GRIP Cloud Microphysics
Table of Contents
Note: The combined CIP+PIP particle size distributions from the GRIP
field campaign were updated on 9/12/2012. These updates include improved
artifact rejection, improved particle sizing, and a correction
for saturation errors on the CIP. The CIP saturation errors
occurred primarily in heavy clouds containing at least 0.3 g/m3
of condensed water content.
The corrected particle concentrations for the CIP may be up to
several times higher than previously reported in the heaviest
cloud conditions.
Derived parameters have been updated accordingly. The PIP, which
measures particles larger than 1mm in diameter, was not affected.
Introduction
The GRIP Cloud Microphysics data set consists of in-situ cloud microphysics data collected from three instruments mounted on the NASA DC-8 aircraft:
- The Cloud, Aerosol, and Precipitation Spectrometer (CAPS) is a combination of two probes: the Cloud Imaging Probe-Greyscale (CIP-G), used for two-dimensional images and size distributions nominally between 25 and 1550 µm, and the Cloud and Aerosol Spectrometer (CAS), which uses forward-scatter and back-scatter techniques to measure particle size distributions between 0.35 and 50 µm.
- The Precipitation Imaging Probe (PIP) is an optical spectrometer which measures the size and shape of particles from 100µm to 6200µm.
- The Cloud Droplet Probe (CDP) is a cloud particle spectrometer which measures droplets in the range of 2-50 µm.
This data set includes the combined particle size distributions and a small sample of images from each probe. Additional information about the data set may be found in the PI readme grip_microphysics_readme.txt.
Campaign
The Genesis and Rapid Intensification Processes (GRIP) experiment was a NASA Earth science field experiment conducted August 5 to September 30, 2010. The major goal was to better understand how tropical storms form and develop into major hurricanes. NASA used the DC-8 aircraft, the WB-57 aircraft and the Global Hawk Unmanned Airborne System (UAS), configured with a suite of in situ and remote sensing instruments that were used to observe and characterize the lifecycle of hurricanes. This campaign also capitalized on a number of ground networks and space-based assets, in addition to the instruments deployed on aircraft from Ft. Lauderdale, Florida ( DC-8), Houston, Texas (WB-57), and NASA Dryden Flight Research Center, California (Global Hawk). More information about this Campaign can be found on the GRIP web site: http://grip.nsstc.nasa.gov/
Instrument Description
Cloud, Aerosol, and Precipitation Spectrometer (CAPS):
This multipurpose particle spectrometer has three instruments packaged into a single integrated measurement system that provides aerosol particle and cloud hydrometeor size distributions from 0.35 to 50 µm, particle shape (discrimination between water and ice), particle optical properties (refractive index), precipitation size distributions from 25 µm to 1550 µm, liquid water content from 0.01 to 3 gm-3 and aircraft velocity and atmospheric temperature and pressure. This instrument replaces PMS Inc.'s FSSP-100, FSSP-300, 2D-C, 2D-P and KLWC.
The CAPS has two optical sensors to derive the size of individual particles: the Cloud Imaging Probe-Greyscale (CIP-G) and the Cloud and Aerosol Spectrometer (CAS).
Cloud Imaging Probe-Greyscale (CIP-G):
This optical spectrometer measures the size and shape of particles passing through its collimated laser beam, from 25µm to 1550 µm, liquid water content from 0.01 to 3 gm-3 and airspeed to 200 ms-1. It uses a fast 64-element photodiode array to generate 2-Dimensional Images of the particles,as well as sizing in 1-Dimensional Histogram form. Included in this instrument package are temperature, pressure and relative humidity sensors. The CIP Greyscale has the functionality of CIP with enhanced particle imaging.
Cloud and Aerosol Spectrometer (CAS):
The CAS collects the light scattered in the forward direction (4-12 °) by particles passing through a focused laser beam and converts the light intensity to a particle diameter between 0.35 and 50 mm using Mie light scattering theory. The CAS also measures backscattered light (168-176 °) in order to derive particle refractive index (Baumgardner et al., 1996) and shape factors (Baumgardner et al., 2004). Three pieces of information are recorded by the CAS about each particle: 1) the forward scattered light intensity, 2) backward scattered light intensity, and 3) the time between each particle. The particle by particle information is used to derive size distributions, particle refractive index and shapes, and concentration fluctuations at scales of a meter or less.
Precipitation Imaging Probe (PIP):
This optical spectrometer measures the size and shape of particles from 100µm to 6200µm. It is the classic airborne 2-Dimensional imaging probe, with the expanded capability of the 64-element diode array and fast Digital Signal Processing electronics. The probe resolution is 100µm with a particle sizing range of 6.2mm. The sample area is 26cm x 6.2mm and the maximum airspeed is 200m/s.
Cloud Droplet Probe (CDP):
This miniature, lightweight, low-power cloud particle spectrometer measures droplets in the range of 2-50 µm in concentrations as high as 2000 particles/cm3. Particle-size and concentration is provided in histogram form with 20, 30 or 40-bin resolution. The concentration range is 0-5000 particles/cm-3, sample area is .24 mm-2, airspeed range is 10-200m/s and maximum altitude is 50,000 feet.
These probes are manufactured by Droplet Measurement Technologies, and additional information can be found here: http://www.dropletmeasurement.com/
File Naming Convention
The data and browse files are of the form:
data:
GRIP_MP_yyyymmdd_CAS.txt
GRIP_MP_yyyymmdd_CDP.txt
GRIP_MP_yyyymmdd_CIPPIP.txt
browse:
GRIP_MP_yyyymmdd_CIPPIP_images.tar
where:
yyyymmdd = year, month and day
MP = microphysics
CAS = Cloud and Aerosol Spectrometer
CDP = Cloud Droplet Probe
CIPPIP = Cloud Imaging Probe / Precipitation Imaging Probe
tar = Tape ARchive
Data Format
These data files are in ASCII, tab delimited, format. An example of the data format from the CAS and the CDP probes are shown below. The concentrations are binned, and not all are shown in these examples.
CAS:
Time Nt(#/m3) LWC(g/m3) Concentration(m^-4)
--------------------------------------------------------------------------------
50595 1.07e+08 1.62e-04 3.57e+14 1.69e+14 1.37e+14 1.39e+14 1.51e+14 .........
CDP:
Time Nt(#/m3) LWC(g/m3) Concentration(m^-4)
--------------------------------------------------------------------------------
50595 5.56e+05 7.85e-06 5.56e+11 0.00e+00 0.00e+00 0.00e+00 0.00e+00 .........
Column headers are described as follows:
TIME - Elapsed UTC seconds from 0 hours on day of flight
Nt(#/m3) - Total concentration
LWC(g/m3) - Liquid water content
Concentration(m^-4) - Particle number concentration normalized by bin width
Additional information on file content and structure can be found in each file header.
References
Baumgardner D., H. Jonsson, W. Dawson, D. O'Connor, and R. Newton, 2001:
The cloud, aerosol and precipitation spectrometer: A new instrument for
cloud investigations. Atmos. Res., 59-60, 251–264.
Contact Information
The data provider is:
Andrew Heymsfield
NCAR
P.O. Box 3000
Boulder, CO 80307-3000
heyms1@ucar.ncar.edu
To order these data or for further information, please contact:
Global Hydrology Resource Center
User Services
320 Sparkman Drive
Huntsville, AL 35805
Phone: 256-961-7932
E-mail: support-ghrc@earthdata.nasa.gov
Web: http://ghrc.nsstc.nasa.gov/
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