is computed as
where T is the temperature, po
the reference pressure (1013.25 mb), p the pressure, R the gas constant for dry air
(287.04 J kg-1 K-1), and Cp the specific heat capacity of dry air at
constant pressure (1004.6 J kg-1 K-1).Last updated: 2012-07-17 by David Stepaniak (davestep@ucar.edu)
The 37 standard pressure levels in ERA-Interim in mb (or hPa) are, from highest isobaric altitude to lowest isobaric altitude in the atmosphere:
1, 2, 3, 5, 7, 10, 20, 30, 50, 70, 100, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 775, 800, 825, 850, 875, 900, 925, 950, 975, 1000
This is the ordering convention of the pressure level vertical coordinate in ERA-Interim. ERA pressure level variables are assigned interpolated values where isobaric surfaces dip below topography. There are no missing values. We do not have specific information about the below topography interpolation scheme used by ECMWF at this time.
The 15 standard isentropic (theta) levels in ERA-Interim in K (Kelvin) are, from lowest isentropic altitude to highest isentropic altitude in the atmosphere:
265, 275, 285, 300, 315, [320 — PV only], 330, 350, 370, 395, 430, 475, 530, 600, 700, 850
This is the ordering convention of the theta level vertical coordinate in ERA-Interim. Please note that PV (potential vorticity) is archived on an additional isentropic level, namely 320 K. There are no missing values. We do not have specific information about the below topography interpolation scheme used by ECMWF at this time.
For convenience, below we show the ERA-Interim pressure and isentropic levels arranged relative to a standard atmosphere. ERA-Interim pressure levels are shown in bold black digits. ERA-Interim theta levels are shown in bold red digits. Note that the global average tropopause height is indicated ( in blue ~~~) as 12 kilometers — in practice the height of the tropopause varies between 8 kilometers (poles) and 17 kilometers (equator). A stratopause ( in green ~~~) at 50 kilometers is also shown, as well as an ozone maximum near 25 kilometers.
For this representation of a standard atmosphere,
potential temperature is computed as
where T is the temperature, po
the reference pressure (1013.25 mb), p the pressure, R the gas constant for dry air
(287.04 J kg-1 K-1), and Cp the specific heat capacity of dry air at
constant pressure (1004.6 J kg-1 K-1).
-------------------------------------------------------------------------------------------------------------------
| | | Potential |
| Pressure | | Temperature |
Height | ERA-I | Temperature | ERA-I | Density
meters km feet mi | mb/hPa mb/hPa | K deg C deg F | K † K | kg m-3
------------------------------------- |----------------- |----------------------------- |--------------- |---------
- 80000 --- 80.0 -- 262467 --- 49.7 - | 0.010 -------- | 198.6 ---- -74.5 --- -102.1 | 5350.0 ------- | 0.00002
- 70000 --- 70.0 -- 229659 --- 43.5 - | 0.052 -------- | 219.5 ---- -53.6 --- -64.5 | 3691.6 ------- | 0.00008
- 60000 --- 60.0 -- 196850 --- 37.3 - | 0.220 -------- | 247.0 ---- -26.1 --- -15.0 | 2750.9 ------- | 0.00030
~ 50000 ~~~ 50.0 ~~ 164042 ~~~ 31.1 ~ | 0.798 ~~~~~~~~ | 270.6 ~~~~ -2.5 ~~~ +27.5 | 2085.5 ~~~~~~~ | 0.00100 ← Ave stratopause
1
- 45000 --- 45.0 -- 147638 --- 28.0 - | 1.491 -------- | 264.1 ---- -9.0 --- +15.8 | 1702.5 ------- | 0.00200
2
- 40000 --- 40.0 -- 131234 --- 24.9 - | 2.871 -------- | 250.3 ---- -22.8 --- -9.0 | 1338.1 ------- | 0.00400
3
5
- 35000 --- 35.0 -- 114829 --- 21.7 - | 5.746 -------- | 236.5 ---- -36.6 --- -33.9 | 1037.0 ------- | 0.00800
7
10 850
- 30000 --- 30.0 -- 98425 --- 18.6 - | 11.970 -------- | 226.5 ---- -46.6 --- -51.9 | 805.3 ------- | 0.01800
20 700
- 25000 --- 25.0 -- 82021 --- 15.5 - | 25.492 -------- | 221.5 ---- -51.6 --- -60.9 | 634.5 ------- | 0.04000 ← Ozone maximum
30 600
50 530
- 20000 --- 20.0 -- 65617 --- 12.4 - | 55.293 -------- | 216.6 ---- -56.5 --- -69.7 | 497.3 ------- | 0.08900
- 19000 --- 19.0 -- 62336 --- 11.8 - | 64.674 -------- | 216.6 ---- -56.5 --- -69.7 | 475.6 ------- | 0.10400
70 475
- 18000 --- 18.0 -- 59055 --- 11.2 - | 75.652 -------- | 216.6 ---- -56.5 --- -69.7 | 454.7 ------- | 0.12200
