Cloud Physics data format

The PMS probe data files produced at NOAA/AOML/HRD were reduced using methods essentially similar to those reported by Black and Hallett (JAS, 1986), henceforth, BH. In the case of the TOGA-COARE 2-D Mono data obtained in rain by the NCAR electra, the rejection criteria of BH were extensively altered so that most partial images were accepted as well. This was done because the NCAR data were exceptionally "clean", and free of splashes and other defects. All files are written in HP/Motorola (HILO) format as opposed to the DEC (LOHI) format. USERS OF DEC OR INTEL COMPUTERS MUST SWAP BYTES to read these files.

File naming conventions are as follows: XYYYYMMDDA
X - First letter of storm name
YYYY - Year
MM - Month
DD - Day
A - Aircraft designator ( H - NOAA-42; I - NOAA-43, DC8 - NASA DC-8)
with "_p.2dg" for 2D-P Grey
or ".2dp" for mono probe data
and "_c.2dg" for 2D-C Grey
or ".2dc" for mono probe data.
A suffix of ".fssp" indicates the file has the FSSP-100 size distributions.

  1. Mono probe data (2D-C + 2D-P; 2D-P only since 1993) NASA DC-8 (CAMEX-III) also. Since 2001, a 2D-C mono probe is available on some flights, but its quality is poor.

    The NOAA 2-D mono probes consist of a 0.2 mm resolution precipitation (2D-P) and a 0.050 mm resolution cloud (2D-C) probe. The size dependence of the 2D-C depth of field noted in the PMS manual is incorrect and is NOT used. Instead, the 2D-C corrections from Korolev and Baumgardner (JAM, 1997) are utilized. These data are normally averaged for 6-seconds, but any other interval may be used. However, the inter-record times on the files are not always the same because of the asynchronous data collection. NOTE: During the NASA CAMEX-III project, the DC-8 used a 0.025 mm resolution 2D-C probe.

    Ice particles and partial raindrop images whose largest dimension was within the diode array were sized by the equivalent circle area. Partial images whose longest dimension was on an edge were rejected. Complete drop images were sized by the longest dimension perpendicular to the diode array.

    Computed parameters include rain rate (mm/hr), radar reflectivity factor (Z, mm/hr), liquid water content in both g/m***3 and n/l, liquid median volume diameter (mm), and the y-intercept and slope of the liquid particle size distribution when plotted as Log(n/l) vs. diameter in millimeters. Measured parameters included in the file are date, time, sample volume (l) for both probes, and elapsed over-load times in seconds for the averaging period.

    Changes Since 1993: Added 4-digit year. Prior to 1993, these data were usually processed together. Thus, both 2D-P and 2D-C data were usually present in the files. Since then, the new DAS's recording method made this practice unsatisfactory. These data are now processed separately and written into separate files.

    The physical records are organized as follows:

    Each averaging period of 2-D MONO data from the WP-3D contains 7 128-byte direct-access records written as 32 4-byte IEE REAL format values associated with it. The first record of each group of 7 contains computed data, plus the date (YYYYMMDD) and time HHMMSS.msec. The contents of the header record are:

    WORDCONTENTS
    1DATE (YYMMDD.) (Some have 4-digit year)
    2TIME (HHMMSS.MSEC) (end time of averaging period)
    3Rain rate (mm/hr), MAX of 2D-C and 2D-P (Old files only)
    4LWC (g/m3), MAX of 2D-C and 2D-P. (Old)
    5IWC (g/m3), MAX of 2D-C and 2D-P. (Old)
    62DP radar reflectivity, dBZ
    75.5 cm radar attenuation from 2D-P (dBZ/km)
    8averaging time, seconds
    9True Airspeed (TAS), m/s
    102DP liquid water content (LWC) (g/m**3) (if any)
    112DP ice water content (IWC) (g/m**3) (if any)
    122DC liquid water content (LWC) (g/m**3) (if any)
    132DC ice water content (IWC) (g/m**3) (if any)
    142DC Sample Volume (Liters)
    152DP Sample Volume (Liters)
    162DC rain rate (mm/hr)
    172DP rain rate (mm/hr)
    18Number of bad records this averaging period
    192DC reflectivity factor dBZ
    20"K" from Heymsfield (1989) method of obtaining Z-M relation
    212D-C Mass-weighted fall speed (cm/s)
    222D-P Mass-weighted fall speed (cm/s) "K" from 2D-P
    23(UNUSED) 2DC "K" from Heymsfield (1989) method of obtaining Z-M relations.
    24(UNUSED) 2DC IWC ("measured" from Heymsfield (1989))
    25Summation 2DC area (sq. mm)
    26mean 2DC area (sq. mm)
    27 Summation 2DP area (sq. mm)
    28 mean 2DP area (sq. mm)
    292DC overload percent
    302DP overload percent
    314-digit year (Since 6/28/01)
    32Ice density used

