Sandra W. Brazel

Diurnal Variations in Arizona Monsoon Precipitation Frequencies

Abstract This paper identifies the spatial and temporal patterns in diurnal variations of Arizonas monsoon precipitation frequencies. Long-term (1948–83) hourly rainfall data reveal a strong nocturnal tendency in the Salt and Gila River basins of central Arizona. First harmonic phase angles suggest that storms tend to develop into the Phoenix area from all directions to ultimately produce a strong maximum frequency near midnight over the city. Other areas of the state appear to have the more normal daytime maximum in their monsoon precipitation. The practical and theoretical utility of the results are briefly discussed.

Recent changes in Phoenix, Arizona summertime diurnal precipitation patterns

SummarySummertime diurnal precipitation patterns for Phoenix, Arizona are analyzed for the period 1954 through 1985. Although the mean precipitation amounts and frequencies for the entire summer monsoon season have not shown any significant effects from the rapidly developing urban heat island, diurnal patterns have displayed substantial changes in the recent period of explosive population growth. During the most recent 16 years, late afternoon and evening storms have become more frequent and produce greater rainfall totals. Sharp declines are noted in the frequency of rain events between midnight and noon; especially large drops occur in the rainfall amounts between 9.00 and 12.00 MST. These findings appear to be consistent with several mechanisms proposed to explain the unusual diurnal character of the summertime rainfall in the Phoenix, Arizona area.ZusammenfassungIn der vorliegenden Arbeit wird der sommerliche Tagesgang des Niederschlags für Phönix, Arizona, analysiert.Obwohl keine signifikante Beeinflussung der durchschnittlichen Niederschlagsmengen und -häufigkeiten über die gesamte Sommermonsunzeit durch die rasch anwachsende städtische Wärmeinsel zu verzeichnen ist, weisen die Tagesgänge in der jüngsten Zeit explosiven Bevölkerungswachstums substantielle Veränderungen auf. In den vergangenen 16 Jahren sind Unwetter spätnachmittags und abends häufiger geworden und führten zu einer größeren Niederschlagssumme. Eine starke Abnahme der Regenfälle zwischen Mitternacht und Mittag ist zu verzeichnen; bei Regenfällen zwischen 9.00 und 12.00 MST ist der Rückgang besonders deutlich.Wie sich zeigt, stehen diese Beobachtungen im Einklang mit einigen Mechanismen, die zur Erklärung der ungewöhnlichen Tagesverteilung der sommerlichen Regenfälle über Phönix, Arizona, angeführt werden.

Temporal Analysis of Long-Term Atmospheric Moisture Levels in Phoenix, Arizona

Abstract Long-term monthly averaged dew point and relative humidity levels for Phoenix, Arizona are examined in this investigation. Dew points are generally unchanged over the 1896–1984 period of instrumental record; relative humidities have dropped sharply during the recent decades. Changes in local land use and a developing urban heat island are suggested causes of the observed patterns in the Phoenix atmospheric moisture levels.

Synoptic classification and physical model experiments to guide field studies in complex terrain

Abstract Synoptic classification is used to identify meteorological conditions characteristic of high-pollution periods at Nogales, Arizona. Low surface winds determined by local surface cooling at night with little vertical mixing were found to be most important. This condition was simulated in a 0.79-m-square box filled with water with the lower surface made to model a 12-km-square region of the surface topography of the United States-Mexico border at Nogales. The aluminum base was cooled to induce the downslope flows. Photographs of dye initially placed on the surface at many locations were used to obtain a set of surface velocities that formed the input to the Diagnostic Wind Model (DWM). The DWM provided hourly velocity data with grids of 500- and 250-m spacings. The similarity arguments used to analyze the relationship of the physical model to the atmosphere are discussed. Although the magnitude of the wind vectors in the physical model cannot be matched to the atmosphere, the directions can be used...

Temporal Variations in Tucson, Arizona Summertime Atmospheric Moisture, Temperature and Weather Stress Levels

Abstract Summertime temperature, dewpoint, relative humidity, apparent temperature and weather stress levels have not changed significantly over the past 37 years at the Tucson, Arizona Municipal Airport. However, several of these variables show substantial trends during the most recent 18-year subperiod when the Tucson growth rate has been highest. The results for Tucson are quite different from the statistically significant changes in local climate reported for the Phoenix Airport during the same period of record. The differences in the changing weather conditions between these two desert cities appear to be related to (a) the smaller population in Tucson, (b) the position of the Tucson airport measurement site near the outskirts of the city as opposed to the centrally located airport in Phoenix and (c) the type of landscapes being replaced by these rapidly growing urban areas. The city of Phoenix is expanding generally into irrigated agricultural lands, while in Tucson, the bulk of the urban expansion ...

Recent changes in smoke/haze events in Phoenix, Arizona

SummaryThe recent explosive population growth in Phoenix, Arizona is forcing policy-makers to develop an increased understanding of air quality meteorology in the desert setting. In this investigation, the long-term smoke/haze data base from Phoenix is analyzed to determine the magnitude of temporal changes in smoke/haze frequencies and durations. The results reveal no changes in smoke/haze frequency and intensity, but significant increases in the duration of these events. The findings appear to be related to the impact of the growing urban heat island on the structure of local inversion layers. The results suggest a link between urban-induced temperature and wind changes and air quality levels within a growing metropolitan area.ZusammenfassungDas zuletzt explosive Bevölkerungswachstum in Phoenix/Arizona zwingt Politiker dazu, der Meteorologie der Luftbeschaffenheit im Wüstenraum gesteigerte Aufmerksamkeit zu widmen. In vorliegender Studie werden die Langzeitdaten von Rauch/Dunst in Phoenix analysiert, um das Ausmaß zeitlicher Veränderungen in Häufigkeit und Dauer des Auftretens von Rauch/Dunst zu bestimmen. Die Ergebnisse zeigen, daß sich zwar die Häufigkeit und Intensität von Rauch/Dunst nicht geändert haben; wohl aber die Dauer ihres Auftretens. Diese Ergebnisse scheinen auf einen Einfluß der wachsenden urbanen Wärmeinsel auf die Struktur der örtlichen Inversionsschichten hinzuweisen. Die Resultate lassen auf einen Zusammenhang zwischen städtisch bedingten Temperatur-und Windveränderungen und unterschiedlicher Luftqualität über wachsenden städtischen Ballungsräumen schließen.