• Very high apparent temperatures that persisted day and night over a 48-hour period. • Minimum apparent temperature did not drop below 89 degrees. EXTREMELY RARE! • Large number of deaths caused by persistently high heat index (apparent temperature) • What kind of effect did the urban heat island have on this unusual event? Can we expect more events like this? • Heat wave is centered around the northern half of Illinois. • The highest minimum temperatures are centered around Chicago. • Paper focuses on the severity and duration of extreme heat waves. • Researched probability of similar events of the same or greater magnitude. • Used the apparent temperature, heat index, to evaluate historical significance of heat wave. Will show on diagram later. • Used an annual series instead of partial duration series to model temperature data from each summer. (Human acclimatization) • Data was gathered for the observed heat index during this event and adjusted for growth of urban heat island. • Algorithm used to model heat island; uses population to model effects on mean monthly max and min temperatures. • Analysis conducted based on Monte Carlo simulations of detrended autoregressive moving-average (ARMA) models. • The chances of this event happening again are very rare. • As seen in the previous diagram, even with an increase in average temperatures the chance of an extended heat wave of this magnitude is still quite rare. (Generally less than 4%) • Two straight days with a minimum apparent temperature greater than 80 degrees is a once in a life time event. • Even with increased variance, increased temperature, and changed persistence, 0.4% chance of this happening again. • Temperatures in Chicago and the Midwest have increased over time, most likely as a result of urbanization. • The HO-83 weather instrument provided some bias in the daily maximum temperatures after 1986. • The persistence and variance are just as critical to the heat wave as the apparent temperatures. What will be discussed? • Increase in human energy production (HEP) • Urban Heat Island effect • Global climate impacts; specifically precipitation • Future outlook • On average, 235 Wm^-2 of energy is conveyed from the sun to the earth and its atmosphere • Human energy production (HEP) is responsible for the release of 0.025 Wm^-2 of energy • HEP accounts for less than 1/3 of the total internal terrestrial energy flux • 2 to 5-fold rise in HEP by the end of the century • Release of air pollutants and CO2 • Variable energy production densities Does HEP affect global climate? Does the release of pollutants and aerosols impact precipitation? Claim A • High concentrations of cloud condensation nuclei • Slowing down coalescence • Suppression of “warm rain” formation • This has been seen in California and Israel Claim B • At higher altitudes, can lift formation of precipitation to the mixed phase region • Enhanced convection via release of enthalpy during freezing • Increased precipitation and 40-85% increase in lightning frequency were seen in and downwind 16 cities of the United States Factors Contributing to Perturbations 1. Higher UHI temperatures (0.6-6.0o C) 2. Enhanced urban frictional turbulence 3. Variable cloud microphysical conditions from high levels of particulates Consequences of Stronger Convection • Transportation of aerosols, water , and pollutant gases to upper troposphere and potentially the stratosphere! • How does this impact global climate? • We don’t know So which claim has been proven? • Satellite observations showed existence of aerosol overseeding effect for pollution plumes at cloud tops warmer than -10o C • Also observed in the Amazon region and in French Guyana • It has been hypothesized that this effect may be more prominent during dry seasons of the tropics due to high Bowen ratios • Suppression of warm cloud formation in the Amazon; however no correlation was seen between lightning frequency and increase HEP • Urbanization is projected to double in the next two decades! • This would put nearly 80% of the world’s population in cities and mega-cities • Social, logistic, medical, and urban heat and air quality consequences of urbanization could be significant • Altering of regional meteorology and possibly global climate Daniel Rosenfeld What will be looked at? • Evidence supporting the hypothesis that urban and industrial air pollution suppresses precipitation • Satellite data showing reduced cloud particle size • Tropical Rainfall Measuring Mission satellite imagery What impact do aerosols from urban and industrial air pollution have on precipitation? • Smoke released by burning vegetation has been proven to suppress precipitation • Initially it was assumed that aerosols from air pollution also suppressed precipitation • Recent studies showed that certain urban settings and also areas downwind of paper mills were experiencing enhanced rainfall • Studies attempting to correlate enhanced rainfall to air pollution have been unsuccessful • Pollution from ships was the first evidence of pollution suppressing precipitation • Pollution tracks over land were not included in previous studies So how do we make sense of this? • The Advanced Very High Resolution Radiometer (AVHRR) on the NOAA orbiting weather satellite • YELLOW is the most important color, as it denotes clouds with small drops • RED represents clouds with larger cloud droplets • GREEN indicates clouds with cloud droplets between the yellow and red sizes Turkey Canada • This pollution track was seen in 47 images on different days • Stratocumulus and cumulus cloud tops warmer than -12oC • Port Augusta (5) is home to a 520-MW power plant operating on brown coal • Port Pirie (6) has the world’s largest lead smelter and refinery • Adelaide (7) holds industry for processing minerals mined in the area • Major oil refinery and power plant (8) • 43 kg/hour of ash particles • 1108 kg/hour of SO2 • 1655 kg/hour of NOx Things to Note: 1. Peak near 2 km 2. Box 2 had no detectable precipitation 3. Boxes 4 and 7 were outside the radar’s range • Cloud top heights and horizontal dimensions had no differences • Data off of the TMI-measured T85 showed that lack of cloud water was NOT the reason for precipitation suppression • First, for those who do not know, coupling is defined as the pairing of two items. • Most of the recent European summer heat waves have been preceded by a pronounced spring precipitation deficit. (10 warmest European summers) • Heat waves are generally associated with quasistationary anticyclonic circulation anomalies. Subsidence, clear skies, warm-air advection, and prolonged hot conditions at surface. • How do land-atmosphere interactions in addition to circulation patterns contribute to heat waves? • Simulations were used to model the four most extreme European heat wave events of the past decades. (Climate High-Res Model CHRM) • They model previous European heat waves; uses the same boundary layer conditions that occurred during event. • One model run uses the actual soil moisture content during the event, the other model run uses the climatological soil moisture content. • We will look at the results of the model runs on the next slide. • Data from the study shows more soil moisture = cooler temperatures. • Temperature amplification through landatmosphere coupling is found to be substantially stronger for daily maximum temperatures compared to min and mean temperatures. • Drought conditions themselves may contribute to higher persistence of the heat wave. • Estimated 90% of surface net radiation was transferred to sensible heat and 10% to latent heat in driest years (Normal: 60%/40%) • The heat waves of 1976, 2003, and 2005 were preceded by a mean precipitation deficit during at least four antecedent months. • Land-atmosphere coupling is found to increase mean, max, and as well to a lesser extent the min temperatures averaged over anomalously warm summers.