Sea Surface Temperature Response Research Articles

Rapid high-latitude cooling in the southeastern Pacific sector driven by North Atlantic warming during 1979–2013 in CESM1

During the 1979–2013 satellite observation period, the sea surface temperature (SST) has cooled substantially in the high-latitude Southern Ocean, with the most pronounced cooling tendency centered in the southeastern Pacific domain. Previous hypotheses have commonly ascribed the recent Southern Ocean cooling to either the tropical eastern Pacific cooling or North Atlantic and tropical Indian Ocean SST warming. However, the mechanisms underpinning significant cooling in the southeastern Pacific sector remain debatable. By diagnosing three pacemaker experiments with a state-of-the-art global climate model in which SSTs in the North Atlantic, tropical central-eastern Pacific, and tropical Indian Ocean-western Pacific are individually nudged to mimic the observed trajectory, we show that the North Atlantic dominates in the cold SST response of the southeastern Pacific sector during 1979–2013. Anomalous North Atlantic warming initiates a quasi-stationary Rossby wave response to a south-to-north cross-equatorial Hadley circulation strengthening, leading to an enhanced Amundsen Sea Low. As a result, due primarily to the increased low-level marine cloud cover, the net surface shortwave radiation reduction triggers rapid SST cooling in the southeastern Pacific domain. The southeastern Pacific cold SST anomalies are further maintained via the shortwave radiation-low-cloud-SST positive feedback on decadal timescales. Our results suggest that the shortwave radiation-low-cloud SST feedback is fundamental to the observed long-term cooling of the high-latitude Southern Ocean, with profound climate consequences worldwide.

The Role of the Subtropical and Extratropical Southern Hemisphere Anomalous Sea Surface Temperature in the Trans‐Seasonal Influence of Southern Annular Mode on Rainfall Over Southeastern South America

AbstractThe current study explores the linkage and possible mechanisms of the Southern Annular Mode (SAM) with rainfall variability over southeastern South America (SESA). The findings indicate that the preceding May SAM can modulate the subsequent rainfall over the SESA region in September‐October‐November (SON), independent of the El Niño‐Southern Oscillation (ENSO) signal. Further analysis suggests that the SAM‐rainfall relationship is mainly due to the response of sea surface temperature (SST) in the subtropical and extratropical Southern Hemisphere to SAM variability via air‐sea interactions. Such SST anomalies persist to the subsequent SON and stimulate an upstream wave train extending into the study region from the South Pacific. Such wave patterns form a cyclone anomaly over SESA, indicating strong subsidence and reduced convection over the region. Meanwhile, the low‐level anomalous cyclone and anticyclone located over the subtropical South Atlantic (on the coast of the study region) are associated with easterly winds to the South (North) of the anomalous cyclone (anticyclone), which advect colder and drier air into the study region due to the cold SST over the subtropical South Atlantic and leading to increased moisture scarcity and decreased rainfall over SESA. Besides, model results based on the joint climate indices (i.e., SAM, ENSO and Indian Ocean Dipole (IOD)) revealed a satisfactory estimate of the SON rainfall compared with either single index, indicating that the SAM can be one of the precursors of the SESA rainfall, besides ENSO and IOD.

Strengthened impact of boreal winter North Pacific Oscillation on ENSO development in warming climate

The North Pacific Oscillation (NPO), an important mode of atmospheric variability, is a crucial trigger for the development of El Niño-Southern Oscillation (ENSO) via the seasonal footprinting mechanism. How the NPO effect on ENSO changes in response to greenhouse warming remains unclear, however. Here, using climate model simulations under high-emission scenarios, we show that greenhouse warming leads to an enhanced influence of NPO on ENSO as is manifested by enhanced responses of winter sea surface temperature (SST), precipitation and wind anomalies in the equatorial Pacific to the preceding winter NPO. The strengthened NPO impact is also reflected in an increased frequency of NPO events that are followed by ENSO events. Warmer background SST enhances the wind-evaporation-SST feedback over the subtropical North Pacific due to a nonlinear SST-evaporation relationship. This strengthens the NPO-generated surface zonal wind anomalies over the equatorial western-central Pacific, which trigger ENSO. Increased impact of winter NPO on ENSO could enable prediction of interannual variability at longer leads.

