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Tuesday, October 26, 2010

Mid-October 2010 SST Anomaly Update

I’ve moved to WordPress.  This post can now be found at Mid-October 2010 SST Anomaly Update
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NOTE: The weekly OI.v2 SST data is available in two periods through the NOAA NOMADS website, from November 1981 to 1989, and from 1990 to present. The mid-month posts now include the full term of the NINO3.4 and Global SST anomalies from 1990 to present and a shorter-term view from 2004 to present to make the recent wiggles easier to see.

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NINO3.4

NINO3.4 SST anomalies for the week centered on October 20, 2010 show that central equatorial Pacific SST anomalies have risen slightly in the past two weeks after their significant drop. They’re at -1.5 deg C.
http://i53.tinypic.com/21b8a5u.jpg
NINO3.4 SST Anomalies
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http://i52.tinypic.com/2u7m4yd.jpg
NINO3.4 SST Anomalies - Short-Term

GLOBAL

Weekly Global SST anomalies have taken a minor step up in the past few weeks, after the major decline. In effect, this returned them to the value they were at four weeks ago.
http://i56.tinypic.com/rk6iyg.jpg
Global SST Anomalies
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http://i53.tinypic.com/11ghtzb.jpg
Global SST Anomalies - Short-Term

COMPARISON TO PAST LA NIÑA EVENTS AND TRANSITIONS

The first graph that follows illustrates how the present NINO3.4 SST anomalies stack up against prior La Niña events. I’ve also provided a comparison of the declines in global SST anomalies in response to the transitions from El Niño to La Niña, using the same years. Note that the first SST anomaly reading for each year has been zeroed, and that all global SST anomalies have been shifted accordingly. The decline in 2010 Global SST anomalies is well within the range of past events.
http://i52.tinypic.com/ouqjwp.jpg
Comparison Of La Niña Evolution – 2010 Versus 1988, 1998, and 2007
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http://i52.tinypic.com/68r2ol.jpg
Comparison Of Global SST Anomalies During La Niña Evolution – 2010 Versus 1988, 1998, and 2007

SOURCE

OI.v2 SST anomaly data is available through the NOAA NOMADS system:
http://nomad3.ncep.noaa.gov/cgi-bin/pdisp_sst.sh?lite

Monday, October 18, 2010

Update And Changes To NODC Ocean Heat Content Data

I’ve moved to WordPress.  This post can now be found at Update And Changes To NODC Ocean Heat Content Data
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As noted in the post October 2010 Update to NODC Ocean Heat Content Data, the National Oceanographic Data Center has updated its OCEAN HEAT CONTENT (OHC) data. This is the dataset based on the Levitus et al (2009) paper “Global ocean heat content(1955-2008) in light of recent instrumentation problems”, Geophysical Research Letters. Refer to Manuscript.

The update to the OHC data also included major changes, which have reduced the long-term rise in OHC. Refer to the gif animation, Figure 1, that shows the global OHC data from their June 2010 update (through March 2010) and from the most recent update and change (though June 2010). The revisions are considerable in many ocean basins. As described in their explanation of ocean heat content (OHC) data changes, the changes result from “data additions and data quality control,” from a switch in base climatology, and from revised Expendable Bathythermograph (XBT) bias calculations. (Refer to the NOAA FAQ webpage What is an XBT?) Immediately following Figure 1 is a link to a graph that shows the difference between the two global datasets, with the June 2010 update subtracted from the September 2010 update.
http://i56.tinypic.com/2vhsta8.jpg
Figure 1 - Global
Link to Graph of the Difference:
http://i51.tinypic.com/2qi07s0.jpg
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Table 1 shows the OHC linear trends (in Gigajoules/Square Meter per Decade) for the global and hemispheric data and for the individual ocean basin subsets. Also shown are the differences (the data from the September 2010 update MINUS the data from the June 2010 update) and the percent change (difference divided by June 2010 update). Note: the June 2010 update included data through March 2010 and the September update/change included data through June 2010, but Table 1 only compares linear trends for the datasets through March 2010. As shown in Table 1, the linear trend for the Northern Hemisphere OHC data only dropped approximately 2%, while the Southern Hemisphere linear trend dropped about 16%. There was a minor increase in North Pacific trend (4%), while there were considerable drops in the linear trends of the South Atlantic (23%), South Pacific (17%) and the Southern Ocean (32%).
http://i52.tinypic.com/1zx5boi.jpg
Table 1

