Horizontal Variability In Microphysical Properties of MixedPhase Arctic Clouds

1
Horizontal Variability In Microphysical
Properties of Mixed-Phase Arctic Clouds David
Brown, Michael Poellot University of North
Dakota
HYSPLIT Trajectory Analysis
Clouds are strong modulators of the radiative
budget in the Arctic. Their influence depends in
part on microphysical properties such as particle
size, liquid water path and particle phase. A
good knowledge of the spatial and temporal
variability of these properties is necessary for
accurate model parameterizations. Data from the
2004 Mixed-Phase Arctic Cloud Experiment (M-PACE)
have been analyzed to provide a quantitative
estimate of the horizontal scale of the
variability in microphysical cloud properties
within individual cloud fields. A trajectory
analysis has also been performed to relate air
parcel trajectories to changes in horizontal
variability of cloud properties from day to day
during the experiment.
Horizontal Scale Analysis

• Methodology
• Fourier analysis of in-situ cloud microphysical
  data
• Determine scales of greatest variability
• Challenges
• Level leg samples not long enough to resolve
  large scales
• Must use time series of ramped ascents and
  descents, contain intervals of no cloud data
• Calculate autocovariance function of time series
  and use to derive power spectrum (Jenkins and
  Watts 1968)
• Can only perform analysis on parameters that do
  not vary with height (number concentration)
• Sampling Profiles

• Trajectory analysis using NOAA HYSPLIT model
  performed for flight cases during second synoptic
  regime of M-PACE (Draxler and Hess 1998)
• Regime consisted of building high pressure over
  ice pack northeast of Alaska coast (Verlinde, et
  al. 2007)
• Associated northeast flow with considerable fetch
  along Arctic Ocean
• Oct. 4 8 scattered, thin, multi-layer clouds,
  Oct. 9 15 single layer stratus
• Observations show less liquid water, more ice in
  Oct. 4 8 clouds
• Figures 7 and 8 shows significant variation in
  spatial structure of cloud properties during
  regime
• HYSPLIT analysis shown in fig. (6) shows
  significant differences in trajectories on Oct. 6
  and 9
• Oct. 6 Trajectories paths mostly over land,
  synoptic scale upward motion
• Oct. 9 Trajectories paths over ocean, synoptic
  scale subsidence
• Differences in trajectories may influence
  parameters that affect spatial structure of cloud
  properties

• Assumptions
• Constant true airspeed of 80 m s-1
• Variability is in horizontal direction
• Vertical displacement is negligible relative to
  horizontal
• Data
• October 9, 2004
• FSSP Total Droplet Concentration
• Time series of ramped ascents and descents
• 76096 78542 s.f.m. UTC
• 2447 s, 195.76 km
• Results