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An Active North Atlantic

Posted by Michael Folmer on 02/05/2013
Posted in: RGB, Uncategorized. Tagged: , , , , . 1 Comment

The latter half of January featured a stormy North Atlantic with a number of cyclones that produced hurricane force winds. An animation of RGB air mass imagery (below) from January 18-26 shows the active pattern. The most impressive storm rapidly developed and the central pressure lowered to 930 mb approximately 1200 UTC January 26th, see surface map below. Considering the strength of the storm, the OPC 96-hour forecast was exceptionally accurate. The GFS and European models were forecasting winds greater than 80 knots (90 mph) and wave heights over 55 feet. The ASCAT passes largely missed the strongest winds (highest observed were 60 knots (70 mph), but there were reports of waves near the Portugal coast between 90 and 100 feet, nearshore! On the RGB Air Mass imagery animation, you can see the red and orange shaded colors drawn into the center of the cyclone. This area represents warm, dry stratospheric air associated with high potential vorticity near a jet streak. As this stratospheric air is drawn into the storm it can be transported downward to produce high winds at the surface.

Eight day SEVIRI (Meteosat-9) RGB Air Mass animation of the North Atlantic valid from 01/18/13 - 01/26/13.

Eight day SEVIRI (Meteosat-9) RGB Air Mass animation of the North Atlantic valid from 01/18/13 – 01/26/13. (Click to animate)

OPC surface verification vs. 96-hr forecast for the 01/26/13 North Atlantic bomb.

OPC surface verification vs. 96-hr forecast for the 01/26/13 North Atlantic bomb.

One interesting note is the storm’s impact on the North Atlantic Oscillation (NAO). The NAO is used to characterize winter temperature and precipitation patterns in the North Atlantic through height/pressure anomalies over Greenland and the central North Atlantic. The index combines parts of the East-Atlantic and West Atlantic patterns identified by Wallace and Gutzler (1981). A positive NAO is indicative of lower heights in the North Atlantic and higher heights in the Central North Atlantic. The top panel on the image below shows the Observed daily NAO indices for the past 120 days. Notice how the NAO index has trended positive since January 24th, and became more strongly positive with time. The intense cyclone reinforced the slightly positive NAO as the lower heights and colder temperatures infiltrated Greenland and the North Atlantic. So why do we care about an active North Atlantic and positive NAO? As the NAO trends toward the positive phase, it could mean above average temperatures for the Eastern US and Northern Europe. The CPC 6-10 day and 8-14 day temperature and precipitation outlooks both predict above average temperature and precipitation for the Eastern US, see http://www.cpc.ncep.noaa.gov/.

The GFS NAO observation and forecast valid on 02/01/13 courtesy of CPC.

The GFS NAO observation and forecast valid on 02/01/13.

A special thank you to Dr. Emily Berndt (post-doc at NASA SPoRT) for providing much of the material for this post and to the OPC Facebook team for the surface comparison image.

Thanks for reading!

Powerful West Pacific Storm

Posted by Michael Folmer on 01/17/2013
Posted in: AIRS, Uncategorized. Tagged: , , , , . Leave a comment

While the majority of us await some semblance of a winter in the U.S., one area that is not accustomed to seeing blizzard conditions (Tokyo, Japan) had a rather rude awakening! Tokyo endured wind gusts to hurricane force and ~3″ of snow (unusual by Tokyo standards) from 1/14/13-1/15/13. The storm underwent extreme rapid intensification with the central pressure dropping 49 mb in 24 hours! That equates to 2.55 bergerons (at 34.5N) in meteorology tech lingo, which may be a record for the North Pacific and is the definition of extreme deepening or bombogenesis!

1 hour MTSAT infrared imagery overlaid with 1 hour accumulated lightning via the Vaisala GLD-360 feed.

1 hour MTSAT infrared imagery overlaid with 1 hour accumulated lightning via the Vaisala GLD-360 feed. (click on image to animate)

I created an animation using the 1-hour MTSAT infrared imagery and 1-hour accumulated lightning provided by the Vaisala GLD-360 feed available at the Ocean Prediction Center (OPC) to emphasize the incredible deepening of the storm. There are indications that Tokyo may have seen some thundersnow as indicated by the cluster of lightning strikes near the area early in the animation. Note the sporadic nature of the lightning activity with a significant burst appearing in the eastern quadrant early on 1/15 as the storm entered the OPC high seas zone (blue outline).