Figure 2 is the gif animation that shows the Southern Ocean OHC data (South of 60S) before and after the September 2010 changes. Prior to the mid-2000s and the introduction of ARGO buoys, the original data (through March 2010) simply appeared to be the climatology with some data added occasionally when it was available. The updated data seems to emphasize that appearance.
http://i54.tinypic.com/111sabn.jpg
Figure 2 – Southern Ocean
Link to Graph of the Difference:
http://i56.tinypic.com/fuqalc.jpg
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And there is good reason for that appearance. Like Sea Surface Temperature datasets based on buoys and ship sensors, there is very little Southern Hemisphere data, at all depths, prior to the ARGO buoys era. Figures 3 through 6 show the 3-month data distribution maps for January through March of 1955, 1975, 1995 and 2005, at depths of zero meters (surface), 250 meters, 500 meters and 700 meters. South of 60S there was little data even in 2005. The maps are available through the NODC Temperature data distribution figures webpage.
http://i52.tinypic.com/2a8orcp.jpg
Figure 3
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http://i55.tinypic.com/aes9lg.jpg
Figure 4
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http://i54.tinypic.com/x6gaig.jpg
Figure 5
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http://i52.tinypic.com/k9ax3.jpg
Figure 6
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THE IMPACT OF CHANGES ON PAST POSTS ABOUT NATURAL OHC VARIATIONS

The recent changes to the OHC data have not had noticeable effects on the timing of the major variations in data that should be attributable to natural variations. For example: The tropical Pacific OHC data still drops during major El Niño events and partially rebounds during most of the La Niña events that follow, Figure 7. The major upward shifts occur during significant La Niña events, which is the recharge/overcharge mode for the tropical Pacific OHC. This, and the similar impact on other ocean basins, was discussed in the post ENSO Dominates NODC Ocean Heat Content (0-700 Meters) Data.
http://i52.tinypic.com/wbqt61.jpg
Figure 7

With the changes to the data, the OHC of the North Pacific north of 20N still drops from the late 1950s to the late 1980s, Figure 8, and then suddenly rises. This increase coincides with a shift in North Pacific sea level pressure. This was discussed in the post North Pacific Ocean Heat Content Shift In The Late 1980s.
http://i55.tinypic.com/v8o60i.jpg
Figure 8

The update/changes caused the OHC for most of the other basins to drop more than the North Atlantic OHC. Refer again to Table 1. This makes the contribution of the North Atlantic OHC to global OHC even greater. And much of the disproportionate rise in North Atlantic OHC is caused by Atlantic Meridional Overturning Circulation (AMOC), sea level pressure, and ENSO, as discussed in North Atlantic Ocean Heat Content (0-700 Meters) Is Governed By Natural Variables. One cell of the gif animation in Figure 9 compares global and North Atlantic OHC. The increase in North Atlantic OHC dwarfs the global rise. The second cell in Figure 9 compares the North Atlantic OHC to the global data with the North Atlantic removed. It assumes the surface area of the North Atlantic is 15% of the global ocean surface area. Note the decrease in the global trends. The "Global" linear trend (blue curve) is 0.072 GJ/square meter per decade and without the North Atlantic, the "Global Minus North Atlantic” data linear trend (green curve) drops to 0.043 GJ/square meter per decade. Also note how sharply the North Atlantic OHC has dropped since 2005. The North Atlantic is a major contributor to the flattening of global data in recent years.
http://i56.tinypic.com/2m2hq1v.jpg
Figure 9

