1. Class #18 Wednesday, February 18, 2009 1 Class #18: Wednesday, February 18 Waves aloft Introduction to Oceanography Ocean Currents

2. Class #18 Wednesday, February 18, 2009 2 Patterns in the upper-level westerlies The pattern of upper-level westerlies has waves, with axes of high height (ridges and highs) and axes of low height (troughs and lows). These appear on day to day weather maps. These wavelike patterns help transport energy poleward (advection) to balance the energy budget of the Earth and atmosphere.

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5. 5 Names for upper-level wind patterns When the waves are small, and the ridges and troughs are weak, the pattern is called zonal, or high index, meaning roughly west to east at constant latitude. When the waves have greater amplitude (north-south dimension), the pattern is called meridional, or low index, meaning that there is a lot of north/south motion.

6. Class #18 Wednesday, February 18, 2009 6 Zonal (high index), Meridional (low index), and split flow patterns

7. Class #18 Wednesday, February 18, 2009 7 More about upper-level patterns Sometimes there is zonal flow at high latitudes and meridional flow at low latitudes. This is a split-flow pattern. Sometimes persistent closed highs and lows form in a split-flow pattern when the meridional pattern is extremely meridional. This is called a blocking pattern, because it can be extremely persistent.

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9. 9 Implications of upper-level winds Blocking highs can lead to drought conditions and prolonged heat waves. Meridional flow accomplishes poleward energy transport that helps balance the energy balance of the Earth and atmosphere.

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12. Class #18 Wednesday, February 18, 2009 12 More implications of upper-level wind patterns Surface low-pressure centers, fronts, cloudiness and precipitation in midlatitude cyclones occur beneath the region east of the trough of waves in the upper-level winds near the jet stream and above the polar front. Hurricanes, in contrast, require weak upper- level winds.

13. Class #18 Wednesday, February 18, 2009 13 More about waves in the westerlies aloft Shorter waves move eastward faster than the longer Rossby waves. Waves of different length can add and subtract to/from one another’s amplitude. Forecasting waves in the westerlies aloft is vital for everyday weather forecasting. El Niño/La Niña affect the westerlies aloft.

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16. Class #18 Wednesday, February 18, 2009 16 The oceans Cover about 70% of the earth’s surface. Cover an even higher percentage in the tropics. Exchange large amounts of energy and water with the atmosphere at the surface. –Give water vapor to the atmosphere. –Give energy to the atmosphere in the form of latent heating. –Exchange energy with the atmosphere by convection and conduction. Advect large amounts of energy from the equator towards the poles

17. Class #18 Wednesday, February 18, 2009 17 Energy gains and losses from the point of view of the oceans When the oceans give up energy (negative, blue, purple) the atmosphere gains energy from the oceans. When the oceans gain energy (positive, red, yellow) the atmosphere loses energy to the oceans. Oceans supply energy to storms in middle latitudes. Oceans warm in summer and cool in winter.

18. Class #18 Wednesday, February 18, 2009 18 The rate of energy transfer between atmosphere and oceans Is greater when the temperature difference is greater. Is in the direction from the higher to the lower temperature. Is greater when the wind speed is greater For latent heating, rates are greatest when saturation vapor pressure in the atmosphere is largest (high temperatures).

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20. Class #18 Wednesday, February 18, 2009 20 Temperature in the oceans Generally there are three layers –The surface zone has the highest temperatures. This is sometimes called the well-mixed (by waves and convection) zone. –The thermocline is a zone of rapidly decreasing temperature as depth increases –In the deep zone the temperature is slightly above freezing. Salt water freezes at a lower temperature than fresh water.

21. Class #18 Wednesday, February 18, 2009 21 Temperature profiles for different latitudes The tropics have the steepest thermocline, because sea surface temperatures are greatest there. The middle latitudes have the deepest surface layer. Polar regions have surface temperatures near freezing.

22. Class #18 Wednesday, February 18, 2009 22 Water, salt water, and air Salt water is denser than fresh water. –Icebergs, made of fresh water, float. Colder water is only very slightly denser than fresh water. Pressure in the oceans increases downward by 1 atmosphere about every 35 feet. Density is nearly constant in the oceans, whatever the depth.

23. Class #18 Wednesday, February 18, 2009 23 The sea surface Is the part of the ocean that interacts directly with the atmosphere. Has a temperature called the sea surface temperature (SST) actually measured a few feet below the surface at the intake level of a ship. Cold water is used by ships for air conditioning. The skin temperature is the temperature right at the surface.

24. Class #18 Wednesday, February 18, 2009 24 Sea Surface Temperatures Are highest in the tropics, lowest at the poles. In middle latitudes and subtropics, are higher on east coasts than west coasts. In polar regions, lowest temperatures on east coasts. In tropical regions, highest temperatures on west coasts. Are highest in the equatorial western Pacific in the “warm pool” and the Indian Ocean. Correspond to warm and cold surface ocean currents.