Mid-latitude Atmospheric Circulation Research Articles

Synoptic processes over the Kodar glacier zone during the ablation period

The small glaciers of the Kodar ridge (south of Eastern Siberia), located inland Asia under the influence of both Atlantic and Pacific air transport, are the valuable objects for studying their response to changes in mid-latitude atmospheric circulation. However, detailed meteorological studies on the glaciers have been limited so far. For the first time, in July–August 2019, the meteorological characteristics were measured on the Sygyktinsky glacier using automatic weather station. We have analyzed the relationship between variations of large-scale atmospheric circulation and meteorological regime of the glacier using the NCEP–NCAR reanalysis data. During the observation period, Kodar was under the influence of a positive geopotential anomaly in the lower troposphere, which determined increased temperatures and decreased relative humidity and precipitation. Quasi-cyclic fluctuations in meteorological time series (e.g. air temperature) reflect the influence of large scale synoptic changes caused by the front passages, warm and cold air advections. High ablation rates on the glacier were associated with anticyclones, subtropical ridges, and warm air advections (from southeast and southwest), while decreased ablation was observed during the cyclone passage and cold air advection (from north, northeast, and west).

Influence of large-scale atmospheric circulation patterns on nutrient dynamics in the Mediterranean Sea in the extended winter season (October-March) 1961-1999

We investigated the effects of variations in the 4 primary mid-latitude large-scale atmospheric circulation patterns on nutrients potentially limiting phytoplankton growth in the Mediterranean Sea (nitrate and phosphate), with a focus on the key deep convective areas of the basin (Gulf of Lions, Southern Adriatic Sea, Southern Aegean Sea and Rhodes Gyre). Monthly indices of these 4 modes of variability, together with a high-resolution hindcast of the Mediterranean Sea physics and biogeochemistry covering the period 1961-1999, were used to determine the physical mechanisms explaining the influence of these patterns on nutrient distribution and variability. We found a decrease in the concentration of phosphate and nitrate for each unit of increase in the index values of the East Atlantic and East Atlantic/Western Russian variability modes in the area of the Gulf of Lions, while a signal of the opposite sign was associated with the North Atlantic Oscillation in the Aegean Sea and Rhodes Gyre. In both cases, the variability observed was related to a significant variation in the mixed layer depth driven by heat losses and wind stress over the areas. The East Atlantic pattern played a major role in driving the long-term dynamics of both phosphate and nitrate availability in the Gulf of Lions, with a particularly pronounced effect in December and January. For both the Aegean Sea and Rhodes Gyre, the most prominent correlations were found between the North Atlantic Oscillation and phosphate, with a highly consistent behavior in the 2 areas associated with common physical forcing and exchange of properties among them.

The Role of Tropical, Midlatitude, and Polar Cloud-Radiative Changes for the Midlatitude Circulation Response to Global Warming

AbstractPrevious studies showed that global cloud-radiative changes contribute half or more to the midlatitude atmospheric circulation response to global warming. Here, we investigate the relative importance of tropical, midlatitude, and polar cloud-radiative changes for the annual-mean, wintertime, and summertime circulation response across regions in AMIP-like simulations. To this end, we study global warming simulations from the ICON model run with the cloud-locking method and prescribed sea surface temperatures, which isolate the impact of changes in atmospheric cloud-radiative heating. Tropical cloud changes dominate the global cloud impact on the 850 hPa zonal wind, jet strength, and storm track responses across most seasons and regions. For the jet shift, a more diverse picture is found. In the annual mean and DJF, tropical and midlatitude cloud changes contribute substantially to the poleward jet shift in all regions. The poleward jet shift is further supported by polar cloud changes across the Northern Hemisphere but not in the Southern Hemisphere. In JJA, the impact of regional cloud changes on the jet position is small, consistent with an overall small jet shift during this season. The jet shift can be largely understood via the anomalous atmospheric cloud-radiative heating in the tropical and midlatitude upper troposphere. The circulation changes are broadly consistent with the influence of cloud-radiative changes on upper-tropospheric baroclinicity and thus the mean potential energy available for conversion into eddy kinetic energy. Our results help to explain the jet response to global warming and highlight the importance of tropical and midlatitude cloud-radiative changes for this response.

