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Questions about Expedition features » Historical Grib data » 12/27/2019 3:03 pm

kasszest
Replies: 11

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Nick wrote:

You can also ask for Grib options to be added. At present, Exp supports lat-lon (equirectangular & thinned), Lambert, Polar Stereographic, Gaussian and the fields you see in the settings interface.

Acceptable fields and levels are contained in internal look-up tables. Some of these are allocated priorities. For example, Exp can use surface winds as 10m winds for routing as some services mis-code them that way. 

At the moment I'm most interested in exploring the usefulness (or not) of the Benjamin-Feir Index field to race routing. This field is produced as part of ECMWF's ocean wave model, and is apparently used by commercial ship routers to avoid conditions in which rogue waves are thought to be more likely.

I suppose for my investigations I could scale the BFI values (0 to 1) to look like significant wave heights (e.g. multiply by 10) and then use the avoid SWH > x option.

Thanks,
Kass

Questions about Expedition features » Historical Grib data » 12/27/2019 2:34 pm

kasszest
Replies: 11

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jweisbaum wrote:

Also, if you find this technique helpful, consider sharing your script on GitHub. That way everyone can benefit and we can build a database of scripts for sailors to convert reanalysis into a useful format for Expedition.

I will do!

Your weather tools Docker container looks extremely handy btw. I'll try it out tomorrow.

Questions about Expedition features » Historical Grib data » 12/27/2019 9:41 am

kasszest
Replies: 11

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Many thanks for that jweisbaum, I will try that. By 'message name' do you mean the Product Definition Section of the grib files? Any hints on where I can find a list of message names Expedition considers meaningful?

Thanks,
Kass

General Discussion » Reanalysis Grib » 12/12/2019 8:10 am

kasszest
Replies: 18

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There are some pretty clear instructions on getting started with the cdsapi here: https://cds.climate.copernicus.eu/api-how-to

You need to register for an api key (and put it in a configuration file that can be found by the module), install the cdsapi module, and then you can write scripts to download whatever you want. Below I've pasted in a script I wrote to download gribs for some post-race analysis on this year's Azores and Back Race (apologies, I'm not sure how to paste it in without the formatting getting mangled, but I'm sure you can sort that aspect out...there are also lots of example scripts on the Copernicus site). If you have any specific problems do ask and I'll help if I can.

--Kass

import cdsapi 
c = cdsapi.Client() 
c.retrieve(    'reanalysis-era5-single-levels',    {        'product_type':'reanalysis',        'variable':[            '10m_u_component_of_wind','10m_v_component_of_wind','mean_sea_level_pressure'        ],        'year': '2019',        'month':'06',        'day':[            '18','19','20',            '21','22','23',            '24','25','26',            '27','28','29',            '30','31'        ],        'area': [51, -26, 37, -4],        'time':[            '00:00','01:00','02:00',            '03:00','04:00','05:00',            '06:00','07:00','08:00',            '09:00','10:00','11:00',            '12:00','13:00','14:00',            '15:00','16:00','17:00',            '18:00','19:00','20:00',            '21:00','22:00','23:00'        ],        'format':'grib'    },    'azab_2_wind_pressure.grib')

Questions about Expedition features » Historical Grib data » 12/03/2019 7:13 am

kasszest
Replies: 11

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I am in the process of preparing for next year's OSTAR which will be starting 3 weeks earlier than previous editions, and so am running a lot of routings using reanalysis data. Getting 10m wind from ERA5 is no problem.

As the Gulf Stream is such a big factor I've also downloaded historical OSCAR ocean surface currents data, but it is in netcdf format, and doesn't appear to be the right kind of netcdf data for Expedition (or else I am doing something wrong). Does anyone have experience with using historical surface current data for routing? Is there a better source?

Thanks,
Kass

General Discussion » Reanalysis Grib » 12/03/2019 6:52 am

kasszest
Replies: 18

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from climate.copernicus.eu climate-reanalysis:
ERA5T
Preliminary data for ERA5 will be published daily, within seven days from real-time, and stored in a separate dataset (ERA5T). This service will be available later in 2019.

^^^ it's now 'later in 2019', and as promised preliminary data for the latest European Reanalysis is now available with only a 5 day lag (previously the wait was 3 months). Christmas has come early!

-Kass 

Questions about Expedition features » Holding wind constant to study tidal effects? » 7/28/2019 2:23 am

kasszest
Replies: 3

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In the August 2019 issue of Yachting World Libby Greenhalgh's Navigation Briefing column focuses on Fastnet preparation. In it she suggests getting a feel for the tidal gates by running a number of routings with the wind fixed to the course average strength and direction while varying the start times. Is there a simple way to do this in Expedition? Or is the solution to create an artificial grib file with spacial and temporal resolution so low that it covers the entire course for the length of the race?

TIA,
Kass

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