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1. Subsurface Ocean Temperature Responses to the Anthropogenic Aerosol Forcing in the North Pacific

   https://doi.org/10.1029/2022GL101035  

   Shi, Jia‐Rui; Kwon, Young‐Oh; Wijffels, Susan E. (January 2023, Geophysical Research Letters)

   Abstract Separating the climate response to external forcing from internal climate variability is a key challenge. While most previous studies have focused on surface responses, here we examine zonal‐mean patterns of North Pacific subsurface temperature responses. In particular, the changes since 1950 driven by anthropogenic aerosol emissions are found by using a pattern recognition method. Based on the single‐forcing large‐ensemble simulations from two models, we show that aerosol forcing caused a nonmonotonic temporal response and a characteristic zonal‐mean pattern within North Pacific, which is distinct from the pattern associated with internal variability. The aerosol‐forced pattern with the nonmonotonic temporal feature shows a substantial temperature change in subpolar regions and a reversed change on the southern flank of the subtropical gyre. A similar characteristic pattern and nonmonotonic time evolution are extracted from the subsurface observations, which likely reflect the subsurface responses to the aerosol forcing, although differences exist with the simulated responses. 

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2. The non-symmetric strong multiplicity property for sign patterns

   https://doi.org/10.13001/ela.2025.8827  

   Curtis, Bryan; Garnett, Colin; Shader, Bryan L; Vander_Meulen, Kevin N (January 2025, The Electronic Journal of Linear Algebra)

   We develop a non-symmetric strong multiplicity property for matrices that may or may not be symmetric. We say a sign pattern allows the non-symmetric strong multiplicity property if there is a matrix with the non-symmetric strong multiplicity property that has the given sign pattern. We show that this property of a matrix pattern preserves multiplicities of eigenvalues for superpatterns of the pattern. We also provide a bifurcation lemma, showing that a matrix pattern with the property also allows refinements of the multiplicity list of eigenvalues. We conclude by demonstrating how this property can help with the inverse eigenvalue problem of determining the number of distinct eigenvalues allowed by a sign pattern. 

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3. Role of Atmospheric Variability in Driving the “Warm‐Arctic, Cold‐Continent” Pattern Over the North America Sector and Sea Ice Variability Over the Chukchi‐Bering Sea

   https://doi.org/10.1029/2020GL088599  

   Guan, Weina; Jiang, Xianan; Ren, Xuejuan; Chen, Gang; Ding, Qinghua (June 2020, Geophysical Research Letters)

   Abstract While the observed decline of sea ice over the Chukchi‐Bering Sea (CBS) has coincided with the “warm‐Arctic, cold‐continent” (WACC) pattern over the North America (NA) sector, there is a debate on the causes of the WACC pattern. Here we present a very similar WACC pattern over the NA sector on both interannual and subseasonal time scales. Lead‐lag regression analyses on the shorter time scale indicate that an anomalous anticyclonic circulation over Alaska/Yukon in conjunction with the downward surface turbulent heat flux and long‐wave radiation anomalies over CBS leads the formation of the WACC pattern by about 1–2 days, while the latter further leads CBS sea ice reduction by about 3 days. These results indicate that atmospheric variability may play an active role in driving both the WACC pattern over NA and CBS sea ice variability. 

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4. The Role of Latent Heating Anomalies in Exciting the Summertime Eurasian Circulation Trend Pattern and High Surface Temperature

   https://doi.org/10.1175/JCLI-D-21-0392.1  

   Kim, Dong_Wan; Lee, Sukyoung (January 2022, Journal of Climate)

   Abstract Dynamical mechanisms for the summer Eurasian circulation trend pattern are investigated by analyzing reanalysis data and conducting numerical model simulations. The daily circulations that resemble the Eurasian circulation trend pattern are identified and categorized into two groups based on surface warming signal over central and eastern Europe. In the group with large warm anomaly, the upper-level circulation takes on a wave packet form over Eurasia, and there are enhanced latent heating anomalies centered over the North Sea and suppressed latent heating anomalies over the Caspian Sea. The numerical model calculations indicate that these latent heating anomalies can excite an upper-level circulation response that resembles the Eurasian circulation trend pattern. Additional analysis indicates that trends of these two latent heating centers contribute to the long-term circulation trend. In the weak warm anomaly group, the circulation pattern takes on a circumglobal teleconnection (CGT) pattern, and there is no heating signal that reinforces the circulation. These results indicate that not all CGT-like patterns excite temperature anomalies that are persistent and in phase with the trend pattern, and that quasi-stationary forcings, such as the latent heating anomalies, play an important role in driving the boreal summer circulation anomaly that accompanies the strong and persistent surface temperature signal. 

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5. Potential Problems Measuring Climate Sensitivity from the Historical Record

   https://doi.org/10.1175/JCLI-D-19-0476.1  

   Dessler, Andrew E. (March 2020, Journal of Climate)

   This study investigates potential biases between equilibrium climate sensitivity inferred from warming over the historical period (ECS_hist) and the climate system’s true ECS (ECS_true). This paper focuses on two factors that could contribute to differences between these quantities. First is the impact of internal variability over the historical period: our historical climate record is just one of an infinity of possible trajectories, and these different trajectories can generate ECS_histvalues 0.3 K below to 0.5 K above (5%–95% confidence interval) the average ECS_hist. Because this spread is due to unforced variability, I refer to this as the unforced pattern effect. This unforced pattern effect in the model analyzed here is traced to unforced variability in loss of sea ice, which affects the albedo feedback, and to unforced variability in warming of the troposphere, which affects the shortwave cloud feedback. There is also a forced pattern effect that causes ECS_histto depart from ECS_truedue to differences between today’s transient pattern of warming and the pattern of warming at 2×CO₂equilibrium. Changes in the pattern of warming lead to a strengthening low-cloud feedback as equilibrium is approached in regions where surface warming is delayed: the Southern Ocean, eastern Pacific, and North Atlantic near Greenland. This forced pattern effect causes ECS_histto be on average 0.2 K lower than ECS_true(~8%). The net effect of these two pattern effects together can produce an estimate of ECS_histas much as 0.5 K below ECS_true. 

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