INDOEX: Maldives Kaashidhoo Climate Observatory Rawinsonde Soundings 1.0 General Description One hundred and eighty three rawinsondes were successfully launched from the Kaashidhoo Climate Observatory (KCO) during INDOEX . All of the soundings were made with Vaisala RS80 sondes which utilized GPS tracking to determine the winds. The Joint Office of Science Support (JOSS) received the KCO rawinsonde dataset from the Atmospheric Technology Division (ATD). This dataset underwent ATD (Section 2.0) and JOSS (Section 6.0) quality control procedures. 2.0 Atmospheric Technology Division (ATD) Quality Control Intro This section is taken from the Quality Control Procedures chapter of the Avaps Editor User Manual (NCAR 1999). ATD performed quality control on the KCO soundings using the AVAPS Editor. A primary purpose of the Avaps editor is applying quality control algorithms to a sounding. The algorithms attempt to systematically detect observations that are likely incorrect, and remove them from the QC data set. QC processing begins with a copy of the original observations. In most cases, all parameters are considered separately except wind observations. In this case, the wind speed and direction are separated into u and v components, and the QC tests are individually applied. If one of the two components fail a test then both components as well as the original speed and direction are removed from the QC data. In some QC algorithms, the checking of one parameter requires input from another. For example, the GPS measured velocity is used as a discriminator for the horizontal wind observations. In another example, the dynamic adjustment procedure requires the time constant of the sensor making the measurement. This time constant is a function of density and ventilation rate, which are obtained from the pressure and vertical velocity. The following is a brief description of the AVAP Editor's QC processing steps for upsondes and the order which they are applied. 2.1 ATD Quality Control Procedures using AVAPS Editor 2.1.2 Launch Parameter overrides. Checks near surface pressure, temperature, or relative humidity. The user specified launch parameters overrides are substituted in place of the original data. This mechanism is especially useful if missing or corrected launch parameters are obtained after the sounding was made. The launch parameters are the surface or aircraft flight level observation made at the time of launch. They become either the bottom or top point in the sounding, depending on the sounding direction. 2.1.3 End of ascent override If user has specified an end of ascent time, all data beyond this time is removed. 2.1.4 Apply fixed offsets Fixed offsets can be added to pressure, temperature, and relative humidity 2.1.5 Limit Checks Absolute bounds checks are used to discard measurements falling out side of hard limits. The limits are between : 1mb and 1200mb for pressure, -100 deg C and 50 deg c for temperature, 0% and 100% for relative humidity, 0 m/s and 150 m/s for wind speed, and 0 and 360 degrees for wind direction. 2.1.6 Satellite Check GPS derived winds are not reliable if an insufficient number of satellites are used in their computation. If the number of satellites is below a minimum, the associated wind observation is discarded. 2.1.7 Buddy Check This test uses the data points on either side of an observation as a consistency check, and is useful for detecting and removing wild points. Since the neighboring points may be separated from the observation by varying time deltas, the buddy check thresholds are specified in terms of change per unit time. A point is discarded if it shows a change greater than the limit for one neighbor, and a change greater than the limit but of the opposite sign, for the other neighbor. Pressure, temperature, relative humidity, and wind undergo this check. 2.1.8 Outliers Check A least squares linear fit to the data series is calculated. Data points that are a specified multiple of the standard deviation from the linear fit are removed from the data set. Pressure, temperature, relative humidity, and wind undergo this check. 2.1.9 Filter Check A copy of the data series is filtered at a given wavelength. Data points are removed if they differ from the filtered series by greater than a fixed amount. Pressure, temperature, relative humidity, and wind undergo this check. 2.1.10 Pressure Smoothing The final filtering is applied to the pressure data. The pressure needs to be smoothed before the pressure monotonic check. 