealing an end vortex at the east end of the Park Avenue street canyon. The upper-level wind direction was between 150° and 215°.

  • View in gallery

    Wind roses for the near-surface sonic anemometers at the Park Avenue–Broadway Avenue intersection at the east end of the Park Avenue street canyon. The upper-level wind direction was between 215° and 240°. For these ambient wind conditions, no end vortex is found.

  • View in gallery

    Vector-averaged wind velocities for the near-surface sonic anemometers at the Park Avenue–Broadway Avenue intersection: (a) a possible end vortex at the east end of the Park Avenue street canyon for upper-level wind direction between 150° and 215°, and (b) unidirectional flow at the east end of the Park Avenue street canyon for upper-level wind direction between 215° and 240°.

  • View in gallery

    Wind roses for the near-surface sonic anemometers at the Park Avenue–Robinson Avenue intersection, possibly revealing an end vortex at the west end of the Park Avenue street canyon. The upper-level wind direction was between 180° and 240°.

  • View in gallery

    Wind roses for the near-surface sonic anemometers at the Park Avenue–Robinson Avenue intersection at the west end of the Park Avenue street canyon. The upper-level wind direction was between 150° and 180°. For these ambient wind conditions, no end vortex is found.

  • View in gallery

    Vector-averaged wind velocities for the near-surface sonic anemometers at the Park Avenue–Robinson Avenue intersection: (a) a possible end vortex at the west end of the Park Avenue street canyon for upper-level wind direction between 180° and 240°, and (b) unidirectional flow at the west end of the Park Avenue street canyon for upper-level wind direction between 150° and 180°.

  • View in gallery

    Daytime-measured wind roses for the near-surface sonic anemometers at the Park Avenue–Robinson Avenue and Park Avenue–Broadway Avenue intersections for upper-level wind direction between 190° and 200° and wind speed between 10 and 15 m s−1.

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    As in Fig. 13, but for nighttime-measured wind roses.

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    Wind roses for the near-surface sonic anemometers, the ladder-mode tethersonde wind vanes, and the wall-mounted, roof-level sonic anemometers at the Park Avenue–Broadway Avenue intersection, possibly revealing an end vortex through the depth of the street canyon. The upper-level wind direction was between 150° and 215°. Note that this is a 3D view looking into the street canyon through the southern building.

  • View in gallery

    Wind roses for the near-surface sonic anemometers and tethersonde wind vane at the Park Avenue–Broadway Avenue intersection. The upper-level wind direction was between 150° and 215°.

  • View in gallery

    Wind roses for the near-surface sonic anemometers at the Park Avenue–Robinson Avenue intersection and locations farther inside the west end of the Park Avenue street canyon. The upper-level wind direction was between 180° and 240°. The overlaid streamlines approximately represent the data from the wind tunnel measurements of Kastner-Klein et al. (2004). The streamlines show that the location of the center of the end vortex was near the southern side of the street; its across-canyon extent may not cover the whole width of the street.

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Flow Patterns at the Ends of a Street Canyon: Measurements from the Joint Urban 2003 Field Experiment

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Abstract

During the Joint Urban 2003 experiment held in Oklahoma City, Oklahoma, an east–west-running street canyon was heavily instrumented with wind sensors. In this paper, the flow patterns at the street canyon ends are investigated by looking at sonic anemometers placed near ground level and tethersonde wind vane systems operated in “ladder” mode that were suspended over the sides of the buildings on each side of the street. For southerly flow conditions, the street-level wind sensors often showed what appeared to be a horizontally rotating “corner” or “end” vortex existing at each end of the street canyon near the intersections. It was found that this vortex flow pattern appeared for a wide range of upper-level wind directions but then changed to purely unidirectional flow for wind directions that were outside this range. The tethersonde wind vane measurements show that this vortexlike flow regime occasionally existed through the entire depth of the street canyon. The horizontal extent of the end vortex into the street canyon was found to be different at each end of the street. Under high-wind conditions, the mean wind patterns in the street did not vary appreciably during the day and night. The end vortex may be important in the dispersal of airborne contaminants, acting to enhance lateral and vertical mixing.

