########################################################################### # Notice on the use of Antarctic Meteorological Research Center data sets # ########################################################################### # The Antarctic Meteorological Research Center (AMRC) collects, archives # # and provides Antarctic meteorological observational data to the # # community and public for research, logistic, and educational activities.# # The AMRC requests acknowledgement for use of the data in any published # # work. See http://amrc.ssec.wisc.edu/acknowledgement.html for details on # # how to acknowledge AMRC data, displays or information. # # If the AMRC data are critical to the work, co-authorship may be # # appropriate. Please contact the AMRC in such a case. # # # # AMRC Contact Information: # # Address: 947 Atmospheric, Oceanic and Space Sciences Building # # 1225 West Dayton Street # # Madison, Wisconsin, USA 53706 # # Telephone: +1 (608) 262-0436 # # Fax: +1 (608) 263-6738 # # E-mail: amrc@ssec.wisc.edu # # Web: http://amrc.ssec.wisc.edu/ # # FTP: ftp://amrc.ssec.wisc.edu/ # # McIDAS ADDE: Group AMRC and ARCHIVE on aws.ssec.wisc.edu # # RAMADDA: https://amrc.ssec.wisc.edu/repository/ # # Facebook: http://www.facebook.com/AMRCAWS # # Twitter: http://twitter.com/antmet # # YouTube: http://www.youtube.com/user/AMRCantmet # # Wikipedia: # # http://en.wikipedia.org/wiki/Antarctic_Meteorological_Research_Center # # http://en.wikipedia.org/wiki/Antarctic_Automatic_Weather_Stations_Project # # # Updated: 24 July 2013 # # # ########################################################################### The following information is based on some recent questions and e-mails between users of South Pole Radiosonde data, the AMRC, and the South Pole Meteorology Office: >> Is the orginal user question > Is the AMRC reply/additional questions/clarificaiton Is the reply from South Pole Meteorology Office --------------------------------------------------------------------------- >> 1) Are the data files named by MMDDTTTT (month, day, time) ? >Yes, they are labeled Month, Day of the Month, and time (UTC) On August 1, 2001 the SP Met department switched from the former AIR radiotheodolite-based atmospheric sounding system to a Vaisala GPS-based system. The AIR system named files MMDDTTTT where 4-digit time was exact to-the-minute time (Zulu) that sounding program was intialized. So the AIR 4-digit times would generally be 09XX for the 1200Z flight, and 21XX for the 0000Z flight. The Vaisala system names files MMDDTTTT where the 4-digit time will either be 0000Z or 1200Z depending on what flight it is. Now that winter operations have begun we have once again reverted to running only the 0000Z flight. >> 2) In all the files I have read, the time entry in the very first row >> (the entry for surface readings) is about 1 min. behind the second row, >> which is supposed to be a few seconds after the launch). Could you please >> tell me why is this? >This I'm not sure about...the delay could be due to the tim needed for GPS >acquisition of the balloon (GPS is used for tracking the balloon). It could >also be due to the South Pole Met Office having the surface data be >recorded at the ground using ground instrumentation, and the balloon >recording everything after launch. Only South Pole Met. Office will know >this for sure. As far as I can tell this delay only occurs with the AIR files prior to 8/1/01. The very first line is the surface data entered by the meteorologist, second is the first line of post-launch data. So here's the explanation... The radiotheodolite system required manual intervention with the tracking antenna in order to maximize the signal received from the radiosonde. The launch was a two-person procedure, one prepares and releases the package, the other operates the tracking and recording software in the office. Immediately after the launch the outside person would relay azimuth and elevation values to inside person to manipulate the antenna and find the strongest signal and correlation with outside person's readings. This would usually take a minute or so, then the surface observations could be entered. It appears that these surface observations - the very first line - were time stamped with the time that they are entered (after locking on to signal), not the true time of launch. Time difference of the first and second lines is therefore an indicator of how long it took to lock on to the strongest signal. This is one of the reasons the AIR system was problematic, GPS is a big improvement. You could probably use the elapsed time to back-calculate the actual time of launch if needed. Again, I do not see this delay in the GPS files. >> 3) I have made quick comparison between the CMDL dew point readings and >> the radiosonde data and found the radiosonde data are lower by quite a few >> degrees. Is this simply the difference between the instruments? >Good question. The instruments are very likely different....but why should >they read so different? That is a good question that I'm