Nancy Selover

Urbanization and warming of Phoenix (Arizona, USA): Impacts, feedbacks and mitigation

This paper examines the impacts, feedbacks, and mitigation of the urban heat island in Phoenix, Arizona (USA). At Sky Harbor Airport, urbanization has increased the nighttime minimum temperature by 5°C and the average daily temperatures by 3.1°C. Urban warming has increased the number of “misery hours per day” for humans, which may have important social consequences. Other impacts include (1) increased energy consumption for heating and cooling of buildings, (2) increased heat stress (but decreased cold stress) for plants, (3) reduced quality of cotton fiber and reduced dairy production on the urban fringe, and (4) a broadening of the seasonal thermal window for arthropods. Climate feedback loops associated with evapotranspiration, energy production and consumption associated with increased air conditioning demand, and land conversion are discussed. Urban planning and design policy could be redesigned to mitigate urban warming, and several cities in the region are incorporating concerns regarding urban warming into planning codes and practices. The issue is timely and important, because most of the worlds human population growth over the next 30 years will occur in cities in warm climates.

Evening Transition Observations in Phoenix, Arizona

Abstract Past research has suggested that the evening transition in complex topography typically has several main features, such as (a) continued weak upslope flows persisting 3–5 h after sunset (if the sidewalls of the valley prevent Coriolis-induced turning of winds), thus signifying delayed transition; (b) unsteady local stagnation and vertical mixing within tens of meters above the surface; and (c) transition of stagnation fronts to downslope/downvalley gravity currents during the evening hours, especially at higher-elevation (steeper) slopes, and their arrival at adjoining low-elevation gentle slopes as “slope breezes.” This transition process typically occurs in locales such as Phoenix, Arizona, which has expansive exposure to plains in one direction (to the west and south) and is adjacent to abrupt change in the terrain in other directions (primarily to the north and east). An analysis of wind records from several automated weather stations and a radar wind profiler for selected characteristic peri...

Using Digital Cloud Photogrammetry to Characterize the Onset and Transition from Shallow to Deep Convection over Orography

An automated method for segmenting digital images of orographic cumulus and a simple metric for characterizing the transition from shallow to deep convection are presented. The analysis is motivated by the hypothesis that shallow convection conditions the atmosphere for further deep convection by moistening it and preventing the evaporation of convective turrets through the entrainment of dry air. Time series of convective development are compared with sounding and surface data for 6 days during the summer of 2003. The observations suggest the existence of a threshold for the initiation of shallow convection based on the surface equivalent potential temperature and the saturated equivalent potential temperature above the cloud base. This criterion is similar to that controlling deep convection over the tropical oceans. The subsequent evolution of the convection depends on details of the environment. Surface fluxes of sensible and latent heat, along with the transport of boundary layer air by upslope flow, increase the surface equivalent potential temperature and once the threshold value is exceeded, shallow convection begins. The duration of the shallow convection period and growth rate of the deep convection are determined by the kinematic and thermodynamic structure of the mid- and upper troposphere.

Expansion of the northern hemisphere subtropical high pressure belt: trends and linkages to precipitation and drought

A critical issue in research concerning long-term climate change is the relationship between circulation features and global temperature variations. We establish that the annual areal size of the northern hemisphere subtropical high pressure belt (SHPB), as defined by seven 500-hPa height isohypses, shares over 70% of the variability with global annual near-surface air temperature since 1948. The area enclosed by the 5850-m isohypse of the 500-hPa surface in the northern hemisphere has more than doubled since the 1950s, with greatest increases over northern Africa, the Middle East and India. A long-term historical run of a coupled global climate model shows rapidly increasing SHPB annual sizes, since the mid-1970s. Since the SHPB’s descending air produces increased aridity, SHPB expansion may transition humid regions to more arid lands. To examine this aspect, first, variations in recorded precipitation using a gridded database for the region experiencing expansion of the SHPB show a decrease in precipitation (though significant only at the 88% confidence level) over the last 60 years. Second, variations in a 0.5° spatial resolution monthly drought index, the Standardized Precipitation Evapotranspiration Index, are highly correlated (+0.78) with annual variations in the area enclosed by the 500-hPa height isohypses. These results support those of previous investigations that suggest further northward expansion of the northern hemisphere subtropical dry zones with continued global climate change.

Evaluating the impact of solar radiation on pediatric heat balance within enclosed, hot vehicles

ABSTRACT Pediatric deaths due to children being left in hot cars remain a significant yet preventable public health concern. The current study aims to demonstrate the influence of vehicle type, time of day, and solar exposure (sun or shade) on the energy balance and core temperature (Tc) of a hypothetical two-year old boy left in a vehicle on a hot day. Cabin temperatures and relative humidity were collected within six enclosed vehicles under sun or full shade in Tempe, Arizona. These variables and radiation estimates were used to estimate the human energy balance and final Tc across 76 measurement cycles lasting approximately 60minutes. Interior temperatures averaged 39.5°C and 47.6°C in the shade and sun, respectively, at steady-state. Based on the specific heat of a human body, the average Tc after 60 minutes in shaded or sun-exposed vehicles was estimated to reach 38.2±0.29°C and 39.1±0.41°C, respectively, with a significantly higher final Tc in sun-exposed vehicles across all days and in the shaded minivan. Extrapolation to 2 hours is estimated to result in heat injury in the sun. Results demonstrate the influence of radiation on a childs thermal balance in a hot and dry environment. In real-world situations, it is critical to acknowledge variability between children, the starting car environment, and climate (e.g., humid versus dry), and that a child left in any vehicle car can experience potentially lethal core temperatures if forgotten, as shown by vehicular heat stroke statistics. Findings may improve public messaging and reinforce the need for policy action and technological adoption to prevent injury and death.

The Weather and Climate of Arizona

Picture Arizona in your minds eye… There are truly amazing physical contrasts (the one-mile-deep Grand Canyon, volcanic peaks like Mount Humphreys, and seemingly endless deserts). Arizona also hos...