Corresponding author address: Suhas U. Pol, Los Alamos National Laboratory, Group D-3, MS-F607, Los Alamos, NM 87545. Email: suhas.pol@asu.edu

Abstract

During the Joint Urban 2003 experiment held in Oklahoma City, Oklahoma, an east–west-running street canyon was heavily instrumented with wind sensors. In this paper, the flow patterns at the street canyon ends are investigated by looking at sonic anemometers placed near ground level and tethersonde wind vane systems operated in “ladder” mode that were suspended over the sides of the buildings on each side of the street. For southerly flow conditions, the street-level wind sensors often showed what appeared to be a horizontally rotating “corner” or “end” vortex existing at each end of the street canyon near the intersections. It was found that this vortex flow pattern appeared for a wide range of upper-level wind directions but then changed to purely unidirectional flow for wind directions that were outside this range. The tethersonde wind vane measurements show that this vortexlike flow regime occasionally existed through the entire depth of the street canyon. The horizontal extent of the end vortex into the street canyon was found to be different at each end of the street. Under high-wind conditions, the mean wind patterns in the street did not vary appreciably during the day and night. The end vortex may be important in the dispersal of airborne contaminants, acting to enhance lateral and vertical mixing.

Corresponding author address: Suhas U. Pol, Los Alamos National Laboratory, Group D-3, MS-F607, Los Alamos, NM 87545. Email: suhas.pol@asu.edu

1. Introduction

As part of the Joint Urban 2003 tracer experiment conducted in Oklahoma City, Oklahoma, in July of 2003, a relatively high concentration of wind sensor equipment was deployed within a one-block-long street canyon on Park Avenue during intensive operation periods (IOPs). These included sonic anemometers placed near ground level, on towers, and just below roof level and two tethersonde wind vane systems operated in ladder mode adjacent to building walls in the street canyon. The wind sensors at each end of the street near the intersection often showed winds on average flowing in opposite directions on the north and south sides of the street, perhaps indicative of a horizontally rotating corner vortex (Brown et al. 2004). This study focuses on understanding the relationship between the upper-level wind conditions and the presence of end vortices in the Park Avenue street canyon. Further, the study of the vertical extent of the end vortices through the whole depth of the street canyon is also explored. The paper begins with a short background on street canyon circulations and end vortices, followed by a brief description of the Park Avenue street canyon experiment, and ends with a presentation and discussion of the experimental measurements.

2. Background

When the wind is nearly perpendicular to the street between two rows of buildings, it is well known that a vertically rotating cylindrical vortex with its central axis horizontally aligned to the street often forms in the street canyon (DePaul and Sheih 1986; Oke 1987; Eliasson et al. 2006). The presence of the street canyon vortex can significantly alter the ventilation and the local pollution patterns within the street (e.g., Yamartino and Wiegand 1986; Boddy et al. 2005). Most flow studies have focused on the vertical structure of the flow in the street canyon rather than on the horizontal structure. Many questions remain regarding the horizontal nature of the flow and how it influences the vertical flow structure and impacts transport and dispersion [see, e.g., the review by Belcher (2005)].

Street-intersection smoke-visualization wind-tunnel experiments by Hoydysh et al. (1974) revealed horizontally rotating, vertically aligned eddies at the end of the street canyon near the intersection. These “corner” or “end” vortices were shown extending up the entire side of the building in a spiral and interacting with the in-canyon vortex in the interior of the street canyon. Kastner-Klein et al. (2004) recently directly measured these end-vortex motions in wind-tunnel experiments for a street canyon of cross-stream length-to-height (L/H) ratio of 5, but when the length of the canyon was increased (L/H = 10) the corner vortex disappeared or was not resolved. End vortices may have also been identified in full-scale outdoor experiments by Brown et al. (2004). They found winds at street level on the opposite side of the street blowing in opposite directions, revealing what appears to be a horizontally rotating eddy (Fig. 1). The details of the experiment and this particular street are given later in this paper.

