Processi di interazione nello strato limite superficiale:

l'esempio dell'estate 2003 e l'esempio del monsone asiatico

Prof. Claudio CassardoDepartment of General Physics – University of Torino, Italy

E-mail: cassardo@ph.unito.it, Web: http://www.ph.unito.it/cassardo/

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Summary

1. General description of the LSPM

2. Simulations during the 2003 summer

3. Simulations over the Asian monsoon in Korea

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1. General description of the model

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The LSPM is a 1D model which calculates energy, momentum and water exchanges between atmosphere and land

The processes in LSPM are described in terms of physical fluxes and hydrological state of the land

The LSPM (Land Surface Process Model)

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LSPM structure• Three main zones: atmosphere,

vegetation and soil• Canopy is considered as an uniform

layer (big-leaf approximation)• All variables are calculated as

weighted averages between atmospheric, canopy and snow components

• Turbulent fluxes are calculated by using the “analogue electric” scheme

• Soil temperature and moisture are calculated using multi-layer schemes

• User can select a variable number of soil layers

• LSPM can evaluate the thermal and hydrological budget in soil, canopy, snow and in atmosphere

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LSPM parameters

• In the atmospheric layer, all variables are calculated as weighted averages between atmospheric and canopy components

• Canopy is characterised by: – vegetation cover, height, leaf area index (LAI), albedo,

minimum stomatal resistance, leaf dimension, emissivity and root depth

• Soil temperature and moisture are calculated using multi-layer schemes, whose main parameters are: – thermal conductivity, hydraulic conductivity, soil porosity,

permanent wilting point, dry volumetric heat capacity, soil surface albedo and emissivity

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The physical processes:

• Radiative fluxes• Momentum flux• Sensible and latent heat

fluxes• Partitioning of latent heat

into canopy evaporation, soil evaporation and transpiration

• Heat transfer in a multi-layer soil or lake

Physical processes

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The hydrological processes:

• Snow accumulation and melt

• Rainfall, interception, infiltration and runoff

• Soil hydrology, including water transfer in a multi-layer soil

Hydrological processes

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The radiative fluxes include absorption, reflection and transmittance of solar radiation and absorption and emission of longwave radiation. They are critical for the surface energy balance. The surface energy balance, expressed in W/m2, is:

THE RADIATIVE BALANCE

Sensib

le hea

t flux

Rn = H + vE + Qg + Ph

Latent h

eat f

lux

Soil-atm

ospher

e hea

t flux

Photosynth

esis h

eat

Net ra

diation

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The hydrological balanceIn the mesoscale modeling the local balance is important storage of water into terrainThe hydrological balance is given by:

Pre

cip

itat

ion

rea

chin

g so

il

Eva

pot

ran

spir

atio

n

Ru

nof

f (e

xces

s of

wat

er in

filt

rati

on in

to s

oil)

Sto

rage

of

wat

er in

to t

erra

in

p = E + r + S

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The turbulent heat fluxes in the surface layer

A flux F of the generic variable in the surface layer can be

described by the flux-gradient equation:

The coefficient K represents the ability of the process in the

transfer of the variable

The above equation can be integrated. The flux F can be

considered constant in the surface layer. The result is an equation similar to the Ohm law:

gradient

Flux = -------------

resistance

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Latent Heat flux for Vegetated Surface

• In the more complicated case of a vegetated surface, E is partitioned into vegetation and ground fluxes that depend on vegetation qv and ground qg humidities or partial vapour pressures

• Assuming that the canopy has negligible capacity to store water vapour, the latent heat flux E between the surface at height z0w+d and the atmosphere at height zatm is partitioned into vegetation and ground fluxes as

L and S are the leaf and stem area indices. rb is the average leaf boundary layer resistance (sm-1) and r’0h is the aerodynamic resistance (sm-1) between the ground (z’0h) and d+z0h. rs is the stomatal resistance (sm-1).

gvvvw

satmpatm EEr

eeCE

1)(

0E

srfw0

g*spatmg r'r

)]T(ee[CE

Eg

)]rr

L)(f1()

r

SL(f)][T(ee[

CE

sbwet

bwetv*s

patmv

Ev

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2. Simulations during the 2003 summer

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L’anomalia di temperatura

I valori rientrano nel range 3-6°C, con il massimo sulla Francia e sulla regione alpinaParagonata con la statistica del periodo 1961-90, quest’anomalia corrisponde a 5

Giugno, luglio ed agosto 2003 sono stati i mesi più caldi mai registrati in Europa centroccidentale: sono stati stabiliti in molti paesi (Portogallo, Germania, Svizzera, Gran-Bretagna) i record nazionali di temperatura massima e in molte stazioni quelli di temperatura massima giornaliera estiva

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Am

eri

ca

A

tlan

tico

E

uro

pa

A

sia

È stata un’anomalia solo europea!!!