2.1.11 Monotonic Pressure Check The pressure trace is required to be monotonically changing, in order for the pressure-based searching to be performed. The pressure time series is scanned; when a point is found which follows the incorrect trend (i.e decreasing for an dropsonde, increasing otherwise) it is removed from the series. 2.1.12 RH Lower Limiting Relative humidity values less than 0.2% are set to 0.2%. 2.1.13 Smoothing Time series of temperature,relative humidity, and wind are smoothed, using the final smoothing wavelength. 2.1.14 Compute Vertical Velocity The pressure series is first smoothed using the final pressure-smoothing wavelength. The time tendency of the pressure is then computed at each data point. The time differentiated hydrostatic equation is then used to compute the vertical velocity of the sonde. 2.1.15 Vertical Velocity Check The GPS measured fall velocity is a good discriminator for the quality of the GPS derived horizontal wind. If the difference between the hydrostatically determined fall velocity and the GPS measured velocity is greater than the specified limit, the horizontal wind point is discarded. 2.1.16 Winds Dynamic Adjustment Each wind component is adjusted with the formula:Unew=Uobs-(du/dt)*(dz/dt)/g. The wind component series is first smoothed, using the final smoothing wavelength for the component. This smoothed series is used to compute a time tendency for each data point. The observation is then adjusted according to the formula, using the previously calculated vertical velocity for dz/dt. 2.1.17 Compute Altitude The hydrostatic equation is integrated from the surface upwards. 2.1.18 Compute Position The horizontal winds are used to integrate the sonde location from the initial launch position. If a time gap of greater than 60 seconds occurs in the wind measurements, the integration terminates. 2.2 ATD Sensor Arm Heating Relative Humidity (SAH) Correction Errors in low level relative humidity can be attributed to direct solar heating of the sensor arm. The heating of the sensor arm affects humidity since the saturation vapor pressure is increased due to the increase in sensor arm temperature (See Cole and Miller , 1995). A few KCO soundings exhibited clear indications of SAH . In order to correct these soundings for low level relative humidity errors due to SAH, an estimate of the RH error due to SAH is made at the surface using a RH and surface temperature from an independent surface sensor and the sonde's surface RH and temperature. The RH error is used with the thermal time constant of the sensor arm to come up with a point by point RH value correction.The correction is run for the first 60 seconds of the sonde ascent. After that amount of time, the ventilation of the sensor brings the sensor arm completely back to thermal equilibrium with its environment. The corrected RH values are then used to derive corrected dew point values. SAH corrected soundings contain the following line in the class format header: "Additional comments: CORRECTED for sensor arm heating:". JOSS class format is described below in section 5.0 and sample headers from a SAH corrected file and an uncorrected file are provided in section 5.3. 2.3 ATD comments on Dry Bias in INDOEX soundings The problem of a dry bias in radiosonde humidity measurement is not apparent in the INDOEX data set. The oldest sondes used in INDOEX were less than three months old and many that were used were closer to two months old. Furthermore, these sondes were manufactured after an August 1998 packaging desicant change made at Vaisala which reduced the sonde RH sensor's susceptibility to dry bias due to contamination. In addition, the currently available correction was created for sondes using a different desicant and thus it would not be appropriate to apply this correction to the INDOEX sondes. Consequently, no dry bias correction was applied to the KCO data set. However a check was performed by running the dry bias correction algorithm based upon a sonde's age (this is determined by using the sonde serial numbers) and the resulting corrected soundings were obviously over corrected. For more information on dry bias, see Cole and Miller, 1999. The sonde data were also quality controlled at the Joint Office for Science Support (JOSS) at NCAR, using methods similar to those used to quality control the TOGA COARE sounding data (Loehrer et al., 1996; their sections 3a-e). See section 6.0 for more details on JOSS quality control procedures for the KCO Rawinsonde data set. 3.0 