FUT., Akure

Carbon, water and energy fluxes in a West African humid tropical ecosystem

1,3Balogun A.A., 1,3Balogun I.A, 1,3Oladosu O.R., 2,3Jegede O.O.

1 Federal University of Technology, Akure, Nigeria

2 Obafemi Awolowo University, Ile-Ife, Nigeria

3Atmospheric Research Group (ARG), Nigeria

CarboAfrica Conference, Pointe Noire, Congo 17 – 19, March 2010

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Introduction

•NlMEX is an on-going collaborative research project between the Atmospheric Research Group (ARG), Nigeria and the University of

Bayreuth (UBT), Bayreuth in Germany with support from IPPS

Sweden.

•Initially designed to study the surface-atmosphere mass and

energy exchange processes at a humid tropical location.

•NIMEX-1 and NIMEX-2 have successfully been conducted in 2004

and 2005 respectively.

•Major results have been reported in the literature, also reviewed

here..

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Introduction Cont’d

•The ARG is now conducting NIMEX-3 between March and April, 2010.

• Aims to expand the scope of the earlier studies to include the monitoring of CO2 fluxes by EC system, using an ultrasonic anemometer (CSAT3) and

a gas analyser (LI-7500).

•NIMEX-3 measurements will complete the gaps that were apparent in NIMEX-1 and NIMEX-2 datasets.

•NIMEX-3 is a first attempt of CO2 flux monitoring in Nigeria, in order to quantify and understand ecosystem carbon, water and energy budgets.

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Nimex Site Location

Ile-Ife, Nigeria

Ile-Ife, Nigeria (7o 33’N, 4o 33’E): Agricultural fallow bush land.

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Site Layout & Instrumentation Ile-Ife, Nigeria

NIMEX is one of the few direct

measurements of all component of the

surface energy balance in tropical West

Africa.

•The measurements in 2004 & 2005, during

the transition from the dry to wet season

using;

•Metek USA-1 sonic: z = 2.48m

•Campbell KH-20 hygrometer: z = 2.48m

•Wind, temperature & humidity profiles

•Soil heat flux, temperature and moisture.

•Precipitation

•IRT surface temperature

Site Picture from Mauder et al., 2007

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Site Layout & InstrumentationSt. Paul, USA

Nimex3-2010;

CSI, Csat3 Sonic

Li-cor LI-7500 CO2

& H20 IRGA

Suburban turf

grass site in St Paul, MN, USA

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Volumetric soil moisture and precipitation aggregated to 30 minutes during NIMEX-1 in Ile-Ife, Nigeria (Mauder et al 2007)

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Radiation balance components for three selected days (Mauder et al 2007)

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Energy balance components of the selected days during NIMEX-1 representing three different typical soil and weather conditions: (Mauder et al 2007)

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Surface energy balance closure during NIMEX-1

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Introduction

•Monin Obukhov similarity theory (MOST) provided the

theoretical foundation for present day understanding of boundarylayer meteorology.

•But, despite the success of MOST in unifying theory and

observations, uncertainties persists in some of the universal functions that it predicts should exist (Andreas et al., 1998).

•Parameterisations for the integral turbulence characteristics of

wind components, temperature and humidity (e.g. Foken et al.,

1991; Andreas et al., 1998; Hogstrom 1990; Panofsky et al., 1977; Wyngaard et al., 1971).

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Introduction

•Flux-variance relationships at two different locations:

•Ile-Ife, Nigeria (7o 33’N, 4o 33’E): Agricultural fallow bush land.

•St. Paul, Minnesota (44o 57’N, 94o 33’W): Suburban turf grass lawn.

•With similar results that differ slightly from the generality in the literature for σw/u* & σq/q*

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St. Paul, MN, USA

Ile-Ife, Nigeria

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Though both sites are at different geographic/climatic

locations, the data sets reported here were for a

period of high temperatures and progressive soil

moisture depletion at both locations.

0

5

10

15

20

25

54 56 58 60 62 64 66 68

Time (DOY)

Pre

cip

itati

on

(m

m)

0

5

10

15

20

Vo

lum

etr

ic S

oil

Mo

istu

re (

%)

Rainfall (mm)

SMC (%)

Top: Rainfall and soil

moisture content between

Feb19 – Mar9, 2004 at

Ile-Ife, Nigeria.