- 17000 --- 17.0 -- 55774 --- 10.6 - | 88.497 -------- | 216.6 ---- -56.5 --- -69.7 | 434.8 ------- | 0.14200
100 430
- 16000 --- 16.0 -- 52493 --- 9.9 - | 103.520 -------- | 216.6 ---- -56.5 --- -69.7 | 415.7 ------- | 0.16600
- 15000 --- 15.0 -- 49213 --- 9.3 - | 121.110 -------- | 216.6 ---- -56.5 --- -69.7 | 397.5 ------- | 0.19500
125 395
- 14000 --- 14.0 -- 45932 --- 8.7 - | 141.700 -------- | 216.6 ---- -56.5 --- -69.7 | 380.1 ------- | 0.22800
150 370
- 13000 --- 13.0 -- 42651 --- 8.1 - | 165.790 -------- | 216.6 ---- -56.5 --- -69.7 | 363.4 ------- | 0.26700
175 350
~ 12000 ~~~ 12.0 ~~ 39370 ~~~ 7.5 ~ | 193.990 ~~~~~~~~ | 216.6 ~~~~ -56.5 ~~~ -69.7 | 347.4 ~~~~~~~ | 0.31200 ← Ave tropopause
200
225
- 11000 --- 11.0 -- 36089 --- 6.8 - | 226.990 -------- | 216.7 ---- -56.4 --- -69.5 | 332.4 ------- | 0.36500
250 330
- 10000 --- 10.0 -- 32808 --- 6.2 - | 264.990 -------- | 223.2 ---- -49.9 --- -57.8 | 327.5 ------- | 0.41300
- 9500 --- 9.5 -- 31168 --- 5.9 - | 285.840 -------- | 226.5 ---- -46.6 --- -51.9 | 325.2 ------- | 0.44000
300
- 9000 --- 9.0 -- 29528 --- 5.6 - | 308.000 -------- | 229.7 ---- -43.4 --- -46.1 | 322.9 ------- | 0.46700
- 8848 --- 
Everest (8848 m, 29028 ft)
- 8500 --- 8.5 -- 27887 --- 5.3 - | 331.540 -------- | 232.9 ---- -40.2 --- -40.4 | 320.5 ------- | 0.49600
350 320 — PV only
- 8000 --- 8.0 -- 26247 --- 5.0 - | 356.510 -------- | 236.2 ---- -36.9 --- -34.4 | 318.4 ------- | 0.52600
- 7500 --- 7.5 -- 24606 --- 4.7 - | 382.990 -------- | 239.4 ---- -33.7 --- -28.7 | 316.2 ------- | 0.55700
400 315
- 7000 --- 7.0 -- 22966 --- 4.3 - | 411.050 -------- | 242.7 ---- -30.4 --- -22.7 | 314.1 ------- | 0.59000
- 6500 --- 6.5 -- 21325 --- 4.0 - | 440.750 -------- | 245.9 ---- -27.2 --- -17.0 | 312.0 ------- | 0.62400
450
- 6000 --- 6.0 -- 19685 --- 3.7 - | 472.170 -------- | 249.1 ---- -24.0 --- -11.2 | 309.9 ------- | 0.66000
500
- 5500 --- 5.5 -- 18045 --- 3.4 - | 505.390 -------- | 252.4 ---- -20.7 --- -5.3 | 308.0 ------- | 0.69700
- 5000 --- 5.0 -- 16404 --- 3.1 - | 540.480 -------- | 255.6 ---- -17.5 --- +0.5 | 305.9 ------- | 0.73600
550
- 4500 --- 4.5 -- 14764 --- 2.8 - | 577.520 -------- | 258.9 ---- -14.2 --- +6.4 | 304.1 ------- | 0.77700
600
- 4000 --- 4.0 -- 13123 --- 2.5 - | 616.600 -------- | 262.1 ---- -11.0 --- +12.2 | 302.1 ------- | 0.81900
650
- 3500 --- 3.5 -- 11483 --- 2.2 - | 657.800 -------- | 265.4 ---- -7.7 --- +18.1 | 300.3 ------- | 0.86300
700 300
- 3000 --- 3.0 -- 9843 --- 1.9 - | 701.210 -------- | 268.6 ---- -4.5 --- +23.9 | 298.4 ------- | 0.90900
- 2500 --- 2.5 -- 8202 --- 1.6 - | 746.910 -------- | 271.9 ---- -1.2 --- +29.8 | 296.7 ------- | 0.95700
750
775
- 2000 --- 2.0 -- 6562 --- 1.2 - | 795.010 -------- | 275.1 ---- +2.0 --- +35.6 | 294.9 ------- | 1.00700
800
825
- 1500 --- 1.5 -- 4921 --- 0.9 - | 845.590 -------- | 278.4 ---- +5.3 --- +41.5 | 293.2 ------- | 1.05800
850
875
- 1000 --- 1.0 -- 3281 --- 0.6 - | 898.760 -------- | 281.6 ---- +8.5 --- +47.3 | 291.5 ------- | 1.11200
900
925
950
- 500 --- 0.5 -- 1640 --- 0.3 - | 954.610 -------- | 284.9 ---- +11.8 --- +53.2 | 289.8 ------- | 1.16700
975 285
1000
- 0 --- 0.0 -- 0 --- 0.0 - |1013.250 -------- | 288.1 ---- +15.0 --- +59.0 | 288.1 ------- | 1.22500 ← Surface
275
265
- -420 --- 
Dead Sea (-420 m, -1378 ft)
------------------------------------- |----------------- |----------------------------- |--------------- |---------
†
Potential temperature is computed as
where T is the temperature, po
the reference pressure (1013.25 mb), p the pressure, R the gas constant for dry air
(287.04 J kg-1 K-1), and Cp the specific heat capacity of dry air at
constant pressure (1004.6 J kg-1 K-1).
‡ Only the simplest complete photochemical cycle for ozone (Chapman cycle) is shown. M represents a third molecule needed to conserve momentum and energy in the recombination of O and O2.
Source of standard atmosphere (height, pressure, temperature, and density): Ahrens, C. Donald, 1994, Meteorology Today, An Introduction to Weather, Climate, and the Environment, Fifth Edition, West Publishing Company, St. Paul (Appendix H).