Generative Adversarial Network for Reconstructing Diurnal Sea Surface Temperature using Satellite Data over North-west Pacific

This study aims to investigate diurnal sea surface temperature (SST) rise in Mutsu Bay, and its relationship with the local atmospheric field. First, the characteristics of diurnal SST warming is revealed, using satellite and buoy data during 1995-2000. Satellite observations can clearly capture large diurnal SST rise that reaches a few degrees, and clarify the spatial distribution of the SST rise. The diurnal variation of the satellite-derived SST will reflect that of skin SST, which is defined as the temperature of the top layer with the thickness of a few tens micrometers. The analysis of the bulk SST observed with buoys at 1-m depth reveals that the frequency of large diurnal amplitude of SST (ΔSST) appearance becomes high from April to August, and the bulk ΔSST exceeds 1.0 K in some places in the bay for 71% of the days in July. Over the bay, surface air temperature in the daytime is higher than the bulk SST on average in April-August. From spring to summer the wind becomes weaker, and the easterly wind becomes frequent. The weak wind plays a role in promoting the diurnal SST rise, and the warm air-temperaturemay also secondarily contribute to large ΔSST.A model experiment is then performed to examine a local atmospheric circulation that develops around the bay under a clear and calm condition in summer, and to address the interaction between the circulation, and the diurnal SST warming. A local circulation forced by the land surface solar heating of this area produces the weak easterly surface wind and the subsidence of the air, and makes the air warmer over the bay. This is consistent with the observational results. In such a case, the diurnal rise of skin SST simulated by an ocean model exceeds 2 K all over the bay, and it is especially large in the northeastern area. If the diurnal skin SST rise is considered in the atmospheric model, although the circulation pattern does not change, the circulation becomes weaker and the surface air temperature increases. This result suggests that the diurnal SST variation will be important for the practical prediction of air temperature in coastal areas.

Estuarine temperature variability: Integrating four decades of remote sensing observations and in-situ sea surface measurements

Sea surface temperature (SST) variability in the equatorial Pacific plays a crucial role in shaping global climate patterns. As El Niño–Southern Oscillation (ENSO)‐related extremes intensify, understanding SST fluctuations and their connection to ENSO becomes increasingly important. However, limited instrumental records hinder the ability to simulate SST variability and distinguish natural variability from anthropogenic trends. Tree rings provide annual data essential for reconstructing past SST and ENSO dynamics. While previous research has successfully reconstructed SST variability in the central equatorial Pacific, capturing signals from the eastern Pacific remains more challenging. This study analyzes P . rodolfovasquezii trees from the central Peruvian Andes (11.72°S, 75.14°W) using ring width and stable oxygen and carbon isotopes to assess their sensitivity to Pacific SST variability. We focus on the two leading modes of SST variability derived from Empirical Orthogonal Functions: EOF1 representing SST variability in the Niño 3.4 region, and EOF2 depicting a west‐east dipole between the Niño 4 and 1 + 2 regions, explaining 66.22% and 10.79% of the variance in tropical Pacific SSTs, respectively. We developed a 129‐year multiproxy tree‐ring record. Trees' sensitivity to local and regional hydroclimate is reflected in the temporal variability of their isotopic content. Tree‐ring oxygen isotopes showed significant correlations with both SST modes, although their ability to capture EOF2 variability was limited—likely due to the trees' distance from the influence region of the Niño 1 + 2. Overall, oxygen isotopes outperformed ring width and carbon isotopes, underscoring their potential for future SST reconstructions in the tropical Andes.

Diurnal Sea Surface Temperature (SST) variations and the near-surface thermal structure of the tropical hot event (HE) have been investigated using advanced in-situ equatorial observations with hourly temporal resolution. The information on the HE area defined by the satellite cloud-free SSTs is used to sample the in-situ observations. The in-situ SSTs sampled for the HE conditions show that a maximum (minimum) SST has a histogram mode at 30.8°C (29.0°C), and frequently appears at 15:00 (07:00) local time. The amplitude of the diurnal SST variation (DSST) is defined by the difference between the maximum and minimum SSTs. The mean DSST during HEs is greater than 0.5°C, and has a maximum of about 0.75°C at the HE peak. The time series of mean DSST gradually increases (rapidly decreases) before (after) the peak. The satellite SST has a systematic positive bias against the corresponding daytime SST measured by the Triangle Trans-Ocean buoy Network. This bias is enhanced under conditions of large in-situ DSST. One-dimensional numerical model simulation suggests that the systematic bias is caused by the sharp vertical temperature gradient in the surface layer of HE. The near-surface thermal structure is generated by conditions of high insolation and low wind speed, which is the typical HE condition.