Parameters in Raw Dataset Parameters Units -------------------------------------- Time Seconds Pressure Millibars Temperature Deg C Dew Point Deg C Relative Humidity % U wind component m/s V wind component m/s Wind Speed m/s Wind Direction Deg Ascension Rate m/s Longitude Deg Latitude Deg Range km Azimuth Angle Deg Altitude Geopotential Meters Pressure Quality Code mb Temp Quality Code Deg C Humidity Quality Code Deg C U comp Quality Code m/s V comp Quality Code m/s UV Quality Code m/s -------------------------------------- 4.0 Conversion to JOSS CLASS format (ASCII text) 4.1 The raw 1 sec vertical resolution time, temperature, relative humidity, altitude, pressure, dew point, wind direction, and wind speed were kept without change. 4.2 The ascension rate was calculated for each data point (excluding the surface, where it was given a missing value) based on the altitude and time at two levels, the current 1 sec level and the previous 1 sec level. If the data point for which the ascension rate was being calculated had missing time or altitude, the ascension rate was not calculated at that level and was flagged as missing. If the data point prior to that for which the ascension rate was being calculated had a missing time or altitude, then the data point two data points prior to the present one was used, and so on until one with non-missing time and altitude was found. If there are no non-missing previous data points the ascension rate is set to missing. 4.3 Due to CLASS format constraints, Dew Points less than -99.9 Deg C were given a value of -99.9 Deg C and were flagged as being questionable. 5.0 JOSS CLASS Format (ASCII text) Description 5.1 Header records The header records (15 total records) contain data type, project ID, site ID, site location, actual release time, nominal release time, and possibly other specialized information. The first five header lines contain information identifying the sounding, and have a rigidly defined form. The following 6 header lines are used for auxiliary information and comments about the sounding, and they vary significantly from dataset to dataset (For KCO these lines contain information on the radiosonde and other information). Line 12 contains the Nominal date and time of the release. The last 3 header records contain header information for the data columns. Line 13 holds the field names, line 14 the field units, and line 15 contains dashes ('-' characters) delineating the extent of the field. The six standard header lines are as follows: Line Label (fixed to 35 char in length) Contents 1 Data Type: Description of type and resolution of data. 2 Project ID: ID of weather project. 3 Release Site Type/Site ID: Description of release site. 4 Release Location (lon,lat,alt): Position of release site, in format described below. 5 UTC Release Time: Time of release, in format: yyyy, mm, dd, hh:mm:ss 12 UTC Nominal Release Time: Nominal release time. The release location is given as: lon (deg min), lat (deg min), lon (dec. deg), lat (dec. deg), alt (m) Longitude in deg min is in the format: ddd mm.mm'W where ddd is the number of degrees from True North (with leading zeros if necessary), mm.mm is the decimal number of minutes, and W represents W or E for west or east longitude, respectively. Latitude has the same format as longitude, except there are only two digits for degrees and N or S for north/south latitude. The decimal equivalent of longitude and latitude and station elevation follow. The six non-standard header lines may contain any label and contents. The label is fixed to 35 characters to match the standard header lines. Sample header records are provided in the sample data file in section 5.3. 5.2 Data records The data records each contain time from release, pressure, temperature, dew point, relative humidity, U and V wind components, wind speed and direction, ascent rate, balloon position data, altitude, and quality control flags (see QC code description). Each data line contains 21 fields, separated by spaces, with a total width of 130 characters. The data are right-justified within the fields. All fields have one decimal place of precision, with the exception of latitude and longitude, which have three decimal places of precision. The contents and sizes of the 21 fields that appear in each data record are as follows: Field Format Missing No. Width Parameter Units Value ---------------------------------------------------------------------- 1 6 F6.1 Time Seconds 9999.0 2 6 F6.1 Pressure Millibars 9999.0 3 5 F5.1 