.. _levels:

Level type values
=================

This table lists the possible values for ``leveltype1`` or
``leveltype2`` and the interpretation of the corresponding numerical
value ``l1`` or ``l2``.  Leveltype values in the range 0-255 can
be used for defining either a single level (``leveltype1``) or a surface
delimiting a layer (``leveltype1`` and ``leveltype2``) with any meaningful
combination of leveltypes; values of ``leveltype`` ``>255`` have a special use
for encoding cloud values in SYNOP reports and they do not strictly
define physical surfaces.

The idea is borrowed from the GRIB edition 2 fixed surface
concept and the values for leveltype coincide with the GRIB standard
where possible.

.. list-table::
   :widths: auto
   :header-rows: 1

   * - Level type
     - Meaning
     - Unit/contents of ``l1``/``l2``

   * - 0
     - Reserved
     - 
   * - 1
     - Ground or Water Surface
     - 
   * - 2
     - Cloud Base Level
     - 
   * - 3
     - Level of Cloud Tops
     - 
   * - 4
     - Level of 0C Isotherm
     - 
   * - 5
     - Level of Adiabatic Condensation Lifted from the Surface
     - 
   * - 6
     - Maximum Wind Level
     - 
   * - 7
     - Tropopause
     - 
   * - 8
     - Nominal Top of the Atmosphere
     - DB-All.e encodes the channel number of polar satellites in L1
   * - 9
     - Sea Bottom
     - 
   * - 10-19
     - Reserved
     - 
   * - 20
     - Isothermal Level
     - K/10
   * - 21-99
     - Reserved
     - 
   * - 100
     - Isobaric Surface
     - Pa
   * - 101
     - Mean Sea Level
     - 
   * - 102
     - Specific Altitude Above Mean Sea Level
     - mm
   * - 103
     - Specified Height Level Above Ground
     - mm
   * - 104
     - Sigma Level
     - 1/10000
   * - 105
     - Hybrid Level
     - 
   * - 106
     - Depth Below Land Surface
     - mm
   * - 107
     - Isentropic (theta) Level
     - K/10
   * - 108
     - Level at Specified Pressure Difference from Ground to Level
     - Pa
   * - 109
     - Potential Vorticity Surface
     - 10-9 K m2 kg-1 s-1
   * - 110
     - Reserved
     - 
   * - 111
     - Eta (NAM) Level (see note below)
     - 1/10000
   * - 112-116 Reserved
     - 
     - 
   * - 117
     - Mixed Layer Depth
     - mm
   * - 118-159 Reserved
     - 
     - 
   * - 160
     - Depth Below Mean Sea Level
     - mm
   * - 161
     - Depth Below Water Surface
     - mm
   * - 162-191 Reserved
     - 
     - 
   * - 200
     - Entire atmosphere (considered as a single layer)
     - 
   * - 201
     - Entire ocean (considered as a single layer)
     - 
   * - 204
     - Highest tropospheric freezing level
     - 
   * - 206
     - Grid scale cloud bottom level
     - 
   * - 207
     - Grid scale cloud top level
     - 
   * - 209
     - Boundary layer cloud bottom level
     - 
   * - 210
     - Boundary layer cloud top level
     - 
   * - 211
     - Boundary layer cloud layer
     - 
   * - 212
     - Low cloud bottom level
     - 
   * - 213
     - Low cloud top level
     - 
   * - 214
     - Low cloud layer
     - 
   * - 215
     - Cloud ceiling
     - 
   * - 220
     - Planetary Boundary Layer
     - 
   * - 222
     - Middle cloud bottom level
     - 
   * - 223
     - Middle cloud top level
     - 
   * - 224
     - Middle cloud layer
     - 
   * - 232
     - High cloud bottom level
     - 
   * - 233
     - High cloud top level
     - 
   * - 234
     - High cloud layer
     - 
   * - 235
     - Ocean Isotherm Level
     - K/10
   * - 240
     - Ocean Mixed Layer
     - 
   * - 241
     - Ordered Sequence of Data
     - 
   * - 242
     - Convective cloud bottom level
     - 
   * - 243
     - Convective cloud top level
     - 
   * - 244
     - Convective cloud layer
     - 
   * - 245
     - Lowest level of the wet bulb zero
     - 
   * - 246
     - Maximum equivalent potential temperature level
     - 
   * - 247
     - Equilibrium level
     - 
   * - 248
     - Shallow convective cloud bottom level
     - 
   * - 249
     - Shallow convective cloud top level
     - 
   * - 251
     - Deep convective cloud bottom level
     - 
   * - 252
     - Deep convective cloud top level
     - 
   * - 253
     - Lowest bottom level of supercooled liquid water layer
     - 
   * - 254
     - Highest top level of supercooled liquid water layer
     - 
   * - 256
     - Clouds
     - 
   * - 257
     - Information about the station that generated the data
     - 
   * - 258
     - (use when ltype1=256) Cloud Data group, L2 = 1 low clouds, 2 middle clouds, 3 high clouds, 0 others
     - 
   * - 259
     - (use when ltype1=256) Individual cloud groups, L2 = group number
     - 
   * - 260
     - (use when ltype1=256) Cloud drift, L2 = group number
     - 
   * - 261
     - (use when ltype1=256) Cloud elevation, L2 = group number; (use when ltype1=264) L2 = swell wave group number
     - 
   * - 262
     - (use when ltype1=256) Direction and elevation of clouds, L2 is ignored
     - 
   * - 263
     - (use when ltype1=256) Cloud groups with bases below station level, L2 = group number
     - 
   * - 264
     - Waves
     - 
   * - 265     Non-physical data level
     - 
     -