Middle Miocene long-term continental temperature change in and out of pace with marine climate records

Reconstructing long-term continental temperature change provides the required counterpart to age equivalent marine records and can reveal how terrestrial and marine temperatures were related during times of extreme climate change such as the Miocene Climatic Optimum (MCO) and the following Middle Miocene Climatic Transition (MMCT). Carbonate clumped isotope temperatures (T(Δ47)) from 17.5 to 14.0 Ma Central European paleosols (Molasse Basin, Switzerland) display a temperature pattern during the MCO that is similar to coeval marine temperature records. Maximum temperatures in the long-term soil T(Δ47) record (at 16.5 and 14.9 Ma) lag maximum ocean bottom water temperatures, lead global ice volume, and mark the initiation of minimum global ice volume phases. The suggested onset of the MMCT, deduced by a marked and rapid decline in Molasse Basin soil temperatures is coeval with cooling reported in high-latitudinal marine records. This is best explained by a change in the seasonal timing of soil carbonate formation that was likely driven by a modification of rainfall seasonality and thus by a major reorganization of mid-latitude atmospheric circulation across Central Europe. In particular, our data suggest a strong climate coupling between the North Atlantic and Central Europe already in the middle Miocene.

Drivers of the Northern Extratropical Eddy‐Driven Jet Change in CMIP5 and CMIP6 Models

AbstractThe wintertime midlatitude atmospheric circulation is evaluated in CMIP6 models. The biases have been reduced since CMIP5 although the low‐level flow is still too zonal. CMIP5 and CMIP6 projections of 850 hPa zonal wind are then analyzed and are consistent under the RCP8.5 and the SSP5–8.5 scenarios, respectively. A poleward shift is identified in the Pacific, while a tripole structure is found in the North Atlantic: The zonal wind strengthens over Western Europe and decreases north and south. A multiple linear regression allows us to quantify the contribution of different drivers to the intermodel spread in zonal wind projections. It supports the importance of projected tropical warming and changes in the stratospheric vortex but also suggests a contribution of the asymmetry in the projected surface warming of the equatorial Pacific and of the present‐day biases in the eddy‐driven jet position. The North Atlantic warming hole plays a weaker role.

Robustness and drivers of the Northern Hemisphere extratropical atmospheric circulation response to a CO$$_2$$-induced warming in CNRM-CM6-1

Understanding the mid-latitude atmospheric circulation response to CO$$_2$$ forcing is challenging and complex due to the strong internal variability and the multiple potential CO$$_2$$-induced effects. While a significant poleward shift of the jet is projected in summer, changes remain uncertain in winter. In this study, we investigate the boreal winter extratropical jet response to an abrupt quadrupling of atmospheric CO$$_2$$ in the CMIP6-generation global climate model CNRM-CM6-1. First, we show that the model performs better than the former generation CNRM-CM5 model in representing the atmospheric dynamics in the northern extratropics. Then, when atmospheric CO$$_2$$ is quadrupled, CNRM-CM6-1 exhibits a strengthening and upward shift of the jet. A poleward shift is identified and robust in the Pacific in boreal winter. In the Atlantic, the jet response rather exhibits a squeezing, especially at the eastern part of the basin. It is found that changes are more robust across the Northern Hemisphere in early-winter than in late-winter season. Finally, the circulation response is broken down into individual contributions of various drivers. The uniform global mean component of the SST warming is found to explain most of the total atmospheric response to a quadrupling of CO$$_2$$, with relatively smaller contributions from faster CO$$_2$$ effects, the SST pattern change and the Arctic sea ice decline. The cloud radiative effect contribution is also assessed and found to be rather weak in the CNRM-CM6-1 model. This study highlights that long experiments are required to isolate the wintertime circulation response from the internal variability, and that idealized experimental setups are helpful to disentangle the physical drivers.

Atmospheric Diffusivity: A New Energetic Framework for Understanding the Midlatitude Circulation Response to Climate Change

