Land surface thermodynamics, PBL and convective processes,

as compared to ocean,and implications

Brian Mapesclimate reading group before Betts visit

MSC 307 classjust back from monsoon meeting

Guesses? monsoon w/ global warming?

Read this for next week

http://alanbetts.com/research/paper/progress-in-understanding-land-surface-atmosphere-coupling-from-lba-research

Dry vs. wet surfaces

animationshttp://www.meted.ucar.edu/nwp/model_physics/navmenu.php?tab=1&page=3.7.1

Surface Energy Balance

ss eo

EG R LE SH F

t

Or for steady state

s eoR LE SH F

Note that soil and rock have about half the heat capacity of water and that penetration of temperature fluctuations into the solid earth is much shallower than into water.

Heat capacity of moist, unfrozen soil is much greater than that of dry soil

soil: 2000x bigger heat capacity (per cubic meter) than air

Heat Budget I

Dry Lake, El Mirage, CA10 June 1950

Heat Budget II

Corn Field, Madison, WI4 September 1952

Heat Budget III

Alfalfa, Hancock, WI19 July 1956

Annual Cycles atMiddle LatitudeSites

Heat Balance Over the Gulf Stream

Note importance of currents, which warm the area Dec-Sep and transport net heat to higher latitudes Oct-NovGulf Stream 38N, 71W

dry soil wet soil

Add same surface energy with different evaporative fraction

mse (virtual) dse

dry soil wet soil

mse dse

Add same surface energy with different evaporative fraction

dry soil wet soil

dry surface wet surface

N-S Wet-dry gradient: monsoon

E-W or global dry-wet sfc gradients(continent-ocean)

To=18q*o = 14 g/kgRHo = 10/14

qo = 10

15 g

/kg10

g/k

g

8 g/

kg6 g/

kg

Current climate, ocean mean conditions: 18C (set by planetary radiation balances)

RH ~ 70% (so that LHF ~ atm. rad. cooling rate)

moisture is whatever it is

T is nearly adiabatic (dry moist adiabat) because vertical convection is efficient (which in turn is because rad. eq. is unstable, so the troposphere is convecting thoroughly).

ql = 8/10 qo Tland=23C = 8 g/kg

15 g

/kg10

g/k

g

8 g/

kg6 g/

kg

Land and ocean T remain equal aloftby efficient horiz. 'mixing'

Land gets whatever humidity it has from the ocean, so its q is some fraction (say 8/10) of the OCEAN's q. That 8/14 depends on (summarizes) continent shape and all myriad wind statistics.

To=21 (3K rise)q*o = 17 g/kgRHo = same (10/14)

qo =10/14 *17=12.1 g/kg

15 g

/kg10

g/k

g

8 g/

kg6 g/

kg

GW

New climate: warmer ocean by 3K because of greater atmospheric emissivity (greenhouse gases), but RH at the surface stays the same because it is set by physics (LHF ~ atm. IR cooling rate, which hasn't changed since radiative fluxes in the new climate are in equilibrium with incoming sunlight, which hasn't changed.)

ql = 8/10 of qo Tland=28C (5K rise) = 8/10 *12.1 = 9.7 g/kg

15 g

/kg10

g/k

g

8 g/

kg6 g/

kg

Land and ocean T remain equal aloftby efficient horiz. 'mixing'

GW

Land q is still that same fraction (say 8/10) of the OCEAN's q. That 8/10 depends on (summarizes) continent shape and all myriad wind statistics, which (conservative assumption) won't have changed with small climate warming.

Fasullo 2010...CMIP3...Despite differences in magnitude, the nature of the feedbacks governing the land–ocean

contrast are largely robust ...

relative humidity (RH) over land decreases with warming because precipitation and the hydrological

cycle are governed pr marily by transports of moisture from the oceans, where increases in lower-

tropospheric temperature and saturated humidity fail to keep pace with those over land.

...decreased RH raises the lifting condensation level, even as CAPE increases, and suppresses

convective clouds.... particularly strong at low latitudes where the dynamical influence of competing

sources of maritime deep convection may further suppress convection....

...the mean increase in OLR over land (1.0 W/m2/K) is almost double that over the ocean (0.6) ...The

contrast results in an increase in the transport of energy from ocean to land relative to the twentieth

century...lasting increases in both OLR and absorbed shortwave radiation globally. A conceptual model...

...while the land–ocean contrast plays a key role in achieving global radiative equilibrium, it entails

disproportionate increases in temperature and aridity over land and therefore is likely to be associated

with substantial environmental impacts.

The extra heat of global warming is absorbed solar, not trapped longwave!

Read this for next week

http://alanbetts.com/research/paper/progress-in-understanding-land-surface-atmosphere-coupling-from-lba-research