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J. K. ANGELL

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J. K. ANGELL

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J. K. Angell

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J. K. ANGELL

Abstract

The magnitude of analysis errors over the northeastern Pacific at 300 and 250 mb. is estimated by means of winds and geostrophic winds derived from operational transosonde flights from Japan. The results suggest that the ratio of vector geostrophic wind error and geostrophic wind varies from 0.15 near the west coast of North America to 0.40 in the North-Central Pacific. The influence of these analysis errors upon numerical forecasting, airplane dispatching, and trajectory estimations is indicated. As one of the, alternative methods for increasing the number of upper-air observations over the oceans, the present stalemate with regard to the horizontal sounding system is considered, and suggestions made for breaking this stalematge.

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J. K. Angell

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J. K. Angell

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The variations in United States cloudiness (percent of sky covered by clouds, as estimated subjectively by observers at 100 National Weather Service stations) and sunshine duration (percent of possible sunshine, as estimated objectively by sunshine recorders at these same 100 stations) are examined for years 1950–88. During this period, the correlation between annual values of cloudiness and sunshine duration within the contiguous United States was −0.86, significant at the 1% level. The years of maximum cloudiness and minimum sunshine duration were 1972 and 1982, when strong El Ninos began. The year of maximum sunshine duration was 1988, but the years of minimum cloudiness were 1952–56 (mini dust bowl); the discrepancy a result of the greater long-term increase in cloudiness than decrease in sunshine duration. In the spring of 1988 them were anomalous values of cloudiness (below average) and sunshine duration (above average) in north central, south central and southeast regions of the United States, the deviations from average approaching 10%. In the summer of 1988 these deviations were anomalous only in north central and northwest regions.

Despite the low value of cloudiness in 1988, based on this analysis the United States cloudiness increased by 2.0, ± 1.3% between 1950–68 and 1970–88 (corresponding to a percentage increase of 3.5% since the average cloudiness was 58%, or 5.8 tenths, during 1950–88). The increase in cloudiness was close to 2% in all six regions of the country, and significant at the 5% level in all regions except the southeast. Most of the increase in cloudiness was in autumn, with a negligible increase in spring. The decrease in United States sunshine duration between 1950–69 and 1970–88, however, is indicated to be only −0.8 + 1.2% (corresponding to a percentage decrease of −1.2% since the average sunshine duration was 63% during 1950–88). The difference between cloudiness increase, and sunshine duration decrease is most apparent in the west and may be due in part to an increase in cirrus not thick enough to turn of the sunshine recorder.

There has been a correlation of 0.79 (significant at the 1% level) between annual cloudiness and precipitation within the United States during 1950–88, but the correlation of −0.43 between annual cloudiness and surface temperature (above-average cloudiness associated with below-average temperature) is not quite significant at the 5% level. Considered is the possible relation between the 1987 El Nino and United States cloudiness and sunshine duration.

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J. K. Angell

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Based on data from the Dobson network, between 1960 and 1987 there has been a zero-lag correlation of 0.48 between the 112 unsmoothed seasonal values of sunspot number and global total ozone, significant at the 1% level taking into account the considerable serial correlation in these data. The maximum correlation of 0.54 is found when sunspot number lags total ozone by two seasons, the result mainly of a phase difference early in the record. On the basis of only 2½ solar cycles, the global total ozone has increased by 1.4% for an increase in sunspot number of 100. The correlation between sunspot number and total ozone has been significant at the 5% level in north temperate and tropical zones—the zones with the most representative data. In the north temperate zone, the correlation between sunspot number and total ozone has been much higher in the west-wind phase of the 50 mb equatorial QBO than in the east-wind phase, but in the tropics the correlation has been much higher in the east-wind phase. Umkehr measurements between 1966 and 1987 in the north temperate zone indicate that the correlation between sunspot number and ozone amount has been higher (0.35, almost significant at the 5% level) in the low stratosphere where transport processes dominate than in the high stratosphere where photochemical processes dominate. During 1932–60 there was a significant correlation of 0.35 between sunspot number and Arosa total ozone 14 seasons later, very different from the nearly in-phase relation found after 1960. Considered is the possible impact of long-term change in transport processes in the low stratosphere on the total-ozone record at a single station such as Arosa.

Between 1966 and 1985 there has been very good agreement between observed global total ozone, and global total ozone calculated from three 2-D stratospheric models that take into account the solar cycle, the time variation in trace gases, and nuclear tests; both observed and calculated variations are closely related to the variation in sunspot number. Between 1960 and 1966, however, the agreement between observation and calculation is poor, the models indicating a pronounced minimum in global total ozone in 1963 due to the nuclear tests of the early 1960s—a minimum not found in this analysis. The observed variation in global total ozone has been compared with the variation predicted by one of the models up to the sunspot maximum in 1990, and the agreement is shown to be good through the northern summer of 1988 if the impact of the QBO on global total ozone is taken into account. On the basis of the present analysis, there has been a 1.0 ± 0.9% decrease in global total ozone between solar cycles 20 and 21, a decrease 70% larger than that indicated by the three stratospheric models.

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J. K. Angell and Korshover

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The global variation in temperature, during the period 1958–75 is investigated using a sample of 63 radiosonde stations. The surface temperature as well as the mean temperature in 850–300 mb and 300–100 mb layers is examined, the latter based on thickness analysis. Between 1958 and 1965 there was a significant cooling averaging about 0.3°C over much of the globe, but since 1965 the temperature variations have been small. During the past few years there has been a slight warming in most latitudes. The meridional temperature gradient between the tropics and temperate latitudes has continuously increased, but since 1965 the temperature gradient between temperate and polar latitudes has decreased, with an especially large surface warming indicated for Antarctica. In the tropical troposphere, a temperature oscillation of about 3-year period and 0.3°C amplitude has been dominant since 1965. The eruption of Mt. Agung in 1963 may have decreased the surface temperature by as much as 0.2°C in the tropics, 0.4°C in the south extratropics and 0.6°C in the north extratropics. In the south extmtropics there was also a 0.7°C warming and cooling in the 300–100 mb and 850–300 mb layers, respectively, in the year of the eruption. Also shown is the variation with longitude of the temperature changes and the tendency for increased spatial variability of temperature.

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J. K. Angell

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The dependence upon frequency of the variance and cross variance of zonal-meridional and natural ageostrophic wind components is determined for twelve 300-mb transosonde flights of 60 to 130 hr duration. The main peaks in the variance of these components occur at periods near 50 hr and are assoriated with the transit time of the transosondes through long waves in the westerlies. Two of the longest flights have a secondary peak in the variance of the zonal wind component at a period of 12 hr. For fluctuations of period near 50 hr, the cross variance indicates that the zonal wind component is usually a maximum slightly upstream from the trajectory crest, and that the maximum flow towards low pressure consistently occurs near the inflection point downstream from the trajectory trough line. The evidence for inertial oscillations is inconclusive, partly due to the difficulty in resolving inertial oscillations and fluctuations associated with the but, pending the analysis of more such data, generalization is not attempted.

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J. K. ANGELL

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On the basis of wind speeds and accelerations derived from U.S. Navy sponsored 300-mb. constant level balloon or transosonde flights made during 1953, 1955, and 1956, statistics are presented on the magnitude of the ageostrophic wind and its variation with latitude and wind speed. These statistics indicate that at 300 mb. the average angle between wind and geostrophic wind is 11 degrees and the mean magnitude of the vector deviation between wind and geostrophic wind is 12m.see.−1. The data also show that, through the use of the geostrophic and gradient wind approximations, half the time errors greater than 29 percent and 11 percent, respectively, are introduced into the derived results.

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