Page History

Page info

infoType	Modified date
prefix	Last modified on
type	Flat

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, for January 1979 to December 2019, 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	-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
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
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	78.0804840088e0320663452e+01
24	1989091219930705	8002100	-7438.051361	16478.160398	-85.3815658569e9963912964e+01
25	1994091419890912	9002100	-74.051	164.160	-17.6730293274e9331817627e+0201
26	1990040219970607	700	-74.051	164.160	5.8469223022e8002792358e+01
27	1993062419970607	600800	-74.051	164.160	61.0172592163e0099096680e+0102
28	1993062419970923	7001900	-74.051	164.160	1.0357415771e3710269165e+02
29	1993062420010423	8002100	-74.051	164.160	7-8.8659744263e0685379028e+01
30	1993062420040327	900800	-74.051	164.160	5-6.5145812988e4567825317e+01
31	1993070520050314	2000800	38-1.080827	78280.333406	8-6.0320663452e1867416382e+01
32	1993070520050314	2100900	38-1.361827	78280.398406	5-9.9963912964e2169509888e+01
33	1994091420060304	2100900	-741.051827	164280.160125	-76.9331817627e3722732544e+01
34	1997060720060328	700800	-741.051827	164280.160406	-5.8002792358e7734420776e+01
35	1997060720060328	800900	-741.051827	164280.160406	-1.0099096680e1018218994e+02
36	1997092320070331	19002100	-74.051	164.160	18.3710269165e7419113159e+0201
37	2001042320090303	2100700	-741.051827	164280.160406	-8.0685379028e9056137085e+01
38	2004032720090303	800	-741.051827	164280.160406	-61.4567825317e3375457764e+0102
39	2005031420090303	800900	-1.827	280.406	-62.1867416382e0406346130e+0102
40	2005031420091218	9002100	-143.827138	28075.406000	-95.2169509888e9425277710e+01
41	2010032520060304	900	-1.827	280.125688	-65.3722732544e4004959106e+01
42	2006032820110127	800900	-1.827	280.406	-5.7734420776e3115798950e+01
43	2006032820111224	9002100	-143.827138	28075.406000	-16.1018218994e8307769775e+0201
44	2007033120130719	2100	-74.051	164.160	8.7419113159e+01		164.160	-6.1746520996e+01
45	20140426	700	-1.265	280.688	5.7151275635e+01
46	2014042620090303	700	-1.827546	280.406	-8.9056137085e5247161865e+01
47	2014042620090303	800	-1.827265	280.406688	-17.3375457764e2114089966e+0201
48	2009030320140426	900800	-1.827546	280.406	-21.0406346130e4157341003e+02
20091218	2100	43.138	75.000	-5.9425277710e+01
49	2014042620100325	900	-1.827546	280.688406	-52.4004959106e0927426147e+0102
50	2011012720160522	9002000	-174.827051	280164.406160	-56.3115798950e6684082031e+01
51	2011122420160522	2100	43-74.138051	75164.000160	-65.8307769775e9349365234e+01
52	2016092920130719	2100	-74.051	164.160	-6.1746520996e5295028687e+01
53	2014042620161128	7002100	-142.265857	28075.688375	-5.7151275635e2441085815e+01	20140426	700

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	19800330
280.406	-8.5247161865e+01
20140426	800	-1.265	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	1982102420160929	2100	-74.051	164.160	6.5295028687e+01	20161128	2100	42.857	75.375	-5.2441085815e4236557007e+01

