New Threat: Global Stilling!

[Matt Rogers]

Winds over the past 30 years have been fading over the continents.

This will work against wind farm efforts:

http://www.ecmwf.int...s/1287402431772

Since it is a 30-year analysis, it could simply be connected to the big kahuna PDO cycle and maybe we'll start an upswing soon.

[Vandy]

I can't read anything more than the abstract at the moment, but if they are just looking at surface winds, then it's hard to say whether or not this would have any impact on wind energy.

[Saggy]

decrease in surface wind speed can be largely explained by an increase in vegetation

That is a surprising statement to me. If anything I would think we would have less vegetation now. Is it even possible for vegetation to have that much influence on surface wind?

[Matt Rogers]

That is a surprising statement to me. If anything I would think we would have less vegetation now. Is it even possible for vegetation to have that much influence on surface wind?

Hmm, interesting point. Plants do love CO2.

[seabreezelou]

Coming from the perspective of a meteorologist in the wind energy development sector, this is a topic that has been talked about quite a bit lately. Since I can only see the abstract, hard to say too much about the research. I know there are serious issues with the NARR / NCEP Reanalysis when it comes to wind.

Regarding vegetation, yes it can have a substantial impact on near-surface wind speeds. The increase in the roughness layer can disrupt the free stream wind quite a bit. Heck, wind farms do a great job of disrupting the wind speeds downwind. This would only be the case for tree growth, ground level vegetation would have a minimal impact on wind speed. Still one would need to look at how development around the stations have impacted wind speed. Sensors have changed over the past few decades. And yes, a 30-yr time period is just long enough for one cycle of the PDO. It will be very telling if wind speeds pick up since the shift in the PDO phase.

[BethesdaWX]

I do know most areas around Here, since 1900, have really wooded up. The areas that were once cut down to build have almost completely filled back in around the houses. I assume this is the case for most areas.

Definitely less old growth trees (250yrs+) since it takes time, probably thats whats sparking the outrage that all the Biggest, oldest trees being cut.........new light hitting the ground = new growth of many trees, in time, growing to what we see now.

[Saggy]

I do know most areas around Here, since 1900, have really wooded up. The areas that were once cut down to build have almost completely filled back in around the houses. I assume this is the case for most areas.

Definitely less old growth trees (250yrs+) since it takes time, probably thats whats sparking the outrage that all the Biggest, oldest trees being cut.........new light hitting the ground = new growth of many trees, in time, growing to what we see now.

Now that you mention it. I drove through the area I grew up a little while back..and even though there are more houses..there are more trees too. And the trees that were there when I was a kid are now HUGE! Many of the places that used to be farms are now wooded. I guess my first thought was more urban sprawl/population = less vegetation.. maybe that thinking is flawed..

I'm still not so sure about an increase in vegetation being responsible for a wind decrease on a large scale though.

[Saggy]

Coming from the perspective of a meteorologist in the wind energy development sector, this is a topic that has been talked about quite a bit lately. Since I can only see the abstract, hard to say too much about the research. I know there are serious issues with the NARR / NCEP Reanalysis when it comes to wind.

Regarding vegetation, yes it can have a substantial impact on near-surface wind speeds. The increase in the roughness layer can disrupt the free stream wind quite a bit. Heck, wind farms do a great job of disrupting the wind speeds downwind. This would only be the case for tree growth, ground level vegetation would have a minimal impact on wind speed. Still one would need to look at how development around the stations have impacted wind speed. Sensors have changed over the past few decades. And yes, a 30-yr time period is just long enough for one cycle of the PDO. It will be very telling if wind speeds pick up since the shift in the PDO phase.

over most land surfaces of the Northern hemisphere mid latitudes, winds have decreased

Not sure why I find this topic so interesting.. and I'm not nearly knowledgeable enough to answer my own questions.. does a PDO phase change mean a bigger temperature gradient between the mid and higher latitudes?

[kylemacr]

Not sure why I find this topic so interesting.. and I'm not nearly knowledgeable enough to answer my own questions.. does a PDO phase change mean a bigger temperature gradient between the mid and higher latitudes?

The positive phase of the PDO refers to anomalously cold waters in North Central/West Pacific and anomalously cold waters in equatorial Pacific (think ENSO pattern). You can see a good picture here: http://jisao.washington.edu/pdo/.

In a broad sense, mid-latitude associations with PDO are similar to those of ENSO, but on longer timescales with less amplitude. Tropical subsidence (high pressure) west of the dateline is common for the positive phase.

To answer your question, the sea surface temperature gradient will be enhanced during a positive PDO, seeing as the northern areas get colder and the warmer areas get warmer. This will enhance the north/south temperature gradient throughout much of the northern hemisphere.

In a nutshell, PDO is a lower frequency version of ENSO, which has led some to believe that they may not be distinct modes of variability after all.

[HM]

The positive phase of the PDO refers to anomalously cold waters in North Central/West Pacific and anomalously cold waters in equatorial Pacific (think ENSO pattern). You can see a good picture here: http://jisao.washington.edu/pdo/.

In a broad sense, mid-latitude associations with PDO are similar to those of ENSO, but on longer timescales with less amplitude. Tropical subsidence (high pressure) west of the dateline is common for the positive phase.

To answer your question, the sea surface temperature gradient will be enhanced during a positive PDO, seeing as the northern areas get colder and the warmer areas get warmer. This will enhance the north/south temperature gradient throughout much of the northern hemisphere.

In a nutshell, PDO is a lower frequency version of ENSO, which has led some to believe that they may not be distinct modes of variability after all.

The +PDO phase has a tendency to support a greater frequency of El Niño events not La Niña events. Therefore, the temp gradient can be reversed with warm anomalies across the northern CONUS and cool anomalies in the south. But just like any broad-brushed connection, there are examples for both sides. I would argue that a -PDO can increase the temp gradient by cooling the NW states and warming the SE states. Couple that with La Niña which should only enhance the pattern further, and you should get some wind.

Perhaps you got them confused?

[kylemacr]

Yikes, I thought one thing but wrote the opposite! While we're at it, here's a nice site comparing PDO and ENSO: http://cses.washington.edu/cig/pnwc/compensopdo.shtml