Diurnal Amplitude Of Sea Surface Temperature Research Articles

Analysis of Diurnal Sea Surface Temperature Variability in the Tropical Indian Ocean

Based on the 30-year global hourly sea surface temperature (SST) dataset (MLSST) produced by the National Marine Environmental Forecasting Center, Ministry of Natural Resources of China, we analyzed the variability of diurnal sea surface temperature amplitude (DSST) of the tropical Indian Ocean at multiple time scales, as well as its influencing factors. The results show that the DSST in the Arabian Sea, Bay of Bengal, and equatorial Indian Ocean exhibits a bimodal seasonal variation with a semi-annual cycle, while the DSST in the southern Indian Ocean shows an annual cycle. The seasonal variation of DSST is mainly influenced by factors such as sea surface wind speed, shortwave solar radiation, and precipitation. The DSST in the equatorial Indian Ocean is generally higher during El Niño years compared to La Niña years. At the intraseasonal scale, the large standard deviation of DSST in boreal winter is mainly distributed in the southern hemisphere, while the large standard deviation of DSST in boreal summer shifts northward. The intraseasonal variation amplitude of DSST in boreal winter of the tropical Indian Ocean is greater than that in boreal summer. The DSST in the tropical Indian Ocean exhibits significant variation characteristics at multi-time scales. This study provides reference for numerical simulation of air-sea interaction patterns in the tropical Indian Ocean, as well as improvement of short-term climate prediction.

Impact of Diurnal Warm Layers on Atmospheric Convection

AbstractThis manuscript presents a study of oceanic diurnal warm layers (DWLs) in kilometer‐scale global coupled simulations and their impact on atmospheric convection in the tropics. With the implementation of thin vertical levels in the ocean, DWLs are directly resolved, and sea surface temperature (SST) fluctuations of up to several Kelvin appear in regions with low wind and high solar radiation. The increase of SST during the day causes an abrupt afternoon increase of atmospheric moisture due to enhanced latent heat flux (LHF), followed by an increase in cloud cover (CC) and cloud liquid water (CLW). However, although the diurnal SST amplitude is even exaggerated in comparison to reanalysis, this effect only lasts for 5–6 hr and leads to an absolute difference of 1% for CC and 0.01 kg m−2 for CLW. This can be explained by the fact that the low wind over the SST anomalies dampens their potential effect on the LHF and hence clouds. All in all, the impact of DWLs on convective CC is found to be negligible in the tropical mean.

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

High frequency coupling between the tropical upper ocean and atmosphere at diurnal time scales is being recognised to be important for the behaviour of large scale climate modes such as the Madden Julian Oscillation (MJO). Sea surface temperature (SST) variability in the Eastern Indian Ocean warm pool and on the Northwest Shelf of Australia is strongly influenced by the MJO activity. In this study, we use the hourly Himawari-8 geostationary satellite SST data to understand the modulation of the amplitude of SST diurnal variations in the region by the MJO during two austral summer seasons of 2015–16 and 2016–17. The high temporal and spatial resolutions of the Himawari-8 SST data are able to capture the temporal and spatial variability of diurnal SST amplitude. Our results show that the MJO onset (active phase) is preceded by strong diurnal SST variations during the MJO suppressed phase. The amplitudes of the SST diurnal variations are mainly modulated by surface wind variability in the region, as denoted by their spatial and temporal correlations. The very strong El Niño event in 2015–16 may have significantly weakened the MJO activities in the region, resulting in prolonged MJO suppressed phase, high diurnal SST variation and mean SST. This study provides background knowledge for future research on how the diurnal SST variation in the region may influence the progression of the MJO events.

