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A few times per year, the analysed low level winds, eg the 10m winds, become very 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.

The tables below give details when each of the two components of the 10m winds, the 10 metre U wind component and 10 metre V wind component, exceed 50 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 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 data (with a grid spacing of 31km), it is thought that in general, 10m wind components higher than 50 ms^-1 are not realistic in ERA5, even if the observed magnitude is higher. This is illustrated in Fig. 1 for Hurricane Ivan in the Caribbean on 12 September 2004 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), 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.

Fig. 1a	Fig. 1b
Image Added	Image Added
Fig. 1a. The analysed 10m winds for 12 September 2004, 20 UTC, featuring Hurricane Ivan. The regional plot domain shows the Caribbean and Gulf of Mexico.	Fig. 1b. As Fig 1a, but for the 4v 10m winds.

For dates before this system check was introduced into ERA5 (i.e. for the period January 1979 to 18 February 2020), the two tables below give details when the analysed 10m wind components (the 10 metre U wind component and 10 metre V wind component) exceed 50 ms^-1. The CDS API script below can be used to retrieve the "4v" 10m wind components, which don't usually suffer from this large wind problem.

Expand

title	CDS API script to retrieve the "4v" 10m winds

Code Block

#!/usr/bin/env python
import cdsapi
 
c = cdsapi.Client()
c.retrieve('reanalysis-era5-complete', {     # do not change this!
    'stream'  : 'oper',
    'type'    : '4v',
    'levtype' : 'sfc',
    'param'   : '165.128/166.128',
    'date'    : '1986-07-23',
    'time'    : '21',
    'step'    : '12',
    'grid'    : '0.25/0.25', # Latitude/longitude grid: east-west (longitude) and north-south resolution (latitude). Default: reduced Gaussian grid
    'format'  : 'grib', # Default: grib, supported netcdf.
}, 'outfile.grib')

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.

Event	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
Date	Time	Latitude	Longitude	10m U value
19790417	900	-74.051	164.160	7.2323150635e+01
19800330	700	-1.827	280.406	-5.9812698364e+01
19800330	800	-1.827	280.406	-9.8439865112e+01
19800330	900	-1.827	280.406	-7.1381820679e+01
19820908	700	-74.051	164.160	-6.9596405029e+01
19820908	800	-74.051	164.160	-5.2189117432e+01
19821024	2100	-74.051	164.160	-1.5377770996e+02
19841004	700	-74.051	164.160	-5.5174591064e+01
19841004	800	-74.051	164.160	-6.8660507202e+01
19841004	900	-74.051	165.120	-7.1647964478e+01
19860724	800	-74.051	164.160	-8.8280364990e+01
19860724	900	-74.051	164.160	-2.9203100586e+02
19871016	2000	-74.051	164.160	-9.4200180054e+01
19871016	2100	-74.051	164.160	-1.5219485474e+02
19890711	2100	38.080	78.333	7.0804840088e+01
19890912	800	-74.051	164.160	-8.3815658569e+01
19890912	900	-74.051	164.160	-1.6730293274e+02
19900402	700	-74.051	164.160	5.8469223022e+01
19930624	600	-74.051	164.160	6.0172592163e+01
19930624	700	-74.051	164.160	18.0357415771e7419113159e+0201
37	1993062420090303	800700	-741.051827	164280.160406	7-8.8659744263e9056137085e+01
38	1993062420090303	900800	-741.051827	164280.160406	5-1.5145812988e3375457764e+0102
39	1993070520090303	2000900	38-1.080827	78280.333406	8-2.0320663452e0406346130e+0102
40	1993070520091218	2100	3843.361138	7875.398000	-5.9963912964e9425277710e+01
41	1994091420100325	2100900	-741.051827	164280.160688	-75.9331817627e4004959106e+01
42	1997060720110127	700900	-741.051827	164280.160406	-5.8002792358e3115798950e+01
43	1997060720111224	8002100	-7443.051138	16475.160000	1-6.0099096680e8307769775e+0201
44	1997092320130719	19002100	-74.051	164.160	1-6.3710269165e1746520996e+0201
45	2001042320140426	2100700	-741.051265	164280.160688	-85.0685379028e7151275635e+01
46	2004032720140426	800700	-741.051546	164280.160406	-68.4567825317e5247161865e+01
47	2005031420140426	800	-1.827265	280.406688	-67.1867416382e2114089966e+01
48	2005031420140426	900800	-1.827546	280.406	-91.2169509888e4157341003e+0102
49	2006030420140426	900	-1.827546	280.125406	-62.3722732544e0927426147e+0102
50	2006032820160522	8002000	-174.827051	280164.406160	-56.7734420776e6684082031e+01
51	2016052220060328	9002100	-174.827051	280164.406160	-15.1018218994e9349365234e+0201
52	2007033120160929	2100	-74.051	164.160	86.7419113159e5295028687e+01
53	20161128	200903032100	700	-1.827	280.406	-8.9056137085e+01
20090303	800	-1.827	280.406	-1.3375457764e+02
42.857	75.375	-5.2441085815e+01

