1. Outline Further Reading: Chapter 11 of the text book - dry and moist subtropical climate regimes - mediterranean regimes - dry mid-latitude and moist continental regimes Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L25: Mid Latitude Climates Apr-23-07 (1 of 16) - marine west coast regimes

2. Introduction Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L25: Mid Latitude Climates Apr-23-07 (2 of 16) Previously, –We looked at low-latitude climates –Tend to be uniformly warm –Principally differentiated by variations in precipitation Today, –We shall look at the mid-latitude climates –As opposed to low-latitude climates these climate regimes are differentiated by their temperature characteristics as well as their precipitation characteristics

3. Mid Latitude Climatic Regimes Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L25: Mid Latitude Climates Apr-23-07 (3 of 16) –Climates located between 25N-55N (mostly in the Northern Hemisphere -> not much land mass in these latitudes in the SH) –Influenced by Pressure and wind systems –Northern zone of subtropical high –Polar front Synoptic changes in Air Masses and fronts –mT, mP, cP –Traveling cyclones Strong seasonality in insolation Seasonality in pressure systems –Land-sea temperature differences –Cyclone formation and movement –Produces 6 different climate regimes 1. Dry Subtropical Regime 2. Moist Subtropical Regime 3. Mediterranean Regime 4. Marine West Coast Regime 5. Dry Mid-latitude 6. Moist Continental

4. Dry Subtropical Climates-1 Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L25: Mid Latitude Climates Apr-23-07 (4 of 16) Pole-ward extension of Dry Tropical regime (25-35N) with slightly higher seasonality in temperature and precipitation

5. Dry Subtropical Climates-2 Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L25: Mid Latitude Climates Apr-23-07 (5 of 16) –Seasonality in temperature due to changes in insolation –There is also some seasonality in precipitation due to the wintertime influence of midlatitude cyclones –Vegetation consists typically of drought-resistant species such as cactus (Yuma, Arizona)

6. Moist Subtropical Climates-1 Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L25: Mid Latitude Climates Apr-23-07 (6 of 16) H Jet Stream –Eastern subtropical regions –Have consistent high humidity due to mT air from the western edge of the subtropical high –In the summer there is also the influence of tropical cyclones

7. Moist Subtropical Climates-2 Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L25: Mid Latitude Climates Apr-23-07 (7 of 16) –Seasonality in temperature due to changes in insolation - typically hot summers; winters are cooler with the occasional incursion of cP air which leads to freezes –Precipitation due mainly to convective activity in the summer and from midlatitude cyclones in the winter –Vegetation is adapted to lots of water, such as mangrove swamps, etc. Charleston, S. Carolina

8. Mediterranean Climates-1 Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L25: Mid Latitude Climates Apr-23-07 (8 of 16) H Jet Stream –West coast of continents (between dry subtropical and marine west coast) –In the summer, the region is under the influence of the subtropical high -> dry, clear, warm; influencd by mT, cT air –In winter, the subtropical high moves south, region receives incursions of mP air, midlatitude cyclones which brings precipitation

9. Mediterranean Climates-2 Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L25: Mid Latitude Climates Apr-23-07 (9 of 16) Temperatures are typically mild throughout the year due to the influence of the ocean, low latitudes (compared with other mid-latitude regions) Vegetation typically is drought resistant, also usually fire- adapted Monterey, California

10. Maritime West Coast Climates-1 Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L25: Mid Latitude Climates Apr-23-07 (10 of 16) –West coast of continents at higher latitudes –Fairly persistent precipitation all year long In winter, region is affected by mid-latitude cyclones In the summer, circulation around the subtropical high results in orographic lifting as westerlies move on shore

11. Maritime West Coast Climates-2 Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L25: Mid Latitude Climates Apr-23-07 (11 of 16) –Temperatures are typically mild throughout the year due to the influence of the ocean –Regions of high productivity –Dense forests in North America (old growth rainforests) –Agricultural centers of Europe Vancouver, BC

12. Dry Mid-latitude Climates-1 Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L25: Mid Latitude Climates Apr-23-07 (12 of 16) cT cP –Continental interiors at mid-latitudes –Low annual precipitation Westerlies flow over mountain ranges, producing strong rainshadows In N. America, region stretches from the Great Basin to the Great Plains –Strong seasonality in temperature Due to changes in insolation Also due to influence of continental air-masses –Winter: cold, dry air associated with cP –Summer: hot, dry air associated with cT

13. Dry Mid-latitude Climates-2 Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L25: Mid Latitude Climates Apr-23-07 (13 of 16) –Any precipitation they do get is from passing midlatitude cyclones –Vegetation is transitional between desert and forest -> grasslands (Pueblo, Colorado)

14. Moist Continental Climates-1 Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L25: Mid Latitude Climates Apr-23-07 (14 of 16) cP mT H –Central and eastern portions of the continents –Strong seasonality in temperature Due to changes in insolation Also due to influence of continental air-masses –Winter: cold, dry air associated with cP –Summer: hot, moist air associated with mT –Typically high precipitation all year long, although variable from day to day Summer: rain associated with warm, moist mT air (usually also associated with passing fronts) Winter: rain associated with mid-latitude cyclones

15. Moist Continental Climates-2 Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L25: Mid Latitude Climates Apr-23-07 (15 of 16) –Note that precipitation decreases in the winter -> due to the fact that the cP air has less moisture in it –Ample water supply -> forests (Madison, WI)

16. Summary Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L25: Mid Latitude Climates Apr-23-07 (16 of 16) Climate dominated by several factors –Latitude -> determines seasonality in temperature, precipitation –Continental v. marine Seasonality in temperature Availability of moisture –East coast v. west coast Interaction of the prevailing winds with land masses Impact of circulation around the subtropical highs –Topography Creates orographic lifting, rainshadows