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EPIC Stratocumulus Integrated Dataset |
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Download the Dataset Go to EPIC Sc Overview Examine Bibliography Examine the Fields |
This page explains and provides access to a set of observational data compiled from 6 days (Oct. 16th-22nd) of the EPIC 2001 stratocumulus field campaign. During this time, the NOAA vessel Ronald H. Brown (RHB) was stationed at 20° S, 85° W, where it served as a platform for 3-hrly radiosonde launches and as a host for a wide array of other meteorological instruments. More information about the stratocumulus segment of the EPIC campaign is available from the link on the left. The dataset presented in this page was compiled from a combination of measurements made aboard the Brown during this time, concomitant output from European Center for Medium-Range Weather Forecasting (ECMWF) and National Center for Environmental Prediction (NCEP) forecast models, data derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite, and idealized tropical profiles from McClatchey et al., 1971 (references available at link on left). The purpose of this data set is to provide modelers with easy access to the EPIC data in order to encourage its use. As such, variables with missing data are provided in two formats: "raw" (with missing values left in) and "filled" (with interpolation used to fill in holes). The "raw" data is best for comparing with model output, while "filled" data is necessary as model input. The data may be downloaded in netcdf format from the link on the left. In addition to the data, this file contains a .source field for each variable which explains how the variable was computed from the observations and, where applicable, a .warning field which points out potentially uncertain data. For convenience, this information is repeated below, along with a plot of each variable. |
Fraction of each 3hrly period in which the
ceilometer
returned a cloud base.
Derived from temperature and humidity measurements taken
on the RHB instrumented tower (10m altitude) using the bulk flux
algorithm described in Fairall et al. 1996.
Computed similarly to SHF.
From the RHB 10m instrumented tower.
Given in degrees from North (increasing
clockwise). Computed similarly to surfwind.
Subsidence rate at the 850mb model level from
ECMWF and
NCEP analyses. The ECMWF data is probably better.
Entrainment rate from ECMWF mass budget as derived in
Caldwell et al. 2005. The uncertainty in this measurement at any
one time is quite large; w_e should only be used an an averaged sense.
Low level temperature advection, an output
field from
ECMWF and NCEP analyses. Note that the NCEP data was only
available at 12hr resolution and is linearly interpolated to 3hrly
(so ECMWF is probably better). Note that this data is signed so
positive values COOL the BL.
Similar to Tadvect, but for specific humidity. Note
that positive values mean that advection is DRYING the BL.
LWP was diagnosed from microwave radiometer following the
procedure of Hogg et al. 1983. (Corrected 7/27/05)
Nighttime values are extrapolated from
daytime values,
which are derived following Dong and Mace 2003 using simultaneous
measurement of cloud thickness, LWP, and optical depth. 
From shipboard radiometer.
From shipboard radiometer.
Surface skin temperature (at 0.5m depth) from RHB.
Surface pressure calculated by linearly
extrapolating 10
and 20mb pressures downward. Due to discord between pressure-measuring
devices and uncertainty in the height at which pressures were measured,
there could be a mean bias of up to ~2mb in this field.
Ozone mixing ratio from McClatchey sounding. Note that
this variable is included solely to provide a complete set of model
inputs - no ozone measurements were taken during EPIC.
This is the height coordinate to which all of the 2D
datasets below have been interpolated to. It has 1mb resolution
and a lowest level of 1020mb. Soundings with surface pressure
lower than 1020mb are accommodated by setting below-surface levels to
NaN.
The data is gridded to 1mb resolution, so height
(altitude) varies slightly with time. The lowest altitude could
be off by ~6m, an effect that would make all heights in the profile 6m
lower than stated here (although the given heights are probably only
accurate to ~10m anyways).
As in hts, but missing values at altitudes
less than 15km
are filled in by interpolating neighboring profiles. If a missing
value doesn't have both a left and a right neighbor, it is copied from
the neighbor it does have. Above 15km, pressure levels are taken
from the McClatchey tropical sounding (McClatchey et al. 1972).
Temperature profiles from radiosonde ascents. Note
that data in the 300m above cloudtop seems to be corrupted. See
Caldwell et al. 2005 for a discussion of this point.
Temp profiles filled using the same process
described for
hts_fill.
Zonal wind component from the radiosondes.
radiosonde-measured u_wind filled by
interpolation of
neighboring profiles to fill missing values. McClatchey data is NOT
used in this case because none exists for winds. Because of this,
data at altitudes above 300mb are based on very few soundings and
should be used with caution.
Meridional wind component from the
radiosondes.
Meridional wind filled in the same manner as
u_fill.
water vapor mixing ratio profiles from radiosonde.
The problem above cloudtop mentioned in the Temp description does NOT
apply to this field.
Qv profiles filled using the same process
described in
hts_fill.
Qt_fill is Qv_fill plus a liquid water mixing
ratio (Ql)
profile calculated by assuming Ql increases linearly from 0 at z_b to
the value at z_i that makes the integral of density times ql over the
BL equal to the LWP.
Synthesized from MMCR, C-band, and
sedimentation/evaporation model results. See Comstock et al. 2005
for details. Note that this quantity is quite uncertain. In this
field, in-cloud precipitation is taken to be the cloud-base value as
discussed in Caldwell et al. 2005.