AbstractThe midlatitude circulation response to climate change is not well understood. Within an energetic framework the circulation is connected to the atmospheric diffusivity. Here we define a novel diagnostic diffusivity framework as a tool for interpreting changes in the midlatitude atmospheric circulation. The diffusivity is computed by dividing the zonally and vertically integrated transient eddy moist static energy (MSE) transport by the zonal‐mean 925 hPa MSE gradient, and we investigate the diffusivity response to global‐scale sea surface temperature (SST) perturbations in aquaplanet and Atmospheric Model Intercomparison Project (AMIP) general circulation model simulations. The midlatitude diffusivity maximum shifts poleward with increasing SST in both the aquaplanet simulations and Southern Hemisphere winter of the AMIP simulations. Our framework indicates that this diffusivity shift is associated with Ferrel circulation and 925 hPa MSE gradient changes, rather than with total MSE transport changes. The MSE gradient‐related shift cannot be understood purely in terms of Clausius‐Clapeyron changes in specific humidity following the global‐mean temperature response, because atmospheric temperature gradients change significantly even when SST gradients are held fixed. The intensity of the diffusivity maximum also increases with SST for the aquaplanet configuration but is relatively insensitive to SST for AMIP Southern Hemisphere winter. Additional energy balance model experiments suggest that while diffusivity changes caused by SST perturbations can be large, their effect on zonal‐mean temperature is minor. Finally, the latitudes and intensities of the diffusivity maxima are strongly correlated with the same properties of the zonal‐mean eddy kinetic energy maxima. However, existing theories cannot adequately explain these linear relationships.

A transient simulation of precession-scale spring dust activity over northern China and its relation to mid-latitude atmospheric circulation

Dust aerosol plays an important role in energy and water cycles of the earth system across multiple spatial and temporal scales, and it is also a key factor in determining air quality in arid and semi-arid areas of Asia. Spring is the season of peak dust activity (i.e. emission, transport, and sedimentation) in Asia. However, on the Earth's orbit scale, spring dust activity in northern China (NC) and its relationship with atmospheric circulation have seldom been investigated. We present the results of an analysis of the evolution characteristic on the astronomical timescale, and dynamic mechanism of spring dust activity in NC, based on a transient numerical simulation over the past 150 kyr spanning multiple precessional cycles. We found that within the precessional band, spring dust transport is in-phase with insolation, the upper Westerly Jet on the north (nWJ) of the Tibetan Plateau (TP), surface wind, and heating of the TP; whereas it is out-of-phase with Siberian high (SH), atmospheric precipitation, and soil water. During the high-insolation stage, the nWJ is strengthened by the thermal forcing of the TP, which causes a northward shift of the location of the Westerly Jet, so that dust activity is enhanced by the propagation of upper-level waves. Meanwhile, during the high-insolation stage, the instability of the lower atmosphere is increased due to the strengthening of the northerly wind associated with the weakening of the SH and surface warming, together with their higher interaction, with the nWJ giving rise to dust mobilization in the Asian arid and semi-arid source areas, and vice versa. Rainfall and soil moisture have little influence on the dust cycle on the orbital scale, although modern observations show they have an important inhibitory effect on dust emission.

Twenty‐First‐Century Changes in the Eastern Mediterranean Etesians and Associated Midlatitude Atmospheric Circulation

AbstractThe Etesians are the dominant synoptically driven winds observed in the Eastern Mediterranean, usually from late spring to late summer. Due to the complex topography, the Etesians can be very strong and pose significant environmental hazards, especially over wildfire incidents. This study assesses the impacts of climate change on future Etesians by analyzing the response of the most recent EURO‐CORDEX regional climate simulations at the 12‐km grid resolution over the twenty‐first century. The mean model ensemble projects a significant increase of the Etesians' frequency and intensity under the two emission scenarios RCP4.5 and RCP8.5. This response is connected to an increase in the zonal wind at 200 hPa, a reinforcement of the midlatitude westerly flow, and a decrease in the wave amplitude. These circulation changes accelerate the mid‐to‐high latitude eastward propagation of the large‐scale circulation systems which can favor enhanced ridges over the Balkans. A strengthening and poleward shift of the subtropical jet stream is also projected, connected with stronger subsidence over the Eastern Mediterranean. The projected changes will have profound environmental and societal implications, including the lengthening of the wildfire season and increasing air pollution risk in the region. On the other hand, the current estimate of future wind power potential in the Aegean Sea will be significantly increased by the end of the century, which might have positive impact in the regional economy.

Amplification of Waveguide Teleconnections in the Boreal Summer

While the influence of climate change on mid-latitude atmospheric circulation remains uncertain, hypotheses based on linear waveguide dynamics have been proposed suggesting amplification of circumglobal quasi-stationary Rossby wave events, which may have led to persistent and high-impact extremes in recent boreal summers. It is thus useful to synthesize these hypotheses and to discuss limitations of this simplified dynamical framework for explaining observed features. The hypothesis that climate change can alter the basic circulation state and thereby enhance circumglobal waveguide teleconnections by increasing their resonance has been proposed but has not yet been verified with models. Furthermore, there is no convincing evidence that the variability of disturbances within the waveguide will increase in future climates projected by the CMIP5 models. On the other hand, recent research indicates that enhanced diabatic heating, particularly that associated with increasing aridity in the mid-latitude, can stimulate the jet stream waveguides, thus suggesting an alternative mechanism which, if properly modeled, could lead to more high-amplitude circumglobal planetary wave events. There could be circumstances that lead to resonant amplification of waveguide Rossby waves in the boreal summer, but an alternative mechanism that involves changes in the forcing rather than the mean state deserves closer attention.

