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A few times per year, the analysed low-level winds, eg e.g. 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 the components of the 10m winds, the 10 metre U wind component and 10 metre V wind component, exceed 50 ms^-1. This value is an arbitrary one which may capture real wind events, such as hurricanes and typhoons.

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. On occasion, erroneously large wind values are also present in the 100m winds.

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.

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

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

DateTimeLatitudeLongitude10m U

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	1.0099096680e+02
28	19970923	1900	-74.051	164.160	1.

6730293274e

3710269165e+02

29

19900402

20010423

700

2100

-74.051

164.160

5

-8.

8469223022e

0685379028e+01

30

19930624

20040327

600

800

-74.051

164.160

-6.

0172592163e

4567825317e+01

31

19930624

20050314

700

800

-

74

1.

051

827

164

280.

160

406

1

-6.

0357415771e

1867416382e+

02

01

32

19930624

20050314

800

900

-

74

1.

051

827

164

280.

160

406

7

-9.

8659744263e

2169509888e+01

19930624

33

20060304

900

-

74

1.

051

827

164

280.

160

125

5

-6.

5145812988e

3722732544e+01

34

19930705

20060328

2000

800

38

-1.

080

827

78

280.

333

406

8

-5.

0320663452e

7734420776e+01

35

19930705

20060328

2100

900

38

-1.

361

827

78

280.

398

406

5

-1.

9963912964e

1018218994e+

01

02

36

19940914

20070331

2100

-74.051

164.160

-7

8.

9331817627e

7419113159e+01

37

19970607

20090303

700

-

74

1.

051

827

164

280.

160

406

5

-8.

8002792358e

9056137085e+01

38

19970607

20090303

800

-

74

1.

051

827

164

280.

160

406

-1.

0099096680e

3375457764e+02

39

19970923

20090303

1900

900

-

74

1.

051

827

164

280.

160

406

1

-2.

3710269165e

0406346130e+02

40

20010423

20091218

2100

-74

43.

051

138

164

75.

160

000

-

8

5.

0685379028e

9425277710e+01

41

20040327

20100325

800

900

-

74

1.

051

827

164

280.

160

688

-

6

5.

4567825317e

4004959106e+01

42

20050314

20110127

800

900

-1.827

280.406

-

6

5.

1867416382e

3115798950e+01

43

20050314

20111224

900

2100

-1

43.

827

138

280

75.

406

000

-

9

6.

2169509888e

8307769775e+01

20060304

44

20130719

900

2100

-

1

74.

827

051

280

164.

125

160

-6.

3722732544e

1746520996e+01

45

20060328

20140426

800

700

-1.

827

265

280.

406

688

-

5.

7734420776e

7151275635e+01

46

20060328

20140426

900

700

-1.

827

546

280.406

-1.1018218994e+02

20070331

2100

-

74.051

164.160

8.

7419113159e

5247161865e+01

47

20090303

20140426

700

800

-1.

827

265

280.

406

688

-8

7.

9056137085e

2114089966e+01

48

20090303

20140426

800

-1.

827

546

280.406

-1.

3375457764e

4157341003e+02

49

20090303

20140426

900

-1.

827

546

280.406

-2.

0406346130e

0927426147e+02

50

20091218

20160522

2100

2000

43

-74.

138

051

75

164.

000

160

-

5

6.

9425277710e

6684082031e+01

51

20100325

20160522

900

2100

-

1

74.

827

051

280

164.

688

160

-5.

4004959106e

9349365234e+01

20110127

52

20160929

900

2100

-

1

74.

827

051

280

164.

406

160

-5

6.

3115798950e

5295028687e+01

53

20111224

20161128

2100

43

42.

138

857

75.

000

375

-

6

5.

8307769775e

2441085815e+01

20130719

2100

-74.051

164.160

-6.1746520996e+01

20140426

700

-1.265

280.688

5.7151275635e+01

20140426

700

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

Event	Date	Time	Latitude	Longitude	10m V
1	19790401	2100	-5.480	137.812	-9.6993362427e+01
2	19800330	900	-1.827

-1.546

280.406

-

8

5.

5247161865e

0487777710e+01

3

20140426

19800831

800

1900

-

1

5.

265

199

280

137.

688

531

7

-6.

2114089966e

5852249146e+01

20140426

4

19800831

800

2000

-

1

5.