Many computational fluid dynamics (CFD) modeling studies have been performed around building complexes that have shown the end vortex; however, only a few CFD studies have looked more closely at the end-vortex structure. Hamlyn and Britter (2005) used a seven-equation Reynolds stress model to compute flow perpendicular to an in-line array of cubes. Their pathline plots of massless tracers revealed what they called side vortices that extended through the depth of the street canyon and resulted in air exchange with the side streets and the air above the street canyon. They found that the building plan area density affected the structure of the end vortices, presumably through spacing differences and a different interaction with the central vertically rotating vortex core. CFD modeling by Assimakopoulos et al. (2006) using a standard k–epsilon turbulence closure scheme also found end vortices in an in-line array of cubes with perpendicular inflow. They found that the strength of the end vortex decreased with height and that the vortex center migrated inward away from the side streets with height. Their simulations also showed that the corner vortices disappeared when the inflow wind speed was reduced to 2 m s−1. Similar k–epsilon modeling by Baik et al. (2003) found end vortices that penetrated nearly into the middle of a long street canyon. Their results show the vortex circulation to be stronger at midcanyon height as compared with near the surface. Vertical planes of wind vectors running down the length of the street canyon show significant outflow (toward the side streets) on the upwind side and even stronger inflow (from the side streets); the authors comment on how the central vertically rotating vortex interacts with the horizontally rotating side vortices. Lien and Yee (2004), commenting on their k–epsilon modeling of flow around an array of in-line cubes, indicated that these interacting vortices make an arch-shaped structure. The k–epsilon simulations by Soulhac et al. (2001) showed that the end vortices can develop even for flow that is not perpendicular to the buildings.

Wind-tunnel dispersion experiments by Cermak et al. (1974), Hoydysh and Dabberdt (1988), Hayden et al. (2002), and Kastner-Klein et al. (2004) have all implicated corner vortices as significantly affecting the concentration levels on the leeward side of the canyon at each end of the street. In a real-world street canyon experiment conducted in York in the United Kingdom, Boddy et al. (2005) suspected that corner vortices play a significant role in the levels of carbon monoxide within the street canyon. Because the street canyon forms a basic geometric unit that can be used to construct larger urban structures (Terjung and Louie 1973; Nunez and Oke 1977), the study of such flow characteristics in an urban street canyon becomes relevant to understanding transport and dispersion in cities.

3. Experimental description

With the goal of gathering high-resolution wind field and dispersion data in a city, the U.S. Defense Threat Reduction Agency and Department of Homeland Security jointly sponsored the Joint Urban 2003 atmospheric dispersion experiment in Oklahoma City in July of 2003. Meteorological measurements were made at 164 different locations (Allwine et al. 2004), and tracer measurements were made at 135 different locations (Clawson et al. 2005) in and around downtown Oklahoma City. As a part of the Joint Urban 2003 experiment, a street canyon subexperiment was performed with a relatively high concentration of sensor equipment deployed within a one-block section of an east–west-running two-lane street named Park Avenue (Brown et al. 2003). The Park Avenue street canyon experiment included participants from the University of Utah (UU), Arizona State University (ASU), the University of Oklahoma, Volpe, the U.K. Defense Sciences Technology Laboratory (DSTL), the U.S. Army’s Dugway Proving Ground (DPG), and Los Alamos National Laboratory (LANL).

Figure 2 is a sketch of the Park Avenue street canyon showing approximate building heights and the instrument locations used to identify the end vortices. The approximately 150-m-long and 24-m-wide Park Avenue street canyon consisted of tall buildings on the western end of the street, a low section of buildings in the middle of the canyon on the northern side, a 3-m-wide alley opening on the north side at the eastern end, and a few trees at the east end. It was therefore not an idealized street canyon but nevertheless was a “typical” U.S. urban street canyon. Vehicular traffic was allowed during the whole period of the experiment; however, at most times the traffic either was nonexistent or was light and at low speeds.

Figure 3 shows the relative distances between the instruments and the building walls at the eastern end of the street canyon. Four 2D sonic anemometers were mounted on tripods at a height of about 2 m above ground level (AGL), and four 3D sonic anemometers were attached to traffic lights at the Park Avenue–Broadway Avenue intersection at about 8 m above ground level. Tethersonde wind vanes were draped over the sides of the buildings on either side of the street and were operated in ladder mode. Velocity and wind direction measurements were made using the tethersonde wind vanes at 1, 5, 10, 20, 30, and 40 m AGL using cup anemometers. Two 3D sonic anemometers were mounted on the north side of the street at 47 m AGL and one was on the south side of the street at 45 m AGL. All three sonics were just slightly below roof level and about 2 m from the wall. Farther to the west, six 3D sonic anemometers were mounted on two towers that were placed on opposite sides of the street, but only the sonic anemometers at 3 m were used in this study.