Changes in Arctic moisture transport over the North Pacific associated with sea ice loss

Recent work has emphasized the important role of midlatitude moisture fluxes in enhancing Arctic warming and sea ice loss. Conversely, less attention has been paid to the impact of Arctic warming and sea ice loss on midlatitude moisture fluxes. Analysis of an atmosphere-only general circulation model indicates that sea ice loss promotes changes in the large-scale midlatitude atmospheric circulation that have a substantial impact on moisture transport into and out of the Arctic. While poleward moisture transport into the Arctic does increase in a reduced sea ice climate, the increase in equatorward moisture transport out of the Arctic is larger, particularly in boreal winter over the North Pacific. A decomposition of the meridional moisture transport reveals that this increase in equatorward moisture transport is driven, at least in part, by changes in the background circulation. Specifically, sea ice loss drives a series of large-scale tropospheric circulation changes, including an increase in cyclonic Rossby wave breaking over the North Pacific that results in a preferential enhancement of equatorward moisture transport out of the Arctic in the days following the peak of the Rossby wave breaking event.

The Tibetan Plateau Uplift is Crucial for Eastward Propagation of Madden-Julian Oscillation

The Tibetan Plateau (TP) and Himalayas have been treated as an essential external factor in shaping Asian monsoon and mid-latitude atmospheric circulation. In this study we perform numerical experiments with different uplift altitudes using the Nanjing University of Information Science and Technology Earth System Model to examine potential impacts of uplift of the TP and Himalayas on eastward propagation of the MJO and the associated mechanisms. Analysis of experimental results with dynamics-based MJO diagnostics indicates two potential mechanisms. First, the uplift considerably enhances low-level mean westerlies in the Indian Ocean and convection in the Maritime Continent, which in turn strengthens boundary layer moisture convergence (BLMC) to the east of the MJO convective center. The increased BLMC reinforces upward transport of moisture and heat from BL to free atmosphere and increases lower tropospheric diabatic heating by shallow and congestus clouds ahead of the MJO center, enhancing the Kelvin-Rossby wave feedback. Second, the uplift increases upper tropospheric mean easterlies and stratiform heating at the west of the MJO center, which contributes to eastward propagation of MJO by generating positive moist static energy at the east of MJO center. This study will contribute to a better understanding of the origin of the MJO and improvement in simulation of MJO propagation.

Understanding the inter‐decadal variability of autumn precipitation over North Central China using model simulations

AbstractA recent study has shown a robust relationship between the Pacific Decadal Oscillation (PDO) and inter‐decadal variations in autumn precipitation over North Central China (NCC). However, the physical processes underlying these inter‐decadal precipitation variations are not fully understood. Here we analyse multi‐member ensembles of atmospheric reanalysis and model simulations to examine the atmospheric and precipitation responses to sea surface temperature (SST) forcing. Despite the large inter‐member spread resulting from atmospheric internal variability, the model simulations forced by the observed SSTs show an important role of mid‐latitude atmospheric circulation in influencing the inter‐decadal precipitation variations over NCC. We also analyse the sensitivity experiments using three atmospheric models forced by the Inter‐decadal Pacific Oscillation (IPO)/PDO‐like SST fields. The results suggest that the SST anomalies associated with a negative IPO phase can induce anomalous positive pressure anomalies over the East Asia‐Japan‐North Pacific region, which weakens the East Asian trough (EAT) and produces southerly advection of warm and moist air into NCC, leading to increased precipitation there. This study provides a depiction of how the IPO/PDO‐associated SSTs induce inter‐decadal oscillations in mid‐latitude atmospheric circulations, which in turn cause inter‐decadal precipitation variations over NCC.

