The Tropical Western Pacific – International Cloud Experiment (TWP-ICE) was held near Darwin, Australia, in January and February 2006 to collect in-situ and remote-sensing measurements of clouds, precipitation, and meteorological variables from the ground to the lower stratosphere. These observations will help improve cloud remote-sensing retrievals and improve our understanding and modeling of deep convective cloud systems.

During TWP-ICE, vertically-pointing profiling radar, surface rain gauge, and disdrometer observations were collected for the whole wet season from November 2005 through March 2006. Vertically-pointing radars provide information on the vertical structure of precipitating cloud systems as they pass directly overhead. Using the measured Doppler velocity information, these observations are converted into estimates of the number and size of raindrops falling in the rain. These raindrop size distributions (DSDs) provide insight into the microphysical processes and dynamics occurring within the precipitating cloud system.

The calibrated observations, retrieved raindrop size distributions, and images are provided through this research page.

The vertically-pointing radars and surface instruments were installed at the Australian Bureau of Meteorology Research Centre (BMRC) wind profiler site (12.443 S, 130.956 E) located 8 km east of the ARM climate observation site (12.425 S, 130.981 E). The location of the BMRC wind profiler site is shown in the two Google maps of Darwin.

During the TWP-ICE field campaign, the following instruments were operating at the BMRC wind profiler site:

• 2 Tipping bucket rain gauges (NOAA)
• 1 Joss-Waldvogel Disdrometer (JWD) (second unit did not function properly) (NOAA)
• 1 Vertically pointing S-band profiler (2835-MHz) (NOAA)
• 1 UHF wind profiler (920-MHz) (BMRC)
• 1 VHF wind profiler (50-MHz) (BMRC)

These instruments are shown in these photographs.

Two tipping bucket rain gauges operated from 3 November 2005 through 10 February 2006. The rain gauges counted the number of tips that occurred in each 10 second interval with each tip corresponding to 1/100 of an inch of rain. The 10-second recorded time stamp corresponds to the end of the accumulation period. The rain gauge clock is the same as the S-band profiler clock. There was also a pressure sensor installed with the rain gauges.

3.1 Daily Images

Daily images in PNG format were generated to show the 10 second surface pressure, 1-minute rain rate, and the rain accumulation throughout the day. The filename follows the format dar_raingauge_yyyy_ddd.png, where yyyy is the year and ddd is the day of year. An example is show below:

The image files can be found on the ftp site: ftp://ftp.etl.noaa.gov/user/cwilliams/Darwin/rain_gauge/images/ .

3.2 ASCII Data Format

The tipping bucket rain gauge data are stored in daily files following the naming convention: dar_raingauge_yyyy_ddd.dat, where yyyy is the year and ddd is the day of year. Each daily file contains 8640 rows (24*60*6) and bad or missing data values are indicated with a value of -99.9.There are 12 columns in each data file with each column having the following variable:

Column     Description

1                    Year

2                    Day of year

3                    Month

4                    Day of month

5                    Hour

6                    Minute

7                    Second (end of accumulation period)

8                    Precipitation unit #1   (1/100 of an inch)

9                    Precipitation unit #2   (1/100 of an inch)

10                Pressure  (hPA)

11                Battery Voltage (Volts)

12                Temperature inside shed (degrees C)

The ASCII data files can be found on the ftp site: ftp://ftp.etl.noaa.gov/user/cwilliams/Darwin/rain_gauge/dat/

Even though two Joss-Waldvogel Disdrometers (JWDs) were installed at the BMRC wind profiler site, only one unit produced usable data. The JWD was operational from 3 November 2005 through 10 February 2006.

The original JWD data were collected at the full 127 diameter channels and with a 10 second dwell time. These high resolution data were reduced to the standard 20 diameter channels and to a 1-minute resolution. A dead-time correction (Sheppard and Joe 1994; Sauvageot and Lacaux 1995) was applied to the raindrop counts. The data products are provided using the dead-time corrected raindrop counts and 60 second dwell time:

• Number of raindrops in each raindrop diameter size
• Number concentration in each raindrop diameter size
• Moments of reflectivity, rain rate, liquid water content, mass-weighted mean diameter, and normalized scale parameter (Nw)

The following constant values are also provided and used in processing the raw observations:

• Standard diameter channels (20 raindrop sizes) (file Dstd.dat)
• Width of each diameter channel (file dDstd.dat)
• Terminal fall speed for each diameter, V=0.65 – 10.3exp(0.6D) (file velocity.dat)
• Sample volume for each diameter, (Surface area)(Dwell Time)(Velocity) (file Volume.dat)

