ureal parameters ol me Sea Breeze and lis vertical structure in the Boston Basin

Save this PDF as:
 WORD  PNG  TXT  JPG

Size: px
Start display at page:

Download "ureal parameters ol me Sea Breeze and lis vertical structure in the Boston Basin"

Transcription

1 ureal parameters ol me Sea Breeze and lis vertical structure in the Boston Basin James P. Barbato Geography Department Fitchburg State College Fitchburg, Mass Abstract The sea breeze is a mesoscale wind whose frequency of occurrence is times annually in the Boston Basin. Boston's sea breeze is among the best developed of all midlatitude sites studied. The complexity of site conditions and an urban concentration alter the characteristics of the sea breeze with inland penetration. Vertical temperature and dew point data have provided the first detailed look at the changes effected in Boston's atmosphere by this local wind. The data have also revealed that Boston's sea breeze is not always a moist flow of marine air but that the moisture content of the air is directly related to the regional wind speed and direction prior to onset of the sea breeze. Transformations of the vertical characteristics of the atmosphere suggest subtle but serious geographic and environmental variations in the spatial distribution of atmospheric contaminants. 1. Introduction The sea breeze is a mesoscale wind system whose frequency of occurrence is related to the establishment of strong temperature gradients induced by the differential heating of adjacent land-sea surfaces. The sea breeze affects the climatology of the Boston Basin some 40 or 50 times annually during the spring, summer, and fall months. Other factors that affect the sea breeze are 1) topography, 2) concavity of the coast, and 3) coastal water temperatures. Urban Boston is situated in a basin surrounded by a low upland rim of higher terrain. Relief in the hemispheric-shaped basin is subdued; the greater part of the lowland is <15 m above sea level. Terrain roughness is not an important factor within the basin, but it becomes a significant topographic constraint along the basin's margin. The most prominent escarpment is located along the west and northwest, where elevations rise abruptly m. The high elevations of the basin rim delay the inland progress of the sea breeze. Only 15 of the 40 sea breeze episodes observed in 1972 penetrated farther inland than the basin rim. The concavity of the coastline complicates the sea breeze penetration at Boston. Sea breezes along straight coastlines advance inland normal to the coast (Fig. 1); however, because of Boston's concave coastline, the flow is initiated normal to the coast and becomes divergent inland as penetration occurs. Additional variations in the flow appear with the passage of time and the effects of the Coriolis force. These will be discussed later in the paper / 78 / $ American Meteorological Society FIG. 1. Generalized sea breeze flow along straight, convex, and concave coastlines. Boston's compact, highly concentrated urban area, with some 2.5 million people, situated along a cold water margin generates two mesoscale breezes: a bay breeze and a sea breeze. The bay breeze is a response to a heated coastline, while the areas adjacent to the immediate coast remain cooler, and is restricted to a very narrow zone along the coast. It is superseded later in the day by the sea breeze. The cold water margin also exerts a strong influence in the seasonal distribution of sea breeze episodes at Boston. Most coastal mid-latitude locations experience their largest number of sea breezes during the spring months, when the temperature contrast between the land and ocean surfaces is normally the greatest (Defant, 1951). Although sea breezes have been recorded as early in the year as February, Boston records its greatest number of sea breeze episodes during th summer months because the temperature contrast between the land-sea surfaces is greatest in July and August at this site. The establishment of sea breezes along the Massachusetts coast may be very localized. Rexroad (1954) reported a vigorous sea breeze at Salem, Mass., but 20 km to the south at Boston, the sea breeze was not present. The combination of elements of the topographic situation, the concavity of the coast, and 1420 Vol. 59, No. 11, November 1978