Bottom: Rainfall and soil

moisture content between

Jul19 – Jul 31, 2006 at

St. Paul, USA.0

5

10

15

20

25

199 201 203 205 207 209 211 213

Time (DOY)

Pre

cip

itati

on

(m

m)

0

5

10

15

20

25V

olu

metr

ic S

oil

Mo

istu

re (

%)

Rainfall (mm)

SMC (%)

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Table after Thomas & Foken 2002

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Parameterisations of Andreas et al., 1998

for -4 < ζ ≤ -0:1,

σw/u* = 1.20(0.70 - 3.0 ζ)1/3

for -1 ≤ ζ ≤ 0,

σw/u* = 1.20

for -1 ≤ ζ ≤ 0,

σw/u* = 1.20(1 – 0.2 ζ)

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Parameterisations of Andreas et al., 1998

Vertical velocity

Temperature and humidity

For temperature, C = 3.2; for humidity, C = 4.1 Andreas, 1998.

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Results: σw/u*

Near Neutral

Nigeria: z/L < ±0.05

USA: z/L < ±0.06

P77: 1.3, Panofsky et al., 1977

0

0.5

1

1.5

2

-0.06 -0.03 0 0.03 0.06

z/L

σw

/u* Nigeria

USA

P77

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σw/u*

Unstable

0

1

2

3

4

0 0.5 1

-z/L

σw

/u*

Nigeria

USA

P77

A98w

A98w: Andreas et al., 1998

P77: Panofsky et al., 1977

Not significantly different from Panofsky and Dutton, 1984

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σw/u*

Stable

Bal: 1.3*(1+(0.25*z/L)), Balogun et al., 2009

0

0.5

1

1.5

2

2.5

0 1 2

z/L

σw

/u* Nigeria

USA

z/LA98

P77

Bal

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Results: σT/T*

Near Neutral

0

5

10

-0.1 0 0.1

z/L

σT/T

*

Nigeria

USA

ThF91

ThF91

ThF91: Foken et al., 1991

see Table 1 for z/L ranges

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Results: σT/T*

Stable

0

5

10

0 0.1 0.2 0.3 0.4 0.5

z/L

σT/T

*

Nigeria

USA

ThF91

A98

A98: Andreas et al., 1998

ThF91: Foken et al., 1991

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Results: σT/T*

Unstable

0

5

10

-2 -1 0

z/L

σT/T

*

Nigeria

USA

ThF91

A98

A98: Andreas et al., 1998

Wyg71: Wyngaard et al, 1971

ThF91: Foken et al., 1991

In good agreement with Wyngaard et al, 1971

0.1

1

10

100

0.001 0.1 10

-z/L

σT/T

* Nigeria

USA

Wyg71

ThF91

A98

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Results: σq/q*

-1/3 law obeyed but with a coefficient of 0.85

0

5

10

-2 -1 0

z/L

σq

/q*

Nigeria

USA

A98

Wyg71

z/L95

z/L85

0.1

1

10

100

0.001 0.1 10

-z/Lσ

q/q

*

Nigeria

USA

z/L85

Hog74

z/L95

A98b

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Conclusions

• Remarkable similarity/agreement in the flux-variance relationships at both sites for w, T & q.

•MO similarity appears to be obeyed at both locations.

•Panofsky et al., 1977 parameterization fits the w flux-variance relationship best for near neutral and unstable conditions at both sites.

• A new parameterization for w, 1.3*(1+(0.25*z/L)), Balogun et al., 2009 under stable conditions fit the data at both sites better than existing parameterizations for the prevailing atmospheric & soil conditions

•The parameterization of Foken et al.,1991 best fitted T for near neutral

and stable conditions.

•While those of Andreas et al., 1998, Wyngaard et al, 1971& Foken et al., 1991 were in good agreement for T for –z/L < -0.05.

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Conclusions Cont’

Conclusions Cont’d

•Though (z/L)-1/3 law was obeyed for q, but with a coefficient

of 0.85 which is lower than the 0.95 – 1 for T at both sites. This differ from most published results where the flux-variance

similarity functions for q are consistently larger in magnitude

than their T counterpart (Katul & Hsieh, 1995; Lamaud & Irvine, 2006).

•The high temperatures and water stress may have been

responsible for this. Data analysis is still ongoing to confirm this suggestion and find other possible causes.

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Note for CarboAfrica Secretariat;

• We have a vibrant & active Micrometeorology/ARG that would be happy to collaborate and participate in the next

phase of the CarboAfrica project.

• How can we have access to the CarboAfrica flux datasets

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Acknowlegement

•The authors acknowledge funding for NIMEX-1 from IPPS,

DAAD, the University of Bayreuth, Germany, The University of Minnesota, USA, the Obafemi Awolowo University, Ile-Ife,

Nigeria and the Federal University of Technology, Akure, Nigeria.

•The efforts of colleagues from all participating institutions are

also acknowledged.

Thank You!