Typhoon-Induced Extreme Sea Surface Temperature Drops in the Western North Pacific and the Impact of Extra Cooling Due to Precipitation

Sea surface temperature (SST) responses have been perceived as crucial to consequential tropical cyclone (TC) intensity development. In addition to regular cooling responses, a few TCs could cause extreme SST drops (ESSTDs) (e.g., SST drops more than 6 °C) during their passage. Given the extreme temperature differences and the consequentially marked air–sea flux modulations, ESSTDs are intuitively supposed to play a serious role in modifying TC intensities. Nevertheless, the relationship between ESSTDs and consequential storm intensity changes remains unclear. In this study, satellite-observed microwave SST drops and the International Best Track Archive for Climate Stewardship TC data from 2001 to 2021 were used to elucidate the relationship between ESSTDs and the consequential TC intensity changes in the Western North Pacific typhoon season (July–October). Subsequently, the distributed characteristics of ESSTDs were systematically examined based on statistical analyses. Among them, Typhoon Kilo (2015) triggered an unexpected ESSTD behind its passage, according to existing theories. Numerical experiments based on the Regional Ocean Modeling System were carried out to explore the possible mechanisms that resulted in the ESSTD due to Kilo. The results indicate that heavy rainfall leads to additional SST cooling through the enhanced sensible heat flux leaving the surface layer in addition to the cooling from momentum-driven vertical mixing. This process enhanced the sensible heat flux leaving the sea surface since the temperature of the raindrops could be much colder than the SST in the tropical ocean, specifically under heavy rainfall and relatively less momentum entering the upper ocean during Kilo.

Revisiting the equatorial Pacific sea surface temperature response to global warming

Revisiting the equatorial Pacific sea surface temperature response to global warming

Tropical Cyclone-Induced Sea Surface Temperature Responses in the Northern Indian Ocean

Tropical cyclones (TCs) exert a significant influence on the upper ocean, leading to sea surface temperature (SST) changes on a global scale. However, TC-induced SST responses exhibit considerable variability in the northern Indian Ocean (NIO), and the general understanding of these responses remains limited. This paper investigates the SST changes caused by 96 TCs over an 18-year period in the NIO. Through a composite analysis utilizing satellite SST data, a comprehensive study is conducted to examine the relationship between TC characteristics, including wind speed and translation speed, and the associated SST changes. The overall findings reveal that within a radius of 300 km from the TC center, SST decreases were observed at 1702 (86%) locations, with an average SST response to TC of −0.46 °C and a maximum decrease of −2.07 °C. The most significant reduction in SST typically occurred two days after the passage of TCs, followed by a gradual recovery period exceeding 15 days for the SSTs to return to their initial values. Consistent with findings in other ocean basins, stronger and slower-moving TCs induced more substantial cooling effects. Conversely, at 279 (14%) locations, particularly associated with TCs of weaker intensities, SST increases were observed following the TC passage. Notably, 140 of these locations were situated at low latitudes, specifically between 8° N and 15° N. This study provides a quantitative analysis of the comprehensive SST response to TCs in the NIO.

Impacts of tidal mixing on diurnal and intraseasonal air-sea interactions in the Maritime Continent

The Maritime Continent (MC) is a region with enhanced tidal mixing and ocean cooling, which influences regional-scale sea surface temperatures (SSTs). We examine the coupled impacts of tidal mixing on near-surface stratification, SST, and deep convection on diurnal and intraseasonal time-scales, using ensembles of high-resolution, coupled ocean-atmosphere regional model simulations, with and without tidal forcing. Results show that the area-averaged SST in the eastern MC is reduced by 0.20 °C due to tidal forcing, with cooling exceeding 1 °C in the nearshore zones of shallow and complex bathymetry. The reduced SSTs decrease surface heat fluxes, leading to tropospheric drying and reduced precipitation, which are most pronounced in the nearshore zones. The results show that the magnitude of tidally-induced SST cooling is phase-dependent during the passage of the Madden Julian Oscillation (MJO). Strong westerly winds enhance entrainment cooling through wind-driven mixing and upwelling during the active phase. Conversely, the upper-ocean stratification is enhanced during the suppressed phase, and SSTs are less sensitive to subsurface cooling. Such spatio-temporal variability in the SST response to tides is accompanied by consistent changes to deep convection and atmospheric circulation. On the diurnal time-scale, nearshore cooling weakens the early-morning convection when the land-based convection propagates offshore and interacts with the cooler SST. On intraseasonal time-scales, the coupling between SST and precipitation is strengthened because of the asymmetric impacts of tide-induced mixing on SST and MJO-induced winds. The robust SST and precipitation responses demonstrated in this study suggest the need for an accurate representation of tidal forcing and vertical mixing processes in local MJO prediction models for the MC.