Dry-bulb Temperature Degrees C 999.0 4 5 F5.1 Dew Point Temperature Degrees C 999.0 5 5 F5.1 Relative Humidity Percent 999.0 6 6 F6.1 U Wind Component Meters/Second 9999.0 7 6 F6.1 V Wind Component Meters/Second 9999.0 8 5 F5.1 Wind Speed Meters/Second 999.0 9 5 F5.1 Wind Direction Degrees 999.0 10 5 F5.1 Ascension Rate Meters/Second 999.0 11 8 F8.3 Longitude Degrees 9999.0 12 7 F7.3 Latitude Degrees 999.0 13 5 F5.1 Variable (see below) 999.0 14 5 F5.1 Variable (see below) 999.0 15 7 F7.1 Altitude Meters 99999.0 16 4 F4.1 QC flag for Pressure Code (see below) 99.0 17 4 F4.1 QC flag for Temperature Code (see below) 99.0 18 4 F4.1 QC flag for Humidity Code (see below) 99.0 19 4 F4.1 QC flag for U Component Code (see below) 99.0 20 4 F4.1 QC flag for V Component Code (see below) 99.0 21 4 F4.1 QC flag for Ascension Rate Code (see below) 99.0 ---------------------------------------------------------------------- Fields 13 and 14 are `variable' because depending on the sounding system the variables used in these positions can vary. For the KCO soundings, these fields have been set to missing. Fields 16 through 21 contain the Quality Control information (flags) generated locally at JOSS. These flags are based on the automated or visual checks made. See Sections 6.0 and 7.0 for further information. The JOSS QC flags are as follows: Code Description ---------------------------------------------------------------------- 99.0 Unchecked (QC information is `missing.') (`UNCHECKED') 1.0 Checked, datum seems physically reasonable. (`GOOD') 2.0 Checked, datum seems questionable on physical basis. (`MAYBE') 3.0 Checked, datum seems to be in error. (`BAD') 4.0 Checked, datum is interpolated. (`ESTIMATED') 9.0 Checked, datum was missing in original file. (`MISSING') ---------------------------------------------------------------------- 5.3 Sample data The following is a sample portion of a JOSS CLASS format file including header records. The data portion is much longer than 80 characters and, therefore, wraps around to a second line. Data Type: High Resolution Sounding Project ID: INDOEX Release Site Type/Site ID: Kaashidhoo KAA Release Location (lon,lat,alt): 73 27.96'E, 4 57.90'N, 73.47, 4.96, 1.0 UTC Release Time (y,m,d,h,m,s): 1999, 03, 29, 12:20:30 Sonde Type/ID/Sensor ID/Tx Freq: VAISALA RS80-15GH 902606703, 0, 403.100 Met Processor/Met Smoothing: NCAR RS80 Processor, 10SECONDS Winds Type/Processor/Smoothing: GPS, Vaisala MWG201, 40SECONDS System Operator/Comments: wilcox, Input File: y3291216.kaa / Nominal Release Time (y,m,d,h,m,s):1999, 03, 29, 12:20:30 Time Press Temp Dewpt RH Ucmp Vcmp spd dir Wcmp Lon Lat Ele Azim Alt Qp Qt Qrh Qu Qv QdZ sec mb C C % m/s m/s m/s deg m/s deg deg deg deg m code code code code code code ------ ------ ----- ----- ----- ------ ------ ----- ----- ----- -------- ------- ----- ----- ------- ---- ---- ---- ---- ---- ---- -1.0 1007.3 29.6 23.7 70.0 1.1 -1.4 1.8 323.0 999.0 9999.000 999.000 999.0 999.0 1.0 3.0 3.0 3.0 99.0 99.0 9.0 0.0 1006.6 29.4 23.6 70.3 0.7 -1.2 1.3 330.3 999.0 73.466 4.965 999.0 999.0 1.0 3.0 3.0 3.0 99.0 99.0 9.0 1.0 1005.1 29.2 23.2 69.9 9999.0 9999.0 999.0 999.0 19.2 73.466 4.965 999.0 999.0 20.2 3.0 2.0 2.0 9.0 9.0 99.0 2.0 1004.1 29.0 23.2 70.2 9999.0 9999.0 999.0 999.0 9.4 73.466 4.965 999.0 999.0 29.6 3.0 2.0 2.0 9.0 9.0 99.0 3.0 1003.4 29.0 23.3 70.8 9999.0 9999.0 999.0 999.0 5.7 73.466 4.965 999.0 999.0 35.3 2.0 99.0 99.0 9.0 9.0 99.0 The following is a sample portion of a JOSS CLASS format file including header records. The data portion is much longer than 80 characters and, therefore, wraps around to a second line. This is a SAH corrected header. Data Type: High Resolution Sounding Project ID: INDOEX Release Site Type/Site ID: Kaashidhoo KAA Release Location (lon,lat,alt): 73 27.96'E, 4 57.96'N, 73.47, 4.97, 1.0 UTC Release Time (y,m,d,h,m,s): 1999, 01, 13, 14:35:52 Sonde Type/ID/Sensor ID/Tx Freq: VAISALA RS80-15GH 849300715, 0, 402.700 Met Processor/Met Smoothing: NCAR RS80 Processor, 10SECONDS Winds Type/Processor/Smoothing: GPS, Vaisala MWG201, 40SECONDS System Operator/Comments: Bhandari, No more change in raw data. Average data all 999 Input File: z1131430.kaa Additional comments: CORRECTED for sensor arm heating: rh_htg = 4.0 Nominal Release Time (y,m,d,h,m,s):1999, 01, 13, 14:35:52 Time Press Temp Dewpt RH Ucmp Vcmp spd dir Wcmp Lon Lat Ele Azim Alt Qp Qt Qrh Qu Qv QdZ sec mb C C % m/s m/s m/s deg m/s deg deg deg deg m code code code code code code ------ ------ ----- ----- ----- ------ ------ ----- ----- ----- -------- ------- ----- ----- ------- ---- ---- ---- ---- ---- ---- -1.0 1008.6 29.0 22.3 66.4 -1.7 -0.6 1.8 69.0 999.0 9999.000 999.000 999.0 999.0 1.0 3.0 3.0 3.0 99.0 99.0 9.0 1.0 1007.5 29.5 22.5 66.1 9999.0 9999.0 999.0 999.0 999.0 73.466 4.966 999.0 999.0 10.5 3.0 3.0 3.0 9.0 9.0 9.0 2.0 1007.0 29.1 22.2 66.3 9999.0 9999.0 999.0 999.0 4.4 73.466 4.966 999.0 999.0 14.9 3.0 3.0 3.0 9.0 9.0 99.0 3.0 1006.5 28.5 21.9 67.7 9999.0 9999.0 999.0 999.0 4.9 73.466 4.966 999.0 999.0 19.8 3.0 3.0 3.0 9.0 9.0 99.0 6.0 Quality Control Procedures This dataset underwent the JOSS QC process which consisted of internal consistency checks. The internal consistency checks included gross limit checks on all parameters and vertical consistency checks on temperature, pressure, and ascension rate. 6.1 Automated Quality Control Procedures 6.1.1 Gross Limit Checks These checks were conducted on each sounding and data were automatically flagged as appropriate. Only the data point under examination was flagged. JOSS conducted the following gross limit checks on the KCO INDOEX sounding dataset. In the table P = pressure, T = temperature, RH = relative humidity, U = U wind component, V = V wind component, B = bad, and Q = questionable. ---------------------------------------------------------------- Parameter(s) Flag Parameter Gross Limit Check Flagged Applied ---------------------------------------------------------------- Pressure < 0 mb or > 1030 mb P B Altitude < 0 m or > 40000 m P, T, RH Q Temperature < -99.9C or > 40C T Q Dew Point < -99.9C or > 30C RH Q > Temperature T, RH Q Relative Humidity < 0% or > 100% RH B Wind Speed < 0 m/s or > 100 m/s U, V Q > 150 m/s U, V B U Wind Component < 0 m/s or > 70 m/s U Q > 150 m/s U B V Wind Component < 0 m/s or > 70 m/s V Q > 150 m/s V B Wind Direction < 0 deg or > 360 deg U, V B Ascent Rate < -10 m/s or > 10 m/s P, T, RH Q ---------------------------------------------------------------- 6.1.2 Vertical Consistency Checks These checks were conducted on each sounding and data were automatically flagged as appropriate. These checks were started at the lowest level of the sounding and compared neighboring values. In the case of checks ensuring that the values increased/decreased as expected, only the data point under examination was flagged. However, for the other checks, all of the data points used in the examination were flagged. All items within the table are as previously defined. ---------------------------------------------------------------- Vertical Consistency Parameter(s) Flag Parameter Check Flagged Applied ---------------------------------------------------------------- Time decreasing/equal None None Altitude decreasing/equal P, T, RH Q Pressure increasing/equal P, T, RH Q > 1 mb/s or < -1 mb/s P, T, RH Q > 2 mb/s or < -2 mb/s P, T, RH B Temperature < -15 C/km P, T, RH Q < -30 C/km P, T, RH B from surface to 150 mb: > 15 C/km (not applied at p < 150mb) P, T, RH Q > 30 C/km (not applied at p < 150mb) P, T, RH B for pressures < 150 mb: > 100 C/km (not applied at p > 150mb) P, T, RH Q > 10000 C/km (not applied at p > 150mb) P, T, RH B Ascent Rate change of > 3 m/s or < -3 m/s P Q change of > 5 m/s or < -5 m/s P B ---------------------------------------------------------------- 7.0 References Cole, H. and E. Miller, 1995: A correction for low level radiosonde temperature and relative humidity measurements. Preprints, Ninth Symposium on Meteorological Observations and Instrumentation, Charlotte, NC, American Meteorological Society,49-54. Cole, H. and E. Miller, 1999: Correction and re-calculation of humidity data from TOGA COARE radiosondes and development of humidity correction for global radiosonde data. Proceedings WCRP COARE-99 Conference, Boulder, CO, WCRP 107, WMO/TD-940, 139-141. Loehrer, S. M., T. A. Edmands and J. A. Moore, 1996: "TOGA COARE upper-air sounding data archive: development and quality control procedures", BAMS, 77, 2651-2671. Lucas, C. and E.J. Zipser, 1996: "The Variability of Vertical Profiles of Wind, Temperature and Moisture During TOGA COARE". Seventh Conference on Mesoscale Processes, September 9-13, 1996, Reading, UK. American Meteorological Society, Boston, 125-127. National Center for Atmospheric Research (NCAR), 1999: "Quality Control Procedures", Avaps Editor User Manual, 19-25. Weller, R. A. and S. P. Anderson, 1996: "Surface meteorology and air-sea fluxes in the western equatorial Pacific warm pool during the TOGA Coupled Ocean Atmosphere Response Experiment", J. Climate, 9, 1959-1990.