[LINK] Depiction of wind at various altitudes, other weather pages

Thu Dec 19 14:32:19 AEDT 2013

The newer computer output pages are better than the old synoptic chart
because you can predicted changes in a 3 hourly basis or the next 3 days
and 6 hours for a week.  Remember to take less notice of small scale
features as the prediction goes out.  The big highs move fairly
predictably; small and transient lows will be swamped by inaccuracies in
the model initial data further out.  These charts can be animated.  They
don't show fronts - you have to gauge them yourself
.
eg
Australia
http://www.bom.gov.au/australia/charts/viewer/index.shtml?domain=combinedA&type=mslp-precip
SE aust:
http://www.bom.gov.au/australia/charts/viewer/index.shtml?type=mslp-precip&tz=AEDT&area=Vic&model=A

You can also look at the 500mb predictions to see where things are going.
As a verrrrrry loose approximation you might say the surface systems are
"blown along" by the 500mb  winds.

http://www.bom.gov.au/australia/charts/viewer/index.shtml?type=pressureHgt&level=500hPa&tz=AEDT&area=Au&model=R&chartSubmit=Refresh+View

Also worth a look is the new MetEye product, lots of weather data with 3
hour predictions for a few days.
http://www.bom.gov.au/australia/meteye/

The Zehr-enhanced satellite loop show where the action is by highlighting
cold clouds.  These are clouds that extend vertically up into the cold
parts of the atmosphere, thus producing rain and storms.
http://www.bom.gov.au/australia/satellite/?tz=AEST&unit=p23&domain=1&view=33&satSubmit=Refresh+View

Hadley cells:
The cells are kind of theoretical concepts.  Air can't travel in straight
lines on the earth because the earth is rotating.  In the ground frame of
reference, air gets pushed sideways so tends to move around in circles and
wavy shapes.  The result is that the theoretical cells break up into the
messy migrating and interacting patterns we actually see on weather maps.
The net effect averaged over time is air moving in Hadley patterns but at
any time you have a bunch of stuff going in any direction.

Jetstreams
It's hard to get an intuitive picture of what is going on here.  I've
tried. We just don't think in three dimensional rotating fluids!  One thing
to notice is that the asymmetries of the horizontal circulation patterns
will result in net north-south momentum transfers.  This obviously will
result somehow in a balancing mechanism that balances this the momentum
flow; this is the jet stream.  However, this is probably an unsatisfying
explanation.  It the end, the fluid flow equations make the jet streams.
As far as I've seen there's no good simple intuitive explanation.  There
are nice pictures on jet streams circling the earth in waxy bands but, like
the Hadley cells, these are idealisations: actual jet streams appear and
disappear just like other meteorological features.

- Jim

On 19 December 2013 12:42, Robin Whittle <rw at firstpr.com.au> wrote:

> Here is a new addition to my collection of weather URLs:
>
>   http://earth.nullschool.net/
>
> I read about it at http://www.universetoday.com.  It is a
> javascript-driven, apparently very fluid, display of wind direction
> anywhere on Earth, with data updated from various models every 3 hours.
>  There is also the ability to look back in time and to look forwards by
> up to 24 hours.
>
> The "earth" thingo at the bottom opens up a menu from which various
> settings can be selected, with the "about" link providing an
> explanation.  Settings can be stored in a URL:
>
>
>
> http://earth.nullschool.net/#current/wind/isobaric/1000hPa/orthographic=-225.44,-36.35,416
>
> It is evident that the jetstream at about 10km (250hPa) is very
> different from winds at the surface.  I don't understand how the
> jetstream makes sense in terms of what I understand about Hadley cells:
>
>   https://en.wikipedia.org/wiki/Hadley_cell
>
> On a day like today in Melbourne, at the western edge of a high pressure
> system, I understand a significant amount of the heat we feel (predicted
> maximum 40C) is due to hotter than normal, very dry, air piling up in
> the troposphere after being transported there from the tropics.  This is
> in addition to air arriving from the inland north.  This somehow
> displaces air on the ground with dryer, hotter, air.  If that's the
> case, I am not sure how it works with the jetstream winds doing
> something apparently unrelated (to my eyes) with the anticlockwise winds
> at ground level which result from the high pressure system.
>
> My other weather links are:
>
>   http://www.bom.gov.au/australia/charts/synoptic_bw.shtml
>   http://www.bom.gov.au/vic/forecasts/melbourne.shtml
>   http://www.bom.gov.au/vic/observations/melbourne.shtml
>
>
> http://www.bom.gov.au/products/IDR023.loop.shtml?looping=1&reloaded=0&topography=true&locations=true&range=true#skip
>   http://www.bom.gov.au/australia/satellite/
>
> http://www.bom.gov.au/jsp/watl/weather/obs.jsp?graph=all_obs&station=86068
>
> The last one is for the nearby Viewbank weather station.  This shows the
> last few days of temperature and other measurements, including the dew
> point.  The dew point is a measure of the moisture content of the air.
> When this drops suddenly, as it did a few hours ago, I understand (from
> an explanation by a meteorologist) this is the dry Hadley cycle air
> descending to ground level and somehow (I have no idea how) displacing
> the more moist air which was previously at ground level.
>
> A final link, which is only for the Melbourne area is:
>
>   http://www.baywx.com.au/melbtemp.html
>
> This page, one of several, shows the predicted minimum and maximum
> temperatures with the observations filled in as the day progresses.
> There's an archive of the graphs, which enabled me to generate
> temperature graphs of the heatwave associated with the 2009 bushfires:
>
>   https://en.wikipedia.org/wiki/Black_Saturday_bushfires
>
>   https://commons.wikimedia.org/wiki/File:Melbourne-temp-2009-02-10.png
>
>
> https://commons.wikimedia.org/wiki/File:Melbourne-temp-2009-02-10-compact.png
>
>
> I understand those dramatic peaks in temperature are driven largely by
> Hadley cells.
>
>  - Robin
>
>
>
>
>
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