GIF ANIMATIONS -- BEFORE AND AFTER CHANGES

Figures 10 through 18 are gif animations that compare the NODC OHC data for the hemispheres and ocean basin subsets before and after the recent changes. I’ve also provided links to graphs of the differences, with the June 2010 data subtracted from the September 2010 data. They are provided without commentary.
http://i53.tinypic.com/aken3m.jpg
Figure 10 – Tropical Pacific
Link to Graph of the Difference:
http://i51.tinypic.com/34fo420.jpg
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http://i51.tinypic.com/2zrks8x.jpg
Figure 11 – Northern Hemisphere
Link to Graph of the Difference:
http://i56.tinypic.com/22xonc.jpg
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http://i52.tinypic.com/2cy5vf5.jpg
Figure 12 – Southern Hemisphere
Link to Graph of the Difference:
http://i53.tinypic.com/2vaim1u.jpg
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http://i52.tinypic.com/r91v7d.jpg
Figure 13 – North Atlantic
Link to Graph of the Difference:
http://i55.tinypic.com/dm9tas.jpg
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http://i55.tinypic.com/2lcwcir.jpg
Figure 14 – South Atlantic
Link to Graph of the Difference:
http://i51.tinypic.com/2akfvaf.jpg
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http://i56.tinypic.com/2n1t0fm.jpg
Figure 15 - Indian Ocean
Link to Graph of the Difference:
http://i56.tinypic.com/2gxfwvq.jpg
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http://i52.tinypic.com/2dtdiyd.jpg
Figure 16 – North Pacific
Link to Graph of the Difference:
http://i56.tinypic.com/nx553a.jpg
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http://i52.tinypic.com/2u4313m.jpg
Figure 17 – South Pacific
Link to Graph of the Difference:
http://i51.tinypic.com/5yz3sw.jpg
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http://i51.tinypic.com/n5lmp1.jpg
Figure 18 – Arctic Ocean
Link to Graph of the Difference:
http://i55.tinypic.com/2d7h387.jpg
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SOURCE
The NODC OHC data is available through the KNMI Climate Explorer:
http://climexp.knmi.nl/selectfield_obs.cgi?someone@somewhere

(Thanks to Dr Geert Jan van Oldenborgh of KNMI for creating and maintaining Climate Explorer.)

Monday, October 11, 2010

September 2010 SST Anomaly Update

I’ve moved to WordPress.  This post can now be found at September 2010 SST Anomaly Update
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MONTHLY SST ANOMALY MAPThe map of Global OI.v2 SST anomalies for September 2010 downloaded from the NOMADS website is shown below. The central equatorial Pacific SST anomalies are continuing their decline associated with the La Niña.

http://i55.tinypic.com/2ev5fg5.jpg
September 2010 SST Anomalies Map (Global SST Anomaly = +0.19 deg C)

A NOTE ABOUT GLOBAL SST ANOMALIES
Global SST anomalies, based on the weekly Reynolds OI.v2 data, dropped 0.13 deg C over the past two weeks. This can be seen in the graph of weekly Global SST anomalies. The present value is 0.1 deg C.
http://i53.tinypic.com/1ig7sl.jpg
Weekly Global SST Anomalies

The next graph is a comparison of the global SST anomalies for 2010 compared to 1988, 1998, and 2007. Those were other transition years from El Niño to La Niña. In the graph, the data has been shifted so that the first weeks were all zeroed. The current transition is well within the range of past transitions from El Niño to La Niña.
http://i54.tinypic.com/rhk286.jpg
Comparison Of Transitions From El Niño To La Nina

MONTHLY OVERVIEW
Monthly NINO3.4 SST anomalies are well below the -0.5 deg C threshold of a La Niña. The Monthly NINO3.4 SST Anomaly is -1.57 deg C. Weekly data has dropped below -1.8 deg C (-1.84 deg C).

Global SST anomalies dropped this month, -0.028 deg C. There were decline in both the Southern Hemisphere (-0.044 deg C) and the Northern Hemisphere
(-0.007 deg C), though the drop in the Northern Hemisphere was so small it’s basically unchanged.
http://i55.tinypic.com/123mlxj.jpg
Global
Monthly Change = -0.028 deg C
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http://i52.tinypic.com/2iasg0p.jpg
NINO3.4 SST Anomaly
Monthly Change = -0.36 deg C

EAST INDIAN-WEST PACIFIC
The SST anomalies in the East Indian and West Pacific made a slight rise this month. Will they continue to rise, noticeably, in response to the La Niña as they have in the past?