    The second and third records are the 2D-P water and 2D-P ice size distribution as n/l per 0.2 mm size channel, respectively. For TOGA, record 3 of 7 is the fractional image data in the same units. If it is desired to exclude the partial images, simply subtract, element by element, the data in record 3 from that in record 2. The result will be the image data size spectra using the "center in" technique described by BH. Records 4 and 5 are the same as records 2 and 3, except for the 2D-C. These are divided into number per liter per 0.05 mm size channel. Records 6 and 7 are 2D-C graupel and 2D-C column data, unused for TOGA-COARE. For 2D-P data processed since 1996, records 4 and 5 contain 2D-P graupel/round images and 2D-P columnar images, respectively.

  2. NOAA WP-3D 2D-Grey probe data

    PMS 2D-Greyscale data are significantly different from the 2D-Mono probe data, and they are consequently treated differently. Grey images utilize 2 bits of information per pixel instead of one, thus giving four levels of shadow depth. Further, the diode array is 64-pixels wide instead of 32 pixels. Thus, grey probes require four (4) times the data of a mono probe to characterize one image. Since the data path from the grey probes is no wider than that for the mono probes, image throughput is significantly reduced, necesitating longer averaging times. The NOAA WP-3D mounts two of these probes, usually, a 2DG-C with a 0.030 mm pixel size, and a 2DG-P with a 0.15 mm resolution

    The NOAA-P3 Grey probe data are handled in a similar manner to the Mono probe data, and partial images whose longest dimension is on the edge are not utilized. A major difference is that the greyscale information are used to eliminate out-of-focus images and most splashes which results in "cleaner" size distributions. The NOAA aircraft used the new 2D-Greyscale probes along with an SEA Inc. model 200 data system. These differences require a much longer averaging period (at least 12 s, 60 s or more for the TOGA data) to obtain a stable size distribution. The 2D-Greyscale files are composed of 7 records, each 256 bytes long consisting of 64 IEEE real format words. Data from only one probe at a time can be analyzed, so several of the records are always blank. At this time, there is no merge program for 2D-Grey records.

    Water images are treated differently from ice particles. If images are assumed to be water, the image is assumed to be an oblate spheriod with an elliptical cross-section. A least-squares ellipse fit to the image perimeter provides the particle area and equivalent circle diameter.

    Ice particles also have an ellipse fitted to their image perimeter, but this is used for habit discrimination rather than for sizing. Ice particles are sized by their equivalent circle area unless they are deemed to be of type column or needle, in which case the volume (and IWC) is computed as though the image was of a rectangular prism, whereas the diameter is still the equivalent circle diameter as before.

    The physical records are organized as follows:

    Each averaging period of 2-D Grey data from the WP-3D contains 7 256-byte direct access records written as 64 4-byte IEE REAL format values associated with it. The first record of each group of 7 contains computed data, plus the date (YYYYMMDD) and time HHMMSS.msec. If the images are assumed to be rain, the program offers the option to filter the spectra to remove extraneous large images from ice particles and un-rejected splashes.


    IMPORTANT CHANGES

    Recent papers by Baumgardner, Korlorev, and others have pointed out the need for complex airspeed and Depth of Field corrections for the 2DG-C. SUCH CORRECTIONS HAVE NOT BEEN MADE TO THESE DATA. FURTHER, THE 2DG-P ALSO REQUIRES SUCH CORRECTIONS. Use these data with appropriate caution, as the number concentrations, water contents, etc. are somewhat smaller than they should be.

    6/2001: The year was stripped from the date because of word overflow during the 1998 season. Now, the 4-digit year is stored in word 59 of the first buffer. Some 1998 files have NO YEAR. ALso, GRAUPEL and NEEDLE categories are now also kept for the 2DG-P data. No more merged data files will be created. These are stored in the same positions as the 2D-C categories.


