TABLE OF CONTENTS Page Summary 1 Introduction 1 Surface Winds 2 Diurnal Wind-Regime Aloft at Uc3A 6 Average Diurnal-Wind Time-Section at u(IIA 9 Areal Pattern on an Individual By 10 Ref e rence s 11 LIST OF FIGURES Figure Title Number 1 Diurnal Changes of Surface Winds in the IDS Angeles Basin, August 1944 2 Prevailing-Wind Flow at Hour of Maximum Sea-Breeze Development (Late Afternoon), over Los Angeles Basin, August 1944 Sample Wind Time-Section, UM, 1 September 1944 4 Time Section ofwinds above KIA, 18-29 Aug- ust 1944 5 Time Section of Winds above Ua, 30August- 10 September 1944. 6 Predominant Daily Winds at UUA 7 Wind-Direction Frequency Roses-- a. 14 Aug. 17 Sep 1944 0300-1100 PWT b. n 1300-1700 PWT n C. 1900-2400 PWT 8 Wind-Direction Frequency Roses-Ua a. 18 Sep-20 Nov. 1944 0300-0900 pwf b. n 1100-1500 m n C. 1700-2400 PWT 9 Wing-Di rectiqn Frequency Roses-m a. 8-31 Jan. 1945 0500-0900 PWT b. n 1100-1500 PRT n C. 1700-,1900 PWT 10 Wind Time-Sections at Various Stations 5-6 September 1944 Oxnard, UUA, Mines Field. 11 Wind Time-Sections at Various Stations 5-6 September 1944 VanNuys, Cal. Tech, 9ntario. 12 Profiles of Land and Sea Winds at Various Hours. Los Angeles Basin, 5-6 September 1944 13 Upper-Air Charts, 5-6 September 1944. STRUCTURE OF THE LOCAL WINDS IN THE LOS ANGELES BASIN SUMMARY Average-wind t ime-sections- are pre- sented for one station for each of the From a large number of slow-ascent pilot- seasons: summer, fall and winter. balloon observations the three-dimensional structure in time of the sea and land breeze regime is described for the Los INTRODUCTION Angeles Basin, California. The cooperative investigation of The sea breeze is directed approxi- coastal stratus in southern California dur- mately perpendicular to the local coast ing the summer of 1944 (1) emphasized the line but follows up the thalweg of inland importance of the sea-land breeze regime as valleys. a factor influencing the local weather. The diurnal oscillation of the height of The sea breeze tends to merge in the the subsidence inversion was found to be lowest levels with valley winds, and the explained ,in large part by this coastal land breeze with mountain winds. The sea- wind pattern. During the stratus investi- land breeze regime is confined to the gation a large amount of wind data were coastal plain west of the coastal mountain collected and augmented by additional ob- range, but flows through the most westerly servations in the late fall and winter. passes and is felt by stations just east of These data constitute the basis for the these passes. present rctport. It is concerned primarily with a description of the sea-land breeze At higher levels there is a tendency regime in the Los Angeles Basin. A discus- for the sea-land breeze pattern to merge sion of some related weather phenomena and with the ocean-continent winds which are the results of attempts to forecast the controlled by the thermal low over the beginning and end of ,the sea breeze on southwqstern desert. When the therm1 low particular days will be covered in a later persists both night and day for short paper. periods of time and is strong even at levels up to 5000 feet, the ocean-con- Most of the data were collected by the tinent regime approaches the character of a Army Weather Station at the University of true monsoon. However, when the land wind California at Los Angeles (VU) by means is strong it separates the sea breeze in of s low - asc e n t p i 1o t - b a 11o ons wh ich a 11 ow- the lower layers from the westerly ocean- ed observations to be taken at vertical in-5 continent wind by a layer of easterly land tervals of about IS0 feet. The periods of winds. observations were 15 August to 20 November 1944 during which 570 ascents were observed, When a high pressure center aloft and 8 to 31 January 1945, 149 ascents. centers over the Great Basin, easterly flow Each ascent was run to 5000 feet if circum- due to the general circulation may merge stances allowed, which constituted approxi- with the land wind and confine the westerly mately 30 readings taken at intervals of sea breeze to a small depth and short either 25 or 30 seconds. In addition, duration. analyses were made of the ordinary pilot- balloon data and surface winds for sur- The combined sea-valley breeze is rounding stations. Of particular import- first noticable near the coast and makes ance is this study were the Rawin data its appearance progressively inland. It taken at Mines Field (XA) which is located deepens during the course of the afternoon nine miles SSE of UCLA. at all stations and reaches a greater