analysis of surface meteorological data at the Gourma sites focus on

radiative fluxes & thermodynamics at diurnal & interannual time scales

automatic weather station of Agoufou, 2002 now wind speed, T, RH, radiative fluxes etc, 15-min samplingno pressure nor wind direction, some holes mostly outside the monsoon season

aeronet sunphotometer of Agoufou, 2003 nowaerosol optical depths, precipitable water, daytime & cloud free conditions

automatic weather station of Bamba 2004 nowwith wind direction

ECMWF-IFS « Agoufou grid-point » time and time-height series, horizontal resolution ~ 40 km, 60 vertical levels

initially, check of data consistencycharacterisation of the sitevaluable Northern Sahel ground truth/modelling purpose (diagnostics)

objectives

data & products

F. Guichard, L. Kergoat, F. Timouk, F. Baup, F. Lavenu & E. Mougin

185 mm

380 mm

water vapour mixing ratio (qv) 2m AGL

430 mm

2002

2003

2005

2004

cumulative precipitation

22

275 mm

day of year

Jul

rainfall per event

AugAgoufou q

v (g.kg

-1)

0

2002

2003

2005

2004

Jul AugAgoufou

day of year

net radiation

3-day running mean

seasonal variations of net radiation

Rnet =

LW - LW + SW - SW

interannual variabilitywith stronger increase of Rnet for wet years (2003,2005) compared to dry years (2002,2004)

partly explained by a stronger decrease of upward longwave flux for wet years ...but not the whole story

surface radiative budget

rainfall per event

2002

2003

2005

2004

Jul AugAgoufou

day of year

albedo

3-day running mean

seasonal variations of

ALBEDO = SW / SW

againinterannual variabilitywith stronger increase of Rnet for wet years (2003,2005) compared to dry years (2002,2004)

differences also before the monsoon season

surface radiative budget, suite

more on albedo to come with Olivier & Laurent

rainfall per event

interannual variations of surface radiative fluxes

-400

-200

0

200

400

-20

-10

0

10

20

LW -LW SW -SW Rnet LWnet SWnet

dLW -dLW dSW -dSW dRnet dLWnet dSWnet

Agoufou August average

(W.m

-2)

(W.m

-2)

2002

2003

2004

2005

Rnet ) ~ 20-35 W.m-2

for Rnet values~ 120 W.m-2

dominated by IR)

less IR flux from a surface that is cooler during wet years

weaker albedo in [2003 & 2005]/[2002 &2004] more that compensates SW decrease of [2003 & 2005]/[2002 &2004]

decrease of SW consistent with a more cloudy atmosphere during wet years

(deviation from the 4-year mean)

-40

-30

-20

-10

0

10

20

2004 ECMWF model

2005 ECMWF model

2004 data

2005 data

dLW -dLW dSW -dSW dRnet dLWnet dSWnet

(deviation from given cstes)

model ~ok for 2004, not for 2005because does too much the same for both years

Bamba 2004

2m-temperature (K) 2m-temperature (K) 2m-temperature (K)

2m-v

ater

vap

our

mix

ing

rati

o (g

/kg)

Agoufou 2004 Agoufou 2005

associated thermodynamics

significant afternoon decrease of water vapour mixing ratio for dry years would be broadly consistent with higher sensible heat fluxes 2004/2005 & simple convective boundary layer dynamics

satu

ratio

n

afternoon (13-16h LT)all points

August

JulyAugust

Bamba 2004 Agoufou 2004Agoufou 2005

diurnal cycle of e (equivalent potential temperature ~ moist enthalpy, with T& q)

no increase of e during daytime for dry years (flat cycle)because of large daytime drying (may further enhances evaporation of precip)

links with diurnal cycle of convection over land & convective indexes used for modelling, although nature of link not necessarily simplemagnitude of convective destabilisation from low levels, intensity of convection

e (

K)

precipitation at Bamba fct(hour of day)

Jul-Aug 5-day running mean

Bamba 2004 Agoufou 2004 Agoufou 2003

also larger time scale variability & nature of thetae (wetter versus drier)

2m-w

ater vapou

r mixin

g ratio (g/kg)

2m-t

emp

erat

ure

(°C

) e=350K e=350K e=350K

Agoufou July-August 2005, daily values

data ECMWF model

2m-w

ater vapou

r mixin

g ratio (g/kg)

2m-t

emp

erat

ure

(°C

)

worse for low e regimes, possible links with –missing- processes?

T-

qv-

T+

qv-

e=347Ke=347K

Plcl (mb)

LW

net (

W.m

-2)

LW

net (

W.m

-2)

JJAS 2005daily values

data

ECMWF model

summary, perspectives

useful dataset, clear signals in meteorological data

to my knowledge, not so numerous such datasets over the area

synthetic diagnostics for analysing & evaluating atmospheric models too (e.g. same vein as Betts) – some caution requiredECMWF: seasonal variations rather good, reasonable T & water vapour, but –for Eric- precipitation very wrong; likely other distinct stories for climate models.

manage to write down a description/characterisation of the site(s) as provided by these data

63 mm

185 mm Agoufou

2004

Bamba2004

Agoufou 2004

Bamba 2004albedo

albedo=0.4

albedo=0.4