Jan 31, 2000
A Kenya Airways Airbus A310 jet carrying 169 passengers and 10 crew members crashed into the sea Sunday night, shortly
after takeoff from Abidjan.
The flight originated in Nairobi and was meant to stop over in Lagos but flew directly to Abidjan
because of weather conditions over Lagos.
Harmattan winds coming down from the Sahara to the north had made skies over
Lagos unusually hazy on Sunday and the airport stopped incoming flights.
After a three-hour layover, the
Kenya Airways Flight 431 took off at 9:08 p.m. and crashed into the Atlantic Ocean off the Ivory Coast one minute later.
Authorities have declined to comment on whether the plane's engines could have been affected by dust
and sand.
The original reports are available by searching for `Kenya Airways' on most news browsers.
Summary:
Below we post our analysis of the weather conditions for the 28th of January through the 1st of February.
These include surface observations of current weather, satellite imagery, weather, and NAAPS aerosol modeling.
These reveal a pulse of dust generated by high surface winds in
the vicinity of Lake Chad, and then borne by the NE Harmattan wind
to the Gulf of Guinea (GOG).
The timing and strength of these events are controlled by the location of the surface high over N. Africa
which in turn is modulated by the passage of mid-latitude weather distrubances across the Mediterranean.
The satellite data show the streaks of dust being generated near Lake Chad, then transported SW.
The NOGAPS weather model shows high winds in the Lake Chad region.
The sunphotometer data show extremely high aerosol optical depths at Ilorin (near Lagos).
The NAAPS aerosol model shows the dust being mobilized and then transported to Nigeria and the GOG.
Most of the dust was below 4 km (13 kft).
The NAAPS aerosol model also shows that biomass burning in the Sudan may add to the haze, though the simulations
are based on a climatology of fires from 1993 which may not reflect the actual conditions on these days.
Additionally, the Harmattan event was preceded and followed by West African dust events.
Observations:
Sahel surface synoptic reports(plot legend)
show a dust outbreak leaving West Africa on 29th; haze and low visibility in Benin and Togo on 30th with similar observations at stations surrounding Nigeria (which does not report); and a dust outbreak over the entire Sudan and Sahel by 31st.
Meteosat, 1200GMT, January 28 - February 1, 2000
shows: 28th, light streaks oriented WSW-ENE over Chad/Niger border. Dust leaving W. Africa near Senegal;
29th, plume broadens and covers central and northern Nigeria, southern Niger, and still in Chad. Dust further off
W. African coast;
30th, dust over southern Nigeria, Bemin, and Togo. West African dust reaching 35 W;
31st, dust over the GOG and along coast;
1st, dust remains along coast. New outbreak appear off W. Africa.
Close-up of IR Meteosat, 1200GMT, January 28 - February 1, 2000.
Dust shows up in the infrared in daytime because the dust cloud is elevated and cooler than the hot ground.
These light streaks are seen in Lake Chad region on all days except 29th. The dust cloud is seen downwind of
Lake Chad on the 29th. It does not appear downwind on the 30th presumably
because the ground-dust temperature contrast
is less or because it is no longer optically thick.
OSEI
analysis of METEOSAT visible imagery for
February 3
and
February 4
shows heavy dust off West Africa and in the GOG.
Smoke may be involved, but the AERONET data (see next item) indicate dust predominates.
AERONET data from
Ilorin, Nigeria
show high background aerosol optical depth (AOD) values of 0.5 (smoke?) preceding dust event. AOD begins to increase on 29th, with
huge values (> 3.0) on 30th, then lower, yet still large values on the 31st.
The angstrom coefficient is low (0.4) indicating dust. The
Dubovik
retrieved size distributions
show the evolution of the aerosol before and during the passage of the dust cloud.
They show a large coarse mode, 3-5 um diameter.
24-hourly NAAPS Sahara Loop, January 28 - Feb 1
7nbsp; (plot legend)
Upper-left panel (smoke and dust optical depths) and lower-left panel (surface concentration
of dust) show
mobilization of dust over Chad and Niger due to high winds on January 28 and 29
and dust arriving over Nigeria on the 29th, with peak values on the day of the 30th.
Also seen is the dust leaving W. Africa on the 29th followed by another outbreak on the 31st and 1st.
Daily NAAPS GOG Loop for January 28 - Feb 1
showing approach of dust in the Haramattan. Upper left shows optical depths of smoke and dust.
Values are 1.5 to 2.5 over the GOG on 30th. Upper right shows dust originating inland and then
being transported SW towards gulf by the NE winds of the Harmattan.