Figure 4 shows the relative distances between the instruments and the building walls at the western end of the street canyon. One 3D and three 2D sonic anemometers were mounted on tripods at a height of about 2 m above ground level, and four 3D sonic anemometers were attached to traffic lights at the Park Avenue–Robinson Avenue intersection at about 8 m above ground level. Farther to the east, eight 3D sonic anemometers were mounted on two towers that were placed on opposite sides of the street, but only the two sonic anemometers at 3 m were used in this study.

Table 1 lists the make of instrument, sampling rate, and height above ground level. Because of security issues and manpower requirements, the tethersonde vanes and the majority of the street-level sonic anemometers were operated only during the IOPs, which occurred during both the day and the night and ran for about 8 h each (see Table 2). Each group that was part of the Park Avenue street canyon experiment was responsible for setup and calibration of its sonic anemometers. Several of the groups placed their sonic anemometers side by side in close proximity before and/or after the field experiment to certify agreement among sonic wind measurements. In general, manufacturer-specified calibration curves were applied to the measurement data. These calibration curves are known to become less precise for large attack angles, that is, a wind with a large vertical velocity relative to the horizontal velocity. For example, van der Molen et al. (2004) performed controlled wind-tunnel experiments and found that up to a 10% error in horizontal velocity measurements could be obtained with a 70° attack angle for a common type of 3D sonic anemometer, whereas a 40° attack angle would result in a 2% error. Figure 5 shows the angle-of-attack histogram for the DSTL7 3D sonic anemometer located on a tripod near the Robinson Avenue intersection for upper-level wind direction between 150° and 170°. The angle of attack for ∼75% of the data was within ±45°, and greater than 95% of the data were within ±70°. For the wind rose binning that we are doing by wind direction and wind speed, a 10% error in velocity would not affect results appreciably, and so it is felt that deficiencies in the sonic anemometer calibration curves can be neglected for this application. Errors can also be introduced through misalignment of the wind instrumentation. Alignment of sonic anemometers in cities can be difficult, because the magnetized needle of a compass is often deflected by steel or electrical apparatus within buildings and because the view of distant landmarks used in line-of-sight methods is often obstructed by the buildings themselves. It is fortunate that the central business district in Oklahoma City is laid out on a grid that runs (true) north–south and east–west and that the majority of buildings are perfectly aligned. Sonics therefore were aligned to be perpendicular or parallel to building walls through different line-of-sight methods.

4. Analysis and discussion

To ascertain the predominant flow patterns at the street canyon ends, the time series velocity data from all of the intensive operating periods were used without any time averaging to obtain wind roses for each wind sensor. Flow patterns were determined under different ambient flow conditions through conditional sampling; that is, wind roses were computed when upper-level winds fell within specific wind direction intervals. The Pacific Northwest National Laboratory (PNNL) sodar, which was located about 2 km south of the Park Avenue street canyon, and the DPG wind vane (PWID), which was 1 km south of the Park Avenue street canyon, were used to specify the upper-level wind direction. The 15-min-averaged winds measured by the PNNL sodar at 250 m and the DPG PWID that was placed 50 m AGL were chosen for our analyses because they should provide information about the undisturbed flow conditions. The wind directions measured at the two locations varied from each other occasionally by about 10°. Street canyon data were only analyzed when the upper-level wind direction of both the PNNL sodar and the DPG PWID fell within the specific wind direction intervals of interest. Figure 6 is a histogram that shows the prevailing wind conditions for the IOPs during the Joint Urban 2003 experiment. These measurements were made at 250 m above ground level by the PNNL sodar. During the IOPs, the upper-level wind direction varied for the most part from 150° to 240°.

a. East end of Park Avenue street canyon

Figure 7 shows the wind roses for the near-surface sonic anemometers close to the Park Avenue–Broadway Avenue intersection for upper-level winds between 150° and 215°. The wind roses were obtained using 55.25 h of 0.5-Hz (2D sonics) and 10-Hz (3D sonics) time series data from all of the IOPs. One can clearly see that the wind direction on the northern side of the street is opposite to that on the southern side and also is stronger, perhaps indicating the presence of a horizontally counterclockwise–rotating vortex at the east end of the street for these upper-level wind directions. The DPG13 sonic anemometer shows that fairly strong south–north channeling is present along Broadway Avenue. At the Park Avenue intersection the wind has a significant easterly component (DPG11) resulting in a fraction of the channeled wind hitting the northern wall, with mass conservation perhaps driving the end vortex.