    The contents of the header record are:

    WORDCONTENTS
    1DATE (YYYYMMDD.) 1998+ MMDD only. Year is in Word 59.
    2TIME (HHMMSS.MSEC) (end time of averaging period)
    3Rain rate (mm/hr), MAX of 2D-C and 2D-P. (Pre-1998 only)
    4LWC (g/m3), MAX of 2D-C and 2D-P. (Old)
    5IWC (g/m3), MAX of 2D-C and 2D-P. (Old)
    62DP radar reflectivity, dBZ
    75.5 cm radar attenuation from 2D-P (dBZ/km)
    8averaging time, seconds
    9True Airspeed (TAS), m/s
    102DP liquid water content (LWC) (g/m**3) (if any)
    112DP ice water content (IWC) (g/m**3) (if any)
    122DC liquid water content (LWC) (g/m**3) (if any)
    132DC ice water content (IWC) (g/m**3) (if any)
    142DC Sample Volume (Liters)
    152DP Sample Volume (Liters)
    162DC rain rate (mm/hr)
    172DP rain rate (mm/hr)
    18Number of bad records this averaging period
    192DC reflectivity factor dBZ
    20"K" from Heymsfield (1989) method of obtaining Z-M relation
    212D-C Mass-weighted fall speed (cm/s)
    222D-P Mass-weighted fall speed (cm/s) "K" from 2D-C
    23(UNUSED) 2DC "K" from Heymsfield (1989) method of obtaining Z-M relations.
    24(UNUSED) 2DC IWC ("measured" from Heymsfield (1989))
    25Summation 2DC area (sq. mm)
    26mean 2DC area (sq. mm)
    27 Summation 2DP area (sq. mm)
    28 mean 2DP area (sq. mm)
    292DC overload fraction
    302DP overload fraction
    312DG-P accepted water particle count
    322DG-P accepted ice particle count
    332DG-C accepted water particle count
    342DG-C accepted ice particle count
    59YEAR (4-digit, 1998+)
    60raw total count (images saved and unsaved) from 2DG-C
    60raw total count (images saved and unsaved) from 2DG-P
    64Ice density used


    NOTE
    SOME 1998 analysis files DO NOT contain the year.


  3. NASA DC-8 2D-Grey probe data (CAMEX-III and TOGA_COARE)

    Same as for the WP-3D, except that during TOGA-COARE, the DC-8 used a 0.025 mm pixel 2DG-C and a 0.040 mm pixel 2DG-C as a precipitation probe. During CAMEX-III, they used a 0.025 mm 2D-C mono probe and the NOAA 0.2 mm pixel 2D-P Mono probe, the 0.040 mm 2DG-C was used instead of the 2D-P for some flights.

    Please contact Mr. Paul Willis (paul.willis@noaa.gov) for information about the status and availability of these data.

  4. NCAR rain data (TOGA-COARE ONLY)

    The NCAR 2-D mono probes consist of a 0.2 mm resolution precipitation (2D-P) and a 0.025 mm resolution cloud (2D-C) probe. The size dependence of the 2D-C depth of field was accounted for. These data were averaged for 6 seconds. However, the inter-record times on the files are not always 6-s apart because of the asynchronous data collection.

    Images whose largest dimension was within the diode array were sized by the equivalent circle area. Partial images whose longest dimension was on an edge were sized by the longest dimension, but these particles were counted as fractional images defined as the image area divided by the area of an equivalent circle of diameter equal to the length of the longest dimension.

    To account for the fact that the old PMS 2D-Mono probes stripped the first slice off each image, zero-area images were added into the computations as particles with area of 0.5 diodes. All other images had areas increased according to the following:

    Area (A) < 17, area=area +0.53707 +0.31552A -0.02030841A**2 +0.00050043A***3

    Area > 16, area=area +2.0385 +0.016346A.

    This correction procedure forces zero-area images into the smallest size category, and increased the size of some images in the first few size channels up to the next larger size.

    The distributions of the partial images included above are saved in the (unused) ice array so that the effects of this usage can be removed if necessary.

    Computed parameters include rain rate (mm/hr), radar reflectivity factor (Z, mm/hr), liquid water content in both g/m***3 and n/l, liquid median volume diameter (mm), and the y-intercept and slope of the liquid particle size distribution when plotted as Log(n/l) vs. diameter in millimeters. Measured parameters included in the file are date, time, sample volume (l) for both probes, and elapsed over-load times in seconds for the averaging period.

