Importance of the atmospheric boundary layer

Life cycle of the Sun and the Earth

The earth will be inhabitable for another 0.5 billion years, if we protect it well enough.

After another 1 billion years, all oceans and rivers will have completely disappeared. The mean global temperature will reach 160 F.

The mission of the atmospheric sciences is to understand and predict weather, climate, and

related disasters

Weather- and climate-related disasters

Weather-related Disasters: Tornadoes U.S. Annual mean fatalities 56,

annual mean loss $777 million

Weather-related Disasters: Tropical Cyclones(Hurricanes, Typhoons, Cyclones)

Global distribution of the paths of major tropical cyclones during the last 150 years. On average, ~ 80 per year around the world.

U.S. Fatalities: normal year 21, Katrina 1836 U.S. Property loss: normal year $5400 million, Katrina $84000 million

Summary: Weather-related Disasters in US

Disastrous effects of 1982-1983 El Nino:1.Australia-Drought and devastating brush fires 2.Indonesia, Philippines-Crops fail, starvation follows3.India, Sri Lanka-Drought,fresh water shortages4.Tahiti-6 tropical cyclones5.South America-Fish industry devastated - decrease in nutrients off Peru- fewer fish (anchovy)6.Across the Pacific-Coral reefs die7.Colorado River basin-Flooding, mud slides8.Gulf states-Downpours cause death, property damage9.Peru, Ecuador-Floods, landslides10.Southern Africa-Drought, disease, malnutrition

Global warming(The Copenhagen Treaty)

The modern meteorology was born in the 1940s (a very young science!),

but has been growing very fast!

Carl-Gustaf Rossby (1898-1957) Generally considered as the “father of modern meteorology”. Founder of the “Chicago School of Meteorology”.

Tools

The current status of weather and climate predictions

• Weather prediction: Generally good within one week, not good beyond 10 days. The skill depends on season and location.

• Tropical cyclone (hurricane, typhoon) prediction: good in track, but bad in intensity

• Climate prediction: Seasonal prediction generally good within 6 months, but not good beyond. Skill depends on season.

• Climate projection: All models project global warming in the 21st century, but with a 3-fold difference in magnitude.

Why is it so difficult to understand and predict weather

and climate?

Problem I: Different parts of the world are strongly connected to each other (The “Teleconnection Problem”)

(Lin et al. 2006, Journal of Climate)

Example: Remote impacts of Amazon deforestation

2006

2002

From Werth and Avissar

Problem II: Different components of the earth system (atmosphere, land, ocean, ice,

clouds, etc) are strongly interacting with each other

(The “Feedback Problem”)

(Lin 2007, Journal of Climate)

Problem III: The earth system composes of both very big objects (such as the whole Pacific Ocean) and very small objects (such as the cloud droplets), making it very difficult to draw them on the same page

(The “Subgrid-Scale Problem”)

Boundary layer process is one of the most important subgrid-scale processes in climate models and weather forecasting models

Vertical Structure of the Atmosphere

• Definition of the atmospheric boundary layer (ABL): "that part of the troposphere that is directly influenced by the presence of the earth's surface and responds to surface forcings with a time scale of about an hour or less.”

• Scale: variable, typically between 100 m - 3 km deep

Importance of ABL:(1) Interface between atmosphere and

ocean/ land/ice - flux transfer and

feedback

Importance of ABL:(2) The human beings are living in the

ABL and changing the climate system • Release of greenhouse gases

• Release of pollutants (aerosols)

• Change of land cover (deforestation and afforestation)

Importance of ABL:(3) A basic subgrid-scale process

Summary• The mission of meteorology is to understand and predict

weather- and climate-related disasters (e.g. tornados, hurricanes, El Nino and global warming).

• The modern climatology (meteorology) was born in the 1940s (a very young science!), but has been growing very fast! Now we have a global observational network with many satellites, ships, radars and surface stations, as well as very comprehensive prediction models running on the world’s largest computers.

• The current status of weather and climate predictions: (1) weather prediction good to 10 days, (2) tropical cyclone prediction good in track but not in intensity, (3) climate prediction good to two seasons, (4) climate change projections have a 3-fold difference in magnitude.

• The main reasons of the difficulties: (1) Teleconnection problem, (2) Feedback problem, and (3) Subgrid-scale problem.

• Importance of the ABL: (1) interface between atmosphere and ocean/land/ice - flux transfer and feedback, (2) the human beings are living in the ABL and change the environment, (3) a basic subgrid-scale process