For upper-level winds between 215° and 240° (representing 3.5 h of data from all of the IOPs), the horizontally rotating end vortex disappears for the most part (Fig. 8). Although there still is clear south–north channeling on Broadway Avenue (see DPG12, DPG13, and DPG14), the wind direction on both sides of the street is most often westerly, indicating that the end vortex does not exist for these ambient wind conditions. The wind rose at the intersection (DPG11) indicates that the wind flows from the street canyon toward the intersection, opposite to that found when the end vortex exists.

Figure 9 shows the vector-averaged vector wind field at the east end of Park Avenue, clearly indicating that the end vortex is found in the mean flow (Fig. 9a) and that channeling is found in the mean flow for other upper-level wind directions (Fig. 9b). In summary, the measurements show that the end vortex can exist at the east end of Park Avenue for winds aloft of up to 35° west of perpendicular but then shuts off at 215°. The end vortex was found to exist for upper-level winds 30° east of perpendicular as well. However, during the IOPs, prevailing winds aloft were seldom less than 150°; thus a definite upper-level wind direction from the southeast could not be established for when the end vortex turned off.

b. West end of Park Avenue street canyon

Figure 10 shows the wind roses for the near-surface sonic anemometers near the Park Avenue–Robinson Avenue intersection for upper-level winds between 180° and 240°. The wind roses were obtained using 43 h of data from all of the IOPs. One can clearly see that the wind direction on the northern side of the street is opposite to that on the southern side, perhaps indicating the presence of a horizontally clockwise–rotating vortex at the west end of the street for these upper-level wind directions. The DPG9 sonic anemometer shows that fairly strong south– north channeling is present along Robinson Avenue. At the Park Avenue intersection, the wind has a significant westerly component (DPG7, DPG8, and DPG10) resulting in a fraction of the channeled wind hitting the northern wall, with mass conservation perhaps driving the end vortex. These observations are similar to those at the east end of the street canyon, although the flow on the south side of the street at the western end of the canyon (Volpe2 and DSTL7) is much more variable and is not as consistently easterly.

For upper-level winds between 150° and 180° (representing 16.25 h of data from all of the IOPs), the end vortex has turned off and the winds on the northern side of the street (Volpe1, LANLgreen) have switched from westerly to easterly (Fig. 11). The winds on the southern side of the street (Volpe2, DSTL7) are also predominately easterly but show some time periods with winds blowing from the west. The wind roses in the street intersection (DPG7, DPG8, and DPG10) show that the winds have more of an easterly component, opposite to the case in which the end vortex consistently forms (see Fig. 10).

Figure 12 shows the vector-averaged vector wind field at the west end of Park Avenue, indicating that the end vortex is found in the mean flow (Fig. 12a) and that channeling is found in the mean flow for other upper-level wind directions (Fig. 12b). In summary, the measurements show that the end vortex can exist at the west end of Park Avenue for winds aloft directly south and up to 60° west of perpendicular, that is, an upper-level wind direction of 240°. The end vortex, however, shut off at 180° and did not exist for upper-level winds with an easterly component. During the IOPs, prevailing winds aloft were seldom less than 150° or greater than 240°; thus a definite range of upper-level wind direction could not be established for when the end vortices form at the west end of the Park Avenue street canyon.

c. End vortex—day versus night

A number of wind-tunnel experiments (Uehara et al. 1998, 1999) and CFD modeling studies (Sini et al. 1996; Kim and Baik 1999) have indicated that heating of walls will significantly modify the nature of street canyon circulations. In addition, a wind-tunnel study by Rafailidis (2001) showed that upwind stable stratification significantly changed the pollutant distribution inside a street canyon, implying that the nature of the street canyon circulation also changed. Figures 13 and 14 show the street-level winds for daytime and nighttime cases under similar upper-level wind conditions. Although there are small differences, both the west and east ends of the streets show similar behavior during the day and night, suggesting that for these cases the strong winds overwhelm any effects of upstream stability or localized heating of building walls. These results—that upwind stability and heating of walls play a minor role in the mean flow patterns in a street canyon—agree with a street canyon study in Göteborg, Sweden, that looked at the vertically rotating street canyon vortex (Offerle et al. 2007) and with analyses by other teams on Park Avenue (Ramamurthy et al. 2007; Klein and Clark 2007).

