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- Author or Editor: James T. Peterson x
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Abstract
Eigenvectors, or empirical orthogonal functions, have been used to study the relationship between the St. Louis heat island and land use and meteorological parameters. The data used in this study consisted of observations of nocturnal surface air temperature over St. Louis on 17 occasions during winter, spring, and summer of 1952–53. The spatial distribution of the heat island was shown to he primarily a function of land use, but meteorological variables, especially wind direction, also influenced the heat island patterns. The magnitude of the heat island had a significant positive correlation with the vertical temperature gradient outside the city. An empirical model is developed for St. Louis to study the heat island that would result from hypothetical land-patterns and meteorological conditions. Examples are presented for two such land-use distributions.
Abstract
Eigenvectors, or empirical orthogonal functions, have been used to study the relationship between the St. Louis heat island and land use and meteorological parameters. The data used in this study consisted of observations of nocturnal surface air temperature over St. Louis on 17 occasions during winter, spring, and summer of 1952–53. The spatial distribution of the heat island was shown to he primarily a function of land use, but meteorological variables, especially wind direction, also influenced the heat island patterns. The magnitude of the heat island had a significant positive correlation with the vertical temperature gradient outside the city. An empirical model is developed for St. Louis to study the heat island that would result from hypothetical land-patterns and meteorological conditions. Examples are presented for two such land-use distributions.
Abstract
Measurements of the downward solar radiant flux in the St. Louis, Mo., area are compared with predictionsfrom an approximate solution to the radiative transfer equation. The atmospheric aerosols were assumedto have a power size distribution, dn/dr∼r-4, and the refractive indices suggested by Fischer (1973) foran urban area. On a relatively clean day, the predictions compared well with observations. On a hazy day,the comparison was poor with the a priori choice of aerosol properties. The particles on the hazy day apparently had more submicron particles than those found in the assumed size distribution, and the particleswere considerably less absorbing than those observed by Fischer. These changes could represent the effectsof relative humidity and different air mass characteristics.
Abstract
Measurements of the downward solar radiant flux in the St. Louis, Mo., area are compared with predictionsfrom an approximate solution to the radiative transfer equation. The atmospheric aerosols were assumedto have a power size distribution, dn/dr∼r-4, and the refractive indices suggested by Fischer (1973) foran urban area. On a relatively clean day, the predictions compared well with observations. On a hazy day,the comparison was poor with the a priori choice of aerosol properties. The particles on the hazy day apparently had more submicron particles than those found in the assumed size distribution, and the particleswere considerably less absorbing than those observed by Fischer. These changes could represent the effectsof relative humidity and different air mass characteristics.
Abstract
The results of an analysis of simultaneous measurements of incident solar radiation from six locations in metropolitan St. Louis, Missouri are described. The measurements were taken continuously from September 1975 through March 1977 with pyranometers with all-wave and 395 and 695 nm cutoff filters. This report documents typical urban-rural variations of incident solar radiation.
Atmospheric pollutants over the center of metropolitan St. Louis reduced incident all-wave solar irradiation by ∼3%. Under cloudless conditions, differences between urban and rural irradiation were ∼4.5% during winter and 2% in summer. At two suburban sites, the irradiation depletion averaged 1 and 2% for summer and winter seasons, respectively. Under all conditions, the ratios between stations for the complete experiment were similar to those for cloud-free conditions.
Although the comparisons were stratified by wind direction and speed, visibility, time of day and day of the week, only wind direction had a significant effect on the interstation ratios. For cloudless days two suburban sites and a rural site north of the city received ∼3.5% less radiation (compared to a control site) with south than north winds. Wind direction had an effect because pollutants were advected from major sources near the city center. The two urban sites exhibited only ∼1% change due to north-south wind differences. The interstation comparisons for all days were also partitioned by wind direction. With north winds, the suburban and northern rural sites showed ∼2–3% more irradiation (compared to a control site south of the city) on all days than on cloudless days for both the summer period and the complete experiment.