4.1 ASCII Data Format

The ASCII data files are day files with 1-minute resolution and contain 1440 rows. Bad or missing data values are indicated with a value of -99.9. The ASCII data files can be found on the ftp site: ftp://ftp.etl.noaa.gov/user/cwilliams/Darwin/disdrometer/dat/

4.1.1 Number of Raindrops in each Diameter Size

The dead-time corrected drop counts for each diameter channel are provided in the files named: dar_jwd_dtc_cnt_yyyy_ddd.dat, where

• dar = Darwin
• jwd = Joss-Waldvogel Disdrometer
• dtc = dead-time corrected
• cnt = number count
• yyyy = year
• ddd = day of year

There are 1440 rows and 20 columns in each day file. Each column corresponds to the raindrop diameter specified in Dstd.dat.

4.1.2 Number Concentration

The dead-time corrected Number Concentration each diameter channel are provided in the files named: dar_jwd_dtc_ND_yyyy_ddd.dat.

• dar = Darwin
• jwd = Joss-Waldvogel Disdrometer
• dtc = dead-time corrected
• ND = N(D) = Number concentration, units of (#/m³) for each diameter size (mm)
• yyyy = year
• ddd = day of year

There are 1440 rows and 20 columns in each day file. Each column corresponds to the raindrop diameter specified in Dstd.dat.

4.1.3 Moments and DSD Parameters

The dead-time corrected N(D) is used to estimate the moments of the DSD and are provided in the files named: dar_jwd_dtc_mom_yyyy_ddd.dat

where

• dar = Darwin
• jwd = Joss-Waldvogel Disdrometer
• dtc = dead-time corrected
• mom = moments
• yyyy = year
• ddd = day of year

There are 1440 rows and 15 columns in each data file. The variable in each column is:

Column       Description

1                            year

2                            day of year

3                            hour

4                            minute

5                            Nt = Total number of drops in distribution

6                            Reflectivity (dBZ)

7                            Rain rate (mm/hr)

8                            Liquid Water Content (g/m^3)

9                            Dm = Mass-weighted mean diameter (mm)

10                        Nw = Normalized Scale Parameter (mm^-1 /m^3)

11                        Variance estimate of Z, var{Z} in (mm^6/m^3)^2

12                        Variance estimate of R, var{R} in (mm/hr)^2

13                        Variance estimate of LWC, var{LWC} in (g/m^3)^2

14                        Variance estimate of Dm, var{Dm} in (mm)^2

15                        Variance estimate of Nw, var{Nw} in (mm^-1 /m^3)^2

The time expressed in this file also corresponds to the time in the raindrop count and number concentration data files. Bad or missing data values are indicated with a value of -99.9.

4.2 Daily Images

Daily images in PNG format were generated to show the minute Joss-Waldvogel Disdrometer (JWD) estimated reflectivity, rain rate, and number concentration N(D). The filename follows the other disdrometer filename format with dar_jwd_dtc_day_yyyy_ddd.png, where yyyy is the year and ddd is the day of year. An example image is shown below.

The 920-MHz wind profiler operates in the Doppler Beam Swinging (DBS) mode and alternates the position of the radar beam from the vertical, East, and North positions. When the beam is pointed in the vertical direction, the wind profiler moments at each range gate provides information on the vertical structure of the precipitation as it passes directly over the profiler site. The observed Doppler velocity power spectra were calibrated to the surface disdrometer reflectivity.

5.1 ASCII Data Format

The 920-MHz profiler moments are saved in hourly ASCII data files. The filenames follow this naming convention: dar920cal_vert_YYYY_DDD_hrHH.dat,

where:

• dar = Darwin
• 920 = 920 MHz profiler
• cal = calibrated to Joss-Waldvogel Disdrometer
• vert = vertical beam
• YYYY = year
• DDD = day of year
• hr = hour
• HH = hour of day

The 920-MHz profiler moments are estimated from 45 second dwell periods. 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 920-MHz profiler moments 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

1                    year

2                    day of year

3                    month number

4                    day of month

5                    hour

6                    minute

7                    second

8                    dayofyear.fraction of day

9                    height above Mean Sea Level (MSL) (m)

10                   number of profiles in minute

11                   Reflectivity (dBZ)

12                   Doppler Velocity, downward is positive (m/s)

13                   Doppler velocity variance (m² s^-2)

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 moments are not generated and the bad or missing data values are indicated with a value of -99.9 (-9.9000000e+001).

