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The static fields marked as * above are available as NetCDF files for the West and East domain respectively here: fractions.west.nc and fractions.east.nc     

Soil level variables

Soil level variables are given for two model depths, where the first depth is the soil surface and the second depth is the so-called root depth. The root depth varies with the cover type climatology. Please note that the soil level variables are accommodated in the Arctic Regional Reanalysis single level variables catalogue entry.

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Pressure level variables

Pressure level variables are interpolated to 23 specific pressure levels: 1000, 950, 925, 875, 850, 800, 750, 700, 600, 500, 400, 300, 200, 100, 70, 50, 30, 20 and 10 hPa. Thus, they are on isobaric surfaces.

Output of diagnostic variables at pressure levels are available in three hourly intervals at 00, 03, 06, 09, 12, 15, 18 and 21 UTC.

Long forecasts are available from the forecasts initiated at 00 and 12 UTC. Long forecasts include forecast lengths of 1, 2, 3, 4, 5, 6, 9, 12, 15, 18, 21, 24 and 30 hours.

Short forecasts of 1, 2 and 3 hours are made for the forecasts initiated at 03, 06, 09, 15, 18 and 21 UTC.

Height level variables

Height level variables are interpolated to 11 specific height levels: 15, 30, 50, 75, 100, 150, 200, 250, 300, 400 and 500 metres above the surface.

Output of diagnostic height level variables is available in three hourly intervals at 00, 03, 06, 09, 12, 15, 18 and 21 UTC.

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The model level variables are computed at the full model levels, and are given as instantaneous values from the most recent model time step relative to the output time. There are 65 vertical model levels in HARMONIE-AROME.  These full model levels are hybrid-sigma coordinates that are counted from the model top toward the surface. They go from being pure pressure levels, i.e. levels with constant pressure starting at 10 hPa, 30 hPa, etc. to being relative to the surface topography in height. Level 64 is at approximately 30 m height and level 65 is at approximately 12 m height above the surface. For a more detailed description of the vertical model layers, see Annex 8.3. The following thermodynamic variables are the output variables at model levels: Temperature [K], u-component of wind [m/s], v-component of wind [m/s], turbulent kinetic energy [J/kg]. Here turbulent kinetic energy is the mean kinetic energy per unit mass from eddies in turbulent flow. Note that the HARMONIE-AROME weather forecasting model with 2.5 x 2.5 km² resolution does not explicitly resolve this turbulent energy. The u- and v- wind components follow the direction of the Lambertian model grid with the u-component being directed 90 degrees clockwise relative to the v-component. From these model level wind components, the model level wind speed and wind direction relative north can be calculated with Equations 3 and 4. The grid rotation angle 𝛼 can be computed with this script: https://github.com/metno/NWPdocs/wiki/From-x-y-wind-to-wind-direction.

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Questions & Answers on field uncertainty estimates

For information and "questions and answers" (Q&A) on the uncertainty estimates for the ERA5 host reanalysis used on the lateral boundaries of this Arctic Regional Reanalysis, see this link:
ERA5: uncertainty estimation

The field uncertainty estimates provided here apply a different approach. The below Q&A is similar to the Q&A for the global reanalysis, adapted to apply for the uncertainty estimates provided here (for the Arctic reanalysis).

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Verification of precipitation forecasts is a difficult task in general, due to large representativeness errors associated with small scale variability in precipitation and observation errors. For the latter, the wind induced under-catch of solid precipitation in measurements (i.e. observations measure only a fraction of the true total precipitation) is of particular importance, while the problem is smaller for liquid precipitation. A thorough investigation of the CARRA precipitation (Arctic areas with higher relative occurrence of solid precipitation) therefore requires substantial efforts and more considerations than for other parameters and are therefore not yet conducted. However, some preliminary insight in the performance of daily CARRA precipitation can be achieved from Figure 15.

Figure 15: The estimated relative bias ((CARRA – observed) / observed) of daily precipitation versus the estimated SDE normalized with observed precipitation for different regions for liquid (red) and solid (blue) precipitation. The units are kg/m² which is the same as mm water equivalent.

