Shoichi Kizu

Japanese Ocean Flux Data Sets with Use of Remote Sensing Observations (J-OFURO)

We have constructed ocean surface data sets using mainly satellite data and called them Japanese Ocean Flux data sets with Use of Remote sensing Observations (J-OFURO). The data sets include shortwave radiation, longwave radiation, latent heat flux, sensible heat flux, and momentum flux etc. This article introduces J-OFURO and compares it with other global flux data sets such as European Centre for Medium Range Weather Forecasting (ECMWF) and National Center for Environmental Prediction (NCEP) reanalysis data and da Silva et al. (1994). The usual ECMWF data are used for comparison of zonal wind. The comparison is carried out for a meridional profile along the dateline for January and July 1993. Although the overall spatial variation is common for all the products, there is a large difference between them in places. J-OFURO shortwave radiation in July shows larger meridional contrast than other data sets. On the other hand, J-OFURO underestimates longwave radiation flux at low- and mid-latitudes in the Southern Hemisphere. J-OFURO latent heat flux in January overestimates at 10°N–20°N and underestimates at 25°N–40°N. Finally, J-OFURO shows a larger oceanic net heat loss at 10°N–20°N and a smaller loss north of 20°N in January. The data of da Silva et al. in July show small net heat loss around 20°S and large gain around 20°N, while the NCEP reanalysis (NRA) data show the opposite. The da Silva et al. zonal wind speed overestimates at low-latitudes in January, while ECMWF wind data seem to underestimate the easterlies.

Biases in Expendable Bathythermograph Data: A New View Based on Historical Side-by-Side Comparisons

AbstractBecause they make up 56% of ocean temperature profile data between 1967 and 2001, quantifying the biases in expendable bathythermograph (XBT) data is fundamental to understanding the evolution of the planetary energy and sea level budgets over recent decades. The nature and time history of these biases remain in dispute and dominate differences in analyses of the history of ocean warming. A database of over 4100 side-by-side deployments of XBTs and conductivity–temperature–depth (CTD) data has been assembled, and this unique resource is used to characterize and separate out the pure temperature bias from depth error in a way that was not previously possible. Two independent methods of bias extraction confirm that the results are robust to bias model and fitting method. It was found that there is a pure temperature bias in Sippican probes of ~0.05°C, independent of depth. The temperature bias has a time dependency, being larger (~0.1°C) in the earlier analog acquisition era and being likely due to ...

Start-up transient of XBT measurement

Abstract The start-up transient of XBT measurements is statistically investigated for five types of recorder system: Z-60-16 II and III by Murayama Electric Co., Ltd., and MK-130 by Tsurumi Seiki Co., Ltd., which are commonly used in Japan, and Sippican MK-9 and MK-12, which are popular in the United States and other countries. The UNESCO recommendation to exclude XBT-measured temperatures in the top 3.7 m layer from the bathythermograph report is justified within a nominal precision of 0.2°C for Tsurumi Seiki T-7 probes. However, it is shown that the depth where the transient ceases differs for different types of recorder. If we require a more strict accuracy constraint of 0.02°C, the estimated depth of the transient is 2 m for MK-130, MK-9 and MK-12, 3 m for Z-60-16 III and 10 m for Z-60-16 II.

XBT Science: Assessment of Instrumental Biases and Errors

AbstractExpendable bathythermograph (XBT) data were the major component of the ocean temperature profile observations from the late 1960s through the early 2000s, and XBTs still continue to provide critical data to monitor surface and subsurface currents, meridional heat transport, and ocean heat content. Systematic errors have been identified in the XBT data, some of which originate from computing the depth in the profile using a theoretically and experimentally derived fall-rate equation (FRE). After in-depth studies of these biases and discussions held in several workshops dedicated to discussing XBT biases, the XBT science community met at the Fourth XBT Science Workshop and concluded that XBT biases consist of 1) errors in depth values due to the inadequacy of the probe motion description done by standard FRE and 2) independent pure temperature biases. The depth error and temperature bias are temperature dependent and may depend on the data acquisition and recording system. In addition, the depth bia...

