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Weather is king in the sense that it is what impacts us every day and
adds up over time into climate. Our weather in Virginia depends a lot
on storms cooked up in the Pacific and the 500 MB flow across the
country. If it is E/W (zonal), then we will see less extreme weather
in general. More N/S (blocked) can give more extremes of warm and
cold and more storminess (again in general). The nature of the flow
(zonal or blocking) is determined by broader scale weather patterns as
measured by indexes like North Atlantic Oscillation (NAO) and the
Artic Oscillation (AO) and others but those two are the most relevant
for us. As can be seen both in the forecasts below and the in running
means in the "Climate" section, NAO and AO can change on a weekly or
monthly basis but also exhibit long term patterns that can last for a
decade. The storms in the pacific that are so important to our weather depend on broader forms of weather such as El Nino Southern Oscillation (ENSO). The ENSO index shown below is multivariate which is a measurement of ENSO effects beyond the sea surface temperature in a particular area of the Pacific ocean. Generally a positive ENSO index (red) is going to give us juicier storms in the southern jet stream, usually in winter and often as rain. Negative ENSO has northern jet stream systems that will often go north and west leaving us drier. A lot depends on AO and NAO (which again are only indexes of weather effects, not causes of weather). |
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The 500 MB foreast plots are shown below. These come from weather models.
Below are the AO and NAO forecasts which also use weather models.
Below is the ENSO forecast (SST only, it is harder to predict the
multivariate effects). That is the closest thing on this page to a
climate model output although the model uses initial conditions from
current weather and ocean measurements and has finer granularity.
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Years of weather get averaged into climate. That means that the
vagaries of weather are added up and become climate. As a chaotic
process, the ripples and vortexes in the jet streams shown at 500MB
above and many other fluctuations will tend to average out over time.
The broader area indexes like NAO, AO, ENSO shown below are simply the
measurements of certain types of weather shown over many years. They
exhibit cycles of behavior over decades that are indications of longer
cycles. For example, through much of the 1990's the AO index had
been relatively high except for a distinct dip after the eruption of
Pinatubo.
The AO and NAO above are atmospheric indexes reflecting the nature of
the ripples in the jet stream. A higher NAO (in red below) means a
more zonal, less blocking pattern for us whih means systems will keep
moving be they warm, cold, high pressure or low. Negative NAO (in
blue below) means that the atmosphere is blocked which can mean
moreeast coast storms under some conditions, arctic outbreaks in
winter and other effects.
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| There were climate science papers written in the late 90's that that claimed that this increase in the AO index was caused by AGW as predicted by models. Since that time, AO has fluctuated and is currently quite negative. That negativity has now been blamed on lack of Arctic sea ice (admittedly a speculative theory). If that is true, why didn't the models predict it back in the 1990's? | |
| During the early 2000's there were a flurry of papers with the idea that global warming was accelerating, mistaking the natural temperature rise from the strong 1998 El Nino for man made warming. Some papers also speculated that El Ninos would increase in prevelance and severity. That has not happened. ENSO has reverted to a more balanced mode and global warming has decelerated. |