d. Vertical extent of end vortex

In this section, we try to answer the question of whether the end vortex extends through the entire depth of the street canyon. The tethersonde wind vane and roof-level, wall-mounted sonic wind measurements located at the eastern end of Park Avenue can be used to help to determine the vertical extent of the end vortex. Figure 15 shows the wind roses for the near-surface sonic anemometers, building-side tethersonde wind vanes, and roof-level, wall-mounted sonic anemometers at the eastern end of Park Avenue for upper-level winds between 150° and 215°. The wind roses were obtained using 55.25 h of data from all of the IOPs. The wind roses (except 3D LANLblue) show that the winds are predominately easterly on the northern side of the street and westerly on the southern side of the street throughout the entire depth of the street canyon, indicating the existence of an end vortex for almost the whole height of the street canyon. The 3D LANLblue sonic anemometer is just below roof level and near the street intersection, perhaps explaining the high variability in wind direction observed at this location. Tethersonde wind vane wind direction measurements on both the northern and southern sides of the street show more of a northerly component with increasing height. These observations possibly indicate that the horizontal penetration of the end vortex into the street canyon is reduced with increasing height. The strength of the vortex appears to be strongest at about 10–20 m above ground level, similar to the CFD results of Baik and Kim (2003). Similar analyses could not be performed for other prevailing wind directions because of the lack of tethersonde wind vane data.

e. Horizontal extent of the end vortex

An attempt to study the horizontal extent of the end vortex at street level was made by plotting the wind roses for measurements made farther inside the street canyon. Figure 16 shows the wind roses for upper-level winds between 150° and 215° for the near-surface sonic anemometers near the Park Avenue–Broadway Avenue intersection, the sonic anemometers on the ASU and DSTL towers, and the wind vanes at the 5-m level on the DPG and UU tethersonde (th) wind vanes. The wind roses were obtained using 55.25 h of data from all of the IOPs. The wind roses show that winds were on average westerly on the northern side of the street for all of the instrument locations considered. The winds measured at DPGth5 and ASU1 farther into the street canyon show more of a northerly component, perhaps indicating the left side of the end vortex. On the southern side of the street, the wind direction was highly variable at the westernmost instrument locations (DSTL6 and UUth5) as compared with the more unidirectional westerly wind direction at the easternmost locations (2D LANLblack and 2D LANLwhite).

Figure 17 shows the wind roses for the near-surface sonic anemometers near the Park Avenue–Robinson Avenue intersection and locations farther inside the street for upper-level winds between 180° and 240°. The wind roses were obtained using 43 h of data from all of the IOPs. The wind roses show that winds were on average westerly on the northern side of the street for all of the instrument locations considered. On the southern side of the street, the wind direction is highly variable but is predominately easterly.

The measurements are consistent with the flow patterns obtained from the wind-tunnel measurements of Kastner-Klein et al. (2004) in that the location of the center of the end vortex was near the southern side of the street, its across-canyon extent may not cover the whole width of the street, and the flow on the northern side of the street obtained a northerly component farther into the street canyon. At full scale (H = 50 m), the wind-tunnel study shows that the center of the vortex was at about 25 m from the building corner and that the horizontal extent of the end vortex was about 50 m for a street canyon having an L/H ratio equal to 5. On the eastern end of the street, if one concludes that the DSTL6 sonic anemometer is near the center of the vortex, then the center of the vortex is located at about 22 m into Park Avenue from the street corner.

