IMPACT OF THE SOUTHERN OSCILLATION ON THE NORTH AMERICAN SOUTHWEST MONSOON

The intensity and spatial variations in the North American Southwest Monsoon are examined to determine the influence of the Southern Oscillation. Sixty-five years (1920–1984) of July and August monthly precipitation data from Arizona and New Mexico are normalized using a square root transformation, converted into z-scores, and stratified according to onset and following years for Warm Events and Cold Events of the Southern Oscillation. The results for July reveal different spatial patterns in the monsoonal precipitation for the extremes of the Southern Oscillation. Warm-Event onset years are associated with positive precipitation anomalies that decline along a northeast-to-southwest gradient across the study area whereas the Cold-Event onset years produce highest positive values in west-central Arizona and negative values throughout the eastern two-thirds of the study area. Spatial patterns for the August precipitation data do not appear to be influenced by the extremes of the Southern Oscillation. [Key words: Southwest Monsoon, Southern Oscillation, Arizona, New Mexico.]     

An analysis of intra-event precipitation variability for the United States (1980–2010)

Hourly precipitation data were collected from 143 first-order US weather stations during the period from 1980 to 2009 to assess the internal distribution of precipitation events lasting at least three hours. A total of 46,595 individual precipitation events were identified and evaluated using the mean, standard deviation, skewness, kurtosis, and the number of peaks occurring within an event. Mean event duration is longest along the West and Northwest coasts, the Mid-South, the Mid-Atlantic, and the Northeast; while shorter-duration events are more frequent in the Rocky Mountains, the Southwest, and the Great Plains. Mean event precipitation and standard deviation are greatest along the Gulf Coast and decrease inland. Precipitation events are positively skewed, indicating that more precipitation tends to occur earlier in the event. The most positively-skewed events are also located in regions flanking the Gulf of Mexico, while less-skewed events are common in the Northwest and Rocky Mountain regions. Event kurtosis is negative throughout the entire USA, with the highest negative values generally west of the Front Range, where cyclonic development and transition produce more evenly distributed precipitation within storms. Intra-event precipitation maxima were also evaluated, with western Florida and the desert Southwest having the greatest number per event.     

Greenhouse warming may moderate British storminess

Summary An analysis of data pertaining to the period 1861–1986 reveals that (1) a 1 °C rise in the mean annual air temperature of the British Isles has historically been associated with a 35% drop in the percentage of days that the United Kingdom has experienced cyclonic flow, and (2) a 2 °C increase in the mean annual air temperature over the sea to the north has typically been matched by a 60% drop in the percentage of days that the isles have experienced cyclonic flow originating from that source region. These findings raise significant questions about the oft-reported claim that CO₂-induced global warming will lead to an increase in world storminess.With 3 Figures     

Wind field analysis using unit-vector density mapping

Summary An automated mapping technique, termed unit-vector density mapping (UVDM), is introduced as a method of displaying continuous instantaneous wind velocities and other vector quantities. The purpose of introducing this technique is to 1) generate renewed interest in meteorological data display techniques and 2) address specific concerns in the display and interpretation of vector quantities of particular interest to meteorologists. With this graphic procedure, the density of short standard-length line segments (unit-vectors) represents wind speed and unit-vector orientation show wind direction. This paper describes the plotting algorithms for producing UVDM maps and compares this technique to existing procedures for mapping wind vectors.

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Zusammenfassung Eine automatisierte kartographische Technik — genannt Unit-Vector Density Mapping (UVDM) — wird als Methode zur kontinuierlichen Darstellung der momentanen Windgeschwindigkeiten und anderer vektoriellen Größen im Bestreben vorgestellt, zum einen vermehrt Interesse auf die Darstellungstechniken meteorologischer Daten zu lenken und zum anderen, um einige speziell für Meteorologen relevante Bereiche der Darstellung und Interpretation von vektoriellen Größen hervorzuheben. Bei der genannten graphischen Vorgangsweise zeigt die Dichte der Einheitsvektoren die Windgeschwindigkeit an, während die Richtung der Einheitsvektoren die Windrichtung angibt. Vorliegende Studie beschreibt die Zeichenroutinen zur Herstellung von UVDM-Karten und vergleicht diese Technik mit vorhandenen Darstellungsmethoden von Windvektoren.