Variability of Diurnal Sea Surface Temperature during Short Term and High SST Event in the Western Equatorial Pacific as Revealed by Satellite Data

Near-surface diurnal warming is an important process in the climate system, driving exchanges of water vapor and heat between the ocean and the atmosphere. The occurrence of the hot event (HE) is associated with the high diurnal sea surface temperature amplitude (δSST), which is defined as the difference between daily maximum and minimum sea surface temperature (SST). However, previous studies still show some inconsistency for the area of HE occurrence and high δSST. The present study produces global δSST data based on the SST, sea surface wind data derived from microwave radiometers, and solar radiation data obtained from visible/infrared radiometers. The value of δSSTs are estimated and validated over tropical oceans and then used for investigating HE in the western equatorial Pacific. A three-way error analysis was conducted using in situ mooring buoy arrays and geostationary SST measurements by the Himawari-8 and Geostationary Operational Environmental Satellite (GOES). The standard deviation error of daily and 10-day validation is around 0.3 °C and 0.14–0.19 °C, respectively. Our case study in the western Pacific (from 110°E to 150°W) shows that the area of HE occurrence coincided well with the area of high δSST. Climatological analysis shows that the collocated area between high occurrence rate of HE and high δSST, which coincides with the western Pacific warm pool region in all seasons. Thus, this study provides more persuasive evidence of the relation between HE occurrence and high δSST.

Opposite responses of the diurnal amplitude of sea surface temperature to the Madden-Julian Oscillation

Both observations and empirical model results show that the responses of the diurnal amplitude of sea surface temperature (DSST) to the Madden-Julian Oscillation (MJO) in the tropical regions are opposite on the two sides of a pivot longitude, which varies seasonally. This pivot longitude occurs at 180° in boreal winter, but moves to 150°E in boreal summer. When the active convection center of the MJO is located to the west of the pivot longitude, reduced solar insolation and enhanced wind speed decrease DSST; when the active convection center moves to the east of the pivot longitude, reduced wind speed increases DSST. Due to the opposing wind speed anomalies across the pivot longitude, opposite responses to the MJO can be seen in latent heat flux anomalies, evaporation rate anomalies and surface roughness anomalies. These findings suggest that opposite responses in the tropical regions on the west and east of the pivot longitude to the MJO be common for variables that are closely related to wind speed.

Evaluation of three temperature profiles of a sublayer scheme to simulate SST diurnal cycle in a global ocean general circulation model

AbstractThe diurnal cycle of sea surface temperature (SST) plays an important role in the upper ocean and climate system. One way to represents the diurnal variation of SST in Ocean General Circulation Models (OGCMs) with coarse vertical resolution is to parameterize the diurnal cycle of SST without considering detailed dynamic processes within the mixed layer. In this study, a diagnostic sublayer parameterization scheme following Schiller and Godfrey (2005) was incorporated into a global OGCM (NEMO), for the first time, to simulate the diurnal cycle of SST. Moreover, three different sublayer temperature profiles (constant, linear, and exponential) were evaluated. Comparison with satellite SST and mooring temperature data indicated that the parameterization scheme with an exponential temperature profile showed the most reasonable diurnal warming simulation results, significantly improving the probability of (from 1.7% with constant temperature profile to 13.4%) diurnal SST amplitude larger than 1.0°C. Furthermore, the mean biases in each season were all reduced to less than 0.16°C, in good agreement with observations.

Validation of MODIS Sea Surface Temperature Product in the Coastal Waters of the Yellow Sea

Sea surface temperature (SST) plays a fundamental role in the exchange of heat, momentum, and water vapor between atmosphere and ocean. Therefore, measurement of SST has been done from ships, buoys, offshore platforms, and satellites. During past decades satellites are being increasingly used, because datasets over wide areas can be obtained. In this paper, moderate resolution imaging spectroradiometer (MODIS) on board Terra and Aqua SST products were examined and validated for coastal waters in the Yellow Sea by using the in situ buoy data. A strict match-up method was adopted in view of the complexity and variability of coastal area, resulting in 154 and 164 match-ups for Terra and Aqua, respectively. The MODIS SST agreed well with in situ buoy SST, with squared correlation coefficients R2 of 0.989 for Terra, and 0.987 for Aqua. Relative to in situ SSTs, the satellite-derived SSTs had a bias of 0.23 °C and 0.06 °C, a standard deviation of 0.79 °C and 0.85 °C, and a root mean square error of 0.83 °C and 0.85 °C, for Terra and Aqua. The differences between MODIS and in situ SST exhibited apparent seasonal variations. The accuracy of MODIS SST products for spring and summer were lower than those for autumn and winter, which could be caused by frequent sea fog along the southern coast of Shandong Peninsula. The SST bias approximately depended on wind velocity; low wind velocity could enhance the diurnal SST amplitude and the bulk-skin temperature difference. However, there is no significant dependence of the bias on air-sea temperature difference or surface flow velocity.

