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A Long-Term Study of Sea-Breeze Characteristics: a Case Study of the Coastal City of Adelaide

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A Long-Term Study of Sea-Breeze Characteristics: a Case Study of the Coastal City of Adelaide FEBRUARY 2019 P A Z A N D E H M A S O U L E H E T A L . 385 A Long-Term Study of Sea-Breeze Characteristics: A Case Study of the Coastal City of Adelaide ZAHRA PAZANDEH MASOULEH,DAVID JOHN WALKER, AND JOHN MCCAULEY CROWTHER School of Civil, Environmental and Mining Engineering, University of Adelaide, South Australia, Australia (Manuscript received 2 January 2018, in final form 13 December 2018) ABSTRACT The sea-breeze characteristics of the Adelaide, Australia, coastline have been studied by applying a sea- breeze detection algorithm to 3- and 6-hourly meteorological records of near-surface and upper-air data at Adelaide Airport from 1955 to 2007. The sea breeze is typically a westerly gulf breeze combined with a later- occurring southerly ocean breeze. Regression analysis showed a significant increasing trend in the intensity of 2 sea breezes but not in their frequency. Over the 52-yr period, there was an average increase of 1 m s 1 in zonal 2 and 0.7 m s 1 in meridional sea-breeze wind speed components. The annually and seasonally averaged maximum wind speeds on sea-breeze days increased significantly over the 52-yr period of the study by 2 2 2 2 0.65 m s 1 for the whole year, 0.48 m s 1 in spring, 1.02 m s 1 in summer, and 1.10 m s 1 in autumn. A com- parison of hourly data for 1985–95 with those for 1996–2007 showed frequencies of sea-breeze onset times less than 4 h from sunrise increasing from 29% to 36%, durations greater than 8 h increasing from 51% to 59%, and times of maximum sea breeze between 2 and 6 h after sunrise increasing from 44% to 50%. The monthly frequency of sea breezes was found to increase by 2.8 percentage points for each degree Celsius rise in monthly average maximum air temperature at Adelaide Airport. The meridional ocean-breeze wind speed, unlike the gulf-breeze wind speed, is also correlated with maximum air temperature at Adelaide Airport. 1. Introduction its impact on locally generated waves and consequently on the general sedimentation pattern has been observed The difference between the thermal and radiative (Psuty 2005). properties of the sea and land surfaces can produce an The city of Adelaide (Fig. 1) is located on a coastal unstable temperature gradient at low levels of the atmo- plain in South Australia, bounded on the west by Gulf sphere that initiates a sea breeze. Several environmental St. Vincent and on the east by the Mount Lofty ranges parameters affect the formation and characteristics of (of which the highest point is 726 m above mean sea these circulations and these may change over long periods level). Adelaide (3485504300S, 13883505500E, elevation of time, for example, surface aerodynamic roughness and 59 m above Australian Height Datum) has a Mediter- land surface heat flux (Crosman and Horel 2010). ranean climate (Köppen classification Csa) with warm to Development of cities along the coast has led to a hot, dry summers and cool to mild winters. Sea breezes change in land surface cover, which modifies the near- in Adelaide occur frequently: 30% of days in spring, surface wind regime by increasing the land surface 42% in summer, 24% in autumn, and 10% in winter frictional drag force. Furthermore, the urban heat island (Pazandeh Masouleh et al. 2016). The sea breezes typi- (UHI) effect can interact with the sea-breeze circulation cally start from an easterly overnight land breeze, which and may cause an increase in sea-breeze intensity and its reverses in the early morning to a westerly sea breeze. frequency of occurrence (Yoshikado 1992). During the midafternoon, the wind direction becomes The effect of sea breeze on precipitation (Baker et al. southwesterly and the wind speed reaches its maxi- 2001), air pollution (Grossi et al. 2000), and coastal mum. During late afternoon and early evening, the wind processes (Masselink and Pattiaratchi 1998; Masselink speed abates and its direction backs to southerly and and Pattiaratchi 2001) has been extensively studied and finally becomes an easterly land breeze in late evening. The climate of South Australia is controlled by sev- Corresponding author: Zahra Pazandeh Masouleh, zahra. eral climate drivers: the southern annular mode, the [email protected] Indian Ocean dipole, the El Niño–Southern Oscillation, DOI: 10.1175/JAMC-D-17-0251.1 Ó 2019 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses). Unauthenticated | Downloaded 10/06/21 12:46 PM UTC 386 JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY VOLUME 58 FIG. 1. Map of the study area showing the two measurement stations of Adelaide Airport and Edithburgh. The two components of the sea breeze and the