David K. AdamsCentro de Ciencias de la Atmósfera

UNAM

The Atmospheric Hydrological Cycle under Global Warming: Precipitation and Tropical

Cyclones

OUTLINE

•Trends in Precipitation

•What Drives Modification of Precipitation?

•Hurricane Trends

•Hurricane: The Physics behind its Energetics

Precipitation Trends: What has been Observed?

•Using the language of the IPCC Report 2013

•Increased Trends (frequency and/or intensity) in Precipitation

(since 1950) over land is likely (Confidence is highest for

North America/Europe)

•Very likely that there have been trends towards heavier

precipitation events in central North America.

Thermodynamic Characteristics of the Tropics

•This 3-way energy balance in the deep tropics implies a dominant

role for convective clouds/precipitation

•How deep convection interacts/links dynamically various scales is

a complex problem (and very relevant for hurricanes)

•For the tropics no simple theory (i.e., Quasi-geostrophic theory)

exists that governs large-scale motions

Extreme Precipitation Events: What has been Observed?

•Extremes in Hydrological Cycle (e.g. heavy precipitation,

hailstorms)

•Not well observed due to existing networks,

•but also due to the nature of isolated events (Convection)

•Suggested increasing trend is hailstorms (size of hail and/or

frequency) in Canada, China and U.S.

•There is low confidence in observed trends in small-scale

severe storms (hailstorms/thunderstorms) due to poor data.

What do We Expect from the Atmospheric Hydrological

Cycle in the Future

•What do Basic Physics tell us?

•Hydrological Cycle: Large-scale average precipitation,

stream flow and runoff, soil moisture, atmospheric water

vapour, and clouds.

•Atmospheric Hydrological Cycle is Intimately to

Atmospheric Energy Budget.

Atmospheric Energy Budget

Precipitable Water Vapor Trends

Simple Physical Basis for Increases in

Precipitation Extremes

•Ignoring Changes in Dynamics or Precipition Efficiency,

Precipitation extremes increase with increased saturation

vapor pressure of water.

•Why are there changes in the saturation vapor pressure of

water?

•Saturation vapor pressure of water is a function of

Temperature

C.C Scaling and Effects on Precipitation

•Clausius-Claperyon gives a sensitivity of 6 to 7% of typical

near surface temperatures in the Tropics.

•Increased humidity implies greater CAPE

•Assuming Relative Humidity remains constant and Dynamic

or Precipitation Efficiencies do not change greatly, global

warming should lead to greater precipitation extremes.

• But Dynamics and Precipitation Efficiency would Change

•Convective Organization truly a Difficult Problem.

Tropical CycloneTrends: What has been Observed?

•Trends Highly Constrained by Observations (like

Precipitation in General)

•Difficult to Separate Anthropogenic Effects from Natural

•Variability

•Substantial increases in the frequency of the most intense

cyclones and it is more likely than not

• The future influence of climate change on tropical cyclones

is likely to vary by region

Land Falling Hurricanes Trends

What do Simple Physics Tells us?

•Hurricane Energetics Depend on Surface Temperature and

Enthalpy.

•Treating a Hurricane as a Carnot Heat Engine (Emanuel)

•Predicts Maximum Intensity (Wind Speeds)

Steady-State Hurricane as Carnot Heat Engine

•Emanuel (1986) idealized mature hurricane as a

Carnot Heat Engine

•Hurricane converts heat extracted from ocean

to mechanical energy

•In steady-state, mechanical energy generated

balances frictional dissipation

Steady-State Hurricane as Carnot Heat Engine

•Emanuel (1986) idealized mature hurricane as a

Carnot Heat Engine

•Hurricane converts heat extracted from ocean

to mechanical energy

•In steady-state, mechanical energy generated

balances frictional dissipation

Summary

•Precipitation in Mid-latitudes Increases,

Decreasing in Tropics.

•Hurricane Intensity Expected to Increase

•Satellite Observations are Becoming more

Important and Viable

•Convection Organization Still a Big Problem

•Theory and Modelling.