not sure anyone >has an answer to. There is a group of us discussing this very issue that >has come up in a different light. Austin is aware of it, as is South Pole >Met. Office. Once we have a better idea of what is going on, I'll try to >remember to let you know...otherwise, please feel free to keep in touch >with me about that. When you say "CMDL dewpoint readings" I'm not sure if you mean their sounding data or the hygrometer on their tower. If you are referring to their sounding data - we are using the same Vaisala radiosondes as the CMDL as of 8/1/01 so the readings should now be similar. The sensor technology on the AIR vs Vaisala must have been significantly different since the dewpoint/RH readings given by the AIR radiosondes, in this environment at least, were garbage. If you were referring to the hygrometer on their tower the Vaisala radiosondes are much better than the AIR but still a slightly lower than the tower instrument. The SPARCLE science group who wintered over here at the Pole last year did quite a bit of work in this area, let me know if you would like to have their contact information. They did a lot of tethered balloon flights to measure humidity above surface and did comparisons with radiosonde data. The sensor technology deployed on the radiosondes is inferior to the fixed instruments such as the one at CMDL. In general measuring dewpoint/RH in this environment is problematic and instrumentation requires a great deal of maintenance. >> 4) What are the scale factors? In the past, raw wind data used to be in meters per second. The scale factors provide for treatment of both wind speed units. The 1.94385 is the conversion from meters per second to knots. >> 5) What are the units of the wind speeds in 1993 and 1994? The wind speeds for 1993 and 1994 are in meters per second unless otherwise idicated. Multiply the wind speeds in meters per second by the factor 1.94385 to obtain the wind speeds in knots. ---------------------------------------------------------------------------- > A sample set of information, based on user questions: > With regards to time labeling, I have verified that the South Pole > Radiosonde data files filed in the pub/raob/hires/southpole directory > are named MMDDHHmm.DAT where the MM is the month, DD is the day, HH is > the hour, mm is the minutes, .DAT or .dat is the file suffix. Yes, the > HHmm or the time is the UTC time. > > The McMurdo Radiosonde data files filed in the pub/raob/hires/mcmurdo > directory are named YYMMDDHH.DAT where the YY is the year, MM is the month, > DD is the day, and HH is hour in UTC of the radiosonde launch. Yet, inside > the file, the time is in local time, not UTC time. > > For the radisonde data saved in the antarctic.YY files (where YY is the > year - these files are filed in pub/raob in the sudirectories 1980 to > 1993), inside the files, each station reporting a radiosonde will be > entitled, for example: > > >STNM = 89001 TIME = 900102/0000 > The STNM is the WMO station number, in this case 89001 is SANAE Station, > the TIME = is a combination of the year, month, day and the time, in > UTC. So the format is YYMMDD/HHMM, where YY is the year, MM is the > month, DD is the day, and HHMM is the time, HH is the hour and MM is the > minutes (either 0000 or 1200) in UTC. > > > For the radiosonde data from 1956 to 1980, which we have for McMurdo > Station filed in pub/raob in the subdirectories 1956 to 1979, the header > will list the station name, the year, the month, the day and then the > time in UTC. You'll find the day and time are often not separated by > spaces, for example: > > >McMurdo Sounding for 1970 1 212 > > This is the radiosonde sounding from McMurdo Station, from 1970, Month 1 > (January), Day 2 at 12 UTC. > > I think the *.uad files from South Pole and the *.mcu and *.dat or *.DAT > files from McMurdo Station, from 1994 to present filed in the pub/raob > directory in the 1994 to 2002 subdrectories, are self explainatory > (denoting the time as Z or UTC time) ---------------------------------------------------------------------------- > Additional Notes from South Pole Meteorology Office on radiosonde data: Below is a little background on the grid wind direction errors with our sounding system. Most of this was written by Brad Halter, one of the summer meteorologists whose extensive experience in studying atmospheric sciences here at the Pole dates back to 1976. At South Pole a grid system for defining wind direction is used, since east and west directions would change by up to 180 degrees in moving around the geographic point in its immediate vicinity if the true wind direction system were used. Winds arriving at the Station along the 0 degree, 90 degree East, 180th, and 90 degree West meridians, respectively, are taken to be arriving from grid N, E, S, and W. An error in the conversion of GPS winds from the true direction to the grid system has caused a mirror image reversal in reported wind direction, with the "mirror" being along the 90W - 90E line. That is to say that there is little