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A few times per year, the analysed low level winds, eg the 10m winds, become unrealistically large in a particular location, which varies amongst a few apparently preferred locations. The largest values seen so far are about 300 ms-1. This problem occurs towards the end of the data assimilation windows (9-21 UTC and 21-9 UTC) because of an instability in the analysis method.
From 19 February 2020 onwards, the ERA5 system examines has examined the 10m wind components and if the magnitude of either component exceeds 50 ms-1, then the analysed parameters are replaced with the "4v" parameters. These latter parameters are similar to the analysed ones, but don't usually suffer from such large values. For more information on 4v and data assimilation, see "Part II Data Assimilation" of the IFS documentation (CY41R2 for ERA5).
The choice of a 50 ms-1 cut off is an arbitrary one, which could miss spurious values that are less than 50 ms-1. This may well occur in the one or two hours just before the critical value of 50 ms-1 is reached. It is also possible that this cut off point could penalise realistic winds, such as in hurricanes. However, given the spatial resolution of ERA5 dataresolution of ERA5 data (with a grid spacing of 31km), it is thought that in general, 10m wind components higher than 50 ms-1 are not realistic for this resolutionin ERA5, even if the observed magnitude is higher, as is the case . This is illustrated in Fig. 1 for Hurricane Ivan in the Caribbean on 12 September 2004 . This case is illustrated in Fig. 1, below, at 20 UTC, where the analysed winds are compared with the 4v winds. The minimum value of the analysed 10 metre V wind components is -53 ms-1, (see Event 57, Table 2) whilst , while the minimum value of the 4v 10 metre V wind components is -29 ms-1. Even though the analysed wind speeds are not as large as the observed ones (the estimated peak wind speeds for Ivan were of order 70 ms-1), the 4v winds are thought to give a more realistic representation of the winds, for this resolution.
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This CDS API script can be used to retrieve the "4v" 10m wind components from the ECMWF data archive, MARS. For more information on how to use CDS API scripts, see How to download ERA5. For the temporal specification, the CDS uses the validity date and time, whereas MARS uses date, time and step (there is further discussion of step in the section "Date and time specification" of the ERA5 data documentation). The 4v model trajectories begin from 9 and 21 UTC and you should use the hourly steps from 1 to 12 hours. In this example in the script above, the validity date/time would be given by adding the step, 12 hours, to the time, 21 UTC, thereby yielding a validity date/time of 1986-07-24 at 9 UTC, which is the 12th event in Table 1 below, for the 10m U. |
CaseEvent | Date | Time | Latitude | Longitude | 10m U |
---|---|---|---|---|---|
1 | 19790417 | 900 | -74.051 | 164.160 | 7.2323150635e+01 |
2 | 19800330 | 700 | -1.827 | 280.406 | -5.9812698364e+01 |
3 | 19800330 | 800 | -1.827 | 280.406 | -9.8439865112e+01 |
4 | 19800330 | 900 | -1.827 | 280.406 | -7.1381820679e+01 |
5 | 19820908 | 700 | -74.051 | 164.160 | -6.9596405029e+01 |
6 | 19820908 | 800 | -74.051 | 164.160 | -5.2189117432e+01 |
7 | 19821024 | 2100 | -74.051 | 164.160 | -1.5377770996e+02 |
