Chapter 9 Wind Small Scale and Local Systems Wind Wind direction is described as the direction from which wind is blowing EX easterly wind blows from east to west A northwesterly wind means the wind is blowing a from northwest to southeast Scales of motions Micro scale 2m small spirals of wind lasts for seconds to minutes EX smoke from a chimney Mesoscale 20 km thunderstorms lasts for hours to days EX sea breeze Synoptic scale 2 000 km lasts for many weeks High and low pressure centers are weather features b synoptic scale Sea breezes are weather features d mesoscale Planetary Boundary Layer PBL The layer of the atmosphere near the surface that is influence by friction Typically the lowest 1 3km of the atmosphere height varies on weather conditions Turbulence any disturbed air flow that produces wind gusts eddies Mechanical turbulence created by obstructions irregularities on the surface lead to disrupted air flow and creates mechanical turbulence Thermal turbulence created by rising thermals stronger during daytime heating destabilization stronger thermals stronger thermal turbulence Both mechanical and thermal turbulence exist in PBL Horizontal airflow that is disturbed by obstructions e g buildings trees mountains etc is called d mechanical turbulence PBL The depth of the PBL depends on three primary factors 1 Surface heating producing a steep lapse rate and strong thermal turbulence 2 Strong wind speeds producing strong mechanical turbulence 3 Rough hilly landscape producing strong mechanical turbulence strongest in cities forests mountains SELECT ALL CORRECT ANSWERS Which of the following contributes to a tall planetary boundary layer a strong surface wind d strong surface heating Wind and Water Wind waves waves formed by wind Height depends on wind speed a weak wind speed b high pressure directly overhead d a short fetch Local Wind Systems EX sea breeze air from sea Thermal Circulations Shallow Weaken with height length of time wind blows fetch distance of deep water over which wind blows EX A sustained 58mph wind lasts 3 days over at least 1600 miles can generate waves with an average height of 49 feet SELECT ALL CORRECT ANSWERS Which of the following contributes to relatively low wind wave heights By convention we name the feature based on the origin of the air Maintained by local surface heating and cooling Sea Breeze An example of thermal circulation Dominant weather feature in Florida during summer Is responsible for scattered afternoon thunderstorms that occur almost every day during the summer WIND Ocean cool Surface high Aloft low EX Land warm Surface low Cloud Development Aloft High Sea Breeze Characteristics Strongest At coast strongest temperature and pressure difference Near time of max temperature Anything that causes greater horizontal temperature difference causes stronger sea breeze SELECT ALL CORRECT ANSWERS The sea breeze b is strongest at the coast c is stronger when horizontal temperature changes are large d is responsible for most of Florida s summer thunderstorms Sea Breeze Front Leading edge of sea breeze Is the boundary between warm drier inland air and cooler humid ocean air Sea breeze front passage cooler temperature higher dew points higher relative humidity wind shift pressure min As front moves inland it collides with inland air creating convergence Convergence causes rising motion and cloud development Sea breeze front is often accompanied by a line of cumulus clouds If atmosphere is conditionally unstable these clouds along sea breeze front can grow to great depths and become thunderstorms Which of the following is NOT a characteristic of a sea breeze front passage d lower relative humidity Other Factors Influencing Strength of the Sea Breeze Ambient synoptic scale wind flow Light offshore synoptic wind enhanced temperature gradient sea breeze pinned to the coast Light onshore synoptic wind decreased convergence potentially weaker temperature gradient sea breeze moves farther inland If the synoptic wind is too strong no true sea breeze Shape of coastline Which of the following would inhibit sea breeze development a strong synoptic scale winds Land Breeze Opposite of sea breeze Caused by temperature difference in sea and land Occurs at night Which of the following is NOT true of a land breeze c it is usually stronger than a sea breeze Lake Breeze Large lakes Same as sea breeze just with a lake Generally weaker than sea breezes because the temperature difference is weaker at night than during the day EX Lake Michigan cools Chicago Lake Superior and Michigan cool the upper peninsula of Michigan Which of the following explains why the upper peninsula of Michigan sees scattered thunderstorms in the summer a colliding lake breezes causing convergence and rising motion In the northern hemisphere as air moves from a mountainous land surface to a large smooth lake the air will d speed up and deflect to the right Mountain and Valley Breezes Thermal Circulation During the day the hillside warms up faster than the surrounding air and rises valley During the night the hillside cools down faster than surrounding air and sinks mountain Air moving down slope of a mountain and warming adiabatically Chinook Winds Warming winds EX East side of the Rocky Mountains Which of the following is NOT a thermal circulation a chinook breeze Santa Ana Winds Downslope winds Causes warm dry conditions Can cause wild fires to spread rapidly c Santa Ana Monsoon Large scale phenomenon Seasonal change in wind direction Which types of winds are favorable for the development and or spread of wildfires in southern California Large scale sea breeze that occurs in summer and land breeze in winter The monsoon causes areas in southeastern Asia to receive most of their rainfall during b summer Chapter 10 Wind Global Systems General Circulation Large scale average patterns Main cause is uneven heating across Earth s surface Doldrums Areas near equator with light winds belt of thunderstorms and clouds low pressure and rising air What causes the ITCZ a convergence of northern and southern hemisphere trade winds The weather near the equator is characterized by a low pressure and scattered thunderstorms along the ITCZ Intertropical Convergence Zone ITCZ area near equator where the NE and SE trade winds converge General Circulation c from west to east Subtropical Highs Large areas with high pressure found near 30 degrees calm wind clear skies warm surface temperature where most desserts are
View Full Document
Unlocking...