ASCAT high resolution wind plot valid at 1248 UTC on 01/15/13.

ASCAT high resolution wind plot valid at 1248 UTC on 01/15/13.

The ASCAT (scatterometer) high resolution wind data above shows many wind barbs over 63 kts (73 mph) in the southwest and southeast quadrants of the storm between 09 UTC and 11 UTC on 01/15/13. Notice how the passes missed the core of the storm, which happen occasionally.

OSCAT high resolution wind plot valid at 1500 UTC on 01/15/13.

OSCAT high resolution wind plot valid at 1500 UTC on 01/15/13.

The OSCAT (scatterometer) high resolution passes are wider and this particular image shows the entire storm in one swath. There is a degradation in the wind quality, but there are many wind barbs greater than 47 knots (54 mph) and some of the white wind barbs suggest winds over hurricane force. The GFS indicated 85 knot (100 mph) winds and the ECMWF had 75 knot (85 mph) winds with max gusts to 107 knots or 122 mph! James Kells (OPC forecaster) mentioned in an email to me that he doesn’t ever recall seeing the ECMWF forecast anything over 65 knots. He was more impressed with the wave models having never seen anything forecasted above 50 feet. Seas were forecast by the ECMWF and GFS to exceed 60 feet although we will have to wait for a post-analysis on how well this verified.

MTSAT enhanced infrared with the OPC surface analysis overlaid valid at 06 UTC on 01/15/13.

MTSAT enhanced infrared with the OPC surface analysis overlaid valid at 06 UTC on 01/15/13.

The OPC surface analysis overlaid on the enhanced infrared image from MTSAT shows the storm at it’s maximum intensity with a surface pressure at 932 mb. From the standpoint of model forecasts, I had received emails from a few Hydrometeorological Prediction Center (HPC) and OPC forecasters about how the GFS and ECMWF were forecasting a very significant storm a few days out. The GFS forecasted a pressure of 936 mb and the ECMWF forecasted 938 mb, so the forecasts were incredibly good for this extreme event!

AIRS Total Column Ozone retrieval valid at 15 UTC on 01/15/13.

AIRS Total Column Ozone retrieval valid at 15 UTC on 01/15/13.

Now, the actual point of this post (I know, finally!) is to demonstrate the operational use of the AIRS Total Column Ozone retrieval product that is produced by NASA SPoRT. The image above shows the ozone retrieval around 15 UTC on 01/15/13 as the storm was continuing the occlusion process and subsequent slow weakening. Although the color bar on the left is incorrect, the red and pink colors suggest ozone readings that exceed 450 or even 500 Dobson units which indicates a highly anomalous stratospheric intrusion. There is no RGB Air Mass product for the Pacific other than what MODIS or VIIRS can provide, therefore the AIRS Total Ozone product can serve as a proxy for the red-coloring seen in the Air Mass imagery and could give forecasters an indication of the strength of a stratospheric intrusion and therefore how strong a storm may get.

Thanks for reading!

Massive Ocean Storm – 12/13/12

Posted by Michael Folmer on 12/19/2012
Posted in: AIRS, RGB, Uncategorized. Tagged: , , , . 1 Comment

Forecasters at the Atlantic High Seas desk at the Ocean Prediction Center (OPC) were challenged by a very large, strong storm that encompassed much of the North Atlantic. This storm was so large, if it was over the U.S., more than 2/3 of the U.S. would have been affected in some way. At maximum intensity, the storm deepened to 948 mb southeast of Greenland and had a very expansive area of storm force winds (greater than 50 knots or 60 mph) and wave heights greater than 35 ft over a large chunk of the North Atlantic!