Description and basic evaluation of simulated mean state, internal variability, and climate sensitivity in MIROC6

Abstract. The sixth version of the Model for Interdisciplinary Research on Climate (MIROC), called MIROC6, was cooperatively developed by a Japanese modeling community. In the present paper, simulated mean climate, internal climate variability, and climate sensitivity in MIROC6 are evaluated and briefly summarized in comparison with the previous version of our climate model (MIROC5) and observations. The results show that the overall reproducibility of mean climate and internal climate variability in MIROC6 is better than that in MIROC5. The tropical climate systems (e.g., summertime precipitation in the western Pacific and the eastward-propagating Madden–Julian oscillation) and the midlatitude atmospheric circulation (e.g., the westerlies, the polar night jet, and troposphere–stratosphere interactions) are significantly improved in MIROC6. These improvements can be attributed to the newly implemented parameterization for shallow convective processes and to the inclusion of the stratosphere. While there are significant differences in climates and variabilities between the two models, the effective climate sensitivity of 2.6 K remains the same because the differences in radiative forcing and climate feedback tend to offset each other. With an aim towards contributing to the sixth phase of the Coupled Model Intercomparison Project, designated simulations tackling a wide range of climate science issues, as well as seasonal to decadal climate predictions and future climate projections, are currently ongoing using MIROC6.

Winter Arctic warming and its linkage with midlatitude atmospheric circulation and associated cold extremes: The key role of meridional potential vorticity gradient

The surface air temperature over the Eurasian continent has exhibited a significant cooling trend in recent decades (1990–2013), which has occurred simultaneously with Arctic warming and Arctic sea ice loss. While many studies demonstrated that midlatitude cold extremes are linked to Arctic warming and Arctic sea ice loss, some studies suggest that they are unrelated. The causal relationship between midlatitude cold extremes and Arctic change is uncertain, and it is thus an unsolved and difficult issue. It has been widely recognized that the severity and location of midlatitude cold extremes are closely related to the persistence, location and movement of blocking systems. It might be possible that the Arctic sea ice decline or the Arctic’s warming influences midlatitude cold extremes by changing the blocking system. This paper reviews the recent research advances on the linkages between the blocking system and Arctic warming. The nonlinear multiscale interaction model of Luo et al. revealed that the magnitude of the meridional gradient (PVy) of the background potential vorticity (PV) is a key parameter that reflects changes in the dispersion and nonlinearity of the blocking system. It was found that Arctic warming played a role in reducing the dispersion of the blocking system and enhancing its nonlinearity by reducing the magnitude of PVy. A small PVy is a favorable background condition for increasing the duration of blocking events and producing midlatitude cold extremes. However, because the magnitude of PVy reflects the difference between the background PV of the Arctic high latitudes and the midlatitude continent, the occurrence of midlatitude cold extremes not only depends on an anomalous background PV over Arctic high latitudes but also on its value over the midlatitudes. Thus, Arctic warming or sea ice decline is not necessary for the occurrence of midlatitude cold extremes.

Impacts of the North Atlantic Warming Hole in Future Climate Projections: Mean Atmospheric Circulation and the North Atlantic Jet

AbstractIn future climate simulations there is a pronounced region of reduced warming in the subpolar gyre of the North Atlantic Ocean known as the North Atlantic warming hole (NAWH). This study investigates the impact of the North Atlantic warming hole on atmospheric circulation and midlatitude jets within the Community Earth System Model (CESM). A series of large-ensemble atmospheric model experiments with prescribed sea surface temperature (SST) and sea ice are conducted, in which the warming hole is either filled or deepened. Two mechanisms through which the NAWH impacts the atmosphere are identified: a linear response characterized by a shallow atmospheric cooling and increase in sea level pressure shifted slightly downstream of the SST changes, and a transient eddy forced response whereby the enhanced SST gradient produced by the NAWH leads to increased transient eddy activity that propagates vertically and enhances the midlatitude jet. The relative contributions of these two mechanisms and the details of the response are strongly dependent on the season, time period, and warming hole strength. Our results indicate that the NAWH plays an important role in midlatitude atmospheric circulation changes in CESM future climate simulations.