546

199

280

137.

406

531

-

1

5.

4157341003e

0360015869e+

02

01

5

20140426

19821024

900

2100

-

1

74.

546

051

280

164.

406

160

-2

5.

0927426147e

4236557007e+

02

01

6

20160522

19830930

2000

-74

42.

051

576

164

84.

160

815

-6

5.

6684082031e

0510147095e+01

7

20160522

19830930

2100

-74

42.

051

576

164

84.

160

815

-5

6.

9349365234e

1684814453e+01

8

20160929

19840811

2100

1800

-

74

5.

051

480

164

137.

160

812

6

1.

5295028687e

3961134338e+

01

02

9

20161128

19840811

2100

1900

42

-5.

857

199

75

137.

375

531

-5

1.

2441085815eDateTimeLatitudeLongitude10m V

19790401

2407348633e+

01

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

02
10	19840811	2000	-5.199	137.531	1.3110269165e+02
11	19840811

2100

-5.

480

199

137.

812

531

-9

1.

6993362427e

2531871033e+

01

02

12

19800330

19850812

900

1900

-

1

5.

827

199

280

137.

406

531

-5

6.

0487777710e

5993698120e+01

19800831

13

19850812

1900

2000

-5.

199

480

137.

531

812

-6

8.

5852249146e

7721923828e+01

14

19800831

19850812

2000

2100

-5.

199

480

137.

531

812

-5

1.

0360015869e

1631915283e+

01

02

15

19821024

19851116

2100

-

74

5.

051

480

164

137.

160

812

5

-8.

4236557007e

0120529175e+01

16

19830930

19860724

2000

900

42

-74.

576

051

84

164.

815

160

5

1.

0510147095e

3616104126e+

01

02

17

19830930

19871016

2100

42

-74.

576

051

84

164.

815

160

6.

1684814453e

7936035156e+01

18

19840811

19890420

1800

2000

-5.480

137.812

1.3961134338e+02

19840811

1900

-5.

199

137.531

1.2407348633e+02

5810119629e+01
19	19890420	2100

19840811

2000

-5.

199

480

137.

531

812

-1.

3110269165e

2454008484e+02

20

19840811

19890711

2100

-5

38.

199

361

137

78.

531

398

1.

2531871033e

4824528503e+02

21

19850812

19890912

1900

900

-

5

74.

199

051

137

164.

531

160

6.

5993698120e

3201354980e+01

22

19850812

19901117

2000

600

-5

41.

480

171

137

39.

812

960

8

-7.

7721923828e

1991546631e+01

23

19850812

19901117

2100

700

-5

41.

480

171

137

39.

812

600

1

-7.

1631915283e

2909973145e+

02

01

24

19851116

19910620

2100

2000

-5.480

137.812

-8

9.

0120529175e

5385955811e+01

25

19860724

19910620

900

2100

-

74

5.

051

761

164

138.

160

094

1.

3616104126e

6087461853e+02

19871016

26

2100

-74.051

164.160

6.7936035156e+01

19920415	800	20.094	84.375	5.1177642822e+01
27	19921108

19890420

2000

-5.480

137.812

-5.5810119629e+01

19890420

2100

-5.

480

199

137.

812

531

-

1

5.

2454008484e

9594894409e+

02

01

19890711

28

2100

19921113

38.361

78.398

1.4824528503e+02

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

19890912

900

-74.051

164.160

6.3201354980e+01

19901117

600

41.171

39.960

-7.1991546631e+01

19901117

700

41.171

39.600

-7.2909973145e+01

19910620

2000

-5.480

137.

812

531

9

-1.

5385955811e

7285772705e+

01

02

32

19910620

19921123

2100

-5

43.

761

138

74.

094

625

1

-7.

6087461853e

4817504883e+

02

01

33

19920415

19930705

800

2000

20

38.

094

361

84

78.

375

398

5

1.

1177642822e

7013420105e+

01

02

34

19921108

19930705

2100

-5

38.

199

361

137

78.

531

398

-5

6.

9594894409e

0669006348e+01

35

19921113

19930815

1800

2000

-5

31.

480

335

137

72.

812

000

-

7

1.

4539321899e

2063990784e+

01

02

36

19921113

19950127

1900

2100

-5

40.

761

890

137

39.

812

600

-

1

9.

