INDOEX C-130: FLIGHT 3, 20 February 1999 Objectives: Gradient Flight: Indirect Effect study Outbound Flight: Microphysics and aerosol sampling run. Report filed by V. Ramanathan & B. Gandrud Flew from Male due south to 7S on the outbound flight with some profiling of the boundary layer, in-cloud and just-above-cloud flights. The southern portion, between 5 S to 7 S, we saw very pristine air subject to the southern trades. Inbound Flight: Flew from 7 S to 5.9 N with 4 stacked flights between 4.11 N and 5.89 N, with fly-by over KCO. Between 7S to 2N, the inbound flight was dedicated to radiation flight at 22000 feet and between 2N to 5.89 N to in-cloud studies. We saw roughly 3 regimes: 5.8 N to 1 S can be classified as the polluted regime subject to NH air; 1 S to 4 S was the transition regime with air varying between NH and SH air; South of 5 S was very clean air. 07:40 am (local time) takeoff UTC 02:45 Ascend to 4400 ft to fly through the middle of low clouds (mix of trade cus and stratus) 03:10 Were seeing two cloud decks; dropped to the middle of lower deck at about 2800 ft; were seeing lots of haze between the clouds 03:22 Descended to about 1800 ft to stay in the middle of the low clouds. 03:32 2N. Mainly single-level cloud deck. Descended to 600 ft for boundary layer sampling. 03:42 Back to mid-cloud altitude of 2000 ft. still in strat cu regime. 04:00 Reached equator. Climbed to cloud top altitude of about 5000 ft and headed north to sample the same air that we sampled before. Maintained this till 0.55N 04:12 Descended to 500 ft at 0.55N to sample boundary layer at 500 ft until equator. 04:24 Crossed equator; climbed to mid-cloud altitude of about 2200 ft. 04:28 Beginning to see classical start cu and trade cu systems ahead of us. 04:33 0.55S. We are still in polluted air 04:45 1S. Beginning to see the pollution indices (ozone; scattering coefft) dropping off 04:54 1.75S. Seeing rapid fluctuations in the pollution indices. In the ITCZ regime. 05:05 4.05S. Descended to 500 feet to sample the boundary layer 05:22 3S. Still seeing polluted clouds (haze mixed up with strat cu systems). Made the decision to head to 7S 05:45 4.8S. The sky is becoming clearer(less dirty and hazy). Ascended to mid cloud level of about 1800ft 05:50 5S. There was no doubt we were seeing pristine air (Ozone dropped to less than 1ppb; scattering coefft dropped by a factor of 30 from the values we saw north of 2N. 06:22 Turned around to head north and also climb to cloud top altitude of 4700 ft 06:26 Finish cloud top run and started to climb to cruising altitude of 22000 ft. 06:43 We were at cruising altitude and at 6S. Decided to fly back to 7S to do the radiation flight from 7S 06:55 Reached 7S. Started drop sonde at 7S. We were seeing only low clouds with very little cirrus activity. Flew at this level for 1 hour, seeing mainly low clouds 07:50 3S. Another drop sonde from 22000 ft 07:55 2S. Started to see patchy cirrus/stratus. 08:07 Had to drop to 21000 ft due to ATC instructions. 08:28 1.3S. cirrus amount and thickness increasing. 08:55 2N. Decided to abandon radiation flight since cirrus amount increased further. Descended to mid-cloud level to sample the same clouds again. 09:06 3.1N. Reached mid-cloud level of 3600 ft. 09:20 4.1N at Male. Still at mid-cloud level. Decided to make 4 stacked flights of 100 miles long, between Male and 5.89N thru KCO. Seeing two cloud decks again. One at around 3600 ft and another above us. 09:40 4.9N. Fly-by KCO. Encountered low clouds all the 09:55 5.89N. Climbed to near cloud top altitude. Cloud tops were not well defined. So, decided to maintain 5800 ft. 10:28 4.2N. Turned around to fly northwards and descended to 590 feet for bl sampling. 10:39 Fly-by KCO 10:58 5.89N. turned around and ascended to 2600 feet to sample the air just above the cloud base all the way home. 11:28 Landed in Hulule after an enjoyable and exciting mission.