Severe Weather

• storms account for 75% of natural disasters deaths and damages in the US

• 1980-2010: 134 weather-related disasters caused > $1 billion in damages each

  • total damages = >$880 billion

Weather

• weather: conditions in the atmosphere at a given time and place

  • temperature

  • moisture

  • wind

  • pressure

• occurs in troposphere

  • first 5-9 miles

Heat

• energy that powers storms

• heat energy from the sun is turned into sensible heat and latent heat

Sensible Heat

• heat we can sense or feel (or measure)

• when we measure temperature, we are measuring sensible heat

• on an atomic level, this is really particles moving around

Latent Heat

• “hidden” heat energy

• energy absorbed during a state change like melting (ice to water)

• can be released as sensible heat if the state change is reversed (ex: condensing, freezing)

• if liquid water becomes gaseous: heat is taken from the surroundings

• if gaseous water becomes liquid: heat is transferred to the surroundings

• therefore, humid air (with lots of gaseous water) can be energy source for storms

Absolute Humidity

• absolute humidity: amount of water vapor in air

• absolute humidity = mass of water/ mass of air

• grams of moisture per m^3

• total amount of water vapor in air varies with temperature

  • more water in warmer air

  • less water in cooler air

• so, the absolute measure is not very useful

Relative Humidity

• relative humidity: percentage of the maximum water vapor that could be in the air at a given temperature

• relative humidity = current absolute humidity/highest possible absolute humidity

• 100% relative humidity = air is completely saturated with water vapor; rain is possible

• highest possible absolute humidity changes with temperature