4339295959e

3620895386e+

02

01

37

19921113

19960710

2000

-5.480

137.

531

812

-1

7.

5561082458e

3640014648e+

02

01

38

19921113

19960710

2100

-5.480

137.

531

812

-

1.

7285772705e

1385275269e+02

39

19921123

19970422

2100

43

40.

138

890

74

39.

625

240

-

7

1.

4817504883e

3644331360e+

01

02

40

19930705

19970617

2000

1700

38

39.

361

766

78

89.

398

297

-1.

7013420105e

0041018677e+02

19930705

41

19970626

2100

1900

38

-5.

361

480

78

137.

398

812

6

5.

0669006348e

7410095215e+01

42

19930815

19970626

2000

31

-5.

335

480

72

137.

000

812

-

1.

2063990784e

2612721252e+02

19950127

43

19970626

2100

40

-5.

890

480

39

137.

600

812

-9

8.

3620895386e

5113784790e+01

19960710

44

19970817

2000

-5.480

137.812

7

5.

3640014648e

6425781250e+01

19960710

45

19970817

2100

-5.480

137.812

1.

1385275269e

4044223022e+02

46

19970422

19970923

2100

1900

40

-74.

890

051

39

164.

240

160

-

1

5.

3644331360e

1563308716e+

02

01

47

19970617

20010127

1700

600

39

41.

766

171

89

39.

297

960

-

1.

0041018677e

2166479492e+02

48

19970626

20010127

1900

700

-5

41.

480

171

137

39.

812

960

5

8.

7410095215e

3281478882e+01

19970626

49

20020602

2000

2100

-5

38.

480

923

137

83.

812

320

1

-6.

2612721252e

7981185913e+

02

01

50

19970626

20030516

2100

-5.480

137.812

8

6.

5113784790e

4198028564e+01

19970817

51

20030704

2000

-5

40.

480

328

137

84.

812

240

5.

6425781250e

8809799194e+01

52

19970817

20040711

2100

1800

-5

40.

480

328

137

87.

812

480

1.

4044223022e

6328262329e+02

19970923

53

20040711

1900

-74

40.

051

328

164

87.

160

480

-5

7.

1563308716e

7149871826e+01

20010127

600

41.171

39.960

1.2166479492e+02

20010127

700

41.171

39.960

8.3281478882e+01

20020602

2100

38.923

83.320

-6.7981185913e+01

20030516

54	20040803	2100	-5.199	137.531	-5.1051910400e+01
55	20040830	2000	-5.199	137.531	-7.2028549194e+01
56	20040830	2100	-5.

480

199

137.

812

250

6

-1.

4198028564e

5628892517e+

01

02

57

20030704

20040912

2000

40

19.

328

532

84

277.

240

031

-5.

8809799194e

3294830322e+01

58

20040711

20050805

1800

2000

40

-5.

328

480

87

137.

480

812

1

-9.

6328262329e

3390945435e+

02

01

59

20040711

20050805

1900

2100

40

-5.

328

480

87

137.

480

812

7

-9.

7149871826e

8295639038e+01

60

20040803

20051208

2100

800

-5

40.

199

890

137

39.

531

960

-5

6.

1051910400e

6637542725e+01

61

20040830

20060304

2000

900

-

5

1.

199

546

137

280.

531

406

-7.

2028549194e

0116149902e+01

62

20040830

20060612

2100

1900

-5.

199

480

137.

250

812

-1

6.

5628892517e

8560852051e+

02

01

63

20040912

20060612

2000

19

-5.

532

480

277

137.

031

812

-5

1.

3294830322e

0062788391e+

01

02

64

20050805

20060612

2000

2100

-5.480

137.812

-9.3390945435e+01

20050805

2100

-5.480

137.812

-9.8295639038e+01

20051208

800

	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

40.890

39.960

6.

6637542725e

5212203979e+01

68

20060304

20061219

900

800

-1

41.

546

171

280

39.

406

600

-7

5.

0116149902e

0869308472e+01

20060612

69

20071227

1900

600

-5

41.

480

171

137

39.

812

600

6

7.

8560852051e

9303802490e+01

70

20060612

20071227

2000

700

-5

41.

480

171

137

39.

812

960

1.

0062788391e

0291072083e+02

71

20060612

20071227

2100

800

-5

41.

480

171

137

39.

812

960

1

8.