Abstract
The results of an analysis of simultaneous measurements of incident solar radiation from six locations in metropolitan St. Louis, Missouri are described. The measurements were taken continuously from September 1975 through March 1977 with pyranometers with all-wave and 395 and 695 nm cutoff filters. This report documents typical urban-rural variations of incident solar radiation.
Atmospheric pollutants over the center of metropolitan St. Louis reduced incident all-wave solar irradiation by ∼3%. Under cloudless conditions, differences between urban and rural irradiation were ∼4.5% during winter and 2% in summer. At two suburban sites, the irradiation depletion averaged 1 and 2% for summer and winter seasons, respectively. Under all conditions, the ratios between stations for the complete experiment were similar to those for cloud-free conditions.
Although the comparisons were stratified by wind direction and speed, visibility, time of day and day of the week, only wind direction had a significant effect on the interstation ratios. For cloudless days two suburban sites and a rural site north of the city received ∼3.5% less radiation (compared to a control site) with south than north winds. Wind direction had an effect because pollutants were advected from major sources near the city center. The two urban sites exhibited only ∼1% change due to north-south wind differences. The interstation comparisons for all days were also partitioned by wind direction. With north winds, the suburban and northern rural sites showed ∼2–3% more irradiation (compared to a control site south of the city) on all days than on cloudless days for both the summer period and the complete experiment.
Abstract
As part of the Los Angeles Reactive Pollutant Project (September–November 1973) continuous measurements were made of incident ultraviolet and total solar irradiance at six sites (five urban and one nonurban) over the Basin. Turbidity and nephelometer measurements were made periodically at two sites. Incident irradiance during cloudless conditions was significantly depleted by the smoggy urban atmosphere. The largest daily measured differences of UV energy between the nonurban and urban sites was about 50%; greater differences were measured for shorter periods. Variations between urban sites of up to 40% for short periods were noted. Less energy was attenuated by the urban atmosphere on weekends than weekdays. For the complete 68-day experiment, the average absolute effect of the urban atmosphere was to reduce ultraviolet irradiance from 11–20% and total irradiance from 6–8% over the Basin.
Atmospheric turbidity decreased from September through October as meteorological conditions changed. The August–September urban mean (0.287 decadic base) is among the highest summertime values in the United States. The greatest daily average was 0.492. Turbidity data were related to simultaneous global total irradiance transmission measurements at the nonurban site. For all data over solar zenith angles from 25–70° a 0.01 turbidity increase corresponded to a global transmission decrease of 0.84%. Comparison of turbidity and diffuse and direct UV and total irradiance showed that the diffuse component directly depended on turbidity and solar zenith angle and inversely depended on wavelength and station elevation. Measurements were applied to several air pollution problems in Los Angeles. Study of coincident irradiance and daily maximum ozone concentrations at downtown Los Angeles showed that low and moderate amounts of radiation define an upper limit for maximum surface ozone concentration. For higher radiation levels, other factors governed ozone levels. Depletion of UV irradiance by the urban atmosphere at EI Monte was strongly related to local visibility for visibilities ≲10 km. Finally, from turbidity and nephelometer data, the thickness of urban air flow over the mountains north of Los Angeles was estimated to average 170 m.
Abstract
As part of the Los Angeles Reactive Pollutant Project (September–November 1973) continuous measurements were made of incident ultraviolet and total solar irradiance at six sites (five urban and one nonurban) over the Basin. Turbidity and nephelometer measurements were made periodically at two sites. Incident irradiance during cloudless conditions was significantly depleted by the smoggy urban atmosphere. The largest daily measured differences of UV energy between the nonurban and urban sites was about 50%; greater differences were measured for shorter periods. Variations between urban sites of up to 40% for short periods were noted. Less energy was attenuated by the urban atmosphere on weekends than weekdays. For the complete 68-day experiment, the average absolute effect of the urban atmosphere was to reduce ultraviolet irradiance from 11–20% and total irradiance from 6–8% over the Basin.