resultant are also shown. (Source: Google Earth.) and the ‘‘subtropical ridge’’ (Australian Bureau of generation of the local wave climate and this in turn Meteorology 2010). A study by Hendon et al. (2007) drives the coastal processes, including the storms that showed that the southern annular mode has an indirect damage beaches and coastal infrastructure. There- impact on maximum surface temperatures of Australia fore, any change in wind climate is significant in the through increased rainfall during the high index po- larity of the southern annular mode, which reduces the maximum temperature across southern and eastern 5.0 Australia. Additionally, the latitudinal position and the 4.5 intensity (mean maximum pressure) of the Subtropical 4.0 3.5 Ridge in Australia has been shown to affect rainfall as ) s / 3.0 m well as air temperature and zonal and meridional ( 2.5 d e winds (Larsen and Nicholls 2009; Williams and Stone e p 2.0 s 1950 1960 1970 1980 1990 2000 2010 2009). The potential impact of other climate drivers d 5.0 n i is mostly on rainfall of the inland areas (Pazandeh W 4.5 Masouleh 2015). 4.0 The establishment of the city of Adelaide in 1836 3.5 began the change from a natural habitat to an urban 3.0 habitat on the Adelaide plain. Since then, the city has 2.5 2.0 expanded vastly so that greater Adelaide currently 1950 1960 1970 1980 1990 2000 2010 covers over 1800 km2 and, as of the 2016 census, had FIG. 2. Summer sea-breeze, average U component at 1500 local a population of almost 1.3 million. The sea breeze time for (a) the entire period and (b) excluding 1972–84 when from Gulf St. Vincent is an important factor for the observation times were changed by an hour for daylight saving. Unauthenticated | Downloaded 10/06/21 12:46 PM UTC FEBRUARY 2019 P A Z A N D E H M A S O U L E H E T A L . 387 FIG. 3. Summer average U component at (left) 1200 and (right) 2100 local time for (a),(c) the entire period and (b),(d) excluding 1972–84, when observation times were changed by an hour for daylight saving. long-term planning of coastal management, which was air, and the other arrives later in the day and is gener- the main motivation for this study. ated over the Southern Ocean. The Southern Ocean Previous studies of the Adelaide metropolitan thermal component is referred to as a continental sea breeze and characteristics were mainly focused on the architectural its arrival is characterized by a cooler and drier air mass. effects of street canyons and energy consumption on the With continuous surface observation of the weather, the climate of the central business district (CBD), suggest- arrival of the two breezes can be observed through ing the presence of a nighttime UHI and a daytime cool changes in temperature and relative humidity (Physick island, with the maximum intensity occurring approxi- and Byron-Scott 1977). A southerly shift in the after- mately 2 h after midday. The arrival of a sea breeze in noon sea-breeze direction was also noted in a study in the afternoon of summer months cools the temperature Western Australia (Masselink and Pattiaratchi 2001) of the coastal area significantly. However, the UHI and is regarded as the effect of synoptic weather patterns intensity increases as air heated above the western and Coriolis forces on what is referred to as a ‘‘pure sea suburbs reaches the CBD, leaving the city warmer than breeze.’’ the suburbs and surrounding parklands (Erell and Williamson 2007; Guan et al. 2013). Note that the UHI 2. Method for the detection of sea breezes in the work by Erell and Williamson (2007) has been considered as a temperature difference between the The method was previously described in Pazandeh CBD and the surrounding suburbs. Masouleh et al. (2016). Parts of the methods are re- The Adelaide shoreline has been observed to expe- peated here for the readers’ convenience. Sea-breeze rience an interaction of two sea-breeze systems: one is detection has been widely studied, but the criteria used generated over Gulf St. Vincent, bringing warm moist have varied according to the availability of the local TABLE 1. Regression analysis of the U component of seasonally averaged wind speed in summer. Here and in subsequent tables, rows with a p value of 0.025 or less are in boldface, indicating rejection of the null hypothesis. Time (ACST) Regression gradient coef Std error of the gradient R2 t statistic p value NRMSE of residuals SB 1200 0.023 0.006 0.25 4.16 0.00 0.18 1500 0.019 0.005 0.24 4.05 0.00 0.14 1800 0.004 0.007 0.05 0.53 0.59 0.89 2100 20.016 0.004 0.24 24.03 0.00 20.31 NON_SB 1200 0.002 0.009 0.00 0.27 0.78 0.45 1500 0.001 0.010 0.00 0.104 0.91 0.50 1800 20.008 0.010 0.01 20.74 0.45 1.41 2100 20.009 0.010 0.01 20.74 0.45 1.25 Unauthenticated | Downloaded 10/06/21 12:46 PM UTC 388 JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY VOLUME 58 TABLE 2.
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