Strengthened linkage between midlatitudes and Arctic in boreal winter

Early studies have suggested a linkage between the surface warming over the Barents-Kara Seas and the strength of the Siberian high in boreal winter. Here, we show that the linkage is not stable, and with an apparent interdecadal change in the late-1990s. Coinciding with Arctic surface warm anomalies in recent decades (1997–2017), the Siberian high has been significantly intensified, the East Asian jet stream has expanded westward, and an apparent Rossby wave has propagated from the Arctic to East Asia, suggesting an atmospheric teleconnection between midlatitudes and Arctic. In contrast, midlatitude atmospheric circulation anomalies coinciding with Arctic surface warm anomalies were barely statistically significant during 1979–1996. The associated strong anomalous ascending/descending motions and divergent/convergent upper troposphere air masses over the Arctic-Eurasian sector seem to have favored the midlatitude-Arctic linkage during 1997–2017. We further hypothesize that Arctic mid-tropospheric warming plays a crucial role for the linkage between midlatitudes and Arctic in boreal winter. Multi-model simulations support this, and also point to internal atmospheric variability as the cause for the interdecadal shift in the strength of the midlatitude-Arctic linkage.

A Study of the Cross-Scale Causation and Information Flow in a Stormy Model Mid-Latitude Atmosphere.

A fundamental problem regarding the storm–jet stream interaction in the extratropical atmosphere is how energy and information are exchanged between scales. While energy transfer has been extensively investigated, the latter has been mostly overlooked, mainly due to a lack of appropriate theory and methodology. Using a recently established rigorous formalism of information flow, this study attempts to examine the problem in the setting of a three-dimensional quasi-geostrophic zonal jet, with storms excited by a set of optimal perturbation modes. We choose for this study a period when the self-sustained oscillation is in quasi-equilibrium, and when the energetics mimick the mid-latitude atmospheric circulation where available potential energy is cascaded downward to smaller scales, and kinetic energy is inversely transferred upward toward larger scales. By inverting a three-dimensional elliptic differential operator, the model is first converted into a low-dimensional dynamical system, where the components correspond to different time scales. The information exchange between the scales is then computed through ensemble prediction. For this particular problem, the resulting cross-scale information flow is mostly from smaller scales to larger scales. That is to say, during this period, this model extratropical atmosphere is dominated by a bottom-up causation, as collective patterns emerge out of independent entities and macroscopic thermodynamic properties evolve from random molecular motions. This study makes a first step toward an important field in understanding the eddy–mean flow interaction in weather and climate phenomena such as atmospheric blocking, storm track, North Atlantic Oscillation, to name a few.

Pacific climate influences on ocean conditions and extreme shell growth events in the Northwestern Atlantic (Gulf of Maine)

The Gulf of Maine is undergoing rapid environmental and ecological changes, yet our spatial and temporal understanding of the climatic and hydrographic variability in this region, including extreme events, is limited and biased to recent decades. In this study, we utilize a highly replicated, multi-century master shell growth chronology derived from the annual increments formed in the shells of the long-lived bivalve Arctica islandica collected in 38 m from the central coastal region in the Gulf of Maine. Our results indicate that shell growth is highly synchronous and inversely related to local seawater temperatures. Using composite analyses of extreme shell growth events from CE 1900 to 2013, we extend our understanding of the factors driving oceanic variability and shell growth in the Northwestern Atlantic back to CE 1761. We suggest that extreme shell growth events are primarily controlled by Gulf of Maine sea surface temperature (SST) and stratification conditions, which in turn appear to be largely influenced by SST patterns in the Pacific Ocean through their influence on mid-latitude atmospheric circulation patterns and the location of the eddy-driven jet. The large-scale jet dynamics during these extreme years manifest as precipitation and moisture transport anomalies and regional SST conditions in the Gulf of Maine that either enhance or inhibit shell growth. Pacific climate variability is thus an important, yet understudied, influence on Gulf of Maine ocean conditions.

California Winter Precipitation Predictability: Insights From the Anomalous 2015–2016 and 2016–2017 Seasons

AbstractThe unexpected dry 2015–2016 El Niño winter and extremely wet 2016–2017 La Niña winter in California challenged current seasonal prediction systems. Using the Met Office GloSea5 forecast ensemble, we study the precipitation and circulation differences between these seasons and identify processes relevant to California precipitation predictions. The ensemble mean accurately predicts the midlatitude atmospheric circulation differences between these years, indicating that these differences were predictable responses to the strong oceanic forcing differences. The substantial California precipitation differences were poorly predicted with large uncertainty. Notable differences in high‐latitude circulation anomalies associated with internal variability distinguish the ensemble members that successfully simulate precipitation from those that do not. Specifically, accurate representation of the Arctic Oscillation phase differences improves the accuracy of simulated precipitation differences but these differences were not well predicted in the ensemble mean for these seasons. Improved representation of high‐latitude processes such as the Arctic Oscillation and polar‐midlatitude teleconnections could therefore improve California seasonal predictions.