8 | 19841004 | 700 | -74.051 | 164.160 | -5.5174591064e+01 |
9 | 19841004 | 800 | -74.051 | 164.160 | -6.8660507202e+01 |
10 | 19841004 | 900 | -74.051 | 165.120 | -7.1647964478e+01 |
11 | 19860724 | 800 | -74.051 | 164.160 | -8.8280364990e+01 |
12 | 19860724 | 900 | -74.051 | 164.160 | -2.9203100586e+02 |
13 | 19871016 | 2000 | -74.051 | 164.160 | -9.4200180054e+01 |
14 | 19871016 | 2100 | -74.051 | 164.160 | -1.5219485474e+02 |
15 | 19890711 | 2100 | 38.080 | 78.333 | 7.0804840088e+01 |
16 | 19890912 | 800 | -74.051 | 164.160 | -8.3815658569e+01 |
17 | 19890912 | 900 | -74.051 | 164.160 | -1.6730293274e+02 |
18 | 19900402 | 700 | -74.051 | 164.160 | 5.8469223022e+01 |
19 | 19930624 | 600 | -74.051 | 164.160 | 6.0172592163e+01 |
20 | 19930624 | 700 | -74.051 | 164.160 | 1.0357415771e+02 |
21 | 19930624 | 800 | -74.051 | 164.160 | 7.8659744263e+01 |
22 | 19930624 | 900 | -74.051 | 164.160 | 5.5145812988e+01 |
23 | 19930705 | 2000 | 38.080 | 78.333 | 8.0320663452e+01 |
24 | 19930705 | 2100 | 38.361 | 78.398 | 5.9963912964e+01 |
25 | 19940914 | 2100 | -74.051 | 164.160 | -7.9331817627e+01 |
26 | 19970607 | 700 | -74.051 | 164.160 | 5.8002792358e+01 |
27 | 19970607 | 800 | -74.051 | 164.160 | 1.0099096680e+02 |
28 | 19970923 | 1900 | -74.051 | 164.160 | 1.3710269165e+02 |
29 | 20010423 | 2100 | -74.051 | 164.160 | -8.0685379028e+01 |
30 | 20040327 | 800 | -74.051 | 164.160 | -6.4567825317e+01 |
31 | 20050314 | 800 | -1.827 | 280.406 | -6.1867416382e+01 |
32 | 20050314 | 900 | -1.827 | 280.406 | -9.2169509888e+01 |
33 | 20060304 | 900 | -1.827 | 280.125 | -6.3722732544e+01 |
34 | 20060328 | 800 | -1.827 | 280.406 | -5.7734420776e+01 |
35 | 20060328 | 900 | -1.827 | 280.406 | -1.1018218994e+02 |
36 | 20070331 | 2100 | -74.051 | 164.160 | 8.7419113159e+01 |
37 | 20090303 | 700 | -1.827 | 280.406 | -8.9056137085e+01 |
38 | 20090303 | 800 | -1.827 | 280.406 | -1.3375457764e+02 |
39 | 20090303 | 900 | -1.827 | 280.406 | -2.0406346130e+02 |
40 | 20091218 | 2100 | 43.138 | 75.000 | -5.9425277710e+01 |
41 | 20100325 | 900 | -1.827 | 280.688 | -5.4004959106e+01 |
42 | 20110127 | 900 | -1.827 | 280.406 | -5.3115798950e+01 |
43 | 20111224 | 2100 | 43.138 | 75.000 | -6.8307769775e+01 |
44 | 20130719 | 2100 | -74.051 | 164.160 | -6.1746520996e+01 |
45 | 20140426 | 700 | -1.265 | 280.688 | 5.7151275635e+01 |
46 | 20140426 | 700 | -1.546 | 280.406 | -8.5247161865e+01 |
47 | 20140426 | 800 | -1.265 | 280.688 | 7.2114089966e+01 |
48 | 20140426 | 800 | -1.546 | 280.406 | -1.4157341003e+02 |
49 | 20140426 | 900 | -1.546 | 280.406 | -2.0927426147e+02 |
50 | 20160522 | 2000 | -74.051 | 164.160 | -6.6684082031e+01 |
51 | 20160522 | 2100 | -74.051 | 164.160 | -5.9349365234e+01 |
52 | 20160929 | 2100 | -74.051 | 164.160 | 6.5295028687e+01 |
53 | 20161128 | 2100 | 42.857 | 75.375 | -5.2441085815e+01 |
Table 1: Occurrences when the 10 metre U wind component exceeds 50 ms-1.
CaseEvent | Date | Time | Latitude | Longitude | 10m V |
---|---|---|---|---|---|
1 | 19790401 | 2100 | -5.480 | 137.812 | -9.6993362427e+01 |
2 | 19800330 | 900 | -1.827 | 280.406 | -5.0487777710e+01 |
3 | 19800831 | 1900 | -5.199 | 137.531 | -6.5852249146e+01 |
4 | 19800831 | 2000 | -5.199 | 137.531 | -5.0360015869e+01 |
5 | 19821024 | 2100 | -74.051 | 164.160 | 5.4236557007e+01 |
6 | 19830930 | 2000 | 42.576 | 84.815 | 5.0510147095e+01 |
7 | 19830930 | 2100 | 42.576 | 84.815 | 6.1684814453e+01 |