Global space-time scales for day-to-day variations of daily-minimum and diurnal sea surface temperatures: their distinct spatial distribution and seasonal cycles

Spatial and temporal scales of day-to-day sea surface temperature (SST) variation were estimated globally based on the microwave cloud-free SST data. By employing the diurnal correction method of SST using sea surface wind (SSW) and solar shortwave radiation data, the scales of daily-minimum SST and diurnal SST amplitude were independently investigated along with seasonal and regional dependency. The daily-minimum SST showed moderate spatial scales of O(150–400 km) and relatively long temporal scales of O(3–4 days). In eddy-rich areas, the small spatial and long temporal scales were found to be associated, which suggests that the sub-mesoscale SST structures could be reproduced by spatial–temporal interpolations. Diurnal SST amplitude, which is strongly affected by air–sea interaction and high activity in the warming seasons, showed extremely long/short scales in the zonal/meridional directions of up to 1000 km/O(100–200 km), and its temporal scales were less than 1 day.

An Analysis of Tropical Ocean Diurnal Warm Layers

Abstract During periods of light surface wind, a warm stable layer forms at the ocean surface with a maximum sea surface temperature (SST) in the early afternoon. The diurnal SST amplitude (DSA) associated with these diurnal warm layers (DWLs) can reach several degrees and impact the tropical climate variability. This paper first presents an approach to building a daily time series of the DSA over the tropics between 1979 and 2002. The DSA is computed over 2.5° of latitude–longitude regions using a simple DWL model forced by hourly-interpolated surface radiative and turbulent fluxes given by the 40-yr ECMWF Re-Analysis (ERA-40). One advantage of this approach is the homogeneity of the results given by the relative homogeneity of ERA-40. The approach is validated at the global scale using empirical DWL models reported in the literature and the Surface Velocity Program (SVP) drifters of the Marine Environmental Data Service (MEDS). For the SVP dataset, a new technique is introduced to derive the diurnal variation of the temperature from raw measurements. This DWL time series is used to analyze the potential role of DWLs in the variability of the tropical climate. The perturbation of the surface fluxes by DWLs can give a cooling of the ocean mixed layer as large as 2.5 K yr−1 in some tropical regions. On a daily basis, this flux perturbation is often above 10 W m−2 and sometimes exceeds 50 W m−2. DWLs can be organized on regions up to a few thousand kilometers and can persist for more than 5 days. It is shown that strong DWLs develop above the equatorial Indian Ocean during the suppressed phase of the intraseasonal oscillation (ISO). DWLs may trigger large-scale convective events and favor the eastward propagation of the ISO convective perturbation during boreal winter. This study also suggests that the simple approach presented here may be used as a DWL parameterization for atmospheric general circulation models.

