- Model levels (Operational, ERA-15 and ERA-40 data).
- Pressure levels (held for Operational, ERA-15 and ERA-40 data).
- Potential Temperature levels (Operational and ERA-40 data).
- Potential Vorticity levels (Operational and ERA-40 data).

This page gives a description of each atmospheric level type.

The use of *model levels* (also often called σ-levels) instead of standard pressure levels addresses the problem of discontinuities by creating atmospheric levels that follow the contours of the Earth's surface in the lower and mid-troposphere. As the altitude increases (i.e. in the upper stratosphere and mesosphere), the effect of the surface orography lessens until the vertical layers in the upper atmosphere are the same as pressure levels.

The ECMWF web pages contain more documentation on model levels.

The current Operational model divides the atmosphere into 91 layers up to 0.1 hPa (about 64 km). The vertical resolution is highest in the planetary boundary layer and lowest in the stratosphere and lower mesosphere. The Operational dataset includes data archived at 31, 60 and 91 model levels. The ERA-40 datasets includes data archived on 60 model levels only.

The BADC archives model level data for the following ECMWF data sets:

- Operational data on a regular 1.125° x 1.125° grid from October 1998 - present (see the parameters page for more details).
- Operational data at a T106 Spectral resolution from March 1994 - October 2000 (see the parameters page for more details).
- Operational data at a T159 Spectral resolution from September 2002 - present (see the parameters page for more details).
- Operational data on a
Reduced N80 Gaussian grid from September 2002 - present (see the parameters page for more details).
- ERA-15 Re-analysis at a T106 Spectral resolution from January 1979 - February 1994 (see the parameters page for more details).
- ERA-15 Re-analysis on a
Reduced N80 Gaussian grid
January 1979 - February 1994 (see the
parameters page for more details).
- ERA-40 Re-analysis at a T159 Spectral resolution (see status page for details of what years are available and the parameters page for details of the data).
- ERA-40 Re-analysis on a Reduced N80 Gaussian grid (see status page for details of what years are available and the parameters page for details of the data).

Model levels are calculated in relation to the surface pressure using a method detailed in the Dynamics and numerical procedures section of the Integrated Forecasting System (IFS) documentation.

Table 1 provides an example of the pressure of the 91 model levels (as used in the current Operational model) when the surface pressure is 1013.250 hPa.

**Table 1.** Pressure of model levels when the surface pressure is 1013.250 hPa.

Level Number | hPa | Level Number |
hPa | Level Number | hPa | Level Number |
hPa
| Level Number | hPa |

1 | 0.0100 | 21 | 15.8844 | 41 | 117.5942 | 61 | 417.7338 | 81 | 925.2226 |

2 | 0.0299 | 22 | 18.5179 | 42 | 125.7453 | 62 | 443.3441 | 82 | 940.4416 |

3 | 0.0568 | 23 | 21.4101 | 43 | 134.3981 | 63 | 470.1659 | 83 | 954.0914 |

4 | 0.1015 | 24 | 24.5653 | 44 | 143.5909 | 64 | 497.9584 | 84 | 966.1707 |

5 | 0.1716 | 25 | 27.9860 | 45 | 153.3538 | 65 | 526.4620 | 85 | 976.6735 |

6 | 0.2768 | 26 | 31.6736 | 46 | 163.7180 | 66 | 555.3989 | 86 | 985.6311 |

7 | 0.4285 | 27 | 35.6281 | 47 | 174.7166 | 67 | 584.4855 | 87 | 993.3027 |

8 | 0.6396 | 28 | 39.8481 | 48 | 186.3837 | 68 | 613.4989 | 88 | 999.8373 |

9 | 0.9244 | 29 | 44.3310 | 49 | 198.7556 | 69 | 642.2899 | 89 | 1005.1222 |

10 | 1.2985 | 30 | 49.0732 | 50 | 211.8697 | 70 | 670.7310 | 90 | 1009.1459 |

11 | 1.7781 | 31 | 54.0701 | 51 | 225.7656 | 71 | 698.7032 | 91 | 1012.0494 |

12 | 2.3800 | 32 | 59.3150 | 52 | 240.4844 | 72 | 726.0656 | ||

13 | 3.1209 | 33 | 64.7978 | 53 | 256.0690 | 73 | 752.6718 | ||

14 | 4.0176 | 34 | 370.5061 | 54 | 272.5644 | 74 | 778.4036 | ||

15 | 5.0860 | 35 | 76.4292 | 55 | 290.0175 | 75 | 803.1575 | ||

16 | 6.3417 | 36 | 82.5725 | 56 | 308.4774 | 76 | 826.8141 | ||

17 | 7.7988 | 37 | 88.9589 | 57 | 327.9948 | 77 | 849.2512 | ||

18 | 9.4706 | 38 | 95.6172 | 58 | 348.6233 | 78 | 870.3798 | ||

19 | 11.3688 | 39 | 102.5813 | 59 | 370.4182 | 79 | 890.1340 | ||

20 | 13.5037 | 40 | 109.8913 | 60 | 393.4375 | 80 | 908.4403 |

The ECMWF converts model level data to pressure levels with a loss of vertical resolution. For example, when the Operational model included 31 model levels, these were available on 15 pressure levels, in the current Operational model 60 model levels are converted to 21 pressure levels.

The BADC archives the following data sets on pressure levels:

- Operational data on a regular 2.5° grid from March 1994 - present (see the parameters page for more details).
- Operational data at a T106 Spectral resolution from March 1994 - February 1999 (see the parameters page for more details).
- Operational data at a T159 Spectral resolution from September 2002 - present (see the parameters page for more details).
- Operational data on a
Reduced N80 Gaussian grid from September 2002 - present (see the parameters page for more details).
- ERA-15 Re-analysis at a
T106 Spectral resolution
January 1979 - February 1994 (see the
parameters page for more details).
- ERA-40 Re-analysis at a T159 Spectral resolution (see status page for details of what years are available and the parameters page for details of the data).
- ERA-40 Re-analysis on a Reduced N80 Gaussian grid (see status page for details of what years are available and the parameters page for details of the data).

The BADC archives the following data sets on potential temperature levels:

- Operational data at a T159 Spectral resolution from September 2002 - present (see the parameters page for more details).
- Operational data on a
Reduced N80 Gaussian grid from September 2002 - present (see the parameters page for more details).
- ERA-40 Re-analysis at a T159 Spectral resolution (see status page for details of what years are available and the parameters page for details of the data).
- ERA-40 Re-analysis on a Reduced N80 Gaussian grid (see status page for details of what years are available and the parameters page for details of the data).

**Table 2.** Isentropic levels and corresponding pressures and heights.

Potential Temperature (K) |
Pressure (hPa) |
Height (km) |
---|---|---|

The BADC archives the following data sets on potential vorticity levels:

- Operational data on a
Reduced N80 Gaussian grid from September 2002 - present (see the parameters page for more details).