Table 1: Occurrences when the 10 metre U wind component exceeds 50 ms^-1.

75.000190011651092529e024805173913574e4808123943984985e5.5520050049e+01

Event	Date	Time	Latitude	Longitude	10m V
1	19790401	2100	-5.480	137.812	-9.6993362427e+01
2	1980033020090303	900	-1.827	280.406	-25.0406346130e0487777710e+0201
200912183	2100	43.138	19800831	1900	-5.9425277710e+01
20100325	900	-1.827	280.688	-5.4004959106e+01
199	137.531	-6.5852249146e+01
4	19800831	2000	-5.199	137.531	20110127	900	-1.827	280.406	-5.3115798950e0360015869e+01
5	2011122419821024	2100	43-74.138051	75164.000160	-65.8307769775e4236557007e+01
6	2013071919830930	21002000	-7442.051576	16484.160815	-65.1746520996e0510147095e+0101
7	2014042619830930	7002100	-142.265576	28084.688815	56.7151275635e1684814453e+01
8	2014042619840811	7001800	-15.546480	280137.406812	-81.5247161865e3961134338e+0102
9	2014042619840811	8001900	-15.265199	280137.688531	71.2114089966e2407348633e+0102
10	2014042619840811	8002000	-15.546199	280137.406531	-1.4157341003e3110269165e+02
11	2014042619840811	9002100	-15.546199	280137.406531	-21.0927426147e2531871033e+02
12	2016052219850812	20001900	-745.051199	164137.160531	-6.6684082031e5993698120e+01
13	2016052219850812	21002000	-745.051480	164137.160812	-58.9349365234e7721923828e+01
14	2016092919850812	2100	-745.051480	164137.160812	61.5295028687e1631915283e+0102
15	2016112819851116	2100	42-5.857480	75137.375812	-58.2441085815e0120529175e+01
16	19860724
Date	Time	Latitude	Longitude	10m V Value
900	-74.051	164.160	1.3616104126e+02
17	1987101619790401	2100	-574.480051	137164.812160	-96.6993362427e7936035156e+01
18	1980033019890420	9002000	-15.827480	280137.406812	-5.0487777710e5810119629e+01
19	1980083119890420	19002100	-5.199480	137.531812	-61.5852249146e2454008484e+0102
20	1980083119890711	20002100	-538.199361	13778.531398	-51.0360015869e4824528503e+0102
21	1982102419890912	2100900	-74.051	164.160	56.4236557007e3201354980e+01
22	1983093019901117	2000600	4241.576171	8439.815960	5-7.0510147095e1991546631e+01
23	1983093019901117	2100700	4241.576171	8439.815600	6-7.1684814453e2909973145e+01
24	1984081119910620	18002000	-5.480	137.812	19.3961134338e5385955811e+0201
25	1984081119910620	19002100	-5.199761	137138.531094	1.2407348633e6087461853e+02
1984081126	2000	-5.199	137.531	1.3110269165e+02
19840811	2100	-5.199	137.531	1.2531871033e+02
19920415	800	20.094	84.375	5.1177642822e+01
27	19921108	2100	19850812	1900	-5.199	137.531	6-5.5993698120e9594894409e+01
28	1985081219921113	20001800	-5.480	137.812	8-7.7721923828e4539321899e+01
29	1985081219921113	21001900	-5.480761	137.812	-1.1631915283e4339295959e+02
30	1985111619921113	21002000	-5.480	137.812531	-8.0120529175e+01	19860724	900	-74.051	164.160	1.3616104126e5561082458e+02
31	1987101619921113	2100	-745.051480	164137.160531	6-1.7936035156e7285772705e+0102
32	1989042019921123	20002100	-543.480138	13774.812625	-57.5810119629e4817504883e+01
