Land-Atmosphere Interaction: Heat Island Effect & Heat Waves
The 1995 Chicago Heat Wave: How Likely Is a Recurrence? T. Karl & R. Knight Contribution of Land-Atmosphere Coupling to Recent European Summer Heat Waves E. M. Fischer, S. I. Senevirante, D. Lüthi, & C. Schär Alec Butner 2nd Year – Atmospheric Science
New Directions: The growing urban heat and pollution “island” effect—impact on chemistry and climatePaul J. Crutzen Suppression of Rain and Snow by Urban and Industrial Air Pollution Daniel Rosenfeld Austin Armstrong 2nd Year-Atmospheric Science and Mathematics
The 1995 Chicago Heat Wave Background • 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?
The 1995 Chicago Heat Wave • Heat wave is centered around the northern half of Illinois. • The highest minimum temperatures are centered around Chicago.
The 1995 Chicago Heat Wave Analysis • 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)
The 1995 Chicago Heat Wave Analysis cont. • 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 detrendedautoregressive moving-average (ARMA) models.
The 1995 Chicago Heat Wave Maximum Apparent Temperatures Minimum Apparent Temperatures
The 1995 Chicago Heat Wave Findings • 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.
The 1995 Chicago Heat Wave Findings • 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.
New Directions: The growing urban heat and pollution “island” effect—impact on chemistry and climate Paul J. Crutzen
“New Directions: The growing urban…” What will be discussed? • Increase in human energy production (HEP) • Urban Heat Island effect • Global climate impacts; specifically precipitation • Future outlook
Earth’s Global Energy Budget: The Numbers • 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^-2of energy • HEP accounts forless than 1/3 of the total internal terrestrial energy flux
The Big Question: Why Should We Care? • 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?
Taking a Closer Look… Claim A 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 • High concentrations of cloud condensation nuclei • Slowing down coalescence • Suppression of “warm rain” formation • This has been seen in California and Israel
Claim B cont’d Factors Contributing to Perturbations 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 • Higher UHI temperatures (0.6-6.0o C) • Enhanced urban frictional turbulence • Variable cloud microphysical conditions from high levels of particulates So which claim has been proven?
Conclusions • 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
What does this tell us and why is it important? • 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
Suppression of Rain and Snow by Urban and Industrial Air Pollution David Rosenfeld
“Suppression of Rain and Snow…” Key Information 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?
Introduction • 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?
Background Information Regarding the Figures • 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
“Pollution Tracks” Turkey
“Pollution Tracks” cont’d Canada
“Pollution Tracks” cont’d 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-MWpower plant operating on brown coal Port Pirie (6) has the world’s largestlead smelter and refinery Adelaide (7) holds industry for processing minerals mined in the area Major oil refinery and power plant (8)
Port Augusta Pollution Statistics • 43 kg/hour of ash particles • 1108 kg/hour of SO2 • 1655 kg/hour of NOx
Precipitation Echo Intensities Things to Note: • Peak near 2 km • Box 2 had no detectable precipitation • Boxes 4 and 7 were outside the radar’s range
Vertical Cross Sections • 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
Land-Atmosphere Coupling Background • 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 quasi-stationary 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?
Land-Atmosphere Coupling Analysis • 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.
Actual Temperatures Modeled Temperatures Coupling (Dry) Modeled Temperatures Uncoupling (Normal)
Land-Atmosphere Coupling Findings • Data from the study shows more soil moisture = cooler temperatures. • Temperature amplification through land-atmosphere 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%)
Land-Atmosphere Coupling Findings • 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.