8 | 19840811 | 1800 | -5.480 | 137.812 | 1.3961134338e+02 |
9 | 19840811 | 1900 | -5.199 | 137.531 | 1.2407348633e+02 |
10 | 19840811 | 2000 | -5.199 | 137.531 | 1.3110269165e+02 |
11 | 19840811 | 2100 | -5.199 | 137.531 | 1.2531871033e+02 |
12 | 19850812 | 1900 | -5.199 | 137.531 | 6.5993698120e+01 |
13 | 19850812 | 2000 | -5.480 | 137.812 | 8.7721923828e+01 |
14 | 19850812 | 2100 | -5.480 | 137.812 | 1.1631915283e+02 |
15 | 19851116 | 2100 | -5.480 | 137.812 | -8.0120529175e+01 |
16 | 19860724 | 900 | -74.051 | 164.160 | 1.3616104126e+02 |
17 | 19871016 | 2100 | -74.051 | 164.160 | 6.7936035156e+01 |
18 | 19890420 | 2000 | -5.480 | 137.812 | -5.5810119629e+01 |
19 | 19890420 | 2100 | -5.480 | 137.812 | -1.2454008484e+02 |
20 | 19890711 | 2100 | 38.361 | 78.398 | 1.4824528503e+02 |
21 | 19890912 | 900 | -74.051 | 164.160 | 6.3201354980e+01 |
22 | 19901117 | 600 | 41.171 | 39.960 | -7.1991546631e+01 |
23 | 19901117 | 700 | 41.171 | 39.600 | -7.2909973145e+01 |
24 | 19910620 | 2000 | -5.480 | 137.812 | 9.5385955811e+01 |
25 | 19910620 | 2100 | -5.761 | 138.094 | 1.6087461853e+02 |
26 | 19920415 | 800 | 20.094 | 84.375 | 5.1177642822e+01 |
27 | 19921108 | 2100 | -5.199 | 137.531 | -5.9594894409e+01 |
28 | 19921113 | 1800 | -5.480 | 137.812 | -7.4539321899e+01 |
29 | 19921113 | 1900 | -5.761 | 137.812 | -1.4339295959e+02 |
30 | 19921113 | 2000 | -5.480 | 137.531 | -1.5561082458e+02 |
31 | 19921113 | 2100 | -5.480 | 137.531 | -1.7285772705e+02 |
32 | 19921123 | 2100 | 43.138 | 74.625 | -7.4817504883e+01 |
33 | 19930705 | 2000 | 38.361 | 78.398 | 1.7013420105e+02 |
34 | 19930705 | 2100 | 38.361 | 78.398 | 6.0669006348e+01 |
35 | 19930815 | 2000 | 31.335 | 72.000 | -1.2063990784e+02 |
36 | 19950127 | 2100 | 40.890 | 39.600 | -9.3620895386e+01 |
37 | 19960710 | 2000 | -5.480 | 137.812 | 7.3640014648e+01 |
38 | 19960710 | 2100 | -5.480 | 137.812 | 1.1385275269e+02 |
39 | 19970422 | 2100 | 40.890 | 39.240 | -1.3644331360e+02 |
40 | 19970617 | 1700 | 39.766 | 89.297 | -1.0041018677e+02 |
41 | 19970626 | 1900 | -5.480 | 137.812 | 5.7410095215e+01 |
42 | 19970626 | 2000 | -5.480 | 137.812 | 1.2612721252e+02 |
43 | 19970626 | 2100 | -5.480 | 137.812 | 8.5113784790e+01 |
44 | 19970817 | 2000 | -5.480 | 137.812 | 5.6425781250e+01 |
45 | 19970817 | 2100 | -5.480 | 137.812 | 1.4044223022e+02 |
46 | 19970923 | 1900 | -74.051 | 164.160 | -5.1563308716e+01 |
47 | 20010127 | 600 | 41.171 | 39.960 | 1.2166479492e+02 |
48 | 20010127 | 700 | 41.171 | 39.960 | 8.3281478882e+01 |
49 | 20020602 | 2100 | 38.923 | 83.320 | -6.7981185913e+01 |
50 | 20030516 | 2100 | -5.480 | 137.812 | 6.4198028564e+01 |
51 | 20030704 | 2000 | 40.328 | 84.240 | 5.8809799194e+01 |
52 | 20040711 | 1800 | 40.328 | 87.480 | 1.6328262329e+02 |
53 | 20040711 | 1900 | 40.328 | 87.480 | 7.7149871826e+01 |
54 | 20040803 | 2100 | -5.199 | 137.531 | -5.1051910400e+01 |
55 | 20040830 | 2000 | -5.199 | 137.531 | -7.2028549194e+01 |
56 | 20040830 | 2100 | -5.199 | 137.250 | -1.5628892517e+02 |
57 | 20040912 | 2000 | 19.532 | 277.031 | -5.3294830322e+01 |
58 | 20050805 | 2000 | -5.480 | 137.812 | -9.3390945435e+01 |
59 | 20050805 | 2100 | -5.480 | 137.812 | -9.8295639038e+01 |
60 | 20051208 | 800 | 40.890 | 39.960 | 6.6637542725e+01 |
61 | 20060304 | 900 | -1.546 | 280.406 | -7.0116149902e+01 |
62 | 20060612 | 1900 | -5.480 | 137.812 | 6.8560852051e+01 |
63 | 20060612 | 2000 | -5.480 | 137.812 | 1.0062788391e+02 |