33	1989042019930705	21002000	-538.480361	13778.812398	-1.2454008484e7013420105e+02
34	1993070519890711	2100	38.361	78.398	16.4824528503e0669006348e+0201
35	1989091219930815	9002000	-7431.051335	16472.160000	6-1.3201354980e2063990784e+0102
36	1990111719950127	6002100	4140.171890	39.960600	-79.1991546631e3620895386e+01
37	1990111719960710	7002000	41-5.171480	39137.600812	-7.2909973145e3640014648e+01
38	1996071019910620	20002100	-5.480	137.812	91.5385955811e1385275269e+0102
39	1991062019970422	2100	-540.761890	13839.094240	-1.6087461853e3644331360e+02
40	1997061719920415	8001700	2039.094766	8489.375297	5-1.1177642822e0041018677e+0102
41	1992110819970626	21001900	-5.199480	137.531812	-5.9594894409e7410095215e+01
42	1997062619921113	18002000	-5.480	137.812	-71.4539321899e2612721252e+0102
43	1992111319970626	19002100	-5.761480	137.812	-18.4339295959e5113784790e+0201
44	1992111319970817	2000	-5.480	137.531812	-15.5561082458e6425781250e+0201
45	1992111319970817	2100	-5.480	137.531812	-1.7285772705e4044223022e+02
46	1997092319921123	21001900	43-74.13805174	164.625160	-75.4817504883e1563308716e+01
47	1993070520010127	2000600	3841.361171	7839.398960	1.7013420105e2166479492e+02
48	1993070520010127	2100700	3841.361171	7839.398960	68.0669006348e3281478882e+01
19930815	2000	31.335	72.000	-1.2063990784e+02
19950127	2100	40.890	39.600	-9.3620895386e+01
49	20020602	2100	38.923	83.320	-6.7981185913e+01
50	20030516	2100	19960710	2000	-5.480	137.812	76.3640014648e4198028564e+01
19960710	2100	-5.480	137.812	1.1385275269e+02
19970422	2100	40.890	39.240	-1.3644331360e+02
19970617	1700	39.766	89.297	-1.0041018677e+02
19970626	1900	-5.480	137.812	5.7410095215e+01
19970626	2000	-5.480	137.812	1.2612721252e+02
19970626	2100	-5.480	137.812	8.5113784790e+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	2005080519970817	2000	-5.480	137.812	5-9.6425781250e3390945435e+01
59	1997081720050805	2100	-5.480	137.812	1-9.4044223022e8295639038e+0201
60	1997092320051208	1900800	-7440.051890	16439.160960	-56.1563308716e6637542725e+01
61	2001012720060304	600900	41-1.171546	39280.960406	1-7.2166479492e0116149902e+0201
62	2001012720060612	7001900	41-5.171480	39137.960812	86.3281478882e8560852051e+01
63	2002060220060612	21002000	38-5.923480	83137.320812	-61.7981185913e0062788391e+0102
64	2003051620060612	2100	-5.480	137.812	1.1736833191e+02
65	20061210	700	41.171	39.600	5.8087677002e6.4198028564e+01
66	2006121020030704	2000800	4041.328171	8439.240600	5.8809799194e1876373291e+01
67	2004071120061219	1800700	4041.328171	8739.480960	16.6328262329e5212203979e+0201
68	2004071120061219	1900800	4041.328171	8739.480600	75.7149871826e0869308472e+01
69	2007122720040803	2100600	-541.199171	13739.531600	-57.1051910400e9303802490e+01
70	2004083020071227	2000700	-541.199171	13739.531960	-71.2028549194e0291072083e+0102
