Importance of the atmospheric boundary layer (2)

Review of last lecture• 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.

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”)

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 main reasons of the difficulties in

weather and climate predictions: (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