difference between reported AIR sonde and GPS sonde wind direction when the winds are arriving at the Station along the 90E or 90W meridians. However, both comparisons of actual balloon sonde movement with reported GPS winds and comparisons of winds from simultaneous AIR sonde and GPS sonde flights indicate that, as the actual wind turns from easterly to become increasingly northerly and northwesterly, reported GPS sonde winds turn in the opposite direction, becoming more southerly and south-westerly, as defined in the grid wind system. This error in GPS winds caused unrealistic low level wind shear to be reported on 17 NOV 2001. At the surface, winds from grid 002 degrees at 17.3 KT were reported by the GPS calculations to have become from 197 degrees at 24.1KT within 28 meters of the surface. The actual winds, I feel confident, had turned not all the way to 197 degrees in the space of 28 meters, but had in fact backed slightly from the surface direction of 002 degrees to 343 degrees, the "mirror image" of the reported 197 degrees. Note that the surface winds (2835 meters) are placed in the sonde wind data report by the weather observer and retained in the final wind report unmodified. Winds above the surface are calculated from GPS data. Below is the correction we applied to the GPS radiosonde wind directions to get values in fair agreement with the comparison AIR radiosonde data obtained last winter. The correction is based on the assumption that the current algorithm used by the MRS to calculate grid wind direction results in wind directions from the NE and NW quadrants being assigned, respectively, to the SE and SW quadrants, and vice versa. The correction then simply puts the wind directions back into the correct quadrants by calculating the complement of a 180 degree angle as follows: IF UWD < 180, CWD = 180 - UWD IF UWD >= 180, CWD = (360 - UWD) + 180 = 540 - UWD where UWD is the uncorrected wind direction and CWD is the corrected wind direction The above correction applies to all flight files from Aug 1, 2001 0000Z through and including the Jan 4, 2002 1200Z sounding. A software upgrade then resulted in the Jan 5, 2002 0000Z sounding through and including the Jan 8, 2002, 1200Z sounding displaying a constant 180 degree error. As of the Jan 9, 2002, 0000Z sounding the grid wind directions reported by our sounding system are correct. We are trying to devise a method for correcting the 5+ months of erroneous wind data but it is yet to be determined whether or not this will be possible. ---------------------------------------------------------------------------- UPDATE 10/01/02: Corrections to the 5-plus months of flawed data files were completed in August. The corrected files were archived and sent to the AMRC. This project represented a major effort to maintain the quality of data produced by the department. It must be noted that completion of this project would not have been possible without the assistance of Jon Berry, Sr. Communications Technician. Mr. Berry was able to use his own software to write a script that applied the correction devised by one of the summer meteorologists to all of the sounding files from August 1, 2001 through January 8, 2002. Once the raw data files were re-processed by Mr. Berry and the corrections were confirmed the meteorologists were able to run the files through the normal post-flight processing routine. After an entire month's files were re-generated in this manner the monthly processing was replicated to produce the monthly upper air files. ---------------------------------------------------------------------------- Here's an explanation for the 00Z and 12Z designations: When we launch the 3K and 7K plastic balloons, their flights will generally last for 2+ hours. During the summer when it is warmer, even the 600 gram balloons will go for about two hours. By the time the flight is over and we have processed the sonde data and emailed it to McMurdo, it's getting close to 00Z or 12Z. In other words, I guess the thought was that the time of dissemination was the consistent factor and so why not use a naming convention that would be simple. Before we started using the GPS sondes, the A.I.R. software program would automatically tag the file names with the launch times. When we switched over to the GPS sondes, we had the ability to label the .gps file however we wanted. Then, our Microsoft Access program would convert that file to a .dat file with the same name before sending it to the A.I.R. program to finish processing. Instead of having files with a variety of names based on the launch time (i.e. 07202058.dat, 07212103.dat, etc.), all files would either be 0000.dat or 1200.dat. ---------------------------------------------------------------------------- Please let AMRC or the South Pole Meteorology Office know if you have any further questions. Hope this helps. Dar Gibson Sr. Meteorologist, RPSC South Pole Station, Antarctica Matthew Lazzara Antarctic Meteorological Research Center Space Science and Engineering Center University of Wisconsin-Madison