71	2004083020071227	2100800	-541.199171	13739.250960	-18.5628892517e6426681519e+0201
72	2004091220090303	2000900	19-1.532827	277280.031406	-56.3294830322e8449584961e+01
73	2005080520091218	2000	-543.480138	13774.812625	-96.3390945435e3902404785e+01
74	2009121820050805	2100	-543.480138	13774.812625	-91.8295639038e5077589417e+0102
75	2005120820100110	8002100	40.890	39.960	6-5.6637542725e4371688843e+01
2006030476	900	-1.546	280.406	-7.0116149902e+01	20060612	20111207	2100	41.171	39.960	-5.480	137.812	6.8560852051e2954406738e+01
77	2006061220111224	2000	-543.480138	13774.812625	1-8.0062788391e1969665527e+0201
78	2006061220111224	2100	-543.480138	13774.812625	-1.1736833191e0727139282e+02
2006121079	70020120629	41.171	39.600	5.8087677002e+01
20061210	800	41.171	39.600	5.1876373291e+01
20061219	700	41.171	39.960	6.5212203979e+01
20061219	800	41.171	39.600	5.0869308472e+01
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	2013122420071227	600	41.171	39.600960	76.9303802490e8190124512e+01
83	2007122720131224	700	41.171	39.960600	16.0291072083e7012496948e+0201
84	2007122720131224	800	41.171	39.960600	85.6426681519e1414718628e+01
85	2009030320140426	900700	-1.827265	280.406	-65.8449584961e4881195068e+01
86	2009121820140426	2000700	43-2.138108	74280.625688	-65.3902404785e8466461182e+01
2009121887	2100	43.138	74.625	-1.5077589417e+02
20100110	2100	40.890	39.960	-5.4371688843e+01
20111207	2100	41.171	39.960	-5.2954406738e+01
20111224	2000	43.138	74.625	-8.1969665527e+01
20111224	2100	43.138	74.625	-1.0727139282e+02
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	2016051620120629	2000	-5.480	137.812531	61.8156173706e5173913574e+0102
92	2012062920160516	2100	-5.480	137.812	57.3109390259e3943984985e+01
2013072793	190020160531	38.080	78.333	6.0674041748e+01
20131224	600	41.171	39.960	6.8190124512e+01
20131224	700	41.171	39.600	6.7012496948e+01
20131224	800	41.171	39.600	5.1414718628e+01
20140426	700	-1.265	280.406	5.4881195068e+01
20140426	700	-2.108	280.688	-5.8466461182e+01
20140426	800	-1.546	280.688	-8.5272201538e+01
20140426	900	-1.546	280.688	-1.0531086731e+02
20150912	1900	-5.199	137.531	6.4281372070e+01
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	20160516	1900	-5.480	137.812	7.	6125183105e+01
102	20160516	20191116	20001900	-5.	199	137.531	1.	4759844971e+02
103	2016051620191116	21002000	-5.	199	137.	531	7.	8542388916e+01
20160531	2000	-5.480	137.812	8.6714050293e+01
20160531	2100	-5.480	137.812	8.5311660767e+01
20160825	1900	-5.480	137.812	8.8643951416e+01
20160825	2000	-5.199	137.531	6.8540237427e+01
20161128	2000	43.138	74.625	-8.1585525513e+01
20161128	2100	43.138	74.625	-1.6854412842e+02
20171011	2100	-5.480	137.812	1.1839462280e+02
20180914	2100	-5.480	137.812

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 Agreement 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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