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

4313874625-81585525513e4808121839462280e48081255520050049e

Date	Time	Latitude	Longitude	10m V
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
19790401	2100	-5.480	137.812	-9.6993362427e+01
19800330	900	-1.827	280.406	-5.0487777710e+01
19800831	1900	-5.199	137.531	-6.5852249146e+01
19800831	2000	-5.199	137.531	-51.0360015869e2407348633e+0102
10	1982102419840811	21002000	-745.051199	164137.160531	51.4236557007e3110269165e+0102
11	1983093019840811	20002100	42-5.576199	84137.815531	51.0510147095e2531871033e+0102
12	1983093019850812	21001900	42-5.576199	84137.815531	6.1684814453e5993698120e+01
13	1984081119850812	18002000	-5.480	137.812	18.3961134338e7721923828e+0201
14	1984081119850812	19002100	-5.199480	137.531812	1.2407348633e1631915283e+02
15	1985111619840811	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	38.361	78.398	1.4824528503e+02
21	19890912	900	-574.480051	137164.812160	-86.0120529175e3201354980e+01
22	1990111719860724	900600	-7441.051171	16439.160960	1-7.3616104126e1991546631e+0201
23	1987101619901117	2100700	-7441.051171	16439.160600	6-7.7936035156e2909973145e+01
24	1989042019910620	2000	-5.480	137.812	-59.5810119629e5385955811e+01
25	1989042019910620	2100	-5.480761	137138.812094	-1.2454008484e6087461853e+02
26	1989071119920415	2100800	3820.361094	7884.398375	15.4824528503e1177642822e+0201
27	1989091219921108	9002100	-745.051199	164137.160531	6-5.3201354980e9594894409e+01
28	1990111719921113	6001800	41-5.171480	39137.960812	-7.1991546631e4539321899e+01
29	1990111719921113	7001900	41-5.171761	39137.600812	-71.2909973145e4339295959e+0102
30	1991062019921113	2000	-5.480	137.812531	9-1.5385955811e5561082458e+0102
31	1991062019921113	2100	-5.761480	138137.094531	-1.6087461853e7285772705e+02
19920415	800	20.094	84.375	5.1177642822e+01
19921108	2100	-5.199	137.531	-5.9594894409e+01
19921113	1800	-5.480	137.812	-7.4539321899e+01
19921113	1900	-5.761	137.812	-1.4339295959e+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	1996071019921113	2000	-5.480	137.531812	-17.5561082458e3640014648e+0201
38	1992111319960710	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	1997062619930815	2000	31-5.335480	72137.000812	-1.2063990784e2612721252e+02
19950127	2100	40.890	39.600	-9.3620895386e+01
43	19970626	2100	19960710	2000	-5.480	137.812	78.3640014648e5113784790e+01
44	1996071019970817	21002000	-5.480	137.812	15.1385275269e6425781250e+0201
45	1997042219970817	2100	40-5.890480	39137.240812	-1.3644331360e4044223022e+02
19970617	1700	39.766	89.297	-1.0041018677e+02
46	19970923	19970626	1900	-574.480051	137164.812160	-5.7410095215e1563308716e+01
47	1997062620010127	2000600	-541.480171	13739.812960	1.2612721252e2166479492e+02
48	2001012719970626	2100700	-541.480171	13739.812960	8.5113784790e3281478882e+01
49	1997081720020602	20002100	-538.480923	13783.812320	5-6.6425781250e7981185913e+01
50	1997081720030516	2100	-5.480	137.812	16.4044223022e4198028564e+0201
51	1997092320030704	19002000	-7440.051328	16484.160240	-5.1563308716e8809799194e+01
52	2001012720040711	6001800	4140.171328	3987.960480	1.2166479492e+02
20010127	700	41.171	39.960	8.3281478882e+01
20020602	2100	38.923	83.320	-6.7981185913e+01
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	2004083020030516	2100	-5.480199	137.812250	6-1.4198028564e5628892517e+0102
57	2003070420040912	2000	4019.328532	84277.240031	-5.8809799194e3294830322e+01
58	2004071120050805	18002000	40-5.32848087	137.480812	1-9.6328262329e3390945435e+0201
59	2004071120050805	19002100	40-5.32848087	137.480812	7-9.7149871826e8295639038e+01
60	2004080320051208	2100800	-540.199890	13739.531960	-56.1051910400e6637542725e+01