A forecast concern that was raised during this event was whether the storm would produce hurricane-force conditions at any point. I talked with one of the forecasters (Hugh McRandall – OPC) and we tried to use the stratospheric intrusion as an indicator and I received some supporting AIRS Total Column Ozone Retrievals from Brad Zavodsky (NASA SPoRT) to dissect the system. Note that the red-coloring in the RGB Air Mass image correlates to stratospheric drying between the 500 mb and 300 mb levels and should be associated with increased ozone levels.

SEVIRI RGB Air Mass image valid at 04z on 12/12/12.

SEVIRI RGB Air Mass image valid at 04z on 12/12/12.

AIRS Total Column Ozone Retrievals valid at 04z on 12/12/12.

AIRS Total Column Ozone Retrievals valid at 04z on 12/12/12.

The two images above show the initial stratospheric intrusion that was associated with a shearing complex upper-level low pressure system. The yellow outline highlights the strongest signal in the RGB Air Mass image with significant drying noted near the shearing potential vorticity (PV) anomalies. This matches up well with the AIRS Total Column Ozone Retrievals in the second image where ozone levels exceed 350-400 Dobson units (this is fairly significant in terms of ozone concentration and indicates the presence of stratospheric air).

SEVIRI RGB Air Mass image valid at 15z on 12/12/12.

SEVIRI RGB Air Mass image valid at 15z on 12/12/12.

AIRS Total Column Ozone Retrievals valid at 15z on 12/12/12.

AIRS Total Column Ozone Retrievals valid at 15z on 12/12/12.

Eleven hours later, the initial PV anomalies and associated stratospheric drying have been sheared and distorted by a stronger impulse moving in from the west near the Canadian maritimes. In the RGB Air Mass image above, there appears to be significant stratospheric drying with the new impulse and evidence that the tropopause fold occurred west of New Foundland. In the AIRS image below this, notice how seemingly low the ozone concentrations are compared to the previous images. There is a thin ribbon of 300+ Dobson units, but the majority of the red-coloring is associated with ozone concentrations between 250-300 Dobson units. This seems rather low for a developing monster storm!

SEVIRI RGB Air Mass image valid at 05z on 12/13/12.

SEVIRI RGB Air Mass image valid at 05z on 12/13/12.

AIRS Total Column Ozone Retrievals valid at 05z on 12/13/12.

AIRS Total Column Ozone Retrievals valid at 05z on 12/13/12.

At 05z on 12/13/12, the storm is maturing and expanding in coverage with a very pronounced area of red-coloring associated with the stratospheric drying. At this time, the storm is completing its bombogenesis cycle with a surface pressure approaching the minimum of 948 mb. The AIRS image shows plenty of ozone co-located near or just northwest of the center of the PV anomaly southeast of Greenland. At this time, the forecaster was still debating whether any verifiable hurricane-force winds would show up. I conjectured that the pressure gradient might be to large, although it was possible that hurricane-force wind gusts were showing up in the southwestern to southeastern quadrants.

ASCAT high resolution image valid between 12z and 15z on 12/13/12.

ASCAT high resolution image valid around 1643z on 12/13/12.

The ASCAT high resolution image above shows a large swath of storm-force winds in the southwest quadrant of between 40 and 48 knots (46-55 mph) with a few flags between 48 and 56 knots (55-66 mph). Another swath of strong winds exists in the northeast quadrant and although not in this image, there was a very strong zone of wind near the tip of Greenland known as the “Tip Jet”. Jame Kells (OPC) noted that the “Tip Jet” did contain 65+ knot (75 mph) winds in a later OSCAT high resolution pass, therefore the hurricane-force wind advisory verified. Unfortunately for me, I did not have the correct quadrant of this storm. This goes to show that the stratospheric drying noted in the RGB Air Mass product may not always be associated with hurricane-force events, but keep in mind that the scatterometer data cannot verify wind gusts. It is my assumption that the southwest quadrant contained some very strong wind gusts well over 65 knots.

Feel free to comment or start a discussion on this topic as I find it very interesting and look forward to observing more of these events with the RGB Air Mass products.

Thank you for reading!

*SEVIRI RGB Air Mass imagery is created using various bands from Meteosat-9 (EUMETSAT) and is disseminated by NASA SPoRT and CIRA.