64 | 20060612 | 2100 | -5.480 | 137.812 | 1.1736833191e+02 |
65 | 20061210 | 700 | 41.171 | 39.600 | 5.8087677002e+01 |
66 | 20061210 | 800 | 41.171 | 39.600 | 5.1876373291e+01 |
67 | 20061219 | 700 | 41.171 | 39.960 | 6.5212203979e+01 |
68 | 20061219 | 800 | 41.171 | 39.600 | 5.0869308472e+01 |
69 | 20071227 | 600 | 41.171 | 39.600 | 7.9303802490e+01 |
70 | 20071227 | 700 | 41.171 | 39.960 | 1.0291072083e+02 |
71 | 20071227 | 800 | 41.171 | 39.960 | 8.6426681519e+01 |
72 | 20090303 | 900 | -1.827 | 280.406 | -6.8449584961e+01 |
73 | 20091218 | 2000 | 43.138 | 74.625 | -6.3902404785e+01 |
74 | 20091218 | 2100 | 43.138 | 74.625 | -1.5077589417e+02 |
75 | 20100110 | 2100 | 40.890 | 39.960 | -5.4371688843e+01 |
76 | 20111207 | 2100 | 41.171 | 39.960 | -5.2954406738e+01 |
77 | 20111224 | 2000 | 43.138 | 74.625 | -8.1969665527e+01 |
78 | 20111224 | 2100 | 43.138 | 74.625 | -1.0727139282e+02 |
79 | 20120629 | 2000 | -5.480 | 137.812 | 6.8156173706e+01 |
80 | 20120629 | 2100 | -5.480 | 137.812 | 5.3109390259e+01 |
81 | 20130727 | 1900 | 38.080 | 78.333 | 6.0674041748e+01 |
82 | 20131224 | 600 | 41.171 | 39.960 | 6.8190124512e+01 |
83 | 20131224 | 700 | 41.171 | 39.600 | 6.7012496948e+01 |
84 | 20131224 | 800 | 41.171 | 39.600 | 5.1414718628e+01 |
85 | 20140426 | 700 | -1.265 | 280.406 | 5.4881195068e+01 |
86 | 20140426 | 700 | -2.108 | 280.688 | -5.8466461182e+01 |
87 | 20140426 | 800 | -1.546 | 280.688 | -8.5272201538e+01 |
88 | 20140426 | 900 | -1.546 | 280.688 | -1.0531086731e+02 |
89 | 20150912 | 1900 | -5.199 | 137.531 | 6.4281372070e+01 |
90 | 20160516 | 1900 | -5.480 | 137.812 | 1.1651092529e+02 |
91 | 20160516 | 2000 | -5.480 | 137.531 | 1.5173913574e+02 |
92 | 20160516 | 2100 | -5.480 | 137.812 | 7.3943984985e+01 |
93 | 20160531 | 2000 | -5.480 | 137.812 | 8.6714050293e+01 |
94 | 20160531 | 2100 | -5.480 | 137.812 | 8.5311660767e+01 |
95 | 20160825 | 1900 | -5.480 | 137.812 | 8.8643951416e+01 |
96 | 20160825 | 2000 | -5.199 | 137.531 | 6.8540237427e+01 |
97 | 20161128 | 2000 | 43.138 | 74.625 | -8.1585525513e+01 |
98 | 20161128 | 2100 | 43.138 | 74.625 | -1.6854412842e+02 |
99 | 20171011 | 2100 | -5.480 | 137.812 | 1.1839462280e+02 |
100 | 20180914 | 2100 | -5.480 | 137.812 | 5.5520050049e+01 |
101 | 20191116 | 1800 | -5.480 | 137.812 | 7.6125183105e+01 |
102 | 20191116 | 1900 | -5.199 | 137.531 | 1.4759844971e+02 |
103 | 20191116 | 2000 | -5.199 | 137.531 | 7.8542388916e+01 |
Table 2: Occurrences when the 10 metre V wind component exceeds 50 ms-1.
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This document has been produced in the context of the Copernicus Climate Change Service (C3S). The activities leading to these results have been contracted by the European Centre for Medium-Range Weather Forecasts, operator of C3S on behalf of the European Union (Delegation agreementAgreement signed on 11/11/2014 and Contribution Agreement signed on 22/07/2021). All information in this document is provided "as is" and no guarantee or warranty is given that the information is fit for any particular purpose. The users thereof use the information at their sole risk and liability. For the avoidance of all doubt , the European Commission and the European Centre for Medium - Range Weather Forecasts have no liability in respect of this document, which is merely representing the author's view. |
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