J.-F. Müller, J. Stavrakou, S. Wallens

Belgian Institute for Space Aeronomy, Brussels, Belgium

IUGG Symposium, July 2007

Interannual variability of biogenic VOC emissions estimated from the MEGAN

model and ECMWF analyses

A. GuentherNational Center for Atmospheric Research, Boulder, Colo., USA

Thanks to: J. Rinne (Univ. Helsinki), M. Potosnak (Desert Res. Institute), B. Munger and S. Wofsy (Harvard Univ.), A. Goldstein (Univ. California),

M. Van Roozendael and I. De Smedt (IASB, Brussels)

Outline MEGAN model : emission algorithm MOHYCAN model: canopy environment

model Results: Inventory for 1995-2006 Interannual variability Comparison with campaign data Evaluation using GOME HCHO data

MEGAN model for estimating the emissions of isoprene from plant foliage

= emission rate in standard conditions

, = response functions to radiation and temperature at leaf level

= dependence to leaf age

= dependence to soil moisture stress

LAI = Leaf Area Index

• LAI from MODIS 2000-2006

• ECMWF analyses provide: canopy top values of downward solar radiation, temperature, wind, and humidity + cloudiness + soil moisture in 4 layers

• values inside the canopy require a multi-layer canopy model (MOHYCAN)

(Wallens, 2004; Müller et al., 2007)

LAIdzdSdtFlux SMageTP

canopy

P TageSM

ε

Results : Emissions in 2003

Very similar to distribution obtained by Guenther et al. (ACP2006) using NCEP meteorological data, except over arid areas

Results: Impact of soil moisture stress

Large reduction over arid areas

Global annual emissions reduced by > 20%

Results: Impact of using leaf (instead of air) temperature in the algorithm

Global annual emission increased by 18%

Results: Zonally averaged emissions

Global annual emission is ~30% than in Guenther et al. (1995, 2006)

Large interannual variability (20% difference between extreme years)

Isoprene emissions and El Niño

Comparison with campaign data: Harvard forest, Mass., 1995

Diurnal cycle is OKDay-to-day variations very well reproduced

Overestimation in spring/fall

Comparison with campaign data: Tapajos, Amazonia, 2000, 2001, 2003

(Here model results scaled down by factor 1.7)

Wet season fluxes (April-July) largely overestimated by model

GOME HCHO data

Slant columns retrieved at IASB-BIRA (I. De Smedt, M. Van Roozendael) from GOME spectra using the WinDOAS technique

Fitting window chosen to avoid artefacts over desert areas and reduce noise

Vertical HCHO profiles taken from IMAGES CTM

http://www.temis.nl, De Smedt et al., in preparation

Vertical HCHO columns calculated by the IMAGES CTM (curves) and retrieved from GOME (diamonds)

Using GEIA inventory

Using MEGAN-based inventory

Id., neglecting soil moisture stress

Conclusions

Isoprene emission inventory 1995-2006 at 0.5°x0.5° resolution available at http://www.oma.be/TROPO/inventory.html in NetCDF format

Müller et al., will be soon submitted to ACP

Soil moisture stress might have a big impact, but the calculated effect depends on choice of meteorological data + wilting point database

Global emission is ~410 Tg/year

Large interannual variability, to a great extent related to El Niño

Short-term variations of isoprene emissions well captured by model, not so much the seasonal variation

Satellite HCHO : a promising tool for constraining the emission distribution and variability also in Tropical regions