2 Bulletin American Meteorological Society the large thermal gradients that can become seasonally established impart distinct characteristics to the sea breeze at Boston. Consequently, criteria found in much of the literature defining the sea breeze along relatively straight coastlines cannot be directly applied to the Boston Basin. 2. Criteria for distinguishing the Boston sea breeze Explicit criteria were required to identify a sea breeze episode at Boston. The general considerations of high solar azimuth, clear skies, and anticyclonic circulation were considered too broad since Boston, under certain synoptic conditions, often experiences these conditions accompanied by easterly winds. Six criteria were defined as essential to the identification of a sea breeze episode: 1) The barometer is recording high pressure and anticyclonic circulation prevails with the center of the anticyclone located west of and at a latitude south of Boston (42 N). 2) The amount of sunshine received that day must be ^50% of the amount possible. 3) Prior to onset of the sea breeze, the regional surface wind must be blowing offshore, i.e., westerly. 4) During the sea breeze, an afternoon wind maximum should be evident from the data collected by the National Weather Service (NWS) at Logan International Airport, East Boston, Mass. 5) The temperature trace at Logan Airport, which first experiences the sea breeze because of its location in Boston Harbor, should clearly indicate a change of air associated with a change in the circulation. Thus, the thermograph trace should record either a distinct temperature decrease accompanying onset of the sea breeze, or a retardation of the diurnal temperature curve, or both these factors. 6) The duration of the sea breeze must be ^5 h at Logan Airport. Criteria 1 and 2 are generally synonomous with each other. Defant (1951) indicated that the probability of a sea breeze event was 90% if these two conditions were met. At Boston, criterion 3 would be a westerly wind blowing from 190 to 350. Onset of the sea breeze causes the surface wind to veer or back to an easterly direction of between 15 and 145. These specific values delineate the concavity of the Boston coastline and are, therefore, unique to this site. The requirement that the regional wind be offshore prior to sea breeze onset represented a strict definition of the sea breeze in accordance with Munn (1966). Some early authors (Dolezel, 1945; Wexler, 1946) termed conditions at Boston in which an afternoon wind maximum was superimposed upon an onshore gradient wind a sea breeze. Although this afternoon wind maximum may be associated with 1421 a strengthening of the land-sea temperature gradient, it is not a true sea breeze. Criteria 4 and 5 are selfexplanatory. Criterion 6 was established after testing determined that sea breezes of shorter duration were restricted to the immediate coastline and subject to confusion with the bay breeze. Those whose duration was ^5 h penetrated inland with well defined characteristics. 3. Data base for the climatology of the Boston sea breeze Standard synoptic data from four Massachusetts sites were used: the NWS office at Logan Airport, the Massachusetts Institute of Technology (MIT) in Cambridge, the University of Massachusetts Suburban Experimental Station at Waltham, and Hanscom AFB, Bedford. The first three sites lie along an east-west inland traverse (Fig. 2). The fourth, Hanscom AFB, was included because of its proximity to the traverse and also because its extrabasin location on the nearby upland justified its inclusion as a data site. Radiosonde data were obtained from Environmental Meteorological Support Unit (EMSU) radiosondes launched twice daily from MIT. The EMSU project began in September 1971 and ended in May The radiosondes were released from a 30 m rooftop at 1000 GMT (0500 EST) and 1500 GMT (1000 EST). Data were gathered at 50 m intervals beginning at 30 m and terminating at 3000 m. On occasion, varied work schedules delayed the radiosondes until 1100 GMT (0600 EST) and 1600 GMT (1100 EST). Landsat-1 (launched as ERTS-1) provided the first satellite photograph of a sea breeze episode in the Boston Basin on 28 July This was used to compute inland penetration of the sea breeze front. 4. Various parameters of the Boston sea breeze The various parameters were determined from data for 40 Boston sea breeze episodes in a. Wind field Mean onset and retreat times of the sea breeze were computed to the nearest hour. Onset was defined as the time when the wind shifted from a westerly direction to an easterly wind between 15 and 145 on a day that fulfilled the six criteria previously discussed. Retreat was defined as the time when the mesoscale sea breeze was supplanted by the regional westerly wind. Mean onset of the Boston Basin sea breeze was 1500 GMT (1000 EST) with the mean wind from 100 at 4.7 ms. Maximum wind occurred at 1900 GMT (1400 EST) from 117 at 7.2 ms". Mean retreat took place at 2300 GMT (1800 EST) with the wind veering from 136 at 5.7 m s". These findings significantly differed from Dolezel's (1945) study; however, the differences are a result of the more accurate definition of what constitutes a sea breeze episode at Boston rather than any faulty technique on Dolezel's part

