Geophysical Fluid Dynamics Institute T-Iorida State University a Study Of
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DECBKBER. 1973 ANDREWjOHNSON. JR.. A NO AMES J O'BRIEN 1267 ContributionNo.-!?3 ~~ GeophysicalFluid DynamicsInstitute t-ioridaState University A Study of an Oregon Sea Breeze Event1 ANDREW JOHNSON, JR.., AND JAMES J. O'BRIEN D.jJl. of M--doD, FloridIJ SIGMUm-sily, TallIJhass. JZJ06 (Manuscript received 30 Apri11913, in reviaed form 4 September 1973) ABSTRACT A series of meteorological observations including aircraft, pilot bal1oon (pibal), rawinaonde, surface buoy, and specialland-based surface observations was taken on 23-24August 1912,on the central~ coast, to investigate the mesoscalethennal and kinematic ~nsesof the lowest 4 km of the atmosphere during a sea breeze event. A desaiption of those field observations is given. Vertical crag sections of the wind field on a line per- pendicular to the coast, extending 00 km inland from data obtained at three pibal stations, are presentedand discussed.Time sections of the wind field and temperature fields at the coast are discussed.Mesoscale fea- tures are presentedand related to prevailing synoptic-scale changesoccurring aloft during the observational period. The seabreeze event on 23 August exhibited the following important characteristics: 1) a sea breezefront, distinguishable in the zonal wind field, which penetrated more than 00 km inland; 2) a distinct wind maxi- mum which followed the front inland; 3) the surface onshore ftow at the coast which took place below the main inversion, deepeningthe marine layer at the onset; and 4) a return ftow above the inversion which ap- peared in quasi-periodic surgesin responseto surgesin the sea breezeftow. 1. Introduction daytime heating which producesa large-scalegradient The land-sea breeze circulation is one of the most wind flow from the north along the coast.This persistent interesting mesoscale atmospheric phenomena observed northerly componentin the local surfacewinds accounts in coastal regions during periods of fair weather. As a for the coastal upwelling phenomenonwhich acts to simple exampleof one of the most fundamental atmo- reducenearshore sea surface temperatures. This unique spheric processes(i.e., the generation of motion by combination of intense heating inland and the cold sea differential heating), the sea breeze occurs in many surface produces very high coastal thermal gradients areas with extraordinary strength and persistence.It which leads to the developmentof a strong sea breeze may differ considerablyin character from one area to circulation. another, varying in direction, intensity and time The importance of the sea breezein central Oregon accordingto local conditions (Flohn, 1969).Interaction cannot be over-emphasizedas it representsthe meso- with other local wind systems may complicate the scale vehicle through which marine air routinely diurnal wind pattern of a particular area making it penetrates the interior valleys. Knowledge of the difficult to extract those atmosphericresponses related quantity of marine air entering the valleys on any given directly to a seabreeze event. The prevailing large-scale summer day is vital to forestry operations and to air synoptic flow alsohas a direct effecton the strength and pollution interests. This quantity is a function of the landward penetration of sea breezes. Koschmieder strength and depth of the seabreeze and the speedwith (1935), Haurwitz (1947), Estoque (1962), and Frizzola which the sea breeze front moves inland. A rapid and Fisher (1963) have presented many examples increasein marine air and associatedmoisture in the illustrating this interdependence. valleys leads to a sudden decreasein heating and Along the Pacific coastof the United States,a unique subsequentlya decreasein coastal pressuregradients. combination of physiographic and oceanographic This diminishes the thermal forcing necessaryto main- characteristics strongly influence the local meteoro- tain a seabreeze as well as the northerly gradient flow. logical conditions during summer. The presenceof the It may even lead to a relaxation of coastal upwelling large sea level Pacific anticyclone dominatesthe large- which would further reduce coastal thermal gradients scaleair flow near the surface.Along the easternfringe and seabreeze forcing. At present, we have no data to of the high, the immediate inland areasreceive intense support these contentions but the ~ breezein an up- welling regimemay representa very important feedback 1 Contribution No. 89 of the GeophysicalFluid Dynamics mechanismbetween major oceanogra;phicand meteoro- Institute, F1orida State University. logical processeson a lafKer scale. 1268 JOURNAL OF APPLIED METEOROLOGY VOLUME 12 ~ ~w~.,!.," I ~ ., la~ i'l~.oo' f 114!1o' ~. I ..w.n . ..~..." ., ~o- I',.