I’ve added this dataset in an attempt to draw attention to what appears to be the upward step responses. Using the 1986/87/88 and 1997/98 El Niño events as references, East Indian-West Pacific SST Anomalies peak about 7 to 9 months after the peak of the NINO3.4 SST anomalies, so we shouldn’t expect any visible sign of a step change for almost 18 to 24 months. We’ll just have to watch and see.
http://i56.tinypic.com/2hye1hv.jpg
East Indian-West Pacific (60S-65N, 80E-180)
Monthly Change = +0.028 deg C

Further information on the upward “step changes” that result from strong El Niño events, refer to my posts from a year ago Can El Niño Events Explain All of the Global Warming Since 1976? – Part 1 and Can El Niño Events Explain All of the Global Warming Since 1976? – Part 2

And for the discussions of the processes that cause the rise, refer to More Detail On The Multiyear Aftereffects Of ENSO - Part 2 – La Niña Events Recharge The Heat Released By El Niño Events AND...During Major Traditional ENSO Events, Warm Water Is Redistributed Via Ocean Currents -AND- More Detail On The Multiyear Aftereffects Of ENSO - Part 3 – East Indian & West Pacific Oceans Can Warm In Response To Both El Niño & La Niña Events

The animations included in post La Niña Is Not The Opposite Of El Niño – The Videos further help explain the reasons why East Indian and West Pacific SST anomalies can rise in response to both El Niño and La Niña events.

NOTE ABOUT THE DATA
The MONTHLY graphs illustrate raw monthly OI.v2 SST anomaly data from November 1981 to September 2010.

MONTHLY INDIVIDUAL OCEAN AND HEMISPHERIC SST UPDATES http://i53.tinypic.com/ay5y6g.jpg
Northern Hemisphere
Monthly Change = -0.007 deg C
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http://i53.tinypic.com/dtj08.jpg
Southern Hemisphere
Monthly Change = -0.044 deg C
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http://i54.tinypic.com/3504579.jpg
North Atlantic (0 to 75N, 78W to 10E)
Monthly Change = -0.059 deg C
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http://i52.tinypic.com/144cwm1.jpg
South Atlantic (0 to 60S, 70W to 20E)
Monthly Change = -0.064 deg C

Note: I discussed the upward shift in the South Atlantic SST anomalies in the post The 2009/10 Warming Of The South Atlantic.

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http://i56.tinypic.com/15817cl.jpg
North Pacific (0 to 65N, 100 to 270E, where 270E=90W)
Monthly Change = +0.054 Deg C
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http://i51.tinypic.com/2w7on5g.jpg
South Pacific (0 to 60S, 145 to 290E, where 290E=70W)
Monthly Change = -0.071 deg C
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http://i56.tinypic.com/4kh6s7.jpg
Indian Ocean (30N to 60S, 20 to 145E)
Monthly Change = -0.011 deg C
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http://i54.tinypic.com/esqpfl.jpg
Arctic Ocean (65 to 90N)
Monthly Change = +0.178 deg C
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http://i55.tinypic.com/2yufsia.jpg
Southern Ocean (60 to 90S)
Monthly Change = +0.024 deg C

WEEKLY NINO3.4 SST ANOMALIES
The weekly NINO3.4 SST anomaly data illustrate OI.v2 data centered on Wednesdays. The latest weekly NINO3.4 SST anomalies are -1.84 deg C.
http://i52.tinypic.com/mb2t6u.jpg
Weekly NINO3.4 (5S-5N, 170W-120W)

SOURCE
The Optimally Interpolated Sea Surface Temperature Data (OISST) are available through the NOAA National Operational Model Archive & Distribution System (NOMADS).
http://nomad1.ncep.noaa.gov/cgi-bin/pdisp_sst.sh
or
http://nomad3.ncep.noaa.gov/cgi-bin/pdisp_sst.sh

Sunday, October 10, 2010

On The Differences Between Surface And TLT Datasets

I’ve moved to WordPress.  This post can now be found at On The Differences Between Surface And TLT Datasets
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OVERVIEWThe differences between surface temperature and lower troposphere temperature (TLT) anomalies are examined in this post. The globe is broken down into sectors in an effort to locate the area with the greatest difference between surface temperature and TLT anomalies. The responses of Sea Surface Temperature (SST) and Sea TLT to El Niño and La Niña events are also examined to see if they may cause part of the divergence between the surface temperature and TLT data after the 1997/98 El Nino. The post also presents animated maps of surface temperatures and TLT anomalies and animated maps of the correlations of NINO3.4 SST anomalies and global temperatures to further highlight the differences.

