Kohtaro Hosoda

Temporal Scale of Sea Surface Temperature Fronts Revealed by Microwave Observations

Sea surface temperature (SST) data for three years from the Advanced Microwave Scanning Radiometer for the Earth Observing System are used to statistically evaluate the temporal scales of the global SST fronts (SSTFs). Using the entropy-based edge detection method which is very resistant to impulsive noises, temporal autocorrelation of the dissimilarities of two SST groups across the SSTF is calculated in 10-km-gridded map. In general, the derived temporal scales, defined as e-folding scales in this study, range from 10 to 40 days. Long temporal scales of up to 100 days are found in areas where the stationary ocean currents maintain the frontal structures.

The production of the new generation sea surface temperature (NGSST-O ver.1.0) in Tohoku University

Satellite sea surface temperature (SST) observations from infrared radiometers (AVHRR, MODIS) and a microwave radiometer (AMSR-E) are objectively merged to generate the new generation SST product (NGSST-O Ver.1.0). The product is a quality-controlled, cloud-free, high-spatial resolution (0.05 degree-grided), wide-covering (13-63N, 116-166E), and daily SST digital map. The real-time production and distribution of the NGSST-O has started from September 2003 as a part of the GODAE High Resolution Sea Surface Temperature Pilot Project. To examine the accuracy of the NGSST-O product, the NGSST-O SST is compared with the in-situ SST that is obtained by the buoys drifting in the analyzed area for July 2002 to October 2004. The match-ups of 396,254 points show that the bias of the NGSST-O is -0.15 K against the buoy observations and the rms error, 0.85 K.

Improvement of New Generation Sea Surface Temperature for Open ocean (NGSST-O) : a new sub-sampling method of blending microwave observations

An improved version (version 1.6) of the blended optimum interpolation sea surface temperature (SST), obtained by use of infrared (IR) and microwave (MW) data of the New Generation SST for Open ocean (NGSST-O) product, has been developed. A major improvement is the introduction of a sub-sampling scheme for MW-SST with a finer grid; this has resulted in reduction of the blocky patterning occasionally found in blended SST products with finer grids. Spectral comparison of along-track sea surface height and NGSST-O suggests that mesoscale turbulence was reproduced in the updated NGSST-O in a wide wavelength range.

Time-Dependent Spatial Wavenumber Spectra Derived from Merged Sea Surface Temperature Data

Monthly wavenumber spectra of sea surface temperatures (SST) have been estimated in two regions near the Kuroshio, in the recirculation and the Kuroshio Extension regions, using the merged SST product to determine the statistical parameter (spatial decorrelation scale) required for optimal interpolation of a high-resolution SST dataset. The two-dimensional wavelet transform was used for analysis. Estimates were made of daily mean and daily minimum SSTs. These do not significantly differ, which suggests that the same covariance matrix can be used for the daily mean and minimum in the merging procedure. The seasonality of wavenumber spectra is significant. There are also large differences between those in the recirculation region and in the Kuroshio Extension region. Therefore, it is recommended that the covariance matrix in the merging process for high-resolution SST dataset be defined as a function of time and space. Improvements of the merging methodology are discussed.

Atmospheric structure favoring high sea surface temperatures in the western equatorial Pacific

We investigated the atmospheric processes over high sea surface temperature called Hot Event (HE) in the western equatorial Pacific from climatological analysis and a case study of the HE which began on 28 May 2003 (hereafter : HE030528). Climatological analysis shows that during the development stage of HE, solar radiation inside the HE area is higher than its climatology and wind speed is lower than the decay stage. During the decay stage, strong westerly wind often occur inside HE area. The case study of HE030528 shows that the suppressed convection above high SST area resulted from the deep convection from the northern and southern areas outside HE. The suppressed convection created a band-shaped structure of low cloud cover along HE area increasing solar radiation during the development stage. Thus, the theory of ‘remote convection’ was supported for the HE030528 formation mechanisms. The large sea level pressure gradient magnitude between the southern side of the terrain gap and the northern coast of the Solomon Islands, through which strong wind blew, indicated the role of land topography for the increase of wind speed during the decay of HE030528. Moreover, surface wind had an important role to influence the variability of solar radiation during the occurrence of HE030528 by controlling the water vapor supply in the upper troposphere through surface evaporation and surface convergence variation. Thus, surface wind was the key factor for HE030528 occurrence. The representativeness of HE030528 and the possible relation between HE and Madden Julian Oscillation are also discussed.