5. Conclusions

As part of the Joint Urban 2003 field campaign, wind measurements from the Park Avenue street canyon subexperiment reveal horizontally rotating end vortices at each end of the street canyon. The Park Avenue street canyon ran east–west, and wind measurements at street level were obtained over many days for prevailing wind direction aloft between 150° and 250°. The end vortex was observed at street level at the western end of the street canyon for upper-level wind directions between 180° and 250°. Unidirectional flow from east to west was apparent at this location for upper-level wind directions between 150° and 170°. At the eastern end of the street canyon, the horizontally rotating vortexlike flow pattern was observed for upper-level wind directions between 150° and 215°. For upper-level wind directions greater than 215°, unidirectional flow from west to east was found at the street ends instead of the horizontally rotating vortex. The wind measurements in the intersections show strong southerly channel flow, but the wind has a component into the street canyon for the cases in which the end vortex is formed at the street ends. It is thought that the wind coming into the canyon hits the north wall and drives the end vortex (a clockwise-rotating eddy on the western end of the canyon and a counterclockwise eddy on the eastern end). The wind measurements in the intersections show that the southerly channel flow has a component out of the street canyon into the street intersection when the end vortex is not formed. Comparisons of mean flow patterns for measurements obtained during the day and night showed little differences, most likely because of the strong prevailing winds that overwhelmed any upwind stability or local heating effects. Tethersonde wind vane measurements on both sides of the street at the eastern end of the street canyon show that the end vortex may exist through the whole depth of the street canyon. However, the horizontal extent of the end vortex may vary with height above the ground level. Because of the sparseness of wind measurements, the horizontal extent of the end vortex into the street canyon could not be determined; however, flow patterns were consistent with high-spatial-resolution wind-tunnel measurements reported by Kastner-Klein et al. (2004).

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Fig. 1.
Fig. 1.

Wind rose plots of 1-Hz (2D sonic anemometers) and 10-Hz (3D sonic anemometers) time series data indicating the presence of an end vortex at one of the street ends for a half-hour period on IOP 6 [0900–0930 central daylight time (CDT) 16 Jul 2003]. Measurements were obtained during the Joint Urban 2003 field experiment.

Citation: Journal of Applied Meteorology and Climatology 47, 5; 10.1175/2007JAMC1562.1

Fig. 2.
Fig. 2.

Plan view of the Park Avenue street canyon showing approximate building heights and sonic anemometer and tethersonde wind vane locations used to identify the end vortices. The figure is not to scale.

Citation: Journal of Applied Meteorology and Climatology 47, 5; 10.1175/2007JAMC1562.1

Fig. 3.
Fig. 3.

Instrument locations relative to building walls at the eastern side of the Park Avenue street canyon. Sonic anemometers were placed on tripod stands near 2 m AGL. Tethersonde wind vanes were placed on each side of the street at heights near 1, 5, 10, 20, 30, and 40 m. The overhang sonic anemometers were placed on booms that were attached to building roof edges and extended toward the street. The overhang sonic anemometers on the Sonic building were near 47 m AGL, and the one on 101 Park Avenue was at 45 m AGL. The figure is not to scale.

Citation: Journal of Applied Meteorology and Climatology 47, 5; 10.1175/2007JAMC1562.1

Fig. 4.
Fig. 4.

Instrument locations relative to building walls at the western side of the Park Avenue street canyon. Sonic anemometers were placed on tripod stands about 2 m AGL. The figure is not to scale.

Citation: Journal of Applied Meteorology and Climatology 47, 5; 10.1175/2007JAMC1562.1

Fig. 5.
Fig. 5.

Probability distribution of the angle of attack for the 3D DSTL7 sonic anemometer for upper-level wind direction between 150° and 170°. Angle of attack for ∼76% of the data was within ±40°.

Citation: Journal of Applied Meteorology and Climatology 47, 5; 10.1175/2007JAMC1562.1

Fig. 6.
Fig. 6.

Histogram showing the prevailing wind conditions for the IOPs during the Joint Urban 2003 experiment. These measurements were made at 250 m AGL by the PNNL sodar.

Citation: Journal of Applied Meteorology and Climatology 47, 5; 10.1175/2007JAMC1562.1

Fig. 7.
Fig. 7.

Wind roses for the near-surface sonic anemometers at the Park Avenue–Broadway Avenue intersection, possibly revealing an end vortex at the east end of the Park Avenue street canyon. The upper-level wind direction was between 150° and 215°.

Citation: Journal of Applied Meteorology and Climatology 47, 5; 10.1175/2007JAMC1562.1

Fig. 8.
Fig. 8.