Sea surface temperature (SST) variations include negative feedbacks from the atmosphere, whereas SST anomalies are specified in stand-alone atmospheric general circulation simulations. Is the SST forced response the same as the coupled response? In this study, the importance of air–sea coupling in the Indian and Pacific Oceans for tropical atmospheric variability is investigated through numerical experiments with a coupled atmosphere-ocean general circulation model. The local and remote impacts of the Indian and Pacific Ocean coupling are obtained by comparing a coupled simulation with an experiment in which the SST forcing from the coupled simulation is specified in either the Indian or the Pacific Ocean. It is found that the Indian Ocean coupling is critical for atmospheric variability over the Pacific Ocean. Without the Indian Ocean coupling, the rainfall and SST variations are completely different throughout most of the Pacific Ocean basin. Without the Pacific Ocean coupling, part of the rainfall and SST variations in the Indian Ocean are reproduced in the forced run. In regions of large mean rainfall where the atmospheric negative feedback is strong, such as the North Indian Ocean and the western North Pacific in boreal summer, the atmospheric variability is significantly enhanced when air–sea coupling is replaced by specified SST forcing. This enhancement is due to the lack of the negative feedback in the forced SST simulation. In these regions, erroneous atmospheric anomalies could be induced by specified SST anomalies derived from the coupled model. The ENSO variability is reduced by about 20% when the Indian Ocean air–sea coupling is replaced by specified SST forcing. This change is attributed to the interfering roles of the Indian Ocean SST and Indian monsoon in western and central equatorial Pacific surface wind variations.

Chlorophyll-a (chl-a) and Sea Surface Temperature (SST) are important indicators of air-sea interaction and primary productivity. It has been widely known that the variability of chl-a and SST in the waters of Central Java Province (CJP) is influenced by the monsoonal cycle. Previous studies did not clearly describe the variability of chl-a and SST when compared to other cycles. This present study investigated the variability of chl-a and SST influenced by monsoonal cycles, IOD, and ENSO in both CJP waters. Our analysis is based on satellite observations and uses daily data to compile climatological data. The analysis found differences between the variability of chl-a and SST during the monsoonal cycle and ENSO-IOD extreme conditions. During the monsoonal cycle, the maximum (minimum) chl-a (SST) in northern CJP is 0.7 mg.L-1 (28.5ºC) is observed in the West Monsoon, and in the southern CJP is 1.5 mg.L-1 (25.5ºC) is observed in the East Monsoon. In addition, the analysis reveals that the ENSO and IOD extremes do not clearly alter the variability of chl-a and SST in the northern CJP. However, ENSO and IOD extremes have clearly altered the variability of chl-a and SST in the southern CJP. The highest impact to variability of chl-a and SST occurred during IOD+ extreme (2019), where the range of value chl-a (SST) in south CJP is 0,35–4,57 mg.L-1 (23,29 – 30,49ºC). The value of chl-a (SST) is greater than 4 mg.L-1 (less than 24ºC) are observed in the east monsoon. It is caused by the intensity of lifting the mass of water from deeper waters to the sea surface, which possibly supplies the nutrients in the surface waters. The result of the investigation showed that the increasing of chl-a and decreasing of SST in the northern CJP dominant by monsoonal cycle and southern CJP dominant by monsoonal cycle and ENSO – IOD.

The northern Bay of Bengal is characterized by freshwater supply from the Ganges and Brahmaputra Rivers. The resulting shallow haline stratification and thick barrier layer lead to temperature inversions in fall and winter, that is, cool surface water overlaying warm subsurface water. This study examines sea surface temperature (SST) variability off Bangladesh and shows that temperature inversions play an essential role in generating seasonal and interannual SST variability there. Two satellite SST datasets reveal that the magnitude of SST variability has a local peak near the coast of Bangladesh on seasonal and interannual time scales. Output from a high-resolution ocean general circulation model, which is validated by satellite SST and Argo float observations, is used to calculate the mixed layer heat budget. Results show that inverted temperature profiles lead to SST warming on the seasonal time scale via heat exchange at the bottom of the mixed layer, which balances climatological atmospheric cooling in fall and winter. On interannual time scales, surface heat flux tends to damp SST variability, whereas heat exchange at the base of the mixed layer contributes to the growth of SST anomalies. SST off Bangladesh tends to be anomalously high in the year after an El Niño event and in the year of negative Indian Ocean dipole and La Niña events. The atmospheric circulations related to these climate modes force anomalous Ekman pumping, which advects more subsurface warm water to the surface in fall and winter, resulting in anomalous mixed layer warming. The deepening of the mixed layer entrains more subsurface warm water, which also contributes to anomalous warming.