3 1422 Vol. 59, No. 11, November 1978 FIG. 2. Data network in the Boston Basin. The rotation of the wind shift at onset and retreat is presented in Table 1. At onset, the wind field veers from westerly to easterly in 67% of the cases. At retreat, the wind veers from easterly to westerly in 90% (36 of 40) of the episodes. Since the Coriolis force causes the sea breeze to veer throughout the day, the sea breeze TABLE 1. Rotation of the wind shift at onset and cessation of the sea breeze at Boston based on 40 episodes in Rotation Onset, days Cessation, days Through north Through south Total flow is usually from 130 to 140 by late afternoon. As the sea breeze weakens, the veering of the wind continues while the regional westerly wind reestablishes itself. The dominance of the right-hand turning of the sea breeze is quite evident from Table 1. Consequently, it would appear that although the regional synoptic wind affects the rotation of the wind at onset, the Coriolis effect strongly influences the wind rotation direction at cessation time. The combination of the sea breeze and the Coriolis veering of the sea breeze flow illustrates a significant mesoscale wind regime in the Boston Basin. More importantly, the diurnal rotation of the sea breeze wind field suggests more subtle geographic and environmental implications associated with the spatial distribution of

4 Bulletin American Meteorological Society T A B L E 2. Characteristics of the sea breeze at Boston (Logan Airport) based on 40 episodes in Characteristic Onset time, EST Cessation time, EST Duration, h Mean The duration of the sea breeze varied at each site. Tables 2 and 3 present data from the two extremes of the linear traverse. The mean duration of 8.1 h at Logan Airport represents a steady wind field, whereas at Hanscom AFB, near the inland limit of penetration, the 4.6 h mean duration is very misleading. On any given sea breeze day, the wind field may vary in a series of pulsations at Hanscom AFB. One hour the sea breeze may be present, the next hour, absent; however, this behavior was expected because the forcing function (i.e., the thermal gradient) weakens inland. This behavior also established that Hanscom AFB, 28 km inland from Logan Airport, is representative of the limit of inland penetration of the Boston sea breeze. An early study (Davis et al., 1890) reported sea breeze penetrations of km along the Massachusetts-New Hampshire coasts. The absence of a data site farther inland prevented the writer from determining if any of the 15 sea breezes observed at Hanscom AFB penetrated any farther inland. topography The basin's upland periphery was verified as a significant topographic obstacle. In 62.5% (25 of 40 cases), the sea breezes were restricted to the basin lowland, 20.1 km inland from Logan Airport. Where the vector resultant of the frictional component and the Coriolis force balance the pressure gradient driving force, the sea breeze stalls since the major component of the frictional force is generally opposite to the wind. The effect of the upland is to significantly increase the frictional component. d. Rate of advance and retreat Analysis of wind shifts, hence sea breeze arrival times at each site, demonstrated that the sea breeze front advanced at a mean rate of 8.8 km h. Between the coast and Kenmore Square (downtown Boston), inland penetration was rapid at 11.7 km h, while farther inland between Kenmore Square and the Waltham data site, the penetration rate slowed to 4.7 km hr. The sea breeze Characteristics of the sea breeze at Bedford, Mass. (Hanscom AFB), based on 15 episodes in Characteristic Mean Onset time, EST Cessation time, EST Duration, h Duration c. Effect of TABLE Range atmospheric contaminants. The transport wind and basin topography may combine to create mesoscale regions of higher pollutant concentrations along the inland limits of the wind field. These implications will be explored in a forthcoming paper. b Range stalled at the basin's margin in 62.5% (25 of 40) of the episodes studied. The speed of inland penetration at Boston is atypical of most sea breeze observations. Simpson et al. (1977) reported a tendency for an acceleration of the rate of sea breeze advance based on the observations of 76 sea breeze fronts that passed Lasham, England, over a 12-year period. Simpson et al. explained this observed acceleration of the front in terms of increased temperature contrast at the front due to the decrease of solar heating of the sea air. Simpson et al. concluded that their observations confirmed the conclusions of a numerical model developed by Neumann and Mahrer (1975) in which one of the most interesting developments of the model depicted the most rapid rates of inland penetration occurring a few tens of kilometers inland. Yet Simpson et al. (1977) acknowledge that sea breeze observations in more complex terrain (the California coast) by Fosberg and Schroeder (1966) have demonstrated contrary resulfs. Fosberg and Schroeder observed the marine air penetrating rapidly early in the day but slowing down later in the day. The Boston Basin is neither the California coast nor Lasham, but the concave coast, the basin rim, and the urban sprawl serve to categorize the area as different. It is possible that the increased temperature contrasts responsible for the rapid inland penetration occur between the coast and the concrete-asphalt landscape of Boston. As the sea breeze front accelerates across the city and reaches the basin margin (also the location of the more vegetated suburbs), the temperature contrasts may be less and the speed of inland penetration reduced. Certainly, the lack of universal agreement suggests that additional research on the relationship(s) between site conditions and the rate of ea breeze advance may be warranted. Retreat or cessation of the sea breeze within the entire basin occurred in ^1.0 h in 80% of the cases examined. Retreat rates ranged from a rapid 24.4 km h to a low of 7.4 km h". On 14 occasions, data from the inland sites at Waltham and Hanscom AFB demonstrated that the sea breeze was still in progress but data from the NWS at Logan Airport indicated that the sea breeze flow had terminated. Further examination of the data revealed that the sea breeze cell was bifurcating along the coast at cessation time. A similar bifurcation and increase in the landward component of the sea breeze in the very lowest layer along the Rhode Island and New York City coastlines at sunset was reported by Fisher (1961) and by Frizolla and Fisher (1963, p. 738), _1 1

