Just some general ideas / realizations for the creation of a heat wave index that have been floating around in my head
1) I think it is important to create a system, which not only allows meteorologists and public health specialists to determine how serious a current heat wave is, but allows the average member of the public to determine how serious the heat wave is as well. This system would be much like the tornado classification system, but instead of f0 to f5, would be from 1 to 100, 1 to 10, or some other simple means by which to visualize. I believe this would allow non-scientists to better notice and take action, even if some of the fine details of the system are over their head. I believe this would also help to keep the system from becoming too mysterious and/or elitist as the current system seems to be.
2) On a public health standpoint, I have an idea of perhaps implementing a letter system from A to F. This letter would be alongside the above number and could be used to inform cities how well they are equipped to deal with a heat wave. The A to F, would be much like the school grading system (which would make it easier to understand for the general public) with ‘F’ being that a city is not well equipped to deal with a heat wave and an ‘A’ meaning that they are well equipped. The determination of how these letters are assigned would probably be up to the public health scientists in each city, but could be influenced by variables such as number of parks, how intense the heat sink of the urban area is, what the most common construction materials are, the prevalence of air conditioning, and/or the population of the young or elderly in the city. This letter alongside the number could then be sent to EMS, hospitals, etc. to help them understand and prepare for a coming heat wave.
3) I have noticed that the Philadelphia system is based upon different types of air masses and whether they are high-risk or “oppressive” air masses. Although this may be a very precise means by which to determine heat waves, it is very limiting. Not all locations on the planet will have exactly the same pattern / set of air masses. Therefore in order to make a universal system for determining heat waves, I think a system that uses commonly found variables would be best.
Here are my proposed meteorological variables for the determination of a heat wave index:
1) Daytime maximum temperature and how it compares to the average maximum temperature for that season / day (can account for acclimization)or some other threshold value
2) Nighttime minimum temperature and how it compares to the average minimum temperature for that season / day (can account for acclimization) or some other threshold value
3) Dewpoint Temperature
4) Consecutive warm nighttime minimum temperatures
5) Consecutive warm daytime maximum temperatures
6) Cloud cover / direct radiation from the sun
- Ignore windspeed (Windspeed varies on how it effects apparent temperature. In some cases it warms and in others it cools. It seems to be based on the atmospheric temperature and how clothed an individual is, which varies from person to person. Karl also found that the correlation between temperature and wind speed is negligible)
- Meehl defines a heat wave as a period of consecutive days that satisfies these three conditions. (T1 = 97.5th percentile; T2 = 81st percentile)
(1) Average daily max temperature must be above T1 for the entire period
(2) Daily max temperature must be above T1 for at least 3 days
(3) Daily max temperature must be above T2 for every day of the entire period
- If these conditions are meet then use the below equation to solve for a heat index ...
Max temperature day 1 = MTD1
Max temperature day 2 = MTD2
Max temperature day 3 = MTD3
Average Max Temperature = (MTD1 + MTD2 + MTD3) / 3 = AvgMTD
Min temperature day 1 = MiTD1
Min temperature day 2 = MiTD2
Min temperature day 3 = MiTD3
Average Min Temperature = (MiTD1 + MiTD2 + MiTD3) / 3 = AvgMiTD
Difference between average max and min = (AvgMTD - AvgMiTD) = DiffAvgT
Dewpoint temperature = Td
Percent cloud cover = %cc
Constant to determine importance = K
Solar constant (not the solar constant) = Ks
= = = = = =
Heat Index = K1 * (1/DiffAvgT) + K2 * AvgMTD + K3*Avg*MiTD + K4*Td + %cc * Ks
Karl, Thomas R. et al. "The 1995 Chicago Heat Wave: How Likely is a Recurrence?" Bulletin of the American Meteorological Society, 1996.
Meehl, Gerald A. and Claudia Tebaldi. "More Intense, More Frequent, and Longer Lasting Heat Waves in the 21st Century." Science 305, 994(2004).