Drizzle and Open Cells in Marine
Stratocumulus – DOCIMS
Don Lenschow and Bjorn Stevens, Co-Investigators
• Study the relationship between pockets of open cells (POCs) and drizzle
• Does drizzle help maintain an open-cell structure in MS?
• Is drizzle associated with the presence of elevated moist layers?
Objectives:
• Study the thermodynamic and dynamic structure of an opencell MS region
• Compare with an adjacent uniform MS region
• Use observations as basis for LES of MS
Pockets of Cells (POCs): Are they caused
by drizzle? (Stevens et al., BAMS, 2004)
Zoomed image from
photo at right with flight
segment overlaid.
Channel 1 GOES-10
reflectance at 0730 LT
11 Jul 02.
Time-height radar reflectivities from RF-02
DYCOMS C-130 flight.
White line is SABL lidar
estimate of cloud top.
Vertical structure of the boundary layer
Stevens et al., BAMS, 84 (2003)
Airplane soundings from DYCOMS-II, RF01. The red circles are from eight 30 min
circles in the PBL and two above the PBL. From right to left: Total water mixing ratio;
liquid water potential temperature; and liquid water mixing ratio. Gray shaded area is
the cloud layer; zi is PBL depth; and h is cloud thickness.
DOCIMS: RF04, circle #1
DOCIMS: RF04, circle #2
DOCIMS: RF04, circle #3
DOCIMS: RF04, circle #4
DOCIMS: RF04, circle #5
Latitude - degrees
Longitude - degrees
top panel – true heading (o)
middle panel – pressure altitude (m)
bottom panel – GPS altitude (m)
middle - bottom ∝ pressure grad.
wind direction - o
wind speed – m/s
1 P
Vg 
 f r
  air density
f  Coriolis parameter
u,v,w Spectra – m3 s2
u
v
Spectra of u,v,w for
Circle # 4
u
the first circle
ondrizzling
RF04.
cellular,
Circle # 1
thin stratus,
no drizzle
stratocumulus
v
w
w
Wave number – rad m-1
Wave number – rad m-1
Spectra of T and mixing ratio (mr)
Circle #1
no drizzle,
thin stratus
mr
T
Circle #4
cellular, drizzling
stratocumulus
mr
T
DOCIMS: RF13, circle #1
DOCIMS: RF13, circle #2
DOCIMS: RF13, circle #3
DOCIMS: RF13, circle #4
What did we learn -- operationally?
•
•
•
Quick deployment to remote locations not
a problem for the G-V
Getting permission without advance
planning to operate at low levels offshore
can be a problem
the G-V can operate without difficulty at
100 m altitude over the ocean at an
airspeed of 110 m s-1
What did we learn -- scientifically?
•
•
•
Satisfactory conditions for this study do
occur in December
A circular flight pattern is useful for
estimating pressure gradient
Comparisons between thin stratus and
cellular stratus regions show differences in
both velocity and scalar spectra