Data from all range gates are saved to the hourly data file. There are 166 range gates in each profile. Therefore, there are 60*166 rows in each hourly data file. In all data files, the data for minute 1 is missing and is set to the bad data flag.

The ASCII data files can be found on the ftp site: ftp://ftp.etl.noaa.gov/user/cwilliams/Darwin/dar920/calibrated_moments/dat/

5.2 Daily Images

Hourly images of the 920-MHz profiler moments of reflectivity, mean Doppler velocity, and Doppler velocity variance were generated from the hourly ASCII data files. The filename for the hourly images follows this format: p_dar920_ZVV_YYYY_DDD_HH_v1.tif,

where

• p_dar920 = plot of Darwin 920 MHz profiler
• ZVV = 3-panel plot of Reflectivity, mean Doppler velocity, and velocity variance
• YYYY = Year
• DDD = Day of year
• HH = hour of day
• v1.tif = version 1, tif format

An example image is shown below:

The hourly images can be found on the ftp site: ftp://ftp.etl.noaa.gov/user/cwilliams/Darwin/dar920/calibrated_moments/images/

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

1                    year

2                    day of year

3                    month number

4                    day of month

5                    hour

6                    minute

7                    second

8                    dayofyear.fraction of day

9                    height above Mean Sea Level (MSL) (m)

10                   Scale Parameter, N_w (mm^-1 m^-3)

11                   Median Diameter, D₀ (mm)

12                   Shape Parameter,  (unitless)

13                   Reflectivity (dBZ)

14                   Surface Rain Rate (Assume surface terminal fall speeds and zero air motion – R is estimated using DSD parameters) (mm hr^-1)

15                   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)

16                   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)

17                   Liquid Water Content (mm)

18                   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://ftp.etl.noaa.gov/user/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://ftp.etl.noaa.gov/user/cwilliams/Darwin/DSD_gamma/images/

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. These hourly data sets contain the mean, median, and the standard deviation of the precipitation parameters retrieved from the ensemble of DSD estimates. The details of estimating the 42 models and how the outlier models were removed before estimating the mean, median, and standard deviation are described in Williams and Gage (2009).

7.1 ASCII Data Format

The ensemble DSDs are saved in hourly ASCII data files. The filenames follow this naming convention: dar920_dsd_ensemble_mean_YYYY_DDD_hrHH.dat,

where:

• dar = Darwin
• 920 = 920 MHz profiler
• dsd = raindrop size distribution
• ensemble_mean = mean, median, and STD of retrieved ensemble DSDs
• 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

1                    year

2                    day of year

3                    month number

4                    day of month

5                    hour

6                    minute

7                    second

8                    dayofyear.fraction of day

9                    height above Mean Sea Level (MSL) (m)

10                    mean scale parameter, N_w (mm^-1 m^-3)

11                    mean median diameter, D₀ (mm)

12                    mean reflectivity (dBZ)

13                    mean rain rate (using altitude fallspeeds & adjusting for vertical air motion) (mm hr^-1)

14                    mean liquid water content (mm)

15                    vertical air motion, positive is upward (m s^-1)

16                    std scale parameter, N_w (mm^-1 m^-3)

17                    std median diameter, D₀ (mm)

18                    std reflectivity (dBZ)

19                    std rain rate (altitude terminal fall speeds & adjusting for vertical air motion) (mm hr^-1)

20                    std liquid water content (mm)

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). The reflectivity is averaged in standard units (mm⁶ m^-3) and then converted to decibel units (dBZ).

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.

These data files can be found at the ftp site: ftp://ftp.etl.noaa.gov/user/cwilliams/Darwin/DSD_ensemble_mean/dat/.

7.2 Daily Images

For each hourly data file, an image showing the mean ensemble liquid water content, scale parameter, and median raindrop diameter is generated as shown below. The filename for the hourly images follows this format: p_dar920_dsd_ensemble_mean_TYPE_YYYY_DDD_HH_v1.tif,

where

• p_dar920 = plot of Darwin 920 MHz profiler
• dsd = raindrop size distribution
• ensemble_mean = mean estimated from ensemble DSDs
• TYPE = WNwD0 = 3-panel plot of liquid water content, scale parameter, and median raindrop diameter
• YYYY = Year
• DDD = Day of year
• HH = hour of day
• v1.tif = version 1, tif format

The image files can be found on the ftp site: ftp://ftp.etl.noaa.gov/user/cwilliams/Darwin/DSD_ensemble_mean/images/.