INTRODUCTION

The differences between the infilled surface-based (GISS and NCDC) temperature anomaly datasets and the Lower Troposphere Temperature (RSS and UAH) anomaly datasets create a multitude of comments from both sides of the global climate change debate whenever the datasets are plotted together. While there may be biases created by surface station location, infilling method, Urban Heat Island (UHI) adjustments (or lack thereof), etc., let’s put the land-based discussions aside for this post and consider the possibility that Sea Surface Temperature (SST) might respond differently than the lower troposphere temperatures to El Niño and La Niña events, and that those differences in response might account for some of the divergence.

Satellite-based TLT data has been available since 1979, providing more than 3 decades of data for comparisons to surface data. Unfortunately, the surface temperatures and TLT between 1982 and 1995 are overwhelmed by the dips and rebounds caused by the volcanic eruptions of El Chichon and Mount Pinatubo. Accounting for these in the global data is relatively easy, but we’ll be dividing the globe into sectors in this post and having to account for the volcanic eruptions in each would add unnecessary complexity, so we’ll only look at the period from 1995 to present. Additionally, GISS Deletes Arctic And Southern Ocean Sea Surface Temperature Data in areas with seasonal sea ice and extends adjoining land surface temperature data (with its higher trend) out over the oceans. GISS does this to infill temperature data in the ocean areas with sea ice. The NCDC product does not take this step. To eliminate that difference, the data north of 60N and south of 60S have been excluded from this post.

So basically we’ll be examining the global land and sea surface temperature and lower troposphere temperature data minus the poles from 1995 to present. Figure 1 illustrates the average of the surface temperature datasets (GISTEMP and NCDC) and the average of the TLT datasets (RSS and UAH). We’ll use the averages initially to simplify the illustrations (and to eliminate discussions of any differences between the individual datasets). The TLT anomalies in Figure 1 have been scaled so that the rise in response to the 1997/98 El Niño is approximately the same as the surface data. (And for those wondering why the data ends in May 2010, I’ve used the KMNI Climate Explorer as the source of data for this post, and the latest RSS TLT anomaly data update there is May 2010.) Note also that the title block states that the surface data has been lagged 2 months. In other words, the surface data responded 2 months earlier to the 1997/98 El Niño than the TLT anomalies, so I’ve shifted the surface data back in time by two months. The linear trend of the surface data is more than twice that of the scaled TLT data. The surface data has a linear trend of approximately 1.1 deg C per Century but the trend of the scaled TLT data is only 0.4 deg C per Century. And much of this appears be caused by the failure of the surface data to respond as fully as the TLT data to the 1998/99/00/01 La Niña.
http://i52.tinypic.com/2uorrsp.jpg
Figure 1

NOTE: The TLT scaling factors and surface data lags vary per subset in the following. The scaling factors and lags are noted in the title blocks.

If we subtract the scaled TLT anomalies from the surface data, Figure 2, we can see that there appears to be an upward shift in the surface data in 1998 that is not present in the TLT data. And after 1998, the surface data rises at a rate that is faster than the TLT anomalies.
http://i55.tinypic.com/rj2nh1.jpg
Figure 2

LET’S DIVIDE THE GLOBE INTO THREE SECTORS
I’ve divided the globe (minus the poles) into three sectors for the comparisons that follow. The areas are split at 180, 78W, and 80E longitude. To simplify the discussion, I’ve identified them as “Far West”, “Near East and Near West,” and “Far East”, based on their proximity to zero longitude. Refer to Figure 3. The “Far West” data includes the Eastern Pacific and most of North America. The “Near East and Near West” includes the Atlantic and Western Indian Oceans and South America, Africa, Europe, and Western Asia. And the “Far East” data includes the East Indian and West Pacific Oceans and Eastern Asia and Australia.
http://i53.tinypic.com/10p51tj.jpg
Figure 3