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With 9 Figures     

Cosmic ray flux impact on clouds? An analysis of radiosonde, cloud cover, and surface temperature records from the United States

Summary ¶Many scientists have suggested that variations in cosmic ray flux may impact cloudiness at regional, hemispheric, or global scales. However, considerable debate surrounds (a) whether high or low clouds are most strongly impacted by cosmic rays, (b) the degree of seasonality in cloud responses to cosmic rays, and (c) the determination of physical processes involved in cosmic ray/cloud interactions. Some scientists find strong correlation coefficients between cloud measurements and cosmic ray flux, while others find no relationship whatsoever; virtually all scientists working on this issue are hampered by the relatively short time period with accurate cloud and cosmic ray flux records. In an attempt to extend the period of record, we assembled surface and radiosonde data for the United States over the period 1957–1996 along with sunspot records which are known to be strongly, but inversely, related to cosmic ray flux. We also assembled cloud cover data and cosmic ray measurements over a reduced time period. We found that periods with low sunspot number (times with high cosmic ray flux) are associated with significantly higher dew point depressions, a higher diurnal temperature range, and less cloud cover. Our results do not support suggestions of increased cloud cover during periods of high cosmic ray flux.Received May 14, 2002; accepted February 17, 2003 Published online May 26, 2003     

A new strategy for analyzing the chronometry of constructed rock features in deserts

The western Great Basin contains thousands of constructed rock features, including rock rings, cairns, and alignments. Unlike subtractive geoglyphs, such as the Nasca Lines of Peru, that remove desert pavement, these surface features alter the location and positioning of cobble‐ to bouldersized rocks. The chronology of surface rock features has remained unconstrained by numerical ages because no prior chronometric approach has been able to yield age control. We propose a new strategy for studying these features by analyzing anthropogenic modifications to rock coatings, an approach that permits the use of several dating methods, two of which are assessed here: radiocarbon dating of pedogenic carbonate and rock‐varnish microlaminations. Initial results from Searles Valley, eastern California, suggest that constructed rock features may be as old as early Holocene and terminal Pleistocene. Archaeological surveys of desert areas would be greatly enhanced if they noted altered positions of rock coatings. © 2006 Wiley Periodicals, Inc.     

TEMPORAL STATISTICS: AN APPLICATION IN SNOWFALL CLIMATOLOGY

A method is introduced for the analysis of temporal distributions of climatic data based on a comparison of a variable's frequency distribution in the time dimension to a standard bell-shaped curve through time. The following statistics are defined using mean monthly snowfall data: the temporal mean, which is the average time for accumulation of 50% of the annual snowfall total; the temporal standard deviation, which characterizes the mean annual spread of snowfall accumulation about the mean; temporal skewness, which characterizes the symmetry of the annual snowfall distribution; temporal kurtosis, which measures the peakedness of the annual distribution; and temporal correlation, which quantifies the degree of association between two temporal distributions. Analysis of snowfall data demonstrates the utility of temporal statistics for quantifying temporal and geographic variations in a climatic variable's seasonal distribution. [Key words: snowfall, climatology, temporal statistics.]     

Localized climatic responses during the 11 July 1991 eclipse: Phoenix AZ

Measurements taken from a variety of land use environments in and around the Phoenix AZ metropolitan area were compared to determine the effects of various land use characteristics on the thermal response to a reduction of 68% in solar radiation during the solar eclipse of 11 July 1991. The results include: (a) The magnitude of the change in ambient air temperature during the eclipse is related to land use. Heavily asphalted military sites and irrigated golf courses recorded small decreases in temperature while natural desert terrain experienced the largest decreases. Variations in thermal response are more closely related to the albedo of the specific land type than to other factors such as thermal admittance but this high correlation is probably an artifact of the combination of other variables such as moisture. (b) Due to the complex mix of land uses and timing of eclipse, marked wind speed changes associated with the eclipse do not appear to be linked directly to land use changes, and, (c) Temperature minima at residential/commercial stations occurred in general, before the minima at stations in agricultural/golf terrains. Because typical albedo differences are not significant between these two land uses, land use characteristics other than albedo are most likely controlling the timing of the temperature minima. Opportunities to empirically examine concepts previously testable only through numerical modeling such as solar reduction experiments should continue to be exploited.