ᅟThe study used a 5 km-resolution regional climate model, the Advanced Research Weather Research and Forecasting Model, to quantify the potential impact of sea surface temperature (SST) west of the Philippines on summer monsoon rainfall on the northwestern coast of the country. A set of control simulations (CTL) driven by ERA-Interim reanalysis data and the monthly National Oceanic and Atmospheric Administration Optimum Interpolation SST dataset was performed for the months of June to August of 1982–2012. A second set of simulations driven by climatological SST values was performed for the same period. The difference between these two simulation sets is analyzed to determine the sensitivity of rainfall to interannual variations in local SST, not remote SST, via a regional climate model. The CTL simulations represented spatial and temporal variations in rainfall well, yielding realistic climatological rainfall values with high spatial correlations with observations. The interannual correlation of monthly rainfall over the northwestern region of the Philippines was also high when compared to observations. The results showed that positive SST anomalies west of the Philippines induced positive rainfall anomalies in the northwestern Philippines via an increase in latent heat flux from the sea surface, implying that summer monsoon rainfall in the northwestern Philippines is modulated by interannual variations in SST west of the Philippines. The impact of SST on latent heat flux and rainfall were 20–40%, greatly exceeding the 7% approximation from the Clausius–Clapeyron equation, which can be explained by the enhancement of low-level winds and a weak warming of surface air temperature over the ocean.

Sea surface temperature (SST) variability in the North Eastern Tropical Atlantic has its center of action in the Senegalese–Mauritanian upwelling system, where its drivers are wind-induced ocean dynamics and air–sea thermodynamic processes. Thus, a better understanding of the local wind variations, together with their predictability, contributes to a more comprehensive assessment of the SST variability in that region. In this study, we use monthly data from two ocean reanalyses, SODA and ORAS-5, and a regional forced-ocean simulation to characterize the interannual SST variability off the Senegalese Coast in the common period 1960–2008. Local indices of the mixed layer heat budget during the major upwelling season (February–March–April) exhibit pronounced interannual to decadal variability. We demonstrate that the local interannual SST variability undergoes inter-decadal fluctuation and concomitant changes in its local and remote drivers. Off-Senegal SST variability was largely controlled by wind-induced Ekman transport during the 1960s–1970s, acting under favorable thermocline and mixed layer conditions. However, from 1980s onwards, the drastically reduced Ekman impact observed on local SSTs is associated with a deeper thermocline. This shift in the effectiveness of the dynamic mechanisms coincides with a more active ENSO teleconnection with upwelling before the 1980s. An extended SODA record reveals that the multidecadal modulator of the ENSO impact on the North-eastern Tropical Atlantic resembles the negative phase of the Atlantic Multidecadal Variability. Our results bring to light the fundamental role played by the global decadal background state in the activation of the drivers and air-sea mechanisms responsible for generating the interannual off-Senegal SST variability.

Spatial and temporal variability of sea surface temperature in the Baltic Sea based on 32-years (1982–2013) of satellite data

Observations and reanalysis products are used to investigate the substantial weakening in the southeastern tropical Atlantic sea surface temperature (SST) variability since 2000. Relative to 1982–1999, the March‐April‐May SST variability in the Angola‐Benguela area (ABA) has decreased by more than 30%. Both equatorial remote forcing and local forcing are known to play an important role in driving SST variability in the ABA. Compared to 1982–1999, since 2000, equatorial remote forcing had less influence on ABA SSTs, whereas local forcing has become more important. In particular, the robust correlation that existed between the equatorial zonal wind stress and the ABA SSTs has substantially weakened, suggesting less influence of Kelvin waves on ABA SSTs. Moreover, the strong correlation linking the South Atlantic Anticyclone and the ABA SSTs has reduced. Finally, multidecadal surface warming of the ABA could also have played a role in the weakening of the interannual SST variability.

