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Disdrometer Data from KWAJEX

 

Disdrometer Data Disdrometer Document


(The following information is based on the documents prepared by TRMM scientists Dr. Ali Tokay and Dave Wolff)

Disdrometers

During KWAJEX, three Joss-Waldvogel disdrometers, two 2-dimensional video disdrometers, and 10 APL disdrometers were operated in the vicinity of the S-Band radar.

The Joss-Waldvogel disdrometers were located on Kwajalein, Meck, and Legan Islands. The unit on Kwajalein was operated by the University of Washington and is not included in this prliminary data set. The NASA TRMM Office operated the unit on Meck from August 17 to September 9, 1999. For the preliminary analysis five priority cases are selected based on the duration and intensity of the rain event, such that longer events with intense rainfall are preferred.

The five priority cases chosen for Meck were August 19, 20, 29, and September 2, 3. The NOAA Aeronomy Laboratory operated the unit on Legan from July 2 to September 15, 1999. The five priority cases chosen for Legan were the same as for Meck except that the August 29 case was replaced by the August 11 case.

The University of Iowa and NASA 2-D video disdrometers were located on Legan and Kwajalein, respectively. The University of Iowa data set is not included in this analysis. The NASA TRMM Office operated the unit on Kwajalein during the period between August 22 and September 14, 1999; however, data were not collected contiguously during that time. The five priority cases chosen for Kwajalein were September 8, 10, 11 (2 cases), and 14.

APL disdrometers were located on Kwajalein, Meck, Legan, Roi-Namur, NOAA Ron-Brown research vessel (2 units), Woja, Lae, and on the west and east buoys. The preliminary analysis of the APL disdrometers on Meck and Legan showed substantial biases with collocated Joss-Waldvogel disdrometer and rain gauges. In addition, the APL disdrometers failed to produce an expected drop size during post-calibration experiments in laboratory conditions at NASA Wallops Flight Facility. Therefore, no APL disdrometer data is included in this analysis.

Data Set

The tables giving the summary of KWAJEX disdrometers measurements for the overall experiment, as well as for specific priority cases are provided.

The following rain event characteristics are included in the project summary tables:

  • Julian Day - day of the year
  • Start and End Time (UTC)< - beginning and ending time of each rain event [hh:mm]
    [The criterion for a "rain event" here is at least one rainy minute per 15 consecutive minutes.]
  • Number of Rainy Minutes - number of minutes containing at least 10 drops and a minimum rain rate of 0.1mm h-1
  • Maximum Rain Rate - [mm h-1]</
  • Total Rainfall* - accumulation [mm]

NOTE: Following the manufacturer instructions, the Joss-Waldvogel Disdrometer data were calculated both with and without the "dead-time correction." The dead-time correction is an empirical formula used to compensate for the underestimation of small drops in heavy rain. However, the user should be cautioned that this correction does not add drops to the channels in which no drops were recorded.

Summary Tables for KWAJEX Data



Selected Case Studies

The tables of priority cases include the following integral rainfall parameters derived from the 1-minute disdrometer records:
  • Julian Day - day of the year
  • Hour (UTC) - hour of the day
  • Minute (UTC) - minute of the rainy hour
  • Total Number of Drops - number of drops counted during specified minute
  • Concentration - [# drops m-3]
  • Liquid Water Content - [g m-3]
  • Rain Rate - [mm h-1]
  • Radar Reflectivity - [10 logZ]

Data from Selected Case Studies



Data Access and Contacts

You may retrieve the disdrometer files from this document or directly via ftp:

ftp disc2.nascom.nasa.gov
logon: anonymous
passwd: <your internet address>
cd data/KWAJ/surface_data/disdrometers/nasa_disdrom/

For more information on this data set please contact the Principal Investigator:

Ali Tokay
Code 910.1, Bld. 22
NASA/Goddard Space Flight Center
Greenbelt, MD 20771
Phone: 301-286-2120
fax: 301-286 -1628
tokay@trmm.gsfc.nasa.gov

For information about KWAJEX data archived at the Goddard DISC, please contact

Hydrology Data Support Team
GSFC DAAC, Code 610.2
NASA/Goddard Space Flight Center
Greenbelt, MD 20771
(301) 614-5165 (voice)
(301) 614-5268 (fax)
hydrology-disc@listserv.gsfc.nasa.gov
Last update:Mon Dec 22 14:49:47 EST 2003
Page Author: Hydrology Data Support Team -- hydrology-disc@listserv.gsfc.nasa.gov
Web Curator: -- Website Curator: Anthony Drake
NASA official: Steve Kempler, DISC Manager -- kempler@disc.gsfc.nasa.gov 		NASA Logo