Getting ECMWF data

So, you've heard 'ECWMF is far better than  NCEP', and you want a piece of some ECMWF data action. Where do you get get it? How do you find it?.  Here's a list to help you (me) out.

There are multiple routes to ECMWF data heaven. The most flexible and powerful, but most complicated is MARS. To use MARS fully you need the client, a piece of open-source software covered by a GPL licences, but costs £100. It is used to communicate with the data servers at ECMWF, and can subset data on the server side to reduce the volume of data needed to be transferred.  Quicker way to MARS is via  Web MARS.

Some links on MARS
www.ecmwf.int/services/computing/training/material/mars.pdf
www.ecmwf.int/publications/manuals/mars/practice/
www.ecmwf.int/publications/manuals/mars/practice/
www.ecmwf.int/services/archive/

The other route is the ECMWF data server. This gives you straight access, no software needed, no (not many) questions asked. It is actually just a linux server sitting outside the ECMWF firewall running MARS, but only allowing access to the disk archive, and not the tape archive.

To grab a dataset requires a request. Some fields used in the request are:

class	ECMWF classification (od, rd, e4, …)
stream	originating forecasting system(oper, wave, enfo, seas, …)
expver	version of the experiment (01 operational, 11, aaaa)
domain	area covered by the data (Global, Mediterranean, …)
system	seasonal forecast operational system (1, 2, 3)
type	type of field (an, fc, …)
levtype	type of level (pl, ml, sfc, pt, pv)
levelist	levels for the specified levtype (off if levtype=sfc)
param	meteorological parameter (t, temperature, 130, 30.128)
number	ensemble member (1, 2, …)
channel	brightness temperature frequency band
diagnostic	iteration sensitivity forecast products
frequency	direction 2-d wave spectra products
product	section,
latitude	longitude
ocean products

An example of a MARS request is:


retrieve,
class = ei,
stream = oper,
expver = 1,
date = 20071201/to/20071231,
time = 00/06/12/18,
type = an,
levtype = sfc,
param = sd,
target = “era-int.200712.sd”


The request is used to build a MARS tree, which describes the data hierachy to work through.

Truncation is done before interpolation to save resources, and is done depending on the final grid specified. The mapping between the final grid and the resolution truncated to is:

Grid increment Truncation

2.5  ≤ Δ T63

1.5  ≤ Δ < 2.5 T106

0.6  ≤ Δ < 1.5 T213

0.4  ≤ Δ < 0.6 T319

0.3  ≤ Δ < 0.4 T511

0.15 ≤ Δ < 0.3 T799

0.09 ≤ Δ < 0.15 T1279

0.0   ≤ Δ < 0.09 T2047

To subset an area use the boundaries North/West/South/East.

Archived data is available to all registered users. Real-time data only to the big spenders!

Testing Google Earth gadget

OK, here is a test to display forecast data using the Google Earth Plugin.  I can't test it at work as I'm not allowed to install the plugin on my own computer!

WRF in Google Earth

Traditionally weather maps aimed to present an enormous array of data as a simple output: a sun, a sun behind a cloud, or some rain.  Or possibly a cloud getting blown along by a face.  That's great, as what most people want to know is: will it rain or not?

But this hides is the beauty and complexity behind the weather, we are immersed in a big mass of swirling fluid, rising, falling, heating, cooling.  Enormous amounts of energy are transported around the world, air masses collide, jet streams arc and split. In the midst of this, occasionally everything stills, and there is hardly a breeze.  It's one big never-ending dance, and it looks beautiful.

That's why I'm trying to put forecast data into Google Earth, because you get a real feel for the fact the UK's weather doesn't end at the edge of the map.

Using NCL and some code from rpavlick, this is my first attempt to put a forecast into Google Earth. At the moment it is just a picture, but hopefully I'll get a Google Earth gadget working soon.