MJO induced diurnal sea surface temperature variations off the northwest shelf of Australia observed from Himawari geostationary satellite

This paper examines characteristic changes in North Pacific sea surface temperature (SST) variability during the boreal winter (December–February) for two subperiods (1956–88 and 1977–2009) during which the 1976/77 and the 1988/89 climate transitions occurred. It is found that the Pacific decadal oscillation (PDO)-like SST variability plays a dominant role in the 1976/77 climate transition, while both the North Pacific Gyre Oscillation (NPGO)-like and PDO-like SST variability contribute to the 1988/89 climate transition. Furthermore, the leading mode changes from PDO-like SST variability during the period 1956–88 to NPGO-like SST variability during the period 1977–2009, indicative of an enhancement of NPGO-like SST variability since 1988. Changes in sea level pressure across the 1976/77 climate transition project strongly onto the Aleutian low pressure system. But sea level pressure changes across the 1988/89 climate transition project primarily onto the North Pacific Oscillation, which is associated with remote changes in the Arctic Oscillation over the polar region as well. This contributes to enhancing the NPGO-like SST variability after 1988. The authors also analyze the output from an ensemble of Tropical Ocean and Global Atmosphere (TOGA) experiments in which the observed SSTs are inserted only at grid points in the tropics between 20°S and 20°N. The results indicate that the changes in the North Pacific atmosphere in the 1976/77 climate transition are mostly due to the tropics, whereas those in the 1988/89 climate transition are not.

Previous studies show that the dominant mode of variability in the Northeastern subtropical Pacific and Atlantic are analogous. Most attention has been given to the wind-evaporation-sea surface temperature (WES) feedback, but more recent studies suggest that clouds and ocean play a role. Here, it is shown that, while the mode of variability is similar, the quantitative role of clouds and ocean are different. Using Community Earth System Model, version 1.2, cloud feedbacks and interactive ocean dynamics are disabled separately to diagnose the relative contributions of each to sea surface temperature (SST) variability in subtropical northeastern ocean basins. Results from four experiments show that the relative contributions from WES and cloud radiative feedback depend on the role of the ocean. Positive cloud radiative feedback is evident in both basins but has less impact on SST variance in the Atlantic than in the Pacific. The reason for this is that ocean processes strongly damp SST anomalies in the Pacific and weakly enhance SST anomalies in the Atlantic. When cloud feedbacks are disabled, ocean processes become a larger driver of SST variability in the Atlantic. In line with previous studies, the Northeast Pacific SST variability may be understood as a white-noise-forced linear stochastic system with positive feedback from cloud and damping by latent heat flux and ocean processes, while Atlantic SST is driven partially by variations in ocean circulation and requires vertical mixing for rendition. Between these two regions, different ocean dynamics lead to different roles for atmospheric feedbacks but still result in similar patterns of SST variability.

—Upper ocean thermal data and surface marine observations are used to describe the three-dimensional, basinwide co-evolution of interannual variability in the tropical Pacific climate system. The phase propagation behavior differs greatly from atmosphere to ocean, and from equatorial to off-equatorial and from sea surface to subsurface depths in the ocean. Variations in surface zonal winds and sea surface temperatures (SSTs) exhibit a standing pattern without obvious zonal phase propagation. A nonequilibrium ocean response at subsurface depths is evident, characterized by coherent zonal and meridional propagating anomalies around the tropical North Pacific: eastward on the equator but westward off the equator. Depending on geographic location, there are clear phase relations among various anomaly fields. Surface zonal winds and SSTs in the equatorial region fluctuate approximately in-phase in time, but have phase differences in space. Along the equator, zonal mean thermocline depth (or heat content) anomalies are in nonequilibrium with the zonal wind stress forcing. Variations in SSTs are not in equilibrium either with subsurface thermocline changes in the central and western equatorial Pacific, with the former lagging the latter and displaced to the east. Due to its phase relations to SST and winds, the basinwide temperature anomaly evolution at thermocline depths on an interannual time scale may determine the slow physics of ENSO, and play a central role in initiating and terminating coupled air-sea interaction. This observed basinwide phase propagation of subsurface anomaly patterns can be understood partially as water discharge processes from the western Pacific to the east and further to high latitudes, and partially by the modified delayed oscillator physics.