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
http://alanbetts.com/research/paper/progre
ss-in-understanding-land-surfaceatmosphere-coupling-from-lba-research
Dry vs. wet surfaces
animations
http://www.meted.ucar.edu/nwp/model_physics/navmenu.php?tab=1&page=3.7.1
Surface Energy Balance
Es
 G  Rs  LE  SH  Feo
t
Or for steady state
Rs  LE  SH  Feo
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, CA
10 June 1950
Heat Budget II
Corn Field, Madison, WI
4 September 1952
Heat Budget III
Alfalfa, Hancock, WI
19 July 1956
Annual Cycles at
Middle Latitude
Sites
Heat Balance
Over the Gulf
Stream
Note importance of currents,
which warm the area Dec-Sep
and transport net heat to higher
latitudes Oct-Nov
Gulf Stream 38N, 71W
dry soil
wet soil
Add same surface energy with
different evaporative fraction
dry soil
mse
(virtual) dse
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)
Current climate, ocean mean conditions:
18C (set by planetary radiation balances)
RH ~ 70% (so that LHF ~ atm. rad. cooling rate)
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).
moisture is
whatever it
is
qo = 10
To=18
q*o = 14 g/kg
RHo = 10/14
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.
Land and ocean
T remain equal aloft
by efficient horiz. 'mixing'
ql = 8/10 qo
= 8 g/kg
 Tland=23C
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
GW
with incoming sunlight, which
hasn't changed.)
qo =
10/14 *17
=12.1 g/kg
To=21 (3K rise)
q*o = 17 g/kg
RHo = same (10/14)
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.
GW
Land and ocean
T remain equal aloft
by efficient horiz. 'mixing'
ql = 8/10 of qo
= 8/10 *12.1
= 9.7 g/kg
 Tland=28C (5K rise)
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/progre
ss-in-understanding-land-surfaceatmosphere-coupling-from-lba-research