The Role of Bjerknes and Shortwave Feedbacks in the Tropical Pacific SST Response to Global Warming

AbstractThe evolution of tropical sea surface temperatures (SSTs) in response to greenhouse warming is of great societal and scientific interest. Most state‐of‐the‐art climate models predict a mean “El Niño‐like” warming pattern by century‐end, characterized by greater warming over the Pacific cold tongue compared to the western warm pool. However, it is unclear which proposed mechanism dominates in this response. Here, we present partially coupled abrupt CO2 doubling experiments in which surface wind stress and shortwave heating are overridden to values from a control simulation. Contrary to previous studies, we find that experiments with overriding of surface wind stress exhibit only 58% of the full reduction in east‐west SST contrast. When both surface wind stress and shortwave flux are overridden, only 34% of the full reduction remains, controlled by spatially‐varying evaporative cooling. These results underscore the importance of Bjerknes and shortwave feedbacks in the tropical Pacific SST response to global warming.

Consistency of Intra-Centennial Oscillations in Length of Day and Oceanic Characteristics

The paper presents analysis of intra-centennial (inter-decadal and multidecadal) variations of the length of day (LOD) and some oceanic parameters such as sea surface temperature (SST) and sea level (SL). Methods of multivariate regression analysis and correlation analysis are used. Results of the regression analysis show a spatially coherent response of SST to LOD variations on the multidecadal time scale. The earlier response is peculiar to the north and tropical Atlantic where the multidecadal SST variations are approximately opposite to the LOD variations. In the most remaining parts of the oceans, except especially in the Nino 3.4 region of the equatorial east Pacific, the multidecadal SST variations are generally lagged relative to the antiphase variations of the LOD. Smoothing of SST averaged over different areas and of the global mean SL shows that the intra-annual variations include inter-decadal, 20–30-year, multidecadal, 60–70-year, components that correspond to similar oscillation components in the LOD. The most striking correspondence of the two components is observed between the LOD and SST averaged over the Nino 3.4 region. Generally, there are significant correlations of the intra-centennial variations on the averaged and smoothed SST series and global mean SL with the LOD variations. We propose that angular momentum exchange processes involving oceanic circulation and interactions between the Earth’s core and the mantle play probably a part in the observed relationships of intra-centennial variations in oceanic parameters with variations in the LOD.

Predicting Tropical Cyclone‐Induced Sea Surface Temperature Responses Using Machine Learning

AbstractThis study proposes to construct a model using random forest method, an efficient machine learning‐based method, to predict the spatial structure and temporal evolution of the sea surface temperature (SST) cooling induced by northwest Pacific tropical cyclones (TCs), a process of the so‐called wind pump. The predictors in use include 12 predictors related to TC characteristics and pre‐storm ocean conditions. The model is shown to skillfully predict the spatiotemporal evolutions of the cold wake generated by TCs of different intensity groups, and capture the cross‐case variance in the observed SST response. Another model is further built based on the same method to assess the relative importance of the 12 predictors in determining the magnitude of the maximum cooling. Computations of feature scores of those predictors show that TC intensity, translation speed and size, and pre‐storm mixed layer depth and SST dominate, depending on the area where the cooling is considered.

Model‐Dependent Atlantic Multidecadal Variability Modulations on North Pacific Sea Surface Temperature Variability and Decadal Prediction

AbstractPrevious studies suggested that Atlantic Multidecadal Variability (AMV) modulations on pan‐Pacific sea surface temperature (SST) variability and prediction are model‐dependent. These results were mainly based on SST forcing experiments in which AMV‐related Atlantic SST anomalies were prescribed. However, the AMV itself is also model‐dependent, but its influences on the Pacific remain unclear. Here, we use multi‐model fully coupled experiments from the Coupled Model Intercomparison Project Phase 6 (CMIP6), along with observations, to study the model‐dependent AMV trans‐basin effects. We found that AMV strength is a key factor: Stronger (Weaker) model AMV than observations overestimates (underestimates) SST response and decadal prediction skills, mainly in the North Pacific. The reason is that stronger positive phased AMV, for example, leads to higher sea level pressure anomalies over the North Pacific, which lifts sea surface height and deepens thermocline to warm SST. Our study highlights the necessity to improve simulations of AMV strength.

