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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.

19930705.080280.406

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
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	.160	-6.4567825317e+01
31	20050314	800	-1.827	280.406	-6.1867416382e+01
32	2005031419890912	900	-741.051827	164280.160406	-19.6730293274e2169509888e+0201
33	1990040220060304	700900	-741.051827	164280.160125	5-6.8469223022e3722732544e+01
34	1993062420060328	600800	-741.051827	164280.160406	6-5.0172592163e7734420776e+01
35	1993062420060328	700900	-741.051827	164280.160406	-1.0357415771e1018218994e+02
36	2007033119930624	8002100	-74.051	164.160	78.8659744263e7419113159e+01
37	1993062420090303	900700	-741.051827	164280.160406	5-8.5145812988e9056137085e+01		2000
38	78.333	8.0320663452e+01
19930705	2100	38.361	78.398	5.9963912964e+01
19940914	2100	-74.051	164.160	-7.9331817627e+01
19970607	700	-74.051	164.160	5.8002792358e+01
19970607	800	-74.051	164.160	1.0099096680e+02
19970923	1900	-74.051	164.160	1.3710269165e+02
20010423	2100	-74.051	164.160	-8.0685379028e+01
	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	20040327	800	-74.051	164.160	-6.4567825317e1746520996e+01
45	2005031420140426	800700	-1.827265	280.406688	-65.1867416382e7151275635e+01
46	2014042620050314	900700	-1.827546	280.406	-98.2169509888e5247161865e+01
47	2014042620060304	900800	-1.827265	280.125688	-67.3722732544e2114089966e+01
48	2006032820140426	800	-1.827546	280.406	-51.7734420776e4157341003e+0102
49	2006032820140426	900	-1.827546	280.406	-12.1018218994e0927426147e+02
50	2007033120160522	21002000	-74.051	164.160	8-6.7419113159e6684082031e+01
51	2009030320160522	7002100	-174.827051	280164.406160	-85.9056137085e9349365234e+01
2009030352	800	-1.827	20160929	2100	-174.3375457764e+02
20090303	900	-1.827	280.406	-2.0406346130e+02
051	164.160	6.5295028687e+01
53	20161128	2100	42.857	75.375	20091218	2100	43.138	75.000	-5.9425277710e2441085815e+01
20100325	900	-1.827	280.688	-5.4004959106e+01

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

Event	Date	Time	Latitude	Longitude	10m V
1	19790401	2100	-5.480	137.812	-9.6993362427e+01
2	1980033020110127	900	-1.827	280.406	-5.3115798950e0487777710e+01
3	2011122419800831	21001900	43-5.138199	75137.000531	-6.8307769775e5852249146e+01
4	2013071919800831	21002000	-745.051199	164137.160531	-65.1746520996e0360015869e+01
5	2014042619821024	7002100	-174.265051	280164.688160	5.7151275635e4236557007e+01
6	2014042619830930	7002000	-142.546576	28084.406815	-85.5247161865e0510147095e+01
7	2014042619830930	8002100	-142.265576	28084.688815	76.2114089966e1684814453e+01
8	2014042619840811	8001800	-15.546480	280137.406812	-1.4157341003e3961134338e+02
9	1984081120140426	9001900	-15.546199	280137.406531	-21.0927426147e2407348633e+02
10	1984081120160522	2000	-745.051199	164137.160531	-61.6684082031e3110269165e+0102
11	2016052219840811	2100	-745.051199	164137.160531	-51.9349365234e2531871033e+0102
12	2016092919850812	21001900	-745.051199	164137.160531	6.5295028687e5993698120e+01
13	2016112819850812	21002000	42-5.857480	75137.375812	-58.2441085815e7721923828e+01
14	19850812	2100	-5.480	137.812

-9

1.

6993362427e

1631915283e+

01

02

15

19790401

19851116

2100

-

1

5.

827

480

280

137.

406

812

-

5

8.

0487777710e

0120529175e+01

16

19800330

19860724

900

-

5

74.

199

051

137

164.

531

160

-6

1.

5852249146e

3616104126e+

01

02

17

19800831

19871016

1900

2100

-

5

74.

199

051

137

164.

531

160

-5

6.

0360015869e

7936035156e+01

18

19800831

19890420

2000

-

74

5.

051

480

164

137.

160

812

-5.

4236557007e

5810119629e+01

19821024

19

19890420

2100

42

-5.

576

480

84

137.

815

812

5

-1.

0510147095e

2454008484e+

01

02

20

19830930

19890711

2000

2100

42

38.

576

361

84

78.

815

398

6

1.

1684814453e

4824528503e+

01

02

21

19830930

19890912

2100

900

-

5

74.

480

051

137

164.

812

160

1

6.

3961134338e

3201354980e+

02

01

22

19840811

19901117

1800

600

-5

41.

199

171

137

39.

531

960

1

-7.