Sensitivity of convective and stratiform rainfall to sea surface temperature

The sensitivity of surface rainfall and associated cloud microphysical processes to sea surface temperature (SST) and its diurnal variation is investigated with a series of two-dimensional cloud-resolving model experiments. Experiments with time-invariant SST of 27 °C (SST27) and 31 °C (SST31) and experiments with diurnal SST amplitudes of 1 °C (SST29D1) and 2 °C (SST29D2) and time-mean SST of 29 °C are, respectively, compared with the control experiment with time-invariant SST of 29 °C (SST29). The model with a cyclic lateral boundary is imposed by zero vertical velocity and a constant zonal wind and is integrated for 40 days to reach quasi-equilibrium states for all experiments. Although the time and model domain mean surface evaporation rate is smaller in SST27 than in SST29, the addition of mean local atmospheric drying rate in SST27 leads similar mean surface rain rates in the two experiments. The smaller surface evaporation associated with the colder SST causes the larger local atmospheric drying rate over clear sky regions and the smaller local atmospheric moistening rate in SST27 than in SST29. The larger surface evaporation over clear sky regions associated with the warmer SST causes the larger water vapor transport to convective regions that leads to the larger convective rain rate and thus the larger mean surface rain rate in SST 31 than in SST29. The mean local atmospheric drying and decrease of mean hydrometeor concentration in SST29D1 and increase of mean hydrometeor concentration in SST29 cause the larger mean surface rain rates in SST29D1 than in SST29. The slight increase of mean surface rain rate with increasing diurnal SST amplitude is simply caused by increase of mean surface evaporation rate.

Diurnal sea surface temperature variation and its impact on the atmosphere and ocean: A review

The importance of the diurnal variability of sea surface temperature (SST) on air-sea interaction is now being increasingly recognized. This review synthesizes knowledge of the diurnal SST variation, mainly paying attention to its impact on the atmosphere or the ocean. Diurnal SST warming becomes evident when the surface wind is weak and insolation is strong. Recent observations using satellite data and advanced instruments have revealed that a large diurnal SST rise occurs over wide areas in a specific season, and in an extreme case the diurnal amplitude of SST exceeds 5 K. The large diurnal SST rise can lead to an increase in net surface heat flux from the ocean of 50–60 Wm−2 in the daytime. The temporal mean of the increase exceeds 10 Wm−2, which will be non-negligible for the atmosphere. A few numerical experiments have indicated that the diurnal SST variation can modify atmospheric properties over the Pacific warm pool or a coastal sea, but the processes underlying the modification have not yet been investigated in detail. Furthermore, it has been shown that the diurnal change of ocean mixing process near the surface must be considered correctly in order to reproduce SST variations on an intraseasonal scale in a numerical model. The variation of mixed-layer properties on the daily scale is nonlinearly related to the intraseasonal variability. The mixed-layer deepening/shoaling process on the daily scale will also be related to biological and material circulation processes.

Study on Diurnal Sea Surface Warming and a Local Atmospheric Circulation over Mutsu Bay

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.

Spatial and temporal variations of model‐derived diurnal amplitude of sea surface temperature in the western Pacific Ocean

The diurnal amplitude of sea surface temperature (SST) at 1‐m depth is estimated with a simple empirical model in the region of 80°E–160°W, 60°S–60°N covering the western Pacific Ocean using 4 years of satellite‐derived wind speed, solar radiation, and latent heat flux data. The advantage of this indirect method is that the diurnal amplitude of SST (ΔSST) can be obtained even in cloudy areas. ΔSST is large in the tropics through the year. Summer ΔSST in the middle and high latitudes of the Northern Hemisphere, especially around Japan, is larger than that of the Southern Hemisphere. However, ΔSST in the Kuroshio and its extension regions is smaller compared with that in its surrounding ones because of higher wind speed. In the Bay of Bengal, the South China Sea, and the Timor Sea, ΔSST becomes largest in spring, when the surface wind becomes weak in the transition of the monsoon. The period of about 35–50 days is clearly seen in the temporal variation of ΔSST in the tropics. This reflects the Madden‐Julian oscillation. Furthermore, there are some differences in ΔSST between El Niño and La Niña periods. The authors then investigate how clouds affect the detection of ΔSST. If sampling is limited to clear areas only, the areas of strong solar radiation and weak wind are selectively picked up, and the probability that larger ΔSST is sampled increases. The mean of the ΔSST sampled from clear areas only is greater by 0.2–0.3 K compared with the actual mean.