~ ..::. + ..-oO'+- r-m-- ., 1UTD .-r-:-~ ...? , o~ ,-, ~ -.1' . D~STA~ ~ ::~",;--- ~ C"W,T,lt,? ~PR£SSuRE SAI.IM . ..- 1 '. ~~ . TTEMPEh~ '- ' . ,,",\ 0 " tAI.IOIn I I 31AY. ,. ,.8AL _R8I~ -44"45 L---~l + + 44~+- ~~ ~~~~~' --- Iw.J'I (Wi' IWi' cp,W,T;Jtn.aw1 N- . .om -- -10 C . moMETER8 ~ ~ 5 10 , ~ . ~ D } 5. III. CORWWS ~TUTE MUS -44830'.- + . I . 4..w+- 84- FIG.1. Map of caltlal ~ a.stal us showingme~ O~ ltaticms. Most seabreeze studies made previously in this area the results of this study to those of previous investiga- have been in terms of the horizontal distributions of tions. The summary and conclusions are presented temperature and humidity at the surface emphA-~zing in Section 5. only the surfacewind field (Lowry, 1962,1966; Cramer and Lynott, 1961,1970). 2.The fteld observations It is the purposeof this study to attempt to evaluate The purposeof this sectionis to provide a description the character of the wnal wind var:iability on the of the special meteorologicalfield observationprogram central Oregon coast based on observations of a sea during a 42-hr period from 0500, 23 August 1972, breezeevent on 23 August 1972,at Newport, Ore. The through (XMX),25 August 1972 (all times PDT). These observationswere taken during the summer of 1972as observationsform the basis for the description of the part of the Coastal Upwelling Experiment (CUE I; seabreeze occurrence. see O'Brien, 1972), a project of the International Fig. 1 is a map of the CUE I area showing the land Decade of Ocean Exploration of the National Science stations and buoys at which meteorologicalobservations Foundation. The experiment represented an intense were taken during the summer of 1972. effort to explore the phenomenonof coastal upwelling. Although the major observationaleffort wasprimarily 4. Swface obsenlatioftS oceanographic,an important, though limited, meteoro- logical observation program was undertaken. These As a part of the overall CUE I meteorologicalob- observationsconcentrated on surfacewinds in order to servationprogram, five portable recordinganemometers determine the temporal and spatial wind stress pat- were installed along the coast to the north and south tern-the forcing function for the observed intense of Newport during August. Surface winds were also observed at the south jetty at Newport, and at five upwelling. The following sections of this paper will provide a surfacebuoys moored within 30 n mi of the coast. Air completedescription of a seriesof specialfield observa- temperature records were also available from these tions documenting a sea breeze event. Included are buoys and from Newport. Specialsurface temperature interpolations of the observedmesoscale changes in the and rdative humidity observationswere made during vertical structure of the lowest 4 km of the atmosphere 23 August at Ellmaker State Park and Corvallis to during the event. assistin the documentation of a seabreeze event. The field observations are described in Section 2. A complete analysis of the data obtained from the b. Aircraftobs~ field observationswith main emphasison a discussion The NCAR (National Center for Atmospheric Re- of the 23 August sea breeze event is contained in search, Boulder, Colo.) Queen Air aircraft, based in Section 3. Section 4 is devoted entirely to comparing Corvallis during the period 4-31 August, played an D~~BER 1973 ANDREW JOHNSON, R., AND JAMES J O'BRIEN 1269 important role in CUE I observations.In addition to 25 rNEWPORT AUG. 1972 V-COMPONENT measuring sea surface temperatureswith an infrared . radiometer, the aircraft recordedBight level winds, air to . temperature, and dew point temperature. Generally, . fiights were made at 500 ft along radial tracks from . 15 . Newport, extending 35 n mi seaward,and at 5(XX)ft . between Newport and Corvallis. In addition, the air- . 10 . craft made vertical soundingsof temperature and dew. point via spiral ascentsand descentsover Corvallis, . Newport, and at a point approximately 35 n mi WNW &: . of Newport. ~ ~ Weather permitting, the low-level fJight tracks over ... ~ the ocean were flown during each aircraft flight. On xio 23 August, however, dense fog immediately offshore (which was later advected onshore) prohibited such -~ operations. Neverthel~, two short flights were made during 23 August in addition to two full flights on -10 24 August to supplement the documentation of atmo- . spheric structure during the observational period. -15 These flights produced valuable vertical soundingsof ~r ~ . - temperature and humidity but compassfailure within . - -20 - -{ . the Doppler radar system preventedany useablewind . - observations. -25 :.. ~- ... c. Pibal and rawinsondeobs~imtS .. 14. 10a 14Ie 1810 I Through the cooperationof Dr. William Elliott and 10rNEWPORT Aue. 1972 the assistanceof Mr. Richard Egami, both of the School U-COMPONENT.