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Land surface thermodynamics, PBL and convective processes, as compared to ocean, and implications. Brian Mapes climate reading group before Betts visit MSC 307 class just back from monsoon meeting Guesses? monsoon w/ global warming?. Read this for next week. - PowerPoint PPT Presentation
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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
E G R LE SH Ft
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