IGRA v2.2 Format Description: Files of Derived Sounding Parameters Last updated: 19 January 2023 --------------------- Notes: --------------------- 1. This format description is formatted for viewing in a text editor such as Windows Notepad or similar Linux-based editor. 2. The below format description applies to versions 2.0 to 2.2 of IGRA. 3. Sounding-derived parameters are available for a subset of the soundings in IGRA. This subset includes soundings at fixed observing stations on land that contain temperature observations and a surface pressure level. The parameters include precipitable water between the surface and 500 hPa, the refractive index, vertical gradients of several variables, and various measures of boundary-layer characteristics and stability. 4. The derived parameters are updated once a day in the early morning Eastern Time. 5. Each "-drvd.txt.zip" file contains the sounding-derived parameters for one station. The name of the file corresponds to a station's IGRAv2.2 identifier (e.g., "USM00072201-drvd.txt.zip" contains the derived parameters for the station with the identifier USM00072201). 6. Each file contains a series of multiline sounding records, each of which consists of a header record followed by one line of data for each pressure level in the sounding. Non-pressure levels are not included. 7. All missing parameter values are coded as -99999. --------------------- Header Record Format: --------------------- --------------------------------- Variable Columns Type --------------------------------- HEADREC 1- 1 Character ID 2- 12 Character YEAR 14- 17 Integer MONTH 19- 20 Integer DAY 22- 23 Integer HOUR 25- 26 Integer RELTIME 28- 31 Integer NUMLEV 32- 36 Integer PW 38- 43 Integer INVPRESS 44- 49 Integer INVHGT 50- 55 Integer INVTEMPDIF 56- 61 Integer MIXPRESS 62- 67 Integer MIXHGT 68- 73 Integer FRZPRESS 74- 79 Integer FRZHGT 80- 85 Integer LCLPRESS 86- 91 Integer LCLHGT 92- 97 Integer LFCPRESS 98-103 Integer LFCHGT 104-109 Integer LNBPRESS 110-115 Integer LNBHGT 116-121 Integer LI 122-127 Integer SI 128-133 Integer KI 134-139 Integer TTI 140-145 Integer CAPE 146-151 Integer CIN 152-157 Integer --------------------------------- These variables have the following definitions: HEADREC is the header record indicator (always set to "#"). ID is the station identification code. See "igrav2.2-stations.txt" for a complete list of stations and their names and locations. YEAR is the year of the sounding. MONTH is the month of the sounding. DAY is the day of the sounding. HOUR is the hour of the sounding (99 = missing). RELTIME is the release time of the sounding (format HHMM, missing=9999). NUMLEV is the number of levels in the sounding (i.e., the number of data records that follow). PW is the precipitable water (mm*100) between the surface and 500 hPa. INVPRESS is the pressure (in Pa or mb*100) at the level of the warmest temperature in the sounding. Only provided if the warmest temperature is above the surface. INVHGT is the height (in meters above the surface) of the warmest temperature in the sounding. Only provided when the warmest temperature is above the surface. INVTEMPDIF is the difference between the warmest temperature in the sounding and the surface temperature (K * 10). Only provided if the warmest temperature is above the surface. MIXPRESS is the pressure (in Pa or mb * 100) at the top of the mixed layer as determined using the parcel method. MIXHGT is the height (in meters above the surface) of the top of the mixed layer As determined using the parcel method. FRZPRESS is the pressure (in Pa or mb * 100) where the temperature first reaches the freezing point when moving upward from the surface. Determined by interpolating linearly with respect to the logarithm of pressure between adjacent reported levels. Not provided if the surface temperature is below freezing. FRZHGT is the height (in meters above the surface) where the temperature first reaches the freezing point when moving upward from the surface. Determined analogously to FRZPRESS. Not provided if the surface temperature is below freezing. LCLPRESS is the pressure (in Pa or mb * 100) of the lifting condensation level. LCLHGT is the height (in meters above the surface) of the lifting condensation level. LFCPRESS is the pressure (in Pa or mb * 100) of the level of free convection. LFCHGT is the height (in meters above the surface) of the level of free convection. LNBPRESS is the pressure (in Pa or mb * 100) of the level of neutral buoyancy (or equilibrium level). LNBHGT is the height (in meters above the surface) of the level of neutral buoyancy (or equilibrium level). LI is the lifted index (in degrees C). SI is the Showalter index (in degrees C). KI is the K index (in degrees C). TTI is the total totals index (in degrees C). CAPE is the convective available potential energy (in J/kg). CIN is the convective inhibition (in J/kg). --------------------- Data Record Format: --------------------- In the data records following each header record, the first record always represents the surface level. The variables in each data record include the following: ------------------------------- Variable Columns Type ------------------------------- PRESS 1- 7 Integer REPGPH 9- 15 Integer CALCGPH 17- 23 Integer TEMP 25- 31 Integer TEMPGRAD 33- 39 Integer PTEMP 41- 47 Integer PTEMPGRAD 49- 55 Integer VTEMP 57- 63 Integer VPTEMP 65- 71 Integer VAPPRESS 73- 79 Integer SATVAP 81- 87 Integer REPRH 89- 95 Integer CALCRH 97-103 Integer RHGRAD 105-111 Integer UWND 113-119 Integer UWDGRAD 121-127 Integer VWND 129-135 Integer VWNDGRAD 137-143 Integer N 145-151 Integer ------------------------------- These variables have the following definitions: PRESS is the reported pressure (Pa or mb * 100). REPGPH is the reported geopotential height (meters). This value is often not available at significant levels. CALCGPH is the calculated geopotential height (meters). The geopotential height has been estimated by applying the hydrostatic balance to the atmospheric layer between the next lower level with a reported geopotential height and the current level. TEMP is the reported temperature (K * 10). TEMPGRAD is the temperature gradient between the current level and the next higher level with a temperature [(K/km) * 10, positive if temperature increases with height]. PTEMP is the potential temperature (K * 10). PTEMPGRAD is the potential temperature gradient between the current level and the next higher level with a potential temperature [(K/km) * 10, positive if potential temperature increases with height]. VTEMP is the virtual temperature (K * 10). VPTEMP is the virtual potential temperature (K * 10). VAPPRESS is the vapor pressure (mb * 1000) as computed from temperature, pressure, and dewpoint depression at the same level. SATVAP is the saturation vapor pressure (mb * 1000) as computed from pressure and temperature at the same level. REPRH is the relative humidity (Percent * 10) as reported in the original sounding. CALCRH is the relative humidity (Percent * 10) as calculated from vapor pressure, saturation vapor pressure, and pressure at the same level. RHGRAD is the relative humidity gradient between the current level and the next higher usable level [(%/km) * 10, positive if relative humidity increases with height]. UWND is the zonal wind component [(m/s) * 10] as computed from the reported wind speed and direction. UWDGRAD is the vertical gradient of the zonal wind between the current level and the next higher level with a wind observation [(m/s per km) * 10, positive if zonal wind becomes more positive with height]. VWND is the meridional wind component [(m/s) * 10] as computed from the reported wind speed and direction. VWNDGRAD is the vertical gradient of the meridional wind component between the current level and the next higher level with a wind observation [(m/s per km) * 10, positive if the meridional wind becomes more positive with height]. N is the refractive index (unitless). -------------------------------------------------------------------------------- --------------------------------------------------------------------------------