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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 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.

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
Date	Time	Latitude	Longitude	10m 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	5.8469223022e+01
19	19930624	600	-74.051	164.160	6.0172592163e+01
20	19930624	700	19860724	900	-74.051	164.160	-21.9203100586e0357415771e+02
21	1993062419871016	2000800	-74.051	164.160	-97.4200180054e8659744263e+01
22	1987101619930624	2100900	-74.051	164.160	-15.5219485474e5145812988e+0201
23	1989071119930705	21002000	38.080	78.333	78.0804840088e0320663452e+01
24	1989091219930705	8002100	-7438.051361	16478.160398	-85.3815658569e9963912964e+01
1989091225	900	-74.051	164.160	-1.6730293274e+02	19940914	2100	19900402	700	-74.051	164.160	5-7.8469223022e9331817627e+01
26	1993062419970607	600700	-74.051	164.160	65.0172592163e8002792358e+01
27	1997060719930624	700800	-74.051	164.160	1.0357415771e0099096680e+02
28	1997092319930624	8001900	-74.051	164.160	71.8659744263e3710269165e+0102
29	1993062420010423	9002100	-74.051	164.160	5.5145812988e+01	19930705	2000	38.080	78.333	-8.0320663452e0685379028e+01
30	1993070520040327	2100800	38-74.361051	78164.398160	5-6.9963912964e4567825317e+01
31	1994091420050314	2100800	-741.051827	164280.160406	-76.9331817627e1867416382e+01
32	1997060720050314	700900	-741.051827	164280.160406	5-9.8002792358e2169509888e+01
33	1997060720060304	800900	-741.051827	164280.160125	1-6.0099096680e3722732544e+0201
34	1997092320060328	1900800	-741.051827	164280.160406	1-5.3710269165e7734420776e+0201
35	2001042320060328	2100900	-741.051827	164280.160406	-81.0685379028e1018218994e+0102
36	2004032720070331	8002100	-74.051	164.160	-68.4567825317e7419113159e+01
37	2005031420090303	800700	-1.827	280.406	-68.1867416382e9056137085e+01
38	2009030320050314	900800	-1.827	280.406	-91.2169509888e3375457764e+0102
39	2006030420090303	900	-1.827	280.125	-6.3722732544e+01	.406	-2.0406346130e+02
40	20091218	2100	43.138	75.000	-5.9425277710e+01
41	20100325	900	20060328	800	-1.827	280.406688	-5.7734420776e4004959106e+01
42	2006032820110127	900	-1.827	280.406	-15.1018218994e3115798950e+0201
43	2007033120111224	2100	-7443.051138	16475.160000	8-6.7419113159e8307769775e+01
44	2009030320130719	7002100	-174.827051	280164.406160	-86.9056137085e1746520996e+01
45	2009030320140426	800700	-1.827265	280.406688	-15.3375457764e7151275635e+0201
46	2009030320140426	900700	-1.827546	280.406	-28.0406346130e5247161865e+0201
47	2009121820140426	2100800	43-1.138265	75280.000688	-57.9425277710e2114089966e+01
48	2010032520140426	900800	-1.827546	280.688406	-51.4004959106e4157341003e+0102
49	2011012720140426	900	-1.827546	280.406	-52.3115798950e0927426147e+0102
50	2011122420160522	21002000	43-74.138051	75164.000160	-6.8307769775e6684082031e+01
51	2013071920160522	2100	-74.051	164.160	-65.1746520996e9349365234e+01
52	2014042620160929	7002100	-174.265051	280164.688160	56.7151275635e5295028687e+01
53	2014042620161128	7002100	-142.546857	28075.406375	-85.5247161865e2441085815e+01	20140426	800

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

265

Event	Date	Time	Latitude	Longitude	10m V
1	19790401	2100	-5.480	137.812	-9.6993362427e+01
2	19800330
280.688	7.2114089966e+01
20140426	800	-1.546	280.406	-1.4157341003e+02
20140426	900	-1.546827	280.406	-25.0927426147e0487777710e+0201
3	2016052219800831	20001900	-745.051199	164137.160531	-6.6684082031e5852249146e+01
4	2016052219800831	21002000	-745.051199	164137.160531	-5.9349365234e0360015869e+01
5	2016092919821024	2100	-74.051	164.160	65.5295028687e4236557007e+01
6	2016112819830930	21002000	42.857576	7584.375815	-5.2441085815e0510147095e+01