FAR WEST COMPARISON

A time-series graph of the surface and TLT anomalies for the Far West sector is shown in Figure 4. These datasets capture the Eastern Pacific and most of North America. The surface temperatures have been lagged 5 months to align the leading edges of the responses to the 1997/98 El Niño. Note also that the TLT anomalies have not been scaled, which means the variations in TLT anomalies for the East Pacific and most of North America are comparable to the changes in surface temperature anomalies. Also note that this is the only one of these three sectors where the TLT anomalies are rising faster than the surface temperatures, though the difference in the trends is relatively small. And of course, the linear trends themselves are very small, with the TLT anomalies having a linear trend of less than 0.3 deg C per Century. This means that this sector of the globe does not contribute to the disparity between surface and TLT anomalies; in fact, this area would suppress the difference.
http://i52.tinypic.com/2uyiqs7.jpg
Figure 4

FAR EAST COMPARISON

The Far East data, Figure 5, represents the East Indian and West Pacific Oceans, along with Eastern Asia and Australia. For this part of the globe, the surface data needed to be advanced one month to align the rises of the responses to the 1997/98 El Niño. The surface data does not drop as far as the TLT data during the 1998/99/00/01 La Niña and remains elevated during the 2002/03 El Niño. The two datasets diverge again during the 2007/08 La Niña. These divergences cause the surface data to have a higher trend than the TLT anomalies. The difference in the linear trends, though, is only approximately 0.2 deg per Century. This accounts for little of the disparity in trends shown in Figure 1.
http://i51.tinypic.com/291m7nq.jpg
Figure 5

And that means much of the divergence in the two global datasets comes from the Near East-Near West sector, so we’ll concentrate on that sector for the rest of the post.

COMPARISON OF NEAR EAST AND NEAR WEST

For the Near East and Near West portion of the globe, Figure 6, the linear trend for the surface temperature data is approximately 1.9 deg C per Century, while the trend for the scaled TLT data is approximately 0.47 deg C per Century. The surface data has very little drop during the 1998/99/00/01 La Niña.
http://i52.tinypic.com/142t7q.jpg
Figure 6

This is confirmed in Figure 7, which illustrates the difference between the scaled TLT and surface data for the Near East and Near West. Note the significant upward step in the latter half of 1998.
http://i56.tinypic.com/2vj74uq.jpg
Figure 7

Animation 1 provides maps of the surface temperature and lower troposphere temperature anomalies of the Near East and Near West datasets used in this post. The surface datasets are on the left and the TLT datasets are on the right. The base years for anomalies (1979 to 2009) are the same for all. The maps provide 12-month average temperatures from July to June for the first five years being examined in this post: the ENSO-Neutral year 1996/1997, the El Niño year 1997/1998, and the three La Niña years of 1998/1999, 1999/2000, and 2000/2001. The period of July to June was used since ENSO events typically peak in November, December and January. The animation is provided to show the similarities and differences in the responses to El Niño and La Niña events between the surface-based and TLT datasets.

http://i54.tinypic.com/2cwwfug.jpg
Animation 1

Figure 8 is the July 1998 to June 1999 cell from the animation. I’ve isolated it because much of the difference between the surface and TLT anomalies (Figure 7) occurs during this period. While there are some differences between land surface temperature and land TLT anomalies during the year from July 1998 to June 1999 in Figure 8, most of the additional warming appears to take place in the sea surface temperature data:
- In the Western North Atlantic,
- In the tropical Eastern South Atlantic in the Benguela and South Equatorial Currents, and
- In the Antarctic Circumpolar Current (ACC) south of South Africa and the western Indian Ocean.
http://i52.tinypic.com/xp0ec0.jpg
Figure 8

NEAR EAST-NEAR WEST SEA SURFACE AND SEA TLT COMPARISON

So far we’ve compared the average of GISTEMP LOTI and NCDC combined surface data to the average of RSS and UAH TLT anomalies. Unfortunately, the RSS TLT data through the KNMI Climate Explorer is not divided into land and sea TLT subsets. Luckily, the UAH data is, so we’ll have to use it alone in the following comparison.