2407348633e

1991546631e+

02

01

23

19840811

19901117

1900

700

-5

41.

199

171

137

39.

531

600

1

-7.

3110269165e

2909973145e+

02

01

24

19840811

19910620

2000

-5.

199

480

137.

531

812

1

9.

2531871033e

5385955811e+

02

01

25

19840811

19910620

2100

-5.

199

761

137

138.

531

094

6

1.

5993698120e

6087461853e+

01

02

26

19850812

19920415

1900

800

-5

20.

480

094

137

84.

812

375

8

5.

7721923828e

1177642822e+01

27

19850812

19921108

2000

2100

-5.

480

199

137.

812

531

1

-5.

1631915283e

9594894409e+

02

01

28

19850812

19921113

2100

1800

-5.480

137.812

-

8

7.

0120529175e

4539321899e+01

29

19851116

19921113

2100

1900

-

74

5.

051

761

164

137.

160

812

-1.

3616104126e

4339295959e+02

19860724

30

19921113

900

2000

-

74

5.

051

480

164

137.

160

531

6

-1.

7936035156e

5561082458e+

01

02

31

19871016

19921113

2100

-5.480

137.

812

531

-

5

1.

5810119629e

7285772705e+

01

02

32

19890420

19921123

2000

2100

-5

43.

480

138

137

74.

812

625

-

1

7.

2454008484e

4817504883e+

02

01

33

19890420

19930705

2100

2000

38.361

78.398

1.

4824528503e

7013420105e+02

19890711

34

19930705

2100

-74

38.

051

361

164

78.

160

398

6.

3201354980e

0669006348e+01

35

19890912

19930815

900

2000

41

31.

171

335

39

72.

960

000

-

7

1.

1991546631e

2063990784e+

01

02

36

19901117

19950127

600

2100

41

40.

171

890

39.600

-

7

9.

2909973145e

3620895386e+01

37

19901117

19960710

700

2000

-5.480

137.812

9

7.

5385955811e

3640014648e+01

19910620

38

19960710

2000

2100

-5.

761

480

138

137.

094

812

1.

6087461853e

1385275269e+02

39

19910620

19970422

2100

20

40.

094

890

84

39.

375

240

5

-1.

1177642822e

3644331360e+

01

02

40

19920415

19970617

800

1700

-5

39.

199

766

137

89.

531

297

-

5

1.

9594894409e

0041018677e+

01

02

41

19921108

19970626

2100

1900

-5.480

137.812

-7

5.

4539321899e

7410095215e+01

19921113

42

19970626

1800

2000

-5.

761

480

137.812

-

1.

4339295959e

2612721252e+02

43

19921113

19970626

1900

2100

-5.480

137.

531

812

-1

8.

5561082458e

5113784790e+

02

01

44

19921113

19970817

2000

-5.480

137.

531

812

-1

5.

7285772705e

6425781250e+

02

01

45

19921113

19970817

2100

43.138

74.625

-

7

5.

4817504883e+01

19921123

2100

480

137.812

38.361

78.398

1.

7013420105e

4044223022e+02

46

19930705

19970923

2000

1900

38

-74.

361

051

78

164.

398

160

6

-5.

0669006348e

1563308716e+01

47

19930705

20010127

2100

600

31

41.

335

171

72

39.

000

960

-

1.

2063990784e

2166479492e+02

48

19930815

20010127

2000

700

40

41.

890

171

39.

600

960

-9

8.

3620895386e

3281478882e+

01

49

19950127

20020602

2100

-5

38.

480

923

137

83.

812

320

7

-6.

3640014648e

7981185913e+01

50

19960710

20030516

2000

2100

-5.480

137.812

1

6.

1385275269e

4198028564e+

02

01

51

19960710

20030704

2100

2000

40.

890

328

39

84.240

-1

5.

3644331360e

8809799194e+

02

19970422

2100

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

39.766

89.297

-1.0041018677e+02

19970617

1700

-5.480

137.812

5.7410095215e+01

19970626

1900

-5.480

137.812

1.2612721252e+02

19970626

2000

-5.480

137.812

8.5113784790e+01

19970626

2100

-5.480

137.812

5.6425781250e+01

19970817

2000

-5.480

137.812

1.4044223022e+02

19970817

2100

-74.051

164.160

-5.1563308716e+01

19970923

1900

41.171

39.960

1.2166479492e+02

20010127

600

41.171

39.960

8.3281478882e+01

20010127

700

38.923

83.320

-6.7981185913e+01

20020602

2100

-5.480

137.812

6.4198028564e+01

20030516

2100

40.328

84.240

5.8809799194e+01

20030704

2000

40.328

87.480

1.6328262329e+02

20040711

1800

40.328

87.480

7.7149871826e+01

20040711

1900

-5.199

137.531

-5.1051910400e+01

20040803

2100

-5.199

137.531

-7.2028549194e+01

20040830

2000

-5.199

137.250

-1.5628892517e+02

20040830

2100

19.532

277.031

-5.3294830322e+01

20040912

2000

-5.480

137.812

-9.3390945435e+01

20050805

2000

-5.480

137.812

-9.8295639038e+01

20050805

2100

40.890

39.960

6.6637542725e+01

20051208

800

-1.546

280.406

-7.0116149902e+01

20060304

900

-5.480

137.812

6.8560852051e+01

20060612

1900

-5.480

137.812

1.0062788391e+02

20060612

2000

-5.480

137.812

1.1736833191e+02

20060612

2100

41.171

39.