5 1424 Vol. 59, No. 11, November 1978 who concluded... that such accelerations probably are a sensitive function of local conditions when small variations between the drivirlg force provided by the horizontal temperature gradients and friction become important. It is therefore likely that the bifurcations and accelerations of the sea breeze at Boston are similar to those observed by Frizolla and Fisher. e. Vertical limits The EMSU radiosonde data made it possible to determine for the first time the vertical extent of the Boston Basin sea breeze. Figure 3 was prepared using those da,y& in 1972 when the sea breeze was present in the 1000 EST (1500 GMT) EMSU sounding at MIT. The difference in wind direction between the 0500 EST (1000 GMT) and 1000 EST (1500 GMT) sounding is particularly evident at the 30 rri level (the height of the rooftop from which the radiosondes were launched at MIT). The actual depth of the sea breeze circulation was derived by determining that height in the radiosonde sounding where the wind veered or backed from the 15 to 145 compass heading. Those wind directions represent the dominant criterion of the sea breeze flow in the Boston Basin. Deviations from these compass headings in the vertical wind profile delineate the upper boundary, or vertical extent, of the inland flow of air into the Boston Basin. It should be noted that a return wind flow aloft (in the case of Boston a seaward flow) is an integral part of the solenoidal sea breeze cell. The orientation of the basin and its geographic location in the westerly wind belt are such that the sea breeze return flow is superimposed in the regional wind field that persists at altitudes above the surface inland component of the sea breeze. The vertical depth (height) of the sea breeze flow in the Boston Basin as determined from the EMSU 1972 data is given below. Date Depth of Inland Flow, m 25 April April April July July July August September 530 The mean depth of the Boston Basin sea breeze was 667 m and ranged from a maximum vertical extent of 1230 m to a minimum depth of 330 m. The shape of the FIG. 3. Vertical wind profiles for 8 sea breeze days in 1972 prepared from EMSU sounding data. The number after the feather indicates wind directions. If the wind shaft is between 0 and 90 and the number is a 1, it signifies a wind from 10. If the shaft is between 90 and 180, the 1 designates a wind from 110, etc. North is toward the top.