depth in summer than in. winter. The description of the wind patterns necessitated some discussion of possible The combined land-mountain wind causes of observed phenomena in order to appears first at stations along the mountain set up a nomenclature to be usedo It is slopes near the coast and progressively af- not presumed that the present report is a fects stations more inland. At times it 'discussion of all factors related to a appears last at the coastal stations. It complete synoptic description of the wind deepens faster inland than at the imedi- regime. However, the presentation of basic ate coast. data in organized form is one of the pre- 8 1 liminary steps toward the complete under- typical of the summer conditions with little standing. change in the general circulation from day to day. Space limitation required the use In this report the sea-land wind of call letters to identify stations on regime is defined as a diurnal oscillation some of the figures. These are listed, of direction at any level due to the effect together with station elevations, in Table of the land-sea temperature difference. A 1 below. diurnal change in wind direction in the Los Angeles Basin is found both below and above TABLE I the temperature inversion which is a characteristic of the summer in this area. CALL LETTERS AND STATION ELEVATIONS Below the inversion the marine stratum is moist compared with the air aloft, but in the present definition, the sea breeze may call Elevation occur both in the lower moist and in the Station Letters (Ft. msl.) upper dry air. Oceanside oc 10 The valley-mountain wind regime is El Tor0 (Marine Corps 332 similarly defined as a diurnal oscillation Air Station) of direction at any level due to temperature Orange County Army Air Dsw 52 differences between the air over the valley Field and air over the lower plain. The%up- Long Beach Army Air HB 40 valley wind is termed simply the valley Fie Id wind while the down-valley wind is called San Pedro (Naval Air Ncx 10 the mountainwind. In general, slope or Station) drainage winds induced by temperature dif- Lomita Flight Strip 106 ferences between the free air and the sur- US Angeles Airpoit 96 face of the mountain slopes are considered (Mines Field) to be part of the valley or mountain wind. University of Cali f ornia 505 at Los Angeles As will be shown, most stations in the Glendde (Grand Central DGX 46 2 Los Angeles Basin experience winds which Terminal) 9 consist of a merger of the sea and valley Van Mys (Metropolitan DVN 7 97 breezes or of the land and mountain breezes. Airport) Surface winds of this type, as well as Newha 11 1190 cases when the true classification cannot Oxnard Flight Strip 82 be determined, will be termed the "sea- Pasadena (CIT) 758 valley" and "land-mountain" winds, respect- Oltario Army Air Field 9 20 lively. Since the studies of the winds San Bemardin0 Army Air 1098 aloft largely involved only stations near Field the coast, where the land and sea breezes Riverside (March Field) 1528 are the primary effects, the term "sea Beaumont 2592 breeze" when applied to winds above the sur- Palm Springs Army Air 420 face will be understood to include any FieId effects of the valley wihd. Similarly the San Nicolas Island NCB so5 term "land breeze", when applied to the (Naval Air Station) upper air will include mountain winds. San Clemente Island NSA 906 (Naval Air Station) Pacific War Time is used throughout Burbank (Lockheed Air 7 25 this report. Terminal) Los Angeles (WW.B.City 5 12 Off ice) SURFACE WINDS Wind direction frequency roses were GENERAL PICTURE prepared for 21 stations from the hourly teletype reports. From these wind roses The diurnal changes in the surface the prevailing wind direction during various winds at a number of stations in the Los portions of the day could be described. Angeles Basin were studied in detail for The surface wind regime for each station is the month of August 1944. Although only summarized in Figure 1 on which are in- 31 days were thus used in deriving the dicated the average time of beginning and averages, it is believed that this month is ending of the prevailing directions. Any 2 hours not included in the station model may ward San Gorgonio Pass in which Beaumont be considered to be times of variable wind (TUT) is located. The sea-valley wind direction, usually the transition fran one regime is felt at Palm Springs (IIPZ) east regime to another, The Beaufort forces of the San Gorgonio Pass and 80 miles in- given by the barbs on the arrows represent land frqm the coast, and slightly affects the average maximum daily speeds.