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

88643951416e68540237427e014313874625-81585525513e

Date	Time	Latitude	Longitude	10m V
7	19830930
19790401	2100	-542.480576	13784.812815	-96.6993362427e1684814453e+01
8	1984081119800330	9001800	-15.827480	280137.406812	-51.0487777710e3961134338e+0102
9	1980083119840811	1900	-5.199	137.531	-61.5852249146e2407348633e+0102
10	1980083119840811	2000	-5.199	137.531	-51.0360015869e3110269165e+0102
11	1982102419840811	2100	-74.051	164.160	5.4236557007e+01
19830930	2000	42.576	84.815	5.0510147095e+01
19830930	2100	42.576	84.815	6.1684814453e+01
199	137.531	1.2531871033e+02
12	19850812	1900	-5.199	137.531	6.5993698120e+01
13	19850812	2000	19840811	1800	-5.480	137.812	18.3961134338e7721923828e+0201
14	1984081119850812	19002100	-5.199480	137.531812	1.2407348633e1631915283e+02
15	1984081119851116	20002100	-5.199480	137.531812	1-8.3110269165e0120529175e+0201
16	1984081119860724	2100900	-574.199051	137164.531160	1.2531871033e3616104126e+02
17	1985081219871016	19002100	-574.199051	137164.531160	6.5993698120e7936035156e+01
18	1985081219890420	2000	-5.480	137.812	8-5.7721923828e5810119629e+01
19	1985081219890420	2100	-5.480	137.812	-1.1631915283e2454008484e+02
20	1985111619890711	2100	-538.480361	13778.812398	-81.0120529175e4824528503e+0102
21	1986072419890912	900	-74.051	164.160	16.3616104126e+02
19871016	2100	-74.051	164.160	6.7936035156e+01
3201354980e+01
22	19901117	600	41.171	39.960	-7.1991546631e+01
23	19901117	700	41.171	39.600	-7.2909973145e+01
24	1991062019890420	2000	-5.480	137.812	-59.5810119629e5385955811e+01
25	1989042019910620	2100	-5.480761	137138.812094	-1.2454008484e6087461853e+02
26	19920415	800	20.094	84.375	5.1177642822e+01
27	1992110819890711	2100	38-5.361199	78137.398531	1-5.4824528503e9594894409e+0201
28	1989091219921113	9001800	-745.051480	164137.160812	6-7.3201354980e4539321899e+01
29	1992111319901117	6001900	41-5.171761	39137.960812	-71.1991546631e4339295959e+0102
30	1990111719921113	7002000	41-5.171480	39137.600531	-71.2909973145e5561082458e+0102
31	1991062019921113	20002100	-5.480	137.812531	9-1.5385955811e7285772705e+0102
32	1991062019921123	2100	-543.761138	13874.094625	1-7.6087461853e4817504883e+0201
33	1992041519930705	8002000	2038.094361	8478.375398	51.1177642822e7013420105e+0102
34	1992110819930705	2100	-538.199361	13778.531398	-56.9594894409e0669006348e+01
35	1992111319930815	18002000	-531.480335	13772.812000	-71.4539321899e2063990784e+0102
36	1992111319950127	19002100	-540.761890	13739.812600	-19.4339295959e3620895386e+0201
37	1992111319960710	2000	-5.480	137.531812	7.3640014648e+01
38	19960710	-1.5561082458e+02	19921113	2100	-5.480	137.531812	-1.7285772705e1385275269e+02
39	1992112319970422	2100	4340.138890	7439.625240	-71.4817504883e3644331360e+0102
40	1993070519970617	20001700	3839.361766	7889.398297	-1.7013420105e0041018677e+02
41	1993070519970626	21001900	38-5.361480	78137.398812	65.0669006348e7410095215e+01
42	1993081519970626	2000	31-5.335480	72137.000812	-1.2063990784e2612721252e+02
43	1995012719970626	2100	40-5.890480	39137.600812	-98.3620895386e5113784790e+01
44	1996071019970817	2000	-5.480	137.812	75.3640014648e6425781250e+01
45	1996071019970817	2100	-5.480	137.812	1.1385275269e4044223022e+02
46	1997042219970923	21001900	40-74.890051	39164.240160	-15.3644331360e1563308716e+0201
47	1997061720010127	1700600	3941.766171	8939.297960	-1.0041018677e2166479492e+02
48	1997062620010127	1900700	-541.480171	13739.812960	58.7410095215e3281478882e+01
49	1997062620020602	20002100	-538.480923	13783.812320	1-6.2612721252e7981185913e+0201
50	1997062620030516	2100	-5.480	137.812	86.5113784790e4198028564e+01
51	1997081720030704	2000	-540.480328	13784.812240	5.6425781250e8809799194e+01
52	20040711	199708171800	2100	40.328	87-5.480	137.812	1.4044223022e+02		1.6328262329e+02
53	20040711	1900	40.328	87.480	7.7149871826e+01
54	20040803	2100	-5.199	137.531	19970923	1900	-74.051	164.160	-5.1563308716e1051910400e+01
55	2001012720040830	6002000	41-5.171199	39137.960531	1-7.2166479492e2028549194e+0201