Figure 9 illustrates the Near East-Near West sea surface and scaled sea TLT data (UAH only) anomalies. The scaled sea TLT linear trend is only 0.27 deg C per Century, while the sea surface temperature (SST) trend is approximately 4 times higher at 1.1 deg C per Century. Much of the divergence occurs during the 1998/99/00/01 La Niña. Then, from 2001 to present, the SST anomalies have climbed higher while the sea TLT anomalies remained relatively flat.
http://i51.tinypic.com/mj5rwy.jpg
Figure 9

Consider now that the Near East-Near West sea surface area represents approximately 63% of the total surface area for this part of the globe. The divergence between sea surface and sea TLT anomalies for this part of the globe, therefore, represents a significant portion of the overall global difference.

A DISCUSSION OF ENSO EVENTS
During an El Niño, warm water from the surface and from up to 300 meters below the surface of the Pacific Warm Pool sloshes to the east and spreads across the surface of the eastern tropical Pacific. This raises SST there. The rise in SST in the eastern Tropical Pacific causes more moisture than normal to be pumped into the atmosphere through evaporation, which is how the ocean releases most of its heat to the atmosphere. The warm and moist air rises in a process known as convection, and the air cools as it rises. The cooler air can’t hold as much water, so the moisture condenses and it rains, releasing the heat into the atmosphere. (During a La Niña, the waters in the eastern tropical Pacific are cooler than normal, and less heat than normal is released to the atmosphere.)

The warmed air is transported to the east and poleward by atmospheric circulation. This can be seen in the animations of TLT anomalies in the two right-hand cells of Animation 2.
http://i52.tinypic.com/23l0ais.jpg
Animation 2

Note: Each of the cells in this animation represents a 12-month average of the temperature anomalies. Again, the surface data are on the left and the TLT data are on the right. The first cell represents the period of Jun 1996 to May 1997. It is followed by the next 12-month period, July 1996 to June 1997, and so on, in sequence. The use of 12-month averages minimizes weather and seasonal noise. I’ve included the eastern Pacific (the Far West sector) in this animation to show the timing of the El Niño in the eastern tropical Pacific and the transition to La Niña. Last, the animation lasts for 36 frames, from the period of July 1996 - June 1997 to the period of June 1999 – May 2000. This captures the evolution and decay of the 1997/98 El Niño plus the first few months of the 1998/99/00/01 La Niña.

It is very apparent in the two left-hand cells of Animation 2 that sea surface temperatures in the tropical North Atlantic rise in response to the El Niño. For a detailed discussion of how this occurs, refer to Wang (2005), "ENSO, Atlantic Climate Variability, And The Walker And Hadley Circulation." Wang (2005) link:
http://www.aoml.noaa.gov/phod/docs/Wang_Hadley_Camera.pdf

Wang (2005) states, “The Walker and Hadley circulations can serve as a ‘tropospheric bridge’ for transferring the Pacific El Niño SST anomalies to the Atlantic sector and inducing the TNA SST anomalies just at the time of year when the warm pool is developing.”

The warm pool being discussed in Wang (2005) is the Western Hemisphere Warm Pool, which is made up of eastern North Pacific west of Central America, the Gulf of Mexico, the Caribbean and the western tropical North Atlantic. The acronym TNA stands for Tropical North Atlantic.

Wang (2005) continues, “The Hadley weakening results in less subsidence over the subtropical North Atlantic, an associated breakdown of the anticyclone, and a weakening of the NE trades in the TNA. The wind weakening leads to less evaporative surface cooling and entrainment of colder water from below the shallow mixed layer, resulting in positive SST anomalies.”

In other words, an El Niño causes changes in atmospheric circulation which causes a weakening of the trade winds in the tropical North Atlantic. In turn, the weaker trade winds cause less evaporation, resulting in warmer SST. The weakening of the trade winds also causes less cool water from below the surface to be drawn to the surface.

Wang (2005) concludes that paragraph on page 27 with, “The opposite is presumed to occur during boreal winters with unusually cool SSTs in the equatorial Pacific,” meaning that it is assumed the opposite takes place during a La Niña.