6 Bulletin American Meteorological Society 1425 basin appears to exert little or no effect upon the vertical development of the sea breeze since the vertical depth measurements are comparable with those reported for other mid-latitude sites by Sutcliffe (1937), Defant (1951), Fisher (1960), and Frizolla and Fisher (1963). In fact, the vertical development of one (2 August) of the Boston sea breezes was quite large. The probable explanation for this great vertical extent was the development of a particularly strong temperature gradient. The EMSU measurements have permitted the determination of the vertical extent of Boston sea breezes. However, it should be noted that most sea breezes at Boston penetrate the coast after midmorning. Consequently, the 1000 EST (1500 GMT) sounding is representative of very early sea breeze passages. It is therefore quite probable that as the sea breeze flow intensifies, a greater vertical extent may develop later in the day. /. Effect on surface temperature and dew point values The temperature and moisture parameters of sea breezes were among the first characteristics of sea breezes studied. Craig et al. (1945) constructed a series of sea breeze cross sections from temperature and psychometric measurements made by balloon and airplane ascents through sea breezes along a line from Marshfield (30 km southeast of Boston) eastward to Provincetown, Mass., on the terminus of Cape Cod. The results of their study demonstrated a marked temperature and moisture gradient across the sea breeze front. The effects of the Boston Basin sea breeze upon temperature and dew point values were consistent with those reported in the literature. Two marked variations in the diurnal temperature profile occurred, depending upon whether onset of the sea breeze was midmorning or delayed at Logan Airport (Fig. 4). On 2 October a 1500 GMT (1000 EST) onsfet produced a flattened temperature profile and retarded the daily maximum temperature. The 1700 GMT (1200 EST) delayed onset of 3 October demonstrated a sharp decline in the temperature profile as cooler air advanced inland. The control day (8 October), used for comparisons, was the closest day with anticyclonic circulation to the 2 sea breeze days except that a sea breeze did not develop. The temperature profile for the control day more closely approximated the expected bell-shaped temperature profile. In 70% (28 of 40) of the sea breeze days, a mean decrease of 3.3 C from the normal temperature was recorded. In 30% (12 of 40) a mean increase of 2.1 C from the normal was observed. Of these, 75% (9 of 12) were those days when onset was delayed (similar to 3 October) and hence the temperature profile rose correspondingly before rapidly declining after onset. Dew point temperatures demonstrated a double pattern. Days with an early, well-defined onset (2 October) depict a marked increase in the dew point temperature (Fig. 4). Late onset times produced a smaller and more poorly defined increase in the dew point temperatures FIG. 4. Temperature and dew point profiles for selected sea breeze days and a control day in (3 October). The data for 4Q sea breeze days in 1972 revealed that the increase in dew point values accompanying onset was between 1.1 C and 3.3 C. It was discovered that much of the variability in dew point values was associated with the wind direction and speed of the previous night. All sea breeze days that experienced significant increases in atmospheric moisture were those days on which the transport wind prior to onset of the sea breeze was ^2.6 m s~\ Air moved offshore had sufficient residence time over the water to be humidified before being entrained in the sea breeze flow and returned landward. Those days with transport wind speeds >2.6 m s -1 prior to onset produced dew point temperature increases ranging from C to 1.1 C.

7 1426 Vol. 59, No. 11, November 1978 g. Vertical temperature distribution Vertical temperature data from radiosonde ascents launched at MIT at 1000 and 1500 GMT provided an opportunity to examine the impact of the sea breeze on the vertical temperature distribution. Data were gathered every 50 m beginning at 30 m (the height of the rooftop from which the radiosondes were released). Examples of representative soundings for spring, summer, and fall sea breeze episodes are presented in Figs. 5, 6, and 7. Figure 5 depicts soundings that are similar to each other fbr 3 sea breeze days (25, 26, 27 April) along with the profile for the control day (1 May), which represents a typical temperature profile on the closest non-sea breeze day with anticyclonic circulation. The large temperature differentials at all levels between the sea breeze days and the control day represent the impact of the cold water adjacent to Boston's coastline in the spring. The significance of the sea breeze as a climatological phenomenon in advecting cooler air landward cannot be underestimated. Higher summer temperatures but similar differentials in temperature are evident in Fig. 6. Figure 7 is representative of a late summer-early fall episode. h. Vertical dew point temperature distribution Detailed radiosonde soundings have provided the first precise look at the vertical moisture distribution during a sea breeze episode. A representative profile (Fig. 8) FIG. 5. Vertical temperature profiles for selected days in 1972.

8 Bulletin American Meteorological Society 1427 for 27 April 1972 illustrates a large dew point temperature increase (8.7 C) that accompanied the 1600 GMT sea breeze inflow 530 m in height. The dew point temperature increase accompanying the 28 July 1972 onset was 2.5 C. Values in this range were more typical (Fig. 9). The most striking result of the analysis of the vertical dew point temperature profiles accompanying onset of a sea breeze was that many profiles did not reveal an increase in atmospheric moisture accompanying the sea breeze flow. Several conclusions were made regarding the sea breeze vertical moisture distribution. The vertical EMSU profiles demonstrated that both shallow (330 m) and deep (1230 m) sea breeze circulations were capable of advecting extremely moist air into the Boston Basin. It was also observed that several sea breezes produced soundings in which the expected increase in the vertical moisture profile was absent. The vertical moisture distribution was found to be entirely dependent upon the regional synoptic wind prior to onset. All sea breeze days that experienced increases in the vertical moisture profile were those on which the speed of the transport wind prior to onset was <2.6 m s _1. The air advected eastward over Boston Bay and the Atlantic Ocean was moving slowly enough to be humidified and returned landward as part of the sea breeze flow. Those days on which the speed of the regional westerly winds was >2.6 m s _1 demonstrated minimal effects on the FIG. 6. Vertical temperature profiles for selected days in 1972.

