Regional Climate Modeling Simulations of the West African

Climate SystemGregory S. Jenkins, Amadou Gaye,

Bamba Sylla

LPASF AF20

Rational for Regional models

• Why use regional climate models for West Africa.– Orography (Guinea highlands, Jos Plateau)

– Lakes (Lake Chad)

– Coastline

– Important physical and meteorological Gradients (vegetation, precipitation, temperature).

– Mesoscale forcing for precipitation (easterly waves, squall lines, mesoscale convective complexes, non squall clusters).

Regional Climate Modeling Approach

1. Drive regional climate model with observations at lateral boundaries.

– Identify biases in regional climate model using present-day observations.

2. Drive regional climate model GCM data for present-day (1980-1984) at lateral boundaries.

– Identify and Compare biases to regional climate model driven by observations.

3. Drive regional climate model with GCM data for 2090-2094.

– Compare regional climate model changes to GCM 21st and 20th century result

Errors associated with regional climate models

• Parameterizations - convection, land-atmosphere, clouds)

• Biases (cold, warm, wet, dry)• Internal model variability (Eg. Does the model

represent easterly waves correctly).• Lateral Boundary conditions (GCM errors)• Climate sensitivity of regional climate model

( how much warming for 1 W/m2 of GHG forcing).

Questions associated with regional climate models

• Can we quantify the individual and collective errors in regional model simulations?

• Can we quantify the error associated with lateral boundary conditions?

• Can we address the added value associated with regional climate models?

Convection Parameterizations

Biases in Zonal winds from convective parameterization

Current Status

• 60 km Regional Climate model simulation for West Africa (25W-25E, 3N-27N).

• Driven at lateral boundaries by NCEP reanalysis.

• Phase I 1993-2002 (Done)

• Phase II. 1982-1993 (Running)

• Phase III. 1972-1982 (April, 2004)

Capacity Building and Regional climate Modeling

• 21 year simulation- download 54 Gigabytes from US.

• 1 Gigabyte download (6-18 hours).• 10 year RegCM simulation uses approximately 50

Gigabytes. • Need to invest infrastructures in Africa for long-

term research. Costs are not prohibitive currently. • Internet getting better.

RegCM/Observations comparison for Temperature

RegCM/Observation comparison for Temperature

Annual cycle of Temperature (Observed and RegCM)-1993-2000

R = 0.88R = 0.92

RegCM/Observation comparison for Precipitation (1993-2000)

RegCM/Observation comparison for Precipitation (1993-2000)

Annual cycle of Precipitation (Observed and RegCM)-1993-2000

R=0.976 R=0.956

NCEP/RegCM 700 hpa/200 hPa wind comparison

Dry(1997)/Wet (1999) Year comparison

Dry(2002)/Wet (1999) Year comparison

RegCM Spectral Signature of Easterly waves (V component)

RegCM Spectral Signature of Easterly waves (U component)

Preliminary Summary

• RegCM does a good job in simulating West African Climate– Precipitation (annual cycle captured) – Temperature (annual cycle captured but cold

bias in Guinea)– AEJ, TEJ captured– African Easterly waves (3-5 day and 6-9 day

AEWs captured).

RegCM data

• Saved every 6 hours surface fields, 12 hours meteorological fields.

• Available at diurnal, monthly timescales.

• Temperature (max, min, mean)

• Precipitation, evaporation, soil moisture, atmospheric moisture,

• Radiation - shortwave, longwave ,net, cloud fractions

• Dynamic field (u,v, SLP, geo-potential heights)

Plans

• Finish RegCM/NCEP simulations.

• Begin driving RegCM with CSM data.