    The physical records are organized as follows:

    Each averaging period of 2-D MONO data from the NCAR ELECTRA contains 7 - 128-byte direct-access records written as 32 4-byte IEE REAL format values associated with it. The first record of each group of 7 contains computed data, plus the date (YYMMDD) and time HHMMSS.msec. The contents of the header record are:

    WORDCONTENTS
    1DATE (YYMMDD.)
    2TIME (SS.MSEC) (end time of averaging period)
    35.5 cm radar attenuation from 2D-P (dBZ/km)
    4averaging time, seconds
    5True Airspeed (TAS), m/s
    6# records/time this file (7)
    72DP liquid water content (LWC) (g/m**3)
    82DP LWC (n/l)
    92DP rain rate (mm/hr)
    102DP ice water content (IWC) (g/m**3) (if any)
    112DP IWC (n/l)
    122DP radar reflectivity factor, Z (mm**6)
    132DP liquid water (LW) Y-intercept, exponential fit)
    142DP LW slope (exp. fit)
    152DP ice water (IW) Y-intercept (exp. fit)
    162DP IW slope (exp. fit)
    172DP LW median volume diameter (mvd) (mm)
    182DP Elapsed o/l time (s), this period
    192DP sample volume (l)
    202DC LWC (g/m**3)
    21 2DC LWC (n/l)
    222DC rain rate (mm/hr)
    232DC IWC (g/m**3)
    242DC IWC (n/l)
    252DC Z (mm**6)
    262DC LW A0 (exp. fit)
    27 2DC LW slope (exp. fit)
    28 2DC IW A0 (exp. fit)
    292DC IW slope (exp. fit)
    302DC LW mvd (mm)
    312DC Elapsed o/l time (s)
    322DC sample volume (l)

    The second and third records are the 2D-P water size distribution as n/l per 0.2 mm size channel, and the fractional image data in the same units, respectively. If it is desired to exclude the partial images, simply subtract element by element, the data in record 3 from that in record 2. The result will be the image data size spectra using the "center in" technique described by BH. Records 4 and 5 are the same as records 2 and 3, except for the 2D-C. These are divided into number per liter per 0.025 mm size channel. Records 6 and 7 are 2D-C graupel and 2D-C column data, unused for TOGA-COARE..

  5. FSSP-100 files.

    Since 1992, the newer FSSP-100 probes now properly account for "Activity", which allows coincidence errors to be accounted for. These data are also written to a 32-word buffer written as a direct-access record. The parameters in each position are:

    1YEAR (YY or YYYY)
    2Month
    3day
    4hour
    5minute
    6seconds
    7milliseconds
    8FSSP Range
    923 FSSP size distribution, (n/cc)
    24Sample volume (cc)
    25liquid water content (g/cc)
    26 Total droplet concentration (n/cc)
    27True Air Speed (TAS), m/s
    28total accepted particle count
    29total strobe count (includes rejected strobes)
    30FSSP Activity counter
    31FSSP reference volts
    32unused

    FSSP Range values are as follows:

    ValueNominal Size Range (microns)
    03 - 45
    12 - 30
    31 - 15
    40.5 - 7.5

  6. Archive Image appearance

    Mono Probes

    1. 2D-C images are sorted by image class and within each class, presented in order of occurrence from left to right. The images themselves are red. Each class is separated by a vertical dashed line. The classes are:

      0liquid water
      1undifferentiated ice.
      2round ice or graupel
      3columns and needles

      Classes higher than 3 are rejects, not included in the size distributions.
      Class 4 images are NOT included in the image archive.

      4streaks
      5Too small a time interval
      6Zero area
      7Image has a y-gap
      8Multiple image (x-gap)
      9Partial image caused by probe overload
      10First (incomplete) image in the record
      11Time interval too large to be real

    2. 2D-P images are green. These are classed as above, except that round and columns (Classes 2 and 3) are not used. This changed for all revisions of the analysis software in use since 1996, as I have permanently abandoned the option of merging 2D-C and 2D-P data files. 2D-P and 2DG-P files processed since then include round/graupel and column categories

      Grey Probes

    3. 2DG-C images are colored according to their depth of shadow. The darkest shadow (75%) is green, the middle level depth (50%) is blue, and the minimum shadow depth (25%) is red. Image type is identified by colored vertical bars. A wide yellow bar separates 2D-Grey records. Within a record, a colored bar following the image identifies its class. No rejected images appear in the archive.

      The accepted image classes are:

      0Liquid water, multi-colored dashed line
      1undifferentiated ice, solid red line
      2round ice or graupel, solid green line
      3column or needle, red/yellow dashed line

      Images classed 4 and higher do not apppear.


LAST UPDATED 3 September 2003
Robert A. Black NOAA/AOML/HRD
Phone (305) 361-4314