Donald G. Baker

Effect of Observation Time on Mean Temperature Estimation

Abstract The increased interest and application of heating degree days (HDD) and growing degree days (GDD) prompted this study into the effect of different observation times upon the mean daily temperature. The study was based upon three years of hourly air temperatures measured at St. Paul. These data were used to calculate 1) a true daily mean, 2) a mean of the maximum and minimum between successive midnights as observed at first order stations, and 3) a mean of the maximum and minimum observed at all other hours of the day to simulate cooperative station means. Comparisons of the annual and monthly mean temperatures showed deviations can be of such magnitude as to discourage comparison of station temperatures and temperature-derived quantities such as HDD and GDD unless observation times are the same or corrections are applied.

Solar Radiation Effects on Pyrgeometer Performance

Abstract In 1973 an Eppley Laboratory pyrgeometer was installed on a field site in St. Paul, Minn., to measure atmospheric radiation (Ld). Based on comparisons between measured and calculated Ld for clear nights and low overcast conditions during days and nights the pyrgeometer provided satisfactory measurements. However, on clear days measured Ld was found to range from 11–20% higher than calculated. When the pyrgeometer dome was shaded from direct solar rays there were reductions in output of about 20–120 W m−2. Calculations showed that transmission of solar radiation by the pyrgeometer dome accounted for a maximum of about 7 W m−2 of this amount. Thus, it was inferred that the high values of measured Ld were primarily caused by solar heating of the dome and its subsequent radiation to the thermopile. This was strengthened by the fact that on clear windy days there were short-term fluctuations in output of 15–35 W m−2. It was determined that these fluctuations were caused by wind gusts cooling the dome....

Frequency, Duration, Commencement Time and Intensity of Temperature Inversions at St. Paul-Minneapolis

Abstract This study is based upon temperatures for the period June 1961 through July 1968, obtained from thermistors installed on a television tower at heights of 70, 170 and 500 ft. The tower was located in the heart of the metropolitan area but well outside of the main business district of either city. Only inversions ≥2 hr in duration were counted.On an annual basis only 2.5 inversions per 100 days occurred in the lower level (70–170ft) compared to 26.3 inversions per 100 days in the upper level (170–500ft). The total frequency, including the two levels and the deeper inversions that extended over both levels, equalled 45.5 per 100 days.The average duration of inversions within both levels was 6.8 hr, the 8.2-hr average in October being the longest of any month. Midnight was the single most common hour for inversion formation. Inversion intensity (defined as the temperature difference between levels) varied directly with duration of the inversions. The average intensity of all inversions within both le...

A Three-Year Study of Net Radiation at St. Paul, Minnesota

Abstract This study is based upon net radiation measurements made with a Suomi-type ventilated net radiometer. The average annual net radiation was 36,247 ly for the study period 1 April 1964–31 March 1967. April–October showed positive net radiation totals, November–February negative net radiation totals, and March had positive net radiation totals in two of the three years studied. Only fourteen days with all negative net radiation and two days with all positive net radiation occurred in the three-year period. Average daily time of positive net radiation ranged from 244 min in January to 749 min in June. Although positive net radiation exceeded negative net radiation an average of 36,247 ly per year, negative or null net radiation was recorded 63% of the time. The ratio of net radiation to incoming solar radiation varied widely during the year. However, from May–August the ratio ranged only from 0.45–0.54 for any one month during the three years and averaged 0.50. Monthly net radiation values calculated...