56	2001012720040830	7002100	41-5.171199	39137.960250	8-1.3281478882e5628892517e+0102
57	2002060220040912	21002000	3819.923532	83277.320031	-65.7981185913e3294830322e+01
58	2003051620050805	21002000	-5.480	137.812	6-9.4198028564e3390945435e+01
59	2003070420050805	20002100	40-5.328480	84137.240812	5-9.8809799194e8295639038e+01
60	2004071120051208	1800800	40.328890	8739.480960	16.6328262329e6637542725e+0201
61	2004071120060304	1900900	40-1.328546	87280.480406	-7.7149871826e0116149902e+01
62	2004080320060612	21001900	-5.199480	137.531812	-56.1051910400e8560852051e+01
63	2004083020060612	2000	-5.199480	137.531812	-71.2028549194e0062788391e+0102
64	2004083020060612	2100	-5.199480	137.250812	-1.5628892517e1736833191e+02
65	2004091220061210	2000700	1941.532171	27739.031600	-5.3294830322e8087677002e+01
2005080566	2000	-5.480	137.812	-9.3390945435e+01
20050805	2100	-5.480	137.812	-9.8295639038e+01
20061210	800	41.171	39.600	5.1876373291e+01
67	20061219	700	41.171	20051208	800	40.890	39.960	6.6637542725e5212203979e+01
2006030468	900	-1.546	280.406	-7.0116149902e+01
20060612	1900	-5.480	137.812	6.8560852051e+01
20060612	2000	-5.480	137.812	1.0062788391e+02
20060612	2100	-5.480	137.812	1.1736833191e+02
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	20061210	700	41.171	39.600960	58.8087677002e6426681519e+01
72	2006121020090303	800900	41-1.171827	39280.600406	5-6.1876373291e8449584961e+01
73	2006121920091218	7002000	4143.171138	3974.960625	-6.5212203979e3902404785e+01
74	2006121920091218	8002100	4143.171138	3974.600625	5-1.0869308472e5077589417e+0102
75	2007122720100110	6002100	4140.171890	39.600960	7-5.9303802490e4371688843e+01
76	2007122720111207	7002100	41.171	39.960	1-5.0291072083e2954406738e+0201
77	2007122720111224	8002000	4143.171138	3974.960625	-8.6426681519e1969665527e+01
78	2009030320111224	9002100	-143.827138	28074.406625	-61.8449584961e0727139282e+0102
79	2009121820120629	2000	43-5.138480	74137.625812	-6.3902404785e8156173706e+01
80	2009121820120629	2100	43-5.138480	74137.625812	-15.5077589417e3109390259e+0201
81	2010011020130727	21001900	4038.890080	3978.960333	-56.4371688843e0674041748e+01
82	2011120720131224	2100600	41.171	39.960	-56.2954406738e8190124512e+01
83	2011122420131224	2000700	4341.138171	7439.625600	-86.1969665527e7012496948e+01
84	2011122420131224	2100800	4341.138171	7439.625600	-15.0727139282e1414718628e+0201
85	2012062920140426	2000700	-51.480265	137280.812406	65.8156173706e4881195068e+01
86	2012062920140426	2100700	-52.480108	137280.812688	-5.3109390259e8466461182e+01
87	2013072720140426	1900800	38-1.080546	78280.333688	6-8.0674041748e5272201538e+01
88	2013122420140426	600900	41-1.171546	39280.960688	6-1.8190124512e0531086731e+0102
89	2013122420150912	7001900	41-5.171199	39137.600531	6.7012496948e4281372070e+01
90	2016051620131224	8001900	41-5.171480	39137.600812	51.1414718628e1651092529e+0102
91	2014042620160516	7002000	-15.265480	280137.406531	51.4881195068e5173913574e+0102
92	2014042620160516	7002100	-25.108480	280137.688812	-57.8466461182e3943984985e+01
93	2014042620160531	8002000	-15.546480	280137.688812	-8.5272201538e6714050293e+01
94	2014042620160531	9002100	-15.546480	280137.688812	-18.0531086731e5311660767e+0201
95	2015091220160825	1900	-5.199480	137.531812	68.4281372070e8643951416e+01
96	2016051620160825	19002000	-5.480199	137.812531	16.1651092529e8540237427e+0201
97	2016051620161128	2000	-543.480138	13774.531625	1-8.5173913574e1585525513e+0201
98	2016051620161128	2100	-543.480138	13774.812625	7-1.3943984985e6854412842e+0102
99	2016053120171011	20002100	-5.480	137.812	81.6714050293e1839462280e+0102
100	2016053120180914	2100	-5.480	137.812	85.5311660767e5520050049e+01
101	2019111620160825	19001800	-5.480	137.812	7.	6125183105e+01
102	2016082520191116	20001900	-5.199	137.531	1.	4759844971e+	02
103	2016112820191116	2000	-5.	199	137.	531	7.	8542388916e+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

...

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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