Early scientific results of GLI ocean

Global Imager (GLI) is the visible to infrared imager aboard ADEOS-II satellite with 30 and 6 channels for 1 km and 250m resolutions, respectively. The sensor was successfully captured the first image on January 25, 2003. Sea surface temperature (SST) will be retrieved in combination with simultaneous SST observation by low-resolution microwave sensor, AMSR-E. Distribution of chlorophyll and other constituents will be obtained from ocean color channels. Frequent observations with 250 m visible channels will be also available, and combination with 1 km ocean color and SST will be useful for coastal applications. Early scientific results of GLI ocean group will be presented in this presentation.

Global Daily High-Resolution Satellite-Based Foundation Sea Surface Temperature Dataset: Development and Validation against Two Definitions of Foundation SST

This paper describes a global, daily sea surface temperature (SST) analysis based on satellite microwave and infrared measurements. The SST analysis includes a diurnal correction method to estimate foundation SST (SST free from diurnal variability) using satellite sea surface wind and solar radiation data, frequency splitting to reproduce intra-seasonal variability and a quality control procedure repeated twice to avoid operation errors. An optimal interpolation method designed for foundation SST is applied to blend the microwave and infrared satellite measurements. Although in situ SST measurements are not used for bias correction adjustments in the analysis, the output product, with a spatial grid size of 0.1°, has an accuracy of 0.48 ∘ C and 0.46 ∘ C compared to the in situ foundation SST measurements derived by drifting buoys and Argo floats, respectively. The same quality against the two types of in situ foundation SST (drifters and Argo) suggests that the two definitions of foundation SST proposed by past studies can provide same-quality information about the sea surface state underlying the diurnal thermocline.

Global Intercomparison of Sea Surface Temperature Mesured by Infrared And Microwave Radiometers on A Single Satellite

Simultaneous measurements of sea surface temperature (SST) by infrared and microwave sensors on single satellites are compared. The sensors are Global Imager (GLI) and Advanced Microwave Scanning Radiometer (AMSR) aboard Advanced Earth Observing Satellite-II (ADEOS-II), and Moderate Resolution Imaging Spectroradiometer (MODIS) and AMSR for Earth Observing System (AMSR-E) aboard Aqua. The characteristics of SST differences are discussed with regard to the spatial distribution and water vapor amount in atmosphere.

Validation of near-real-time sea surface temperature from MODIS in the ocean around Japan

We have examined accuracies of Moderate Resolution Imaging Spectroradiometer (MODIS) aboard Terra and Aqua using near-real-time sea surface temperature (SST) algorithm produced by Japan Aerospace Exploration Agency, Earth Observation Research and application Center (JAXA/EORC). The algorithm was tuned by buoy bulk SST observation around Japan in the period from February to April, 2004. The Multi-Channel SST (MCSST) coefficients were derived for each satellite and day/night separately. In daytime algorithm, the triple-window algorithms are applied using the brightness temperatures at 8.7, 11, and 12 μm. In nighttime algorithm, the brightness temperature at 3.7 μm is adopted additionally. The estimated SST is evaluated with reference to the buoy bulk observation in the period from April 2003 to July 2004. In daytime algorithm, accuracies of MODIS SST show the seasonal change.

Validation and applications of GLI Ocean product

After ADEOS-2 launch on 14 December 2002, GLI ocean group has investigated vicarious calibration, algorithm improvement and product validation, and released version-1 products on 24 December 2003. Although we lost ADEOS-2/GLI on 24 October 2003, we continue product evaluation and algorithm revision toward the future product updates. For example, we are investigating absorptive aerosol correction and 250-m ocean color image processing. The absorptive aerosol correction is very important especially in the East Asia where is surrounded by the fast developing countries and influenced frequently by a kind of carbon aerosols. The 250-m products are made using GLI 250-m channels from blue to near-infrared, and enable to detect fine spatial structures in the coastal areas.