INDOEX C-130: FLIGHT 4, 24 February 1999 Objective: Gradient Flight Report filed by V. Ramanathan Summary The goal of this flight is to document indirect effect of aerosols. The outbound flight was due south of Male to about 5.6S and then headed westwards to 71.86E; then a North-South flight track between 4.5S and 6S. This part of the flight was done at cloud level and at the boundary layer, to sample variations in aerosols, CCN and cloud drop size and concentration. On the inbound flight, we ascended from 2000 ft at 6S to 20000 ft at 7S, flew eastwards to 73.15E (due south of Male) and headed northwards making radiometric measurements all the way. When we reached 4N, we headed south and descended to cloud level at about 2.5N and flew home at mid-cloud level. Encountered mixed cumulus, trade cumulus and stratocumulus. The clouds between 4N and about 1S were surrounded by a haze layer. We hit really pristine air south of about 4.5S and collected data on both polluted and pristine air. 07:38 am (local time) takeoff UTC 02:38 Take off- seeing strat-cu 02:45 Ascend to mid-cloud altitude of low level cloud 02:47 Strat-cu system - very sparse -- 1800ft high 02:55 Not seeing enough strat-cu 03:00 Descending to 100 ft for next 20 minutes - (2.8N) to boundary-layer flight 03:05 Altitude at 100 ft 03:10 Realized that we are going westward 03:10 Asked him to maintain 73.15E from now onwards starting to see more strat-cu systems 03:15 2N still at 100 ft. 03:20 1.89N. Beginning to see low-level clouds 03:22 Climbing to cloud base 1.7N 03:25 1.5N, reached cloud base at 1670 ft. Very hazy (Starting to see more clouds) 03:30 Ascending to mid-cloud level at 1.2N 03:34 0.1N. Reached mid-cloud altitude, level at 2340 ft 03:41 0.6N. Aerosol indices are dropping 03:45 0.35N. Seeing a bit more strat-cu. Aerosol indices are still dropping 03:52 Around equatorial region, in Southern Hemisphere flying still at 2370 ft. 03:53 0.6S. Seeing more of thicker clouds, cu. Starting to see some anvils from low-level cumulus clouds 03:55 Climbing to about 2900 ft to catch mid-level deeper cumulus clouds 03:57 Reached 3700 ft 04:00 Beginning to see deeper systems; westerly winds 04:09 Flying at 3600 ft; westerly winds 04:10 Very convective--deeper systems, altitude 3700 ft cloud top may be 4-5 km reaching mid-level systems 04:20 Clearing up. Seeing lower level deck descending to 1800 ft 04:22 1.9S. Climbing down to 2250 ft. Short cus 04:27 2S. Scattered strat-cus, still the winds from the west, haze layer 04:30 2.45S. Descended to boundary layer 100 ft to boundery layer flight 04:35 2.6S. Reached BL altitude; westerly winds 04:45 3.281S. Flight altitude is 130 ft 05:00 Cloud altitude at 3 to 4S, 2500 ft. Seeing patchy clouds 05:10 4.6S, 2500 ft. Seeing more cleaner clouds; no haze 05:19 4.984S. Seeing upper-level altostratus (advancing convection); clouds are really pristine. 05:26 5.4S. Very clean sky 05:32 5.6S. Descending to 100 ft--heading westwards 05:36 At 100 ft heading westwards. Sampling boundary layer ssa -- 1.1 x 10-6 m-1, sabs = 0.0, CN Ratio = 0.2 05:45 73E, 5.6S at 120 ft strat-cu, some cu 06:00 At 72E, we decided to do north-south tracks of 150 km; heading south at boundary layer (6S). 06:05 6.20S (heading southward). Profiling thru low level strat-cu systems 06:07 Turning north 6.4S 06:15 6.2S. Reached mid-cloud attitude at 4500ft, classical strato-cu systems Practically no cirrus clouds. From 6.4S going north to 4.75S then going south again to 6.4S, profiling at 4500 ft 06:25 At 5.584S. North easterly; multiple decks; decided to drop to the lower deck at 3500 ft 06:30 Heading westwards from 5.2S (seeing very thick system) 06:50 Decided to turn back southwards to follow a low cloud system 5.4S, 71.6E at 3500 ft (heading southwestwards) seeing big convective systems 06:54 Sampling clouds for 5 minutes 06:57 Starting descent to 2300 ft and climb to 20000 ft but heading south 07:14 6.7S, 14500 ft. No Cirrus. Winds still westerly 07:18 7S, 11000 ft to 18000 ft. Strato-cu below, thin cirrus above at 7.2S 07:25 Heading eastwards at 7.36S, 70.9E. Seeing strat-cu below Dropped sonde. 7.4S. Partly cirrus overhead; strat-cu below 07:33 Strat with trade cu below. Some patchy cu and stratus 07:45 7.4S, 72.55E. Dropped sondes (2) 07:55 Heading north. Thick cirrus overhead 08:10 6.15S, 20000 ft 08:30 In cloud at 4.00S, mid-level clouds, trade cus below; other deeper systems reaching flight altitude 08:35 Dropped sonde (4S). No cirrus! 08:47 3.4S, 73.2E. Still multi-layered systems CN = 471. Plenty of strat-cu below but masked by the thicker systems 08:50 3.00S. Deep convective system, plane went through this 08:55 Dropped sonde at 3.00S. Still mixed trade-cu and cumulus; almost clear sky above 09:10 1.75S, 73.24E, 20105 ft. Still lots of upper level systems; no clouds below 09:25 0.54S, 73.25E. No clouds below 09:27 0.29S, 73.25E. AVHRR maneuver started; strat-cus; some deeper system ahead of us; very dry 09:30 Flying under neat anvil!!! around 20000 ft 09:31 0.SN. Dropped sonde; MUCH MUCH cleaner clouds! 09:39 AVHRR maneuver completed 09:50 1.4N, 73.23E. Low-level mixed cloud systems: St-cu, trade-cu, etc. No cirrus. 10:00 Dropped sonde at 2N, 73.32E; clouds are few and far in between! 10:13 Dropped sonde at 3N, 73.4E; broken trade-cu and st-cu at 800m or 2500 ft. Some convective activities; southwesterly winds 10:30 3.8N. Heading south, doing the MCR maneuver; haze layer below 20000 ft. doesn't seem to go above 14000 ft 10:40 3.95N, 73.48E. Haze and clouds below; starting descent and heading southwards 10:47 3.5N, 73.50E, 14000 ft. Large layer is still below us (sky is very hazy) 11:03 Reached 2237 ft. Turned around heading home to Male at cloud level of 2232 ft. 11:18 2.9N, 73.396E. Still flying through strat-cu and haze ss = 36, sa =2.6 x 10-6 11:23 3.285N, 73.4E. Still seeing dirty strat-cus 11:30 3.645N, 73.42E. sa = 5 - 3; first time ssc = 48 11:38 Landed