Atmospheric turbidity decreased from September through October as meteorological conditions changed. The August–September urban mean (0.287 decadic base) is among the highest summertime values in the United States. The greatest daily average was 0.492. Turbidity data were related to simultaneous global total irradiance transmission measurements at the nonurban site. For all data over solar zenith angles from 25–70° a 0.01 turbidity increase corresponded to a global transmission decrease of 0.84%. Comparison of turbidity and diffuse and direct UV and total irradiance showed that the diffuse component directly depended on turbidity and solar zenith angle and inversely depended on wavelength and station elevation. Measurements were applied to several air pollution problems in Los Angeles. Study of coincident irradiance and daily maximum ozone concentrations at downtown Los Angeles showed that low and moderate amounts of radiation define an upper limit for maximum surface ozone concentration. For higher radiation levels, other factors governed ozone levels. Depletion of UV irradiance by the urban atmosphere at EI Monte was strongly related to local visibility for visibilities ≲10 km. Finally, from turbidity and nephelometer data, the thickness of urban air flow over the mountains north of Los Angeles was estimated to average 170 m.
Abstract
The formation of dew or frost on the outer glass hemisphere of pyranometers was found to cause erroneous values of incident hemispheric solar radiation. An air flow system was designed to continually ventilate the instrument and thereby prevent moisture formation on the outer hemisphere. Comparison of instantaneous early morning readings from ventilated and non-ventilated pyranometers indicate that substantial errors can occur because of dew or frost. Since the moisture from dew or frost naturally evaporates by mid-morning, daily totals of solar energy are not likely to be significantly affected on clear days.
Abstract
The formation of dew or frost on the outer glass hemisphere of pyranometers was found to cause erroneous values of incident hemispheric solar radiation. An air flow system was designed to continually ventilate the instrument and thereby prevent moisture formation on the outer hemisphere. Comparison of instantaneous early morning readings from ventilated and non-ventilated pyranometers indicate that substantial errors can occur because of dew or frost. Since the moisture from dew or frost naturally evaporates by mid-morning, daily totals of solar energy are not likely to be significantly affected on clear days.
Abstract
Atmospheric turbidity (aerosol optical thickness) was measured with sunphotometers across the Los Angeles Basin. Automobiles were used for east-west traverses of the metropolitan area (a distance of ∼100 km) on two days with distinctly different meteorological conditions: a hazy, relatively humid day and a warmer, dryer, less hazy day with easterly Santa Ana wind flow. Additionally, incident global UV and total solar irradiance were measured at six sites (five urban and one rural) and nephelometer measurements of aerosol concentrations were made at two locations.
On the hazy day turbidity was remarkably uniform across the Los Angeles Basin. In contrast, significant variation of turbidity from west to east occurred on the less polluted day. Solar radiation measurements also reflected the day-to-day and spatial turbidity differences. During the hazy day the urban sites received only 64–76% as much UV energy as did the rural mountain site. With easterly Santa Ana wind flow, San Bernardino received 17% more total solar energy than on the hazy day.
Abstract
Atmospheric turbidity (aerosol optical thickness) was measured with sunphotometers across the Los Angeles Basin. Automobiles were used for east-west traverses of the metropolitan area (a distance of ∼100 km) on two days with distinctly different meteorological conditions: a hazy, relatively humid day and a warmer, dryer, less hazy day with easterly Santa Ana wind flow. Additionally, incident global UV and total solar irradiance were measured at six sites (five urban and one rural) and nephelometer measurements of aerosol concentrations were made at two locations.
On the hazy day turbidity was remarkably uniform across the Los Angeles Basin. In contrast, significant variation of turbidity from west to east occurred on the less polluted day. Solar radiation measurements also reflected the day-to-day and spatial turbidity differences. During the hazy day the urban sites received only 64–76% as much UV energy as did the rural mountain site. With easterly Santa Ana wind flow, San Bernardino received 17% more total solar energy than on the hazy day.
