NSF C-130 Mission Summary Report (EPIC)

RF16 - C-130 SST Front Stacks

Mission Summary - This flight represented the second of two SST front stack
missions.  The weather of the area included a more active ITCZ than during
the previous SST front mission of 3 October.  It also featured a large clear
area south of the equator (more about this below).  The operating region on this
flight was entirely south of 3.5 N, and except for descent and ascent soundings,
limited to the region of the ABL and immediately above.  The ABL over the 
SST front and cold tongue (as on the flight of 3 October) featured relatively
brisk southerlies over and on the north side of the SST front.  An important
difference was that the SST front was south of its position on 3 October
(e.g., the SST at 0.6 N was 23.8 on 10/5 and 21.3 on 10/3).  This seems
to have had a significant effect on the ABL winds; relative to 3 October, the
ABL southerlies were weaker (stronger) at 2 N (0.5 N).  In general, the 
ABL southerlies during the two days seem to have been responding to the
meridional gradient in SST.  A successful 4-level (100', 1200', 3000' and
3500') stack was carried out north of the SST front at 2 N.  An abrupt
edge to the ABL clouds was encountered at the equator during the southbound
porpoising to the southern stack.  Because of the lack of clouds along
0.5 S in the vicinity of 95 W, we executed this stack relative to the
low-level wind max (155 @ 15 m/s at the 530 m level), choosing the levels
of 100', 300', 800', 1500' and 2400'.  The latter level was in a region of
considerable vertical wind shear above the wind max, but also large static
stability in association with the TWI.  There were virtually no clouds above
the ABL during any portion of the low-level work.  The ABL over the cold
tongue was about 0.5-1 g/kg drier on 5 than on 3 October and presumably
this accounts for the lack of ABL clouds.  Fifteen BT's were deployed, of
which eleven were successful.
  
Flight Notes -

1451	Take Off
1537	Lat 12.6, Flight-level winds 107 @ 14 m/s, ABL rolls below,
	Cb's in the distance south
1618	Lat 9.5, wind 100 @ 11 m/s
1640	Lat 7.6, passed east of a large, mature Cb
1703	Lat 6.0, As deck at 2.0 km, looks to be another layer of BL Sc
	between 700 and 1200 m, CLR above, flight-level winds 90 @ 9 m/s
1728	Lat 3.9, start descent
1737	Lat 3.2, cloud tops/bases at 1100-1150/400-450 m
1741	Lat 3.0, 100', SST 27.3, TA 25.0, light chop, whitecaps, wind
	180 @ 11 m/s, thetae 340, q 15, BL Sc (400-750 m based on SABL)
1747	Begin ascent, cloud base 420-450 m
1748	Lat 2.7, BT (good)
1749	Cloud top 930 m
1752	Lat 2.5, BT (good)
1753	Lat 2.4, 5000', wind 106 @ 1 m/s, thetae 344, q 12, uniform tops
1755	Lat 2.2, begin descent, BT (good), tops 950 m, bases 550 m
1800	Lat 2.0, start of 100' E-W leg, SST 25.9, TA 24.0, wind 180 @ 9,
	thetae 335, q 14, light chop, some whitecaps
1807	Start ascent to 1200'
1808	Start of 1200' leg, wind 160 @ 9-10 m/s, a bit less turb. than
	on 100' leg, just below cloud base, fairly uniform OVC
1815	Briefly in cloud
1816	End of 1200' leg and start of climb
1817	Start of 3000' (cloud top) leg, almost always in cloud, wind
	170 @ 8 m/s
1820	Lon -95.28, BT (good)
1822	Went out of cloud and descended to 2800'
1824	Start of ascent for 3500' run (about 500' above clouds)
1826	Lat 2.0, Lon -95.48, BT (bad)
1827	Lat 2.0, 3500', wind 55 @ 3 m/s, near top of inversion and
	main layer of wind shear on top of ABL southerlies
1833	Lon -95.08, start descent, BT (good), cloud tops/bases 920/450 m
1837	Lat 1.8, 100', SST 25.7, TA 23.8, wind 175 @ 9-10, thetae 335,
	q 14, some whitecaps and swell
1843	Lat 1.4, begin ascent
1844	Lat 1.4, BT (bad), bases/tops 450/1000 m, quasi-uniform undercast
1848	Lat 1.2, start of 4500', BT (good), wind 130 @ 5, thetae 342, q 12
	CLR above
1853	Lat 0.9, start descent, BT (good), tops/bases 970/440 m
1858	Lat 0.6, start of 100', SST 23.8, TA 22.3, wind 150 @ 12, whitecaps
	and swell, some bases at 400 m and some at 500-600 from SABL, tops
	lowering, lightening of the OVC
1901	Some small breaks in OVC
1903	Lat 0.3, start ascent to 4000', SST still 23.1, bases/tops 430/670 m
1905	Lat 0.3, BT (good to 150 m), more structure to clouds
1908	Lat 0.04, BT (bad), edge of undercast approaching, wind 160 @ 4
1912	Lat -0.2, start of descent, BT (good), only widely SCT ABL Sc below
	wind max at 530 m (155 @ 15 m/s)
1917	Lat -0.5, start of 100' E-W leg, SST 17.8, TA 20.0, thetae 326
	q 12, minor whitecaps, light chop, wind 145 @ 7
1925	Start of ascent for 2nd (800') leg which is midway up to speed max
1927	Level at 800', wind 150 @ 10 m/s, thetae 327, q 10
1933	A few clouds to the east
1935	Added a westbound leg at 300', wind 140 @ 7 m/s
1939	Possibly a few wisps of cloud floated by
1943	Start of ascent for 1500' (just below speed max)
1944	Start of 1500', hazy, wind 145 @ 13 m/s
1945	Lat -0.48, Lon -94.9, BT (good)
1954	Lat -0.49, Lon -95.2, BT (good), 2400', in inversion layer, and
	windshear above speed max., no turbulence, wind 152 @ 8, some 
	clouds to the south
1957	Lon -94.9, BT (bad)
2001	Begin ascent for ferry to HUX, Lat -0.4, clouds forming underneath
2140	Vigorous Cb's near 7.5 N
2240	Lat 11.7, flight-level wind 65 @ 8 m/s
2321	Lat 14.9, begin descent
2342	Landing