Climate Oscillations 8: The NPI and PDO

By Andy May

The North Pacific Index (NPI) and the Pacific Decadal Oscillation (PDO)

The North Pacific Index (NPI) is computed from the area-weighted sea level air pressure (SLP) over the region 30°N-65°N and 160°E-140°W. It measures interannual to multidecadal variations in Pacific atmospheric circulation. As explained in Trenberth and Hurrel, the winter Aleutian low pressure system moves on a decadal time scale and changes the climate and sea surface temperature (SST) along western North America and in the Northern Central Pacific. These changes are closely related to the PDO (Pacific Decadal Oscillation), which describes the same multidecadal weather and SST pattern in the same region but is calculated with SSTs using a different statistical method. Other oscillations that describe this pattern or something similar are the Interdecadal Pacific Oscillation (IPO) and the North Pacific Oscillation (NPO).

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Review of Politics and Climate Change

By Andy May

I published Politics & Climate Change: A History in 2020, but it has seen a welcome uptick in sales and interest lately. Of note Dr. Patrice Poyet has written a new and updated detailed review of the book that is available on Researchgate here.

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Climate Oscillations 7: The Pacific Mean SST

By Andy May

I originally planned to discuss the North Pacific Index (NPI) in this post, but while researching it, I discovered something interesting about Pacific sea surface temperature (SST) and how it relates to the HadCRUT5 global average surface temperature. As a result, this post is about the total Pacific mean SST and its correlation to HadCRUT5.

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Climate Oscillations 6: Atlantic Meridional Mode (AMM)

By Andy May

The Atlantic Meridional Mode Index (AMM) describes meridional variability in the tropical Atlantic. The area of interest is the ocean area inside 32°N to 21°S and from 75°W to the West African coastline (~15°E). Sometimes the boundaries are given as: 22°S-32°N and 74°W to the West African coast. This is the region where the Intertropical Convergence Zone (ITCZ) exists as it moves north and south with the seasons (Chiang & Vimont, 2004).

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Climate Oscillations 5: SAM

By Andy May

The Antarctic Oscillation (AAO) is also called the Southern Annular Mode or SAM. It is defined as the difference between the zonal (meaning east-west or circumpolar) sea level air pressure between 40°S and 65°S. That is the sea level pressure at 65°S is subtracted from the sea level pressure at 40°S (Gong & Wang, 1999). As the difference increases and SAM becomes more positive, the Southern Hemisphere circumpolar westerly (clockwise as viewed from above the South Pole) winds move closer to Antarctica and generally increase in intensity.

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Climate Oscillations 4: The Length of Day (LOD)

By Andy May

In post 1, I ranked fourteen climate oscillations in Table 1 by their regression statistics against the HadCRUT5 global surface mean temperature. In this regression study the AMO is number one, the Western Hemisphere Warm Pool Area is #2, and the Northern Hemisphere sea ice area is #3. The fourth in importance is the Length of Day or “LOD.” Longer periods (>10 years) of acceleration in Earth’s rotation speed (shorter LOD) correspond to years of increasing zonal (east-west) circulation and global warming, whereas periods of deceleration (longer LOD) indicate less zonal acceleration and periods of cooling (Lambeck & Cazenave, 1976).

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Climate Oscillations 3: Northern Hemisphere Sea Ice Area

By Andy May

Northern Hemisphere sea ice area is an important climatic indicator because it determines how much of the Arctic Ocean and surrounding seas are open to the atmosphere. Ice is a good insulator and traps heat in the water below it (Peixoto & Oort, 1992, p. 361). Ice is also a good reflector of sunlight (high albedo), whereas water is a good absorber (low albedo). While we have no accurate data on Northern Hemisphere sea ice area (called NH_ice here) before 1978, the first year of good satellite data, it does appear to follow the global 60-70-year global climate oscillation (Wyatt, 2020). This may be because the closely related AMO affects the sea ice area as it warms and cools, of course the reverse could also be true.

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Climate Oscillations 2: The Western Hemisphere Warm Pool (WHWP)

By Andy May

As seen in the first post of this series the AMO (Atlantic Multidecadal Oscillation) and the WHWP (Western Hemisphere Warm Pool) area are the two climate oscillations that explain most of the variability (64%) in the HadCRUT5 global mean surface temperature reconstruction (GMST) since 1950. Adding the Southern Annular Mode (SAM) explains 77% of HadCRUT5 variability.

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Climate Oscillations 1: The Regression

By Andy May

Introduction to the “Climate Oscillations” series

My last two posts, Musings on the AMO and The Bray Solar Cycle and AMO were fun to research and write, and they helped show that solar variations and cycles do have an impact on climate change regardless of what the IPCC says in AR6 WGI and their other reports.

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The Bray Solar Cycle and AMO

By Andy May

My last post on the AMO and HadCRUT5 generated some interest and some criticism. As I explained, there are two common methods of computing the AMO index. One is to fit a least squares line to the AMO SSTs (sea surface temperatures in the North Atlantic) and use the line to detrend the AMO, creating an index. This was the original methodology as described by Enfield, et al. and Gray, et al. It is the method I prefer because it makes no assumptions about the origin of the increasing SSTs in the North Atlantic.

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