Abstract
Some 8500 observations of atmospheric turbidity, taken at Raleigh, North Carolina from July 1969 to July 1975 are analyzed for within-day and day-to-day variations and their dependence on meteorological parameters. The annual average turbidity of 0.147 (0.336 aerosol optical thickness) is near the highest non-urban turbidity in the United States. A distinct diurnal turbidity cycle was evident with a maximum in early afternoon. Annually, highest turbidity and day-to-day variation occurred during summer with lowest values and variation during winter. Daily averages revealed an asymmetric annual cycle, with a minimum on 1 January and a maximum on 1 August. Turbidity showed a slight inverse dependence on surface wind speed. Aside from winter, highest turbidities occurred with southeast surface winds. Turbidity was directly proportional to both humidity and dew point. Correlations between turbidity and local visibility were best for visibilities <7 mi. Air mass trajectories arriving at Raleigh were used to study the dependence of turbidity on synoptic air mass. Air masses with a southern origin had greatest turbidities. Turbidity of an air mass significantly increased as the residence time of that air mass over the continental United States increased, with the most rapid changes during summer. A combination of Raleigh (1969–present) and Greensboro, North Carolina (1965–76) records showed a distinct summer increase through 1976, but no change during winter. A linear regression of annual averages for the complete record gave an 18% per decade turbidity increase.
Abstract
Some 8500 observations of atmospheric turbidity, taken at Raleigh, North Carolina from July 1969 to July 1975 are analyzed for within-day and day-to-day variations and their dependence on meteorological parameters. The annual average turbidity of 0.147 (0.336 aerosol optical thickness) is near the highest non-urban turbidity in the United States. A distinct diurnal turbidity cycle was evident with a maximum in early afternoon. Annually, highest turbidity and day-to-day variation occurred during summer with lowest values and variation during winter. Daily averages revealed an asymmetric annual cycle, with a minimum on 1 January and a maximum on 1 August. Turbidity showed a slight inverse dependence on surface wind speed. Aside from winter, highest turbidities occurred with southeast surface winds. Turbidity was directly proportional to both humidity and dew point. Correlations between turbidity and local visibility were best for visibilities <7 mi. Air mass trajectories arriving at Raleigh were used to study the dependence of turbidity on synoptic air mass. Air masses with a southern origin had greatest turbidities. Turbidity of an air mass significantly increased as the residence time of that air mass over the continental United States increased, with the most rapid changes during summer. A combination of Raleigh (1969–present) and Greensboro, North Carolina (1965–76) records showed a distinct summer increase through 1976, but no change during winter. A linear regression of annual averages for the complete record gave an 18% per decade turbidity increase.
Abstract
The study presents an analysis of atmospheric CO2 measurements at Ocean Weather Station P (50°N, 145°W) and sea surface temperatures over the North Pacific for the period 1974–78. The results show that during 1976 and 1977 sea surface temperatures over the Northwest Pacific were significantly below normal and, coincidentally, atmospheric CO2 levels at Station P also were lower than expected. This indirect evidence does not prove but suggests that the Northwest Pacific (40–45°N) may have been a major sink for atmospheric CO2 during 1976 and 1977. However, a specific mechanism for this sink is not established. Broecker et al. (1979) presented direct evidence of a C02 sink at 40°N, 180°W in late 1973 and early 1974. In the future direct observations of pertinent parameters obtained at appropriate times could establish the significance of the North Pacific as a sink for atmospheric C02 and lead to studies of the mechanism for such a sink.
Abstract
The study presents an analysis of atmospheric CO2 measurements at Ocean Weather Station P (50°N, 145°W) and sea surface temperatures over the North Pacific for the period 1974–78. The results show that during 1976 and 1977 sea surface temperatures over the Northwest Pacific were significantly below normal and, coincidentally, atmospheric CO2 levels at Station P also were lower than expected. This indirect evidence does not prove but suggests that the Northwest Pacific (40–45°N) may have been a major sink for atmospheric CO2 during 1976 and 1977. However, a specific mechanism for this sink is not established. Broecker et al. (1979) presented direct evidence of a C02 sink at 40°N, 180°W in late 1973 and early 1974. In the future direct observations of pertinent parameters obtained at appropriate times could establish the significance of the North Pacific as a sink for atmospheric C02 and lead to studies of the mechanism for such a sink.