For liquid precipitation a moderate, mostly positive, bias is found for all regions (CARRA precipitation within 20% of observed values). However, the standard deviation of the error varies between regions with the largest values at Svalbard and smallest errors in Iceland. For solid precipitation, large positive biases are found for Iceland and Svalbard, windy regions where we expect the wind-induced under-catch of solid precipitation in the observations to be substantial. This means that the observations underestimate the true precipitation and these biases are therefore artificially high, and are in reality lower, but the true biases are difficult to quantify. A modest positive bias over the Scandinavian inland areas will also be reduced (or changed to an underestimation), but to a smaller degree since this is a less wind exposed region. All regions exhibit a larger SDE for solid than liquid precipitation and observation errors can be a part of the explanation for this. The only exception is the Scandinavian inland areas, for which the SDE is higher for liquid than solid precipitation. This is a region with substantial convective activity in summer which is less predictable, and where other verification methodologies are needed than point verification. It should be noted that at the Norwegian coast, the CARRA precipitation is smaller than in the observations for both liquid and solid precipitation, which after considering the wind-induced under-catch of solid precipitation indicates a substantial underestimation of the winter precipitation amounts along the Norwegian coast.

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 Definition of the 65 vertical layer structure in HARMONIE 

The CARRA vertical coordinate system is a terrain-following hybrid vertical coordinate, which means that it is terrain following at the bottom and pressure based on the top of the atmosphere. It has the advantage to describe the surface terrain properly, but also benefitting the advantage of having the pressure coordinate at the top of the atmosphere.

CARRA uses 65 model levels (level 65 is the surface and level 1 is the top of the atmosphere), which is further splitted into the so called half levels. CARRA has 66 half levels and the pressure of each half level can be obtained by the following formula:

P (k+1/2) = A (k+1/2) + B (k+1/2) * Ps

where k=0.... 65, Ps is surface pressure and the A and B coefficients (see below) valid at each half level. 

The full model level pressure [1, 2, ...65] is defined as the mean of the pressure of each pair of neighbouring half levels [0,5, 1.5, ...65.5]. The model variables are defined in the full model levels. 

The A and B coefficients are listed below (from the top to the bottom).

'AHALF'=>'0.00000000, 2000.00000000, 4000.21287319, 6002.09662113, 7911.25838577, 9633.01049417,11169.37146237, 12522.57753978, 13695.00149653, 14689.11546998, 15507.49052823, 16154.69697732, 16632.12471208, 16940.14949960,  17082.34869816, 17065.28164099, 16898.18367797, 16592.58939571,  16161.90395878,  15620.94340550,  14985.46502362, 14271.70773051, 13495.95994372, 12674.16909910, 11821.60314859, 10952.57042620, 10080.20053763, 9216.28565403, 8371.17893039, 7553.74479607, 6771.35457397, 6029.92021691, 5333.95880836, 4686.68074804, 4090.09511346, 3545.12645110, 3051.73811264, 2609.05813936, 2215.50455766, 1868.90774223, 1566.62821060, 1305.66882073, 1081.85503306, 890.47596795, 727.74548529, 590.17748096, 474.58767980, 378.08857614, 298.07947335, 232.23312781, 178.48015386, 134.99207440, 100.16369201, 72.59529482, 51.07508967, 34.56216490, 22.17022046, 13.15225964, 6.88641310, 2.86306141, 0.67344356, 0.00000000, 0.00000000, 0.00000000, 0.00000000, 0.00000000

'BHALF'=>'0.00000000,  0.00000000,  0.00000000, 0.00000000, 0.00095468, 0.00382570, 0.00862327, 0.01535782, 0.02404046, 0.03468314, 0.04729839, 0.06195102, 0.07868187, 0.09744325, 0.11815586, 0.14071098, 0.16497348, 0.19078554,   0.21797086, 0.24633925, 0.27569119, 0.30582244, 0.33652825, 0.36760726, 0.39886479, 0.43011564, 0.46118624, 0.49191624, 0.52215946, 0.55178443, 0.58067442, 0.60872709, 0.63585388, 0.66197911, 0.68703898, 0.71098036, 0.73375964, 0.5534143, 0.77569737, 0.79480486, 0.81264598, 0.82920633, 0.84454000, 0.85875505, 0.87191802, 0.88409276, 0.89534045,  0.90571965, 0.91528643, 0.92409452, 0.93219549, 0.93963895, 0.94647277, 0.95274328, 0.95849551, 0.96377340, 0.96862008, 0.97307803, 0.97718944, 0.98099640, 0.98454132, 0.98786727, 0.99102462, 0.99406510, 0.99703923, 1.00000000

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