Wind roses for the near-surface sonic anemometers at the Park Avenue–Broadway Avenue intersection at the east end of the Park Avenue street canyon. The upper-level wind direction was between 215° and 240°. For these ambient wind conditions, no end vortex is found.

Citation: Journal of Applied Meteorology and Climatology 47, 5; 10.1175/2007JAMC1562.1

Fig. 9.
Fig. 9.

Vector-averaged wind velocities for the near-surface sonic anemometers at the Park Avenue–Broadway Avenue intersection: (a) a possible end vortex at the east end of the Park Avenue street canyon for upper-level wind direction between 150° and 215°, and (b) unidirectional flow at the east end of the Park Avenue street canyon for upper-level wind direction between 215° and 240°.

Citation: Journal of Applied Meteorology and Climatology 47, 5; 10.1175/2007JAMC1562.1

Fig. 10.
Fig. 10.

Wind roses for the near-surface sonic anemometers at the Park Avenue–Robinson Avenue intersection, possibly revealing an end vortex at the west end of the Park Avenue street canyon. The upper-level wind direction was between 180° and 240°.

Citation: Journal of Applied Meteorology and Climatology 47, 5; 10.1175/2007JAMC1562.1

Fig. 11.
Fig. 11.

Wind roses for the near-surface sonic anemometers at the Park Avenue–Robinson Avenue intersection at the west end of the Park Avenue street canyon. The upper-level wind direction was between 150° and 180°. For these ambient wind conditions, no end vortex is found.

Citation: Journal of Applied Meteorology and Climatology 47, 5; 10.1175/2007JAMC1562.1

Fig. 12.
Fig. 12.

Vector-averaged wind velocities for the near-surface sonic anemometers at the Park Avenue–Robinson Avenue intersection: (a) a possible end vortex at the west end of the Park Avenue street canyon for upper-level wind direction between 180° and 240°, and (b) unidirectional flow at the west end of the Park Avenue street canyon for upper-level wind direction between 150° and 180°.

Citation: Journal of Applied Meteorology and Climatology 47, 5; 10.1175/2007JAMC1562.1

Fig. 13.
Fig. 13.

Daytime-measured wind roses for the near-surface sonic anemometers at the Park Avenue–Robinson Avenue and Park Avenue–Broadway Avenue intersections for upper-level wind direction between 190° and 200° and wind speed between 10 and 15 m s−1.

Citation: Journal of Applied Meteorology and Climatology 47, 5; 10.1175/2007JAMC1562.1

Fig. 14.
Fig. 14.

As in Fig. 13, but for nighttime-measured wind roses.

Citation: Journal of Applied Meteorology and Climatology 47, 5; 10.1175/2007JAMC1562.1

Fig. 15.
Fig. 15.

Wind roses for the near-surface sonic anemometers, the ladder-mode tethersonde wind vanes, and the wall-mounted, roof-level sonic anemometers at the Park Avenue–Broadway Avenue intersection, possibly revealing an end vortex through the depth of the street canyon. The upper-level wind direction was between 150° and 215°. Note that this is a 3D view looking into the street canyon through the southern building.

Citation: Journal of Applied Meteorology and Climatology 47, 5; 10.1175/2007JAMC1562.1

Fig. 16.
Fig. 16.

Wind roses for the near-surface sonic anemometers and tethersonde wind vane at the Park Avenue–Broadway Avenue intersection. The upper-level wind direction was between 150° and 215°.

Citation: Journal of Applied Meteorology and Climatology 47, 5; 10.1175/2007JAMC1562.1

Fig. 17.
Fig. 17.

Wind roses for the near-surface sonic anemometers at the Park Avenue–Robinson Avenue intersection and locations farther inside the west end of the Park Avenue street canyon. The upper-level wind direction was between 180° and 240°. The overlaid streamlines approximately represent the data from the wind tunnel measurements of Kastner-Klein et al. (2004). The streamlines show that the location of the center of the end vortex was near the southern side of the street; its across-canyon extent may not cover the whole width of the street.

Citation: Journal of Applied Meteorology and Climatology 47, 5; 10.1175/2007JAMC1562.1

Table 1.

Instrument characteristics.

Table 1.
Table 2.

Joint Urban 2003 intensive operating periods.

Table 2.
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