Animation 2 shows the differences and similarities between the patterns of surface and TLT anomalies during the evolution and decay of an El Niño. The surface temperature anomalies are responding to changes in atmospheric circulation, while the TLT anomalies are responding to the heat released from the oceans.

For a further discussion of how these patterns are created, refer to Trenberth et al (2002) “Evolution of El Nino–Southern Oscillation and global atmospheric surface temperatures":
http://www.cgd.ucar.edu/cas/papers/2000JD000298.pdf

Trenberth et al (2002) use a time sequence of correlation maps, their Figure 8, to illustrate the evolution of ENSO events. They write in paragraph 29, “To explore where the heat in the oceans and its effects on the atmosphere actually occur, we have computed correlation and regression maps for several fields at various lags, a subset of which are given here.” And they continue, “This sequence reveals the mean evolution of ENSO and is quite coherent and traceable from about -12- to +12-months lag with N3.4, but becomes quite weak at larger lags. The panels presented in Figure 8 and the [delta] 4-month sequence are chosen to illustrate the evolution in the fewest panels.”

CORRELATION MAP ANIMATIONS
Animating correlation maps of NINO3.4 SST anomalies with surface and TLT anomalies does help to illustrate the evolution and decay in global temperatures in response to ENSO. The areas where there are differences between the surface and TLT datasets also become apparent. And although we are discussing the Near East and Near West sector, we’ll start with an animation of global maps. Keep in mind that the RSS does not present data north of 82.5N or south of 70S, where GISS deletes SST data in these areas and extends land surface data out over the oceans.

Animation 3 shows maps of the correlation of December NINO3.4 SST anomalies with GISS LOTI global surface temperature anomalies in the left-hand cell and RSS global TLT anomalies on the right. GISS data was included because they use satellite-based Reynolds OI.v2 SST data during this period. December NINO3.4 SST anomalies were used because El Niño events normally peak in November-December-January. The animation starts with zero-month lag and continues monthly through a 12-month lag. Like the other animations, there are differences and similarities between the surface and TLT datasets. What caught my eye was the significant positive correlation in the North Atlantic during lags 10 through 12, where they did not appear in the TLT data.
http://i56.tinypic.com/wrny9i.jpg
Animation 3

Since the animation can’t be stopped, I’ve included the frames with the 10-, 11-, and 12-month lags as Figures 10 through 12.
http://i55.tinypic.com/9anzmh.jpg
Figure 10
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http://i54.tinypic.com/2zzukhk.jpg
Figure 11
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http://i52.tinypic.com/123y6u0.jpg
Figure 12
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I decided to take the animation of the correlation maps one step further. I’ve presented the Atlantic Ocean SST data only in Animation 4, using Reynolds OI.v2 SST data. The correlation maps also use 3-month averages of NINO3.4 and Atlantic SST data. I found the animation quite interesting. During the early lag months, warm waters created by the El Niño appear to migrate from the tropical South Atlantic to the tropical North Atlantic. The warm waters in the tropical North Atlantic then appear to follow ocean currents west into the Caribbean and Gulf of Mexico, before entering the Gulf Stream. Starting around the 9-month lag, warm waters migrate south from the southern tip of Greenland and the Davis Strait. Is that from glacial ice melt in Greenland and Arctic sea ice melt, with the melt caused by the El Niño? They're correlated with NINO3.4 SST anomalies.
http://i52.tinypic.com/2gtai6d.jpg
Animation 4

That would be a good lead-in animation for a new post on the AMO.

CLOSING
A significant portion of the difference between global surface temperature and TLT anomalies occurs in the North Atlantic Ocean. And the additional warming that takes place appears to be caused by ocean processes correlated with ENSO. Why don’t the TLT anomalies respond to these additional ocean processes?

SOURCE

The data and maps presented in this post are available through the KNMI Climate Explorer:
http://climexp.knmi.nl/selectfield_obs.cgi?someone@somewhere

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Comment Policy, SST Posts, and Notes

Comments that are political in nature or that have nothing to do with the post will be deleted.
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The Smith and Reynolds SST Posts DOES NOT LIST ALL SST POSTS. I stopped using ERSST.v2 data for SST when NOAA deleted it from NOMADS early in 2009.

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