61	2004083020060304	2000900	-51.199546	137280.531406	-7.2028549194e0116149902e+01
62	2004083020060612	21001900	-5.199480	137.250812	-16.5628892517e8560852051e+0201
20040912	2000	19.532	277.031	-5.3294830322e+01
63	2006061220050805	2000	-5.480	137.812	-91.3390945435e0062788391e+0102
64	2005080520060612	2100	-5.480	137.812	-91.8295639038e1736833191e+0102
65	2005120820061210	800700	4041.890171	39.960600	65.6637542725e8087677002e+01
2006030466	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
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	20061210	700	41.171	39.600	57.8087677002e9303802490e+01
70	2006121020071227	800700	41.171	39.600960	51.1876373291e0291072083e+0102
71	2006121920071227	700800	41.171	39.960	68.5212203979e6426681519e+01
72	2009030320061219	800900	41-1.171827	39280.600406	5-6.0869308472e8449584961e+01
73	2007122720091218	6002000	4143.171138	3974.600625	7-6.9303802490e3902404785e+01
74	2007122720091218	7002100	4143.171138	3974.960625	-1.0291072083e5077589417e+02
75	2007122720100110	8002100	4140.171890	39.960	8-5.6426681519e4371688843e+01
76	2009030320111207	9002100	-141.827171	28039.406960	-65.8449584961e2954406738e+01
77	2009121820111224	2000	43.138	74.625	-68.3902404785e1969665527e+01
78	2009121820111224	2100	43.138	74.625	-1.5077589417e0727139282e+02
79	2010011020120629	21002000	40-5.890480	39137.960812	-56.4371688843e8156173706e+01
80	2012062920111207	2100	41-5.171480	39137.960812	-5.2954406738e3109390259e+01
81	2011122420130727	20001900	4338.138080	7478.625333	-86.1969665527e0674041748e+0101
82	2011122420131224	2100600	4341.138171	7439.625960	-16.0727139282e8190124512e+0201
83	2012062920131224	2000700	-541.480171	13739.812600	6.8156173706e7012496948e+01
84	2012062920131224	2100800	-541.480171	13739.812600	5.3109390259e1414718628e+01
85	2014042620130727	1900700	38-1.080265	78280.333406	65.0674041748e4881195068e+01
86	2013122420140426	600700	41-2.171108	39280.960688	6-5.8190124512e8466461182e+01
87	2013122420140426	700800	41-1.171546	39280.600688	6-8.7012496948e5272201538e+01
88	2013122420140426	800900	41-1.171546	39280.600688	5-1.1414718628e0531086731e+0102
89	2014042620150912	7001900	-15.265199	280137.406531	56.4881195068e4281372070e+01
90	2014042620160516	7001900	-25.108480	280137.688812	-51.8466461182e1651092529e+0102
91	2014042620160516	8002000	-15.546480	280137.688531	-81.5272201538e5173913574e+0102
92	2014042620160516	9002100	-15.546480	280137.688812	-17.0531086731e3943984985e+0201
93	2015091220160531	19002000	-5.199480	137.531812	68.4281372070e6714050293e+01
94	2016051620160531	19002100	-5.480	137.812	18.1651092529e5311660767e+0201
95	2016051620160825	20001900	-5.480	137.531812	18.5173913574e8643951416e+0201
96	2016051620160825	21002000	-5.480199	137.812531	76.3943984985e8540237427e+01
97	2016053120161128	2000	-543.480138	13774.812625	-8.6714050293e1585525513e+01
98	2016053120161128	2100	-543.480138	13774.812625	8-1.5311660767e6854412842e+0102
99	2016082520171011	19002100	-5.480	137.812	81.8643951416e1839462280e+0102
100	2016082520180914	20002100	-5.199480	137.531812	65.8540237427e5520050049e+01
101	2016112820191116	20001800	-5.	480	137.	812	7.	6125183105e+01
20161128	2100	43.138	74.625	-1.6854412842e+02
102	20191116	1900	20171011	2100	-5.	199	137.	531	1.	4759844971e+02
103	2018091420191116	21002000	-5.	199	137.	531	7.	8542388916e+01
20191116	1800	-5.480	137.812	7.6125183105e+01
20191116	1900	-5.199	137.531	1.4759844971e+02
20191116	2000	-5.199	137.531	7.8542388916e+01

...

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.}

Space shortcuts

Page tree

Versions Compared

Old Version 18

New Version Current

Key

Related articles