Fast and Slow Responses of the Tropical Pacific to Radiative Forcing in Northern High Latitudes

Abstract This study investigates the transient evolution of tropical Pacific sea surface temperature (SST) responses to a constant northern high-latitude solar heating in fully coupled CESM 1.2. The study identifies two stages through multiple ensemble runs. 1) In the first 3 years, a hemispherically asymmetric pattern emerges, caused by air–sea interactions associated with the anomalous cross-equatorial Hadley cell. The northern tropics experience warming that is blocked north of the equator by the intertropical convergence zone. The southeast Pacific cooling reaches the equatorial region and is amplified by the equatorial Ekman divergence. 2) Within a decade, the equatorial cooling is replaced by warming in the eastern equatorial basin. The anomalous warming that appears faster than the time scales of the oceanic ventilation is attributed to anomalous meridional heat convergence and weakening of the northern subtropical cell. Our findings highlight the influence of ocean dynamics on the temporal and spatial evolution of tropical SST response to hemispherically asymmetric heating. The initial cooling caused by Ekman divergence delays the arrival of slow warming, while initial wind and temperature anomalies set the stage for the weakening of the subtropical cell. The results have important implications for understanding the evolution of tropical SST patterns in observational records and future climate change simulations, as they show strong interhemispheric temperature asymmetry in the extratropics.

Response of high-altitude clouds to the galactic cosmic ray cycles in tropical regions

Galactic cosmic rays are one of the possible mediators of the solar influence on climate. However, the impacts of GCR on clouds and climate systems are not fully understood. In this paper, we show that the high-altitude clouds associated with deep convective activities are responding to the decadal-scale cycles of GCRs and that the susceptible areas are seasonally variable. Most notable responses were found in August over tropical land areas, suggesting that the susceptivity of clouds to GCRs depends on the depth of convective activities and the abundance of aerosol precursor materials. Furthermore, following the activation of high-altitude cloud formation, an increase in sea surface temperature (SST) gradient was observed over the Pacific. Although the response of sea surface temperature to solar activity has mostly been discussed as mediated by solar radiations, we propose that another mechanism is possible: through the impact of GCRs on clouds and the resultant changes in atmospheric circulations.

Response of the sea surface temperature to heatwaves during the France 2022 meteorological summer

Abstract. The summer of 2022 was memorable and record-breaking, ranking as the second hottest summer in France since 1900, with a seasonal surface air temperature average of 22.7 ∘C. In particular, France experienced multiple record-breaking heatwaves during the meteorological summer. As the main heat reservoir of the Earth system, the oceans are at the forefront of events of this magnitude which enhance oceanic disturbances such as marine heatwaves (MHWs). In this study, we investigate the sea surface temperature (SST) of French maritime basins using remotely sensed measurements to track the response of surface waters to the atmospheric heatwaves and determine the intensity of such feedback. Beyond the direct relationship between SSTs and surface air temperatures, we explore the leading atmospheric parameters affecting the upper-layer ocean heat budget. Despite some gaps in data availability, the SSTs measured during the meteorological summer of 2022 were record-breaking, the mean SST was between 1.3 and 2.6 ∘C above the long-term average (1982–2011), and the studied areas experienced between 4 and 22 d where the basin-averaged SSTs exceeded the maximum recorded basin-averaged SSTs from 1982 to 2011. We found a significant SST response during heatwave periods with maximum temperatures measured locally at 30.8 ∘C in the north-western Mediterranean Sea. Our results show that in August 2022 (31 July to 13 August), France experienced above-average surface solar radiation correlated with below-average total cloud cover and negative wind speed anomalies. Our attribution analysis based on a simplified mixed-layer heat budget highlights the critical role of ocean–atmosphere fluxes in initiating abnormally warm SSTs, while ocean mixing plays a crucial role in the cessation of such periods. We find that the 2 m temperatures and specific humidity that are consistently linked to the advection of warm and moist air masses are key variables across all the studied regions. Our results reveal that the influence of wind on heatwaves is variable and of secondary importance. Moreover, we observe that the incident solar radiation has a significant effect only on the Bay of Biscay (BB) and the English Channel (EC) areas. Our study findings are consistent with previous research and demonstrate the vulnerability of the Mediterranean Sea to the increasing frequency of extreme weather events resulting from climate change. Furthermore, our investigation reveals that the recurring heatwave episodes during the summer of 2022 had an undeniable impact on all the surveyed maritime areas in France. Our study therefore provides valuable insights into the complex mechanisms underlying the ocean–atmosphere interaction and demonstrates the need for an efficient and sustainable operational system combining polar-orbiting and geostationary satellites to monitor the alterations that threaten the oceans in the context of climate change.