1736833191e

6426681519e+

02

01

72

20061210

20090303

700

900

41

-1.

171

827

39

280.

600

406

5

-6.

8087677002e

8449584961e+01

73

20061210

20091218

800

2000

41

43.

171

138

39

74.

600

625

5

-6.

1876373291e

3902404785e+01

74

20061219

20091218

700

2100

41

43.

171

138

39

74.

960

625

6

-1.

5212203979e

5077589417e+

01

02

75

20061219

20100110

800

2100

41

40.

171

890

39.

600

960

-5.

0869308472e

4371688843e+01

20071227

76

20111207

600

2100

41.171

39.

600

960

7

-5.

9303802490e

2954406738e+01

77

20071227

20111224

700

2000

41

43.

171

138

39

74.

960

625

1

-8.

0291072083e

1969665527e+

02

01

78

20071227

20111224

800

2100

41

43.

171

138

39

74.

960

625

8

-1.

6426681519e

0727139282e+

01

02

79

20090303

20120629

900

2000

-

1

5.

827

480

280

137.

406

812

-

6.

8449584961e

8156173706e+01

80

20091218

20120629

2000

2100

43

-5.

138

480

74

137.

625

812

-6

5.

3902404785e

3109390259e+01

81

20091218

20130727

2100

1900

43

38.

138

080

74

78.

625

333

-1

6.

5077589417e

0674041748e+

02

01

82

20100110

20131224

2100

600

40

41.

890

171

39.960

-5

6.

4371688843e

8190124512e+01

20111207

83

20131224

2100

700

41.171

39.

960

600

-5

6.

2954406738e

7012496948e+01

84

20111224

20131224

2000

800

43

41.

138

171

74

39.

625

600

-8

5.

1969665527e

1414718628e+01

20111224

85

20140426

2100

700

43

-1.

138

265

74

280.

625

406

-1

5.

0727139282e

4881195068e+

02

01

86

20120629

20140426

2000

700

-

5

2.

480

108

137

280.

812

688

6

-5.

8156173706e

8466461182e+01

87

20120629

20140426

2100

800

-

5

1.

480

546

137

280.

812

688

5

-8.

3109390259e

5272201538e+01

88

20130727

20140426

1900

900

38

-1.

080

546

78

280.

333

688

6

-1.

0674041748e

0531086731e+

01

02

89

20131224

20150912

600

1900

41

-5.

171

199

39

137.

960

531

6.

8190124512e

4281372070e+01

90

20131224

20160516

700

1900

41

-5.

171

480

39

137.

600

812

6

1.

7012496948e

1651092529e+

01

02

91

20131224

20160516

800

2000

41

-5.

171

480

39

137.

600

531

5

1.

1414718628e

5173913574e+

01

02

92

20140426

20160516

700

2100

-

1

5.

265

480

280

137.

406

812

5

7.

4881195068e

3943984985e+01

93

20140426

20160531

700

2000

-

2

5.

108

480

280

137.

688

812

-5

8.

8466461182e

6714050293e+01

94

20140426

20160531

800

2100

-

1

5.

546

480

280

137.

688

812

-

8.

5272201538e

5311660767e+01

95

20140426

20160825

900

1900

-

1

5.

546

480

280

137.

688

812

-1

8.

0531086731e

8643951416e+

02

01

96

20150912

20160825

1900

2000

-5.199

137.531

6.

4281372070e

8540237427e+01

20160516

1900

-5.480

137.812

1.1651092529e+02

20160516


97	20161128	2000	43.138	74.625	-8.1585525513e+01
98	20161128	2100	43.138	74.625	-1.6854412842e+02
99	20171011	2100

2000

-5.480

137.

531

812

1.

5173913574e

1839462280e+02

100

20160516

20180914

2100

-5.480

137.812

7

5.

3943984985e

5520050049e+01

20160531

101

20191116

2000

1800

-5.480

137.812

8

7.

6714050293e

6125183105e+01

102

20160531

20191116

2100

1900

-5.

480

199

137.

812

531

8

1.

5311660767e

4759844971e+

01

02

103

20160825

20191116

1900

2000

-5.

480

199

137.

812

531

8

7.

8643951416e

8542388916e+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

5.5520050049e+01

...

Image Added

Figure 2: Locations with 10m wind > 50m/s detailed in tables.

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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