The 50-MHz and 920-MHz profiler spectra were analyzed to estimate the raindrop size distribution (DSD) from 1.5 to 4.0 km directly above the profiler site. The retrieval method is described in detail in Williams and Gage (2009) (Ann. Geophys., 27, 555-567. 2009 www.ann-geophys.net/27/555/2009/). Basically, the retrieval method estimates the DSD at each range gate using 42 different models. One of those models assumes the raindrop size distribution has a Gamma functional form and the retrieved parameters are provided in hourly ASCII data files.
6.1 ASCII Data Format
The Gamma function DSDs are saved in hourly ASCII data files. The filenames follow this naming convention: dar920_dsd_gamma_YYYY_DDD_hrHH.dat.
Where:
- dar = Darwin
- 920 = 920 MHz profiler
- dsd = raindrop size distribution
- gamma = DSD assumed to have a gamma functional form
- YYYY = year
- DDD = day of year
- hr = hour
- HH = hour of day
The DSD retrievals were processed using the vertical beam observations of the 920-MHz profiler. The profiler is configured to observe in the vertical beam direction at the start of every minute and dwell for 45 seconds. The profiler then observes in either the North or East beam for 15 seconds. Then the profiler repeats this pattern indefinitely alternating between the North and East beams. In the following data files, only the data from the vertical beam are provided. The time stamp the data file corresponds to the beginning of the dwell period.
The DSD data files are in sequential format. Each row corresponds to a particular pixel in the time-height plane. Each column corresponds to a particular variable:
Column          Description
1Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â year
2Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â day of year
3Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â month number
4Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â day of month
5Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â hour
6Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â minute
7Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â second
8Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â dayofyear.fraction of day
9Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â height above Mean Sea Level (MSL) (m)
10Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Scale Parameter, Nw (mm-1 m-3)
11Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Median Diameter, D0 (mm)
12Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Shape Parameter, Â (unitless)
13Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Reflectivity (dBZ)
14Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Surface Rain Rate (Assume surface terminal fall speeds and zero air motion – R is estimated using DSD parameters) (mm hr-1)
15Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Altitude and Air Motion Compensated Rain Rate (Uses altitude dependent terminal fall speeds and corrects for vertical air motion – R is the rain rate in this pulse volume – but it may be moving upward) (mm hr-1)
16Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Flux of Rain Rate (Adjusts the Altitude and Air Motion Compensated Rain Rate (column 15) by the actual vertical air motion. Negative values indicate an upward flux of rain.) (mm hr-1)
17Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Liquid Water Content (mm)
18Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Vertical air motion, positive is upward (m s-1)
The ASCII numbers are expressed in exponential notation using the format: 1.2345678e+123. The sign of the exponent could be either a ‘+’ or ‘-’. There are two spaces between each number, but one space is used for the ‘-’ symbol with negative numbers.
If the power return is below the level of detectability, the DSDs are not estimated and the bad or missing data values are indicated with a value of -99.9 (-9.9000000e+001).
Data from the 25 ranges gates between 1.5 and 4 km are saved in the hourly data file. Therefore, there are 60*25= 1500 rows in each hourly data file. In all hourly data files, the data for minute 1 is missing and is set to the bad data flag. The data files can be found on the ftp site: ftp://ftp1.esrl.noaa.gov/users/cwilliams/Darwin/DSD_gamma/dat/
6.2 Daily Images
For each hourly data file, three images are generated and examples are shown below. The filename for the hourly images follows this format: p_dar920_dsd_gamma_TYPE_YYYY_DDD_HH_v1.tif,
where
- p_dar920 = plot of Darwin 920 MHz profiler
- dsd = raindrop size distribution
- gamma = DSD assumed to have a gamma functional form
- TYPE = ZD0mu = 3-panel plot of Reflectivity, median raindrop diameter, and shape parameter
- TYPE = NwD0R = 3-panel plot of Scale parameter, median raindrop diameter, and surface rain rate
- TYPE = RRomega = 3-panel plot of surface rain rate, altitude rainrate, and vertical air motion
- YYYY = Year
- DDD = Day of year
- HH = hour of day
- v1.tif = version 1, tif format
The above figure is p_dar920_dsds_gamma_NwD0R_2006_022_15_v1.tif.
The above figure is p_dar920_dsds_gamma_RRomega_2006_022_15_v1.tif.
The above figure is p_dar920_dsds_gamma_ZD0mu_2006_022_15_v1.tif.
The image files can be found on the ftp site: ftp://ftp1.esrl.noaa.gov/users/cwilliams/Darwin/DSD_gamma/images/