Diagrammi di Hovmoller dell’anomalia termica a 850 hPa rispetto al periodo (1972–2001) delle analisi ERA-40 mediate sul rettangolo 35°N–60°N nel mese di agosto. Isolinee ogni 2°C. Sono evidenziate le regioni con anomalie superiori a |4°C|

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La stazione di Torino

• Negli ultimi 200 anni si sono verificati almeno una dozzina di anomalie (rispetto al periodo 1961-90) dell’ordine di 2°C

• Nell’estate 2003, l’anomalia è stata 5.3 °C

Torino temperature anomalies (°C)

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

17531763177317831793180318131823183318431853186318731883189319031913192319331943195319631973198319932003

Years

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Bilancio energetico a Torino• Simulazione eseguita con LSPM sul periodo 1999-2003 su due stazioni:

Torino ed Alessandria• A Torino la radiazione globale, molto alta nel periodo marzo-settembre,

nell’estate 2003 è stata circa 50 W/m2 superiore alla norma• La radiazione netta è stata circa 25 W/m2 superiore alla norma

Il flusso di calore latente è stato inferiore alla norma a luglio, quasi normale negli altri mesi

Il flusso aria-vegetazione-suolo è stato normale

Il flusso di calore sensibile è stato 45 W/m2 superiore alla norma

Energy balance

-50

0

50

100

150

200

250

300

1999 2000 2001 2002 2003 2004years

W/m

2

GRNRHAFAQF+QG

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Andamenti di alcune grandezze

Radiazione solare (Wm2) Precipitazione cumulata (mm)

Flusso di calore sensibile (Wm2) Flusso di calore latente (W/m2)

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Andamenti di alcune grandezze

Rateo di evaporazione (mm) Temperatura del primo strato di suolo (°C)

Umidità del primo strato di suolo

Conclusioni• Riscaldamento prodotto da due cause:• Moti subsidenti (riscaldamento

adiabatico)• Suolo troppo secco per consentire

un’adeguata evapotraspirazione solo flusso di calore sensibile surriscaldamento (effetto quantificato in 2°C circa su Torino, e non presente sul Piemonte orientale)

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3. Simulations over the Asian monsoon in Korea

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The East Asian monsoon

• The East Asian monsoon, known as jangma ( ) in Korea and bai-u or shurin in Japan, is characterized by southwesterly winds in late June to water the Korean peninsula and Japan, leading to reliable precipitation spikes in July and August, and daytime T > 32°C with dew-points > 24°C

• Over Japan and Korea, the monsoon boundary typically has the form of a quasi-stationary front separating cooler air mass associated with the Okhotsk High (to the North) from hot, humid air mass associated with subtropical ridge (to the South)

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Description of the experiment

• Source data: 900 stations from Korean Meteorological Administration (KMA)

• Input data: temperature, pressure and humidity, wind speed, precipitation, solar radiation

• Period: 2005 summer

– This period has been selected as the rainy season has been relatively intense if compared with other seasons

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Sensible heat flux (Wm-2)

• SHF is larger in the urban area of Seoul and over the great island of Jeju and in the extreme south-west

• Generally SHF is also larger in the other areas with less rainfall• The absolute values in July are about half than those in June,

and in August even smaller evapotranspiration still requires most of net radiation

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Latent heat flux (Wm-2)

• LHF is larger in the areas showing an elevate rainfall (west Korea) and also in correspondence of the maxima of net radiation, and low in the Seoul urban area

• August LHF values are larger than July ones• Large LHF = large evapotranspiration lower soil

moisture

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Surface soil moisture

• The surface soil moisture (expressed as fraction of the porosity) is larger in the western part of the peninsula, and appears to be not too much correlated with the precipitation

• The central and south-eastern area have smaller soil moistures, due to the strong evaporation but also to lower precipitation

• The north-western area has a surface soil moisture close to the field capacity during all summer months

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Conclusions and perspectives

• The spatial distribution of variables shows that the mountainous areas, which get the maxima of precipitation, have a very strong evapotranspiration which consumes efficiently the soil moisture

• The urban and suburban area of Seoul shows lower values of soil moisture and evapotranspiration, and higher values of sensible heat flux and soil temperature (with respect to neighbouring areas)

• The south-eastern areas, in which precipitation is lower, are the warmer areas of Korea

• A future analysis could be the validation of LSPM over the main climatic Korean areas by comparing some variables calculated by the model with observations

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