9 1428 Vol. 59, No. 11, November 1978 FIG. 7. Vertical temperature profiles for selected days in moisture profiles. The residence time of this fastermoving air over the water was so brief that it was not humidified before it was returned inland in the sea breeze. 5. Conclusions The spatial characteristics of the sea breeze in the Boston Basin have illustrated its role as a dynamic mesoscale wind system. The results from the transect line revealed that the rate of inland penetration varied from 4.7 to 11.7 km hr and that these values were within the range considered 1 as normal for a mid-latitude site. Inland penetration of the sea breeze varied. The majority of sea breezes stalled along the topographic boundary of the basin. Those sea breeze episodes that advanced farther inland reached their maximum limits of penetration km from the base data point at Logan Airport. The sea breeze was found to diverge inland along a hemispheric arc that delineated the sea breeze front as analogous to a miniature macroscale cold front. The effect of the Coriolis force was evident in the right-hand turning of the sea breeze wind as the day progressed. Vertical analysis of the sea breeze circulation resulted in several findings. The vertical extent of the sea breeze

10 Bulletin American Meteorological Society 1429 inflow was found to vary between 330 and 1230 m, which is also within the normal range for a sea breeze in the middle latitudes. The vertical temperature profiles were shifted to the left; i.e., lower temperatures were recorded at each successive pressure surface on sea breeze days. Dew point temperature data from 30 m illustrated that the increase accompanying the sea breeze ranged from +0.6 C to +8.7 C. The study of the temporal characteristics determined that 40 sea breezes annually was a normal level of occurrence for a mid-latitude site. However, the cold water margin of Boston skewed the frequency and season of occurrence from the normal spring maximum to a midsummer maximum (July and August). Two effects on the temperature regime were noted. A flattening of the diurnal temperature profile accompanied all sea breeze episodes, and the diurnal maximum temperature on sea breeze days was below the normal for those dates as cooler air was advected inland off the water. The results of the dew point analysis produced an unexpected finding. Historically, it was assumed that the sea breeze advected moist marine air inland. This analysis determined that the speed of the wind in the Boston Basin prior to onset of the sea breeze was instrumental in de- FIG. 8. Vertical dew point profiles for 27 April 1972.

11 1430 Vol. 59, No. 11, November 1978 FIG. 9. Vertical dew point profiles for 28 July termining whether moist air would be advected inland. If the speed of the evening and early morning wind was >2.6 m s _1, the air advected seaward would have had little time to become humidified. Hence, the sea breeze would advect the air, which had recently arrived over the water from a prior land trajectory, back inland. The rotation of the sea breeze wind by the Coriolis force during the afternoon hours emphasized that even mesoscale wind systems are subject to certain macroscale forces. Furthermore, it has also been shown that the sea breeze advects cooler, more stable marine air into the basin behind a frontal zone, exhibiting vigorous turbulent motion, similar to the passage of a macroscale cold front. The three later characteristics, i.e., the Coriolis effect, the frontal zone, and the transport of more stable air inland, provide an indication that, aside from its spatial and temporal characteristics, the sea breeze may also affect the urban atmosphere in a manner previously unrecognized. The turbulent motions at the sea breeze front and the potential "piling up" of atmospheric pollutants in advance of the front by the regional wind may be responsible for significant short-term increases of pollutants accompanying the onset of the sea breeze. Furthermore, the cooler, more stable marine air may restrict the ability of the urban atmosphere to diffuse and disperse gaseous contaminants. Consequently, it is