Drivers of low-frequency Sahel precipitation variability: comparing CMIP5 and CMIP6 ensemble means with observations

Phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6) both grossly underestimate the magnitude of low-frequency Sahel rainfall variability; but unlike CMIP5, CMIP6 mean historical precipitation does not even correlate with observed multi-decadal variability. We demarcate realms of simulated physical processes that may induce differences between these ensembles and prevent both from explaining observations. We partition all influences on simulated Sahelian precipitation variability into (1) teleconnections from sea surface temperature (SST); (2) atmospheric and (3) oceanic variability internal to the climate system; (4) the SST response to external radiative forcing; and (5) the “fast” (not mediated by SST) precipitation response to radiative forcing. In a vast improvement from previous ensembles, the mean spectral power of Sahel rainfall in CMIP6 atmosphere-only simulations is consistent with observed low-frequency variance. Low-frequency variability is dominated by teleconnections from observed global SST, and the fast response only hurts the performance of simulated precipitation. We estimate that the strength of simulated teleconnections is consistent with observations using the previously-established North Atlantic Relative Index (NARI) to approximate the role of global SST, and apply this relationship to the coupled ensembles to infer that both fail to explain low-frequency historical Sahel rainfall variability mostly because they cannot explain the observed combination of forced and internal variability in North Atlantic SST. Yet differences between CMIP5 and CMIP6 in mean Sahel precipitation and its correlation with observations do not derive from differences in NARI, but from the fast response or the role of other SST patterns.

The future of the El Niño–Southern Oscillation: using large ensembles to illuminate time-varying responses and inter-model differences

Abstract. Future changes in the El Niño–Southern Oscillation (ENSO) are uncertain, both because future projections differ between climate models and because the large internal variability of ENSO clouds the diagnosis of forced changes in observations and individual climate model simulations. By leveraging 14 single model initial-condition large ensembles (SMILEs), we robustly isolate the time-evolving response of ENSO sea surface temperature (SST) variability to anthropogenic forcing from internal variability in each SMILE. We find nonlinear changes in time in many models and considerable inter-model differences in projected changes in ENSO and the mean-state tropical Pacific zonal SST gradient. We demonstrate a linear relationship between the change in ENSO SST variability and the tropical Pacific zonal SST gradient, although forced changes in the tropical Pacific SST gradient often occur later in the 21st century than changes in ENSO SST variability, which can lead to departures from the linear relationship. Single-forcing SMILEs show a potential contribution of anthropogenic forcing (aerosols and greenhouse gases) to historical changes in ENSO SST variability, while the observed historical strengthening of the tropical Pacific SST gradient sits on the edge of the model spread for those models for which single-forcing SMILEs are available. Our results highlight the value of SMILEs for investigating time-dependent forced responses and inter-model differences in ENSO projections. The nonlinear changes in ENSO SST variability found in many models demonstrate the importance of characterizing this time-dependent behavior, as it implies that ENSO impacts may vary dramatically throughout the 21st century.

Deep learning approach for forecasting sea surface temperature response to tropical cyclones in the Western North Pacific

Tropical cyclones (TCs) induce sea surface temperature cooling (SSTC), which is important for TC development itself as well as for variations of regional air-sea environment. TC-induced SSTC patterns and its prediction is still a challenge. In this study, a long short-term memory neural network deep learning model is developed to forecast TC-induced SSTC in the western North Pacific (WNP) using TCs during 2002–2016 as training cases and TCs during 2017–2018 as prediction and test cases. The 6-h TC-induced SSTC biases to the right-rear area of TC center, with a maximum of ∼0.6 °C on average, while SSTC is greater in higher latitudes than lower latitudes. The input variables for the deep learning model are surface wind at 10 m (U10 and V10), sea surface height (SSH), sea surface temperature (SST), and temperature at 100 m depth (T100), the output variable is SST 6 h after TCs. The model can predict TC-induced SSTC patterns, with an average mean absolute error of ∼0.081 °C, a root mean square error of ∼0.126 °C and a spatial anomaly correlation coefficient of ∼0.948. This work indicates that post-TC SSTC follows similar physical processes and nonlinear relationships with TC wind, initial SSH and ocean temperature, especially in deep-water regions. Although with some limitations, the deep learning model has the potential to be applied to operational forecasts.

