According to the authors,
The Mt. Logan Aleutian Low proxy record is significantly (p < 0.05) correlated and coherent with solar irradiance proxy records over various timescales, with stronger solar irradiance generally associated with a weaker Aleutian Low and La Niña-like tropical conditions. However, a step-like increase in Aleutian Low strength during the Dalton solar minimum in 1820 AD is associated with enhanced Walker Circulation. Furthermore, rising CO2 forcing or internal [natural] variability may be masking the 20th century rise in solar irradiance.
Indeed, solar activity levels of the latter 20th century were at the highest levels of the past 3,000 - 9,400 years. The paper thus suggests two additional solar amplification mechanisms [along with many others described in the scientific literature] by which increased solar activity may weaken the Aleutian Low circulation pattern and influence frequency of La Ninas.
Mt. Logan Ice Core Record of Tropical and Solar Influences on Aleutian Low Variability: 500–1998 AD
Erich C. Osterberg et al
Continuous, high-resolution paleoclimate records from the North Pacific region spanning the past 1500 years are rare, and the behavior of the Aleutian Low (ALow) pressure center, the dominant climatological feature in the Gulf of Alaska, remains poorly constrained. Here we present a continuous, 1500 year long, calibrated proxy record for the strength of the wintertime (December-March) ALow from the Mt. Logan summit (PR Col; 5200 m a.s.l.) ice core soluble sodium time series. We show that ice core sodium concentrations are statistically correlated with North Pacific sea level pressure and zonal wind speed. Our ALow proxy record reveals a weak ALow from ca. 900–1300 AD and 1575–1675 AD, and a comparatively stronger ALow from ca. 500–900 AD, 1300–1575 AD, and 1675 AD to present. The Mt. Logan ALow proxy record shows strong similarities with tropical paleoclimate proxy records sensitive to the El Niño-Southern Oscillation, and is consistent with the hypothesis that the MCA [Medieval Warm Period] was characterized by more persistent La Niña-like conditions while the LIA [Little Ice Age] was characterized by at least two intervals of more persistent El Niño-like conditions. The Mt. Logan ALow proxy record is significantly (p < 0.05) correlated and coherent with solar irradiance proxy records over various timescales, with stronger solar irradiance generally associated with a weaker ALow and La Niña-like tropical conditions. However, a step-like increase in ALow strength during the Dalton solar minimum ca. 1820 is associated with enhanced Walker Circulation. Furthermore, rising CO2 forcing or internal [natural] variability may be masking the 20th century rise in solar irradiance.
Mt. Logan Ice Core Record of Tropical and Solar Influences on Aleutian Low Variability: 500–1998 AD
Erich C. Osterberg et al
Continuous, high-resolution paleoclimate records from the North Pacific region spanning the past 1500 years are rare, and the behavior of the Aleutian Low (ALow) pressure center, the dominant climatological feature in the Gulf of Alaska, remains poorly constrained. Here we present a continuous, 1500 year long, calibrated proxy record for the strength of the wintertime (December-March) ALow from the Mt. Logan summit (PR Col; 5200 m a.s.l.) ice core soluble sodium time series. We show that ice core sodium concentrations are statistically correlated with North Pacific sea level pressure and zonal wind speed. Our ALow proxy record reveals a weak ALow from ca. 900–1300 AD and 1575–1675 AD, and a comparatively stronger ALow from ca. 500–900 AD, 1300–1575 AD, and 1675 AD to present. The Mt. Logan ALow proxy record shows strong similarities with tropical paleoclimate proxy records sensitive to the El Niño-Southern Oscillation, and is consistent with the hypothesis that the MCA [Medieval Warm Period] was characterized by more persistent La Niña-like conditions while the LIA [Little Ice Age] was characterized by at least two intervals of more persistent El Niño-like conditions. The Mt. Logan ALow proxy record is significantly (p < 0.05) correlated and coherent with solar irradiance proxy records over various timescales, with stronger solar irradiance generally associated with a weaker ALow and La Niña-like tropical conditions. However, a step-like increase in ALow strength during the Dalton solar minimum ca. 1820 is associated with enhanced Walker Circulation. Furthermore, rising CO2 forcing or internal [natural] variability may be masking the 20th century rise in solar irradiance.
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