12 Bulletin American Meteorological Society 1431 a logical assumption that potential increases in contaminant levels may be recorded during a sea breeze episode in the Boston Basin. Similarly, the combination of the turning of the sfea breeze wind by the Coriolis force and the tendency of the frontal zone to stall along the basin's periphery may demonstrate that particular geographic locations within the Boston Basin, especially the northwest quadrant, may experience a serious decline in air quality, while sensors located closer to the coast are recording acceptable background contaminant levels. These hypothesized effects suggest that the validity of these statements concerning the transformation of the ventilation characteristics of the Boston urban atmosphere be examined since the magnitude and scope of the effect of the sea breeze in transforming the urban atmosphere may be particularly significant to air quality levels in the Boston Basin. The author plans to report on these effects in a paper currently in preparation. References Craig, R., I. Katz, and P. J. Harney, 1945: Sea-breeze cross sections from psychrometric measurements. Bull. Am. Meteorol. Soc., 26, Davis, W. M., L. G. Schultz, and R. DeC. Ward, 1890: An investigation of the sea breeze. Ann. Harvard College Observ., 21, Defant, F., 1951: Local winds. Compendium of Meteorology, edited by Thomas Malone, AMS, Boston, pp Dolezel, E. J., 1945: Ari analysis of the sea breeze in the Boston area. AAF Weather Station, MIT, Cambridge, Mass. (Unpublished manuscript.) Fisher, E. L., 1960: An observational study of the sea breeze. /. Atmos. Sci., 17, Fosberg, M., and M. Schroeder, 1966: Marine air penetration in central California. J. Appl. Meteorol., 5, Frizolla, J. A., and E. L. Fisher, 1963: A series of sea breeze observations in the New York City area. J. Appl. Meteorol 2, Munn, R. E 1966: Descriptive Micrometeorology. Academic, New York, 245 pp. Neumann, J., and Y. Mahrer, 1975: A theoretical study of the lake and land breezes of circular lakes. Mon. Wea. Rev., 103, Rexroad, F. H., 1954: Boston's east wind. Weatherwise, 7, 60-63, 67. Simpson, J. E., D. A. Mansfield, and J. R. Milford, 1977: Inland penetration of sea breeze fronts. Quart. J. Roy. Meteorol. Soc., 103, Sutcliffe, R. C., 1937: The sea breeze at Felixstowe: A statistical investigation of pilot-balloon ascents up to 5500 feet. Quart. J. Roy. Meteorol. Soc., 63, Wexler, R., 1946: Theory and observations of land and sea breezes. Bull. Am. Meteorol. Soc., 27, announcements continued from page 1419 Directory of upwelling researchers The Scientific Committee on Oceanic Research (SCOR) Working Group 56, Equatorial Upwelling Processes, is assembling a directory of scientists and engineers interested in physical arid biological processes of upwelling occurring within the Upper ocean in the region between 15 N and 15 S. Scientists and engineers primarily interested in the biological aspects of equatorial upwelling should send name, affiliation, and address to: Dr. Richard T. Barber, Chairman, SCOR WG 56 Biological Panel, Duke University, Marine Lab., Beaufort, N.C Those primarily interested in the physical aspects of equatorial upwelling should contact: Dr. David Halpern, Chairman, SCOR WG 56 Physical Panel, NOAA Pacific Marine Environmental Lab., th Ave. N.E., Seattle, Wash Climatological data summaries The National Climatic Center (NCC) has recently published Climatography of the U.S. No. 20 (Substation Summaries) and the revised and updated Climatography of the U.S. No. 60 (Climate of the States). Climatography of the U.S. No. 20 includes climate summaries for 1063 NWS cooperative climatological observing stations in all 50 states and Puerto Rico. The 4-page data summaries contain for each location a means and extremes table; sequential tables for monthly and annual mean maximum, mean minimum, and average temperature, total precipitation, and total snowfall; monthly normals ( ) of temperature, precipitation, and total heating and cooling degree days; probability statistics for monthly precipitation; and probability statistics for spring and fall freeze dates and the length of the growing season for five temperature thresholds. These summaries were prepared for stations with a complete record for and are based upon the period of record 1951 through the latest complete year of record available at the time of preparation. Climatography of the U.S. No. 60 has been revised and reprinted for each of the 50 states and for Puerto Rico and the U.S. Virgin Islands combined. It contains a narrative description of the general climate of the state (or area), the normals, means, and extremes table for each First Order Station in the state, and the means and extremes table for those substations in the state that are included in Climatography of the U.S. No. 20. Copies of these publications are available from NCC. The "Substation Summaries" are priced at $0.15 per station; "Climate of the States" is priced at $0.50 per state. Requests for copies should be addressed to: Director, National Climatic Center, Federal Bldg., Asheville, N.C (tel: , ext. 683). Continued on page 1473