Relationships between the Hadley circulation and tropical sea surface temperature with different meridional structures simulated in CMIP6 models

The variability of the Hadley Circulation (HC) is greatly impacted by the meridional structure of sea surface temperature (SST), which has varied effects depending on its symmetrical or asymmetrical pattern relative to the equator. By using the Coupled Comparison Program International Project Phase 6 (CMIP6) model outputs and reanalysis datasets, this study assesses the capacity of CMIP6 models to simulate the relationship between the HC and tropical SST under different meridional structures, as well as investigates the possible causes for simulation biases. It is shown that the CMIP6 models can successfully reproduce climatological HC, tropical SST, and their spatial patterns of first leading modes under different meridional structures, where the correlation coefficient between simulations and observations reaches 0.8 or above. By comparison, the CMIP6 model outputs exhibit substantial differences in simulating the HC to SST response over the different meridional structures, with obvious inter-model differences. Considering the capability in simulating the HC to tropical SST response, the CMIP6 models are divided into two types, Type I model and Type II model. Models of Type I are those whose simulation results are basically close to the reanalysis data, with the biases being less than 20%. The models of Type II are those whose simulated response ratios are much stronger than those of the reanalysis. It is found that the models of Type II overestimate the intensity of El Niño-Southern Oscillation (ENSO) events, and remarkably underestimate the HC and SST correlation in the equatorial symmetric part, resulting in the inability of the models of Type II to capture the connection of the HC and tropical SST. The results indicate that, the component of the CMIP6 models in reproducing the ENSO events has a considerable impact on the simulation of the HC and tropical SST relationship, which offers recommendations for enhancing the capability of models to simulate large-scale tropical air-sea interactions.

Modulation of Cyclones With Tropical and Extratropical Origins by Mesoscale SSTs in the Kuroshio Extension Region

AbstractTwo typical classes of cyclones originating from the tropics (ToCs) and extratropics (EoCs) with distinct preconditions, and passing the Kuroshio Extension (KE) region in cold season in the North Pacific are detected and tracked based on high‐resolution atmospheric simulations with and without mesoscale sea surface temperature (SST) forcing. A comparison between ToC‐to‐mesoscale SST and EoC‐to‐mesoscale SST responses indicates that the different cyclone development and the environmental water vapor restoration in the KE are primarily attributed to different ToC and EOC's preconditions. The higher initial intensity of ToCs leads to stronger atmospheric response to mesoscale SSTs and extended cyclone growth whilst the colder and drier precondition of EoCs induces stronger water vapor restoration in the KE after EoCs passing‐by. It is further demonstrated that the water vapor restoration is dominated by moisture convergence. The study provides new insights into the physical understanding of mesoscale SSTs' influence on cyclogenesis in the midlatitudes.

Changes in Sea Surface Temperature and Sea Ice Concentration in the Arctic Ocean over the Past Two Decades

With global warming, the decrease in sea ice creates favorable conditions for Arctic activities. Sea surface temperature (SST) is not only an important driven factor of sea ice concentration (SIC) changes but also an important medium of the ocean–atmosphere interaction. However, the response of sea surface temperature to Arctic sea ice varies in different sea areas. Using the optimal interpolated SST data from the National Centers for Environmental Information (NCEI) and SIC data from the University of Bremen, the temporal and spatial characteristics of SST and SIC in the Arctic above 60°N and their relationship are studied, and the melting and freezing time of sea ice are calculated, which is particularly important for the prediction of Arctic shipping and sea ice. The results show that (1) the highest and lowest monthly mean Arctic SST occur in August and March, respectively, while those of SIC are in March and September. The maximum trends of SST and SIC changes are in autumn, which are +0.01 °C/year and −0.45%/year, respectively. (2) There is a significant negative correlation between the Arctic SST and SIC with a correlation coefficient of −0.82. (3) The sea ice break-up occurs on Day of the Year (DoY) 143 and freeze-up occurs on DoY 296 in the Arctic. The melting and freezing processes lasted for 27 days and 14 days, respectively. (4) The Kara Sea showed the strongest trend of sea ice melting at −1.22 d/year, followed by the Laptev Sea at −1.17 d/year. The delay trend of sea ice freezing was the most significant in the Kara Sea +1.75 d/year, followed by the Laptev Sea +1.70 d/year. In the Arctic, the trend toward earlier melting of sea ice is smaller than the trend toward later freezing.