600

960

-5.

8087677002e

2954406738e+01

77

20061210

20111224

700

2000

41

43.

171

138

39

74.

600

625

5

-8.

1876373291e

1969665527e+01

78

20061210

20111224

800

2100

41

43.

171

138

39

74.

960

625

6

-1.

5212203979e

0727139282e+

01

02

79

20061219

20120629

700

2000

41

-5.

171

480

39

137.

600

812

5

6.

0869308472e

8156173706e+01

80

20061219

20120629

800

2100

41

-5.

171

480

39

137.

600

812

7

5.

9303802490e

3109390259e+01

20071227

81

20130727

600

1900

41

38.

171

080

39

78.

960

333

1

6.

0291072083e

0674041748e+

02

01

82

20071227

20131224

700

600

41.171

39.960

8

6.

6426681519e

8190124512e+01

20071227

83

20131224

800

700

-1

41.

827

171

280

39.

406

600

-

6.

8449584961e

7012496948e+01

84

20090303

20131224

900

800

43

41.

138

171

74

39.

625

600

-6

5.

3902404785e

1414718628e+01

85

20091218

20140426

2000

700

43

-1.

138

265

74

280.

625

406

-1

5.

5077589417e

4881195068e+

02

01

86

20091218

20140426

2100

700

40

-2.

890

108

39

280.

960

688

-5.

4371688843e

8466461182e+01

87

20100110

20140426

2100

800

41

-1.

171

546

39

280.

960

688

-

5

8.

2954406738e

5272201538e+01

88

20111207

20140426

2100

900

43

-1.

138

546

74

280.

625

688

-

8

1.

1969665527e

0531086731e+

01

02

89

20111224

20150912

2000

1900

43

-5.

138

199

74

137.

625

531

-1

6.

0727139282e

4281372070e+

02

01

90

20111224

20160516

2100

1900

-5.480

137.812

6

1.

8156173706e

1651092529e+

01

02

91

20120629

20160516

2000

-5.480

137.

812

531

5

1.

3109390259e

5173913574e+

01

02

92

20120629

20160516

2100

38

-5.

080

480

78

137.

333

812

6

7.

0674041748e

3943984985e+01

93

20130727

20160531

1900

2000

41

-5.

171

480

39

137.

960

812

6

8.

8190124512e

6714050293e+01

94

20131224

20160531

600

2100

41

-5.

171

480

39

137.

600

812

6

8.

7012496948e

5311660767e+01

20131224

95

20160825

700

1900

41

-5.

171

480

39

137.

600

812

5

8.

1414718628e

8643951416e+01

20131224

96

20160825

800

2000

-

1

5.

265

199

280

137.

406

531

5

6.

4881195068e

8540237427e+01

97

20140426

20161128

700

2000

-2

43.

108

138

280

74.

688

625

-

5

8.

8466461182e

1585525513e+01

98

20140426

20161128

700

2100

-1

43.

546

138

280

74.

688

625

-

8

1.

5272201538e

6854412842e+

01

02

99

20140426

20171011

800

2100

-

1

5.

546

480

280

137.

688

812

-

1.

0531086731e

1839462280e+02

20140426

100

20180914

900

2100

-5.

199

480

137.

531

812

6

5.

4281372070e

5520050049e+01

101

20150912

20191116

1900

1800

-5.480

137.812

1

7.

1651092529e

6125183105e+

02

01

102

20160516

20191116

1900

-5.

480

199

137.531

1.

5173913574e

4759844971e+02

103

20160516

20191116

2000

-5.

480

199

137.

812

531

7.

3943984985e

8542388916e+01

20160516

2100

-5.480

137.812

8.6714050293e+01

20160531

2000

-5.480

137.812

8.5311660767e+01

20160531

2100

-5.480

137.812

8.8643951416e+01

20160825

1900

-5.199

137.531

6.8540237427e+01

20160825

2000

43.138

74.625

-8.1585525513e+01

20161128

2000

43.138

74.625

-1.6854412842e+02

20161128

2100

-5.480

137.812

1.1839462280e+02

20171011

2100

-5.480

137.812

5.5520050049e+01

20180914

2100

Table 2: Occurrences when the 10 metre V wind component exceeds 50 ms^-1.

Info

icon	false

_{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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