Atmospheric Forces: Weather and Climatology Mr. Ross Brown Brooklyn School for Law and Technology

How do we understand the weather? 4 January 2015 Do now: Take out your Reference Tables. – What is the dewpoint when the dry-bulb temperature is 24°C and the wet-bulb temperature is 15°C? a)8°C b)-18°C c)36°C d)4°C

Air Mass Large, uniform temperature and moisture content Types: – Polar (P) cold – Tropical (T) warm – Maritime (m) oceans – Continental (c) land

Air Masses Combinations – Maritime Polar (mP) – Maritime Tropical (mT) – Continental Polar (cP) – Continental Tropical (cT)

North American Air Masses

Air Masses An airmass originating over the North Pacific Ocean would most likely be a)continental polar b)continental tropical c)maritime polar d)maritime tropical On a weather map, an airmass that is very warm and dry would be labeled a)mP b)mT c)cP d)cT

Fronts Air masses of different densities meet along a Front. Warm front: warm air overtakes cool air. Warm air rises over cool.

Fronts Cold front: cold air mass overtakes a warm air mass, lifting the warm air. May cause storms. A big storm ahead of the front is a squall.

Fronts Stationary front: two air masses meet but neither is displaced

Fronts Occluded front: fast cold front completely lifts warm front and keeps it high in the atmosphere.

How do Hurricanes form? Windspeed >120 km/ hour Spiral toward intense low-pressure center Warm, moist air over ocean rises Moisture condenses, releasing heat energy

Wind patterns

The arrows on the diagram below represent surface wind directions on a weather map. The points represent the locations of four weather stations in the Northern Hemisphere. Which weather station probably has the lowest air pressure? A B C D

Forecasting the weather

Forecasting weather This question may require the use of the Earth Science Reference Tables. The station model below shows the weather conditions at Massena, New York, at 9 a.m. on a particular day in June. What was the barometric pressure at Massena 3 hours earlier on that day? Earth Science Reference Tables a)997.1 mb b)999.7 mb c) mb d) mb

The weather map Isobars: lines connecting points of equal atmospheric pressure. Lines closer together mean faster winds.

Heat Energy and Water Water changes state from ice  water  steam and back again Absorbs and releases heat during this process

Sublimation The change from ice directly to steam or steam to ice. For example, steam going out on a winter’s day.

Humidity Humidity: Water vapor in the atmosphere When the air holds as much water vapor as it can, it is saturated As temperature rises, ability to hold water vapor rises Relative humidity: ratio of water vapor in the air to amount that could be held (%)

How do we measure relative humidity? Psychrometer: instrument with 2 thermometers, one with a wet wick Dew point: temperature at which water vapor begins to condense

Atmospheric Pressure Gravity pulls atmospheric gases toward the Earth’s surface – 99% of mass of atmospheric gases are within 32 km of surface – A reading of 1 atmosphere = average atmospheric pressure at sea level – 1 millibar (mb) equals of standard atmospheric pressure

How do we measure atmospheric pressure? Barometer – Mercurial barometer: atmospheric pressure presses on liquid mercury in a glass tube. We read how high it gets pressed.

How do we measure atmospheric pressure? Aneroid barometer: Sealed container with air removed. As pressure increases, sides of container bend inward.

Layers of the Atmosphere Troposphere: closest to Earth’s surface – Up to ~ 10 km Stratosphere: troposphere to 50 km – Ozone is contained here Mesosphere: stratosphere to 80 km Thermosphere: above

Layers of the Atmosphere