Recorder-Dependent Temperature Error of Expendable Bathythermograph

The accuracy of temperature measurement by the expendable bathythermograph (XBT) is examined for five types of recorders by comparison with co-located CTD measurements and statistical analysis of temperature profiles including an isothermal layer. A positive temperature error increasing downward is occasionally detected for two types of Japanese recorder which have been commonly used among Japanese oceanographic institutions and marine observatories. This error resembles to that reported by Bailey et al. (1989) and Wright (1991) for a different type of recorders, although its cause is not clearly understood. The irregular occurrence of the error suggests that the problem is not solely due to the recorders but rather by some inconsistency of the whole measuring system including them, an XBT probe and sea water. The error is estimated to increase at a rate of O (0.1°C/100 m), and it could be close to 1°C at the deepest part of the profiles (760 m for Tsurumi T-7).

Systematic Errors in Estimation of Insolation by Empirical Formulas

Systematic errors in the estimation of surface, insolation,Q, by two popular empirical formulas are investigated statistically by using coincident measurements of the global solar radiation and the total cloud cover at JMA observatories over Japan. The results show that Reed’s (1977) widely-accepted formula remarkably overestimatesQ under overcast conditions. The overestimation is particularly evident in the summer months. The formula also overestimatesQ in cloud-free conditions, which may be due to an overestimation of the clear-sky transmittance by Seckel and Beaudry, (1973). By contrast, Kondo and Miura’s (1985) formula underestimatesQ under overcast conditions, whereas it slightly overestimates in partially cloudy conditions. It is shown that these systematic errors can explain some, of the published differences between the estimation ofQ by the two formulas. The users of these formulas should be careful since these cloudiness-dependent errors can contaminate not only the absolute values but also the temporal anomalies or the spatial variability of the insolation, predicted by them. In particular, it can be serious in regions of dense cloud cover such as the northern North Pacific, the northern North Atlantic and the Southern Ocean. It is also shown that the ratio ofQ to the insolation at the top of the atmosphere,QTOA, takes on a range of values, particularly under dense cloud cover. This implies an inherent difficulty in estimation ofQ by a simple empirical formula utilizing only readily-available observables such as cloudiness.

A new set of MCSST equations for NOAA-9/AVHRR

A new set of multi-channel sea surface temperature (MCSST) equations for the Advanced Very High Resolution Radiometer (AVHRR) on NOAA-9 is derived from regression analyses between two-channel brightness temperatures andin situ SST obtained from moored buoys around Japan. Two equations are derived: one for daytime and the other for nighttime. They are linear split window type and both the equations contain a term dependent on satellite zenith angle, which has not been accounted for in the previous daytime split window equations for NOAA-9. It is shown that the new set of equation can give SSTs in much better precision than those without the zenith-angle-dependent terms. It is also found that the split window equation for NOAA-9 provided by the National Oceanographic and Atmospheric Administration/National Environmental Satellite, Data and Information Service (NOAA/NESDIS) considerably underestimates the daytime SSTs; sometimes nighttime SSTs are evenhigher than daytime SSTs. This is because the zenith angle effect to the radiation deficiet is neglected in the daytime equation by NOAA/NESDIS. By using the new MCSST equations, it is expected that the quality of satellite MCSST would be much improved, at least in regional applications around Japan, for the period of NOAA-9s operation.

Degradation of the VISSR Visible Sensor on GMS-3 during June 1987–December 1988

Abstract Degradation of the VISSR (Visible-Infrared Spin Scan Radiometer) visible sensor on the GMS-3 is estimated for a period from June 1987 to December 1988 by monitoring reflectances obtained from four targets on the earth. Samples of the highest brightness of midday cloud images and albedos observed over three desert target areas (the Great Sandy Desert, the Taklamakan Desert, and the Gobi Desert) are employed as targets. The results show that the brightness measured by the satellite sensor had appreciably deteriorated during the study period. The rate of degradation is estimated to be 5.3% per year from the analysis of the highest brightness, and 3.7%, 3.7%, and 5.0% for the case of the Great Sandy Desert, the Taklamakan Desert, and the Gobi Desert, respectively. For the average of four cases, the estimated rate of degradation is 4.4% per year.

Heat transport variation due to change of North Pacific subtropical gyre interior flow during 1993–2012

Applying segment-wise altimetry-based gravest empirical mode method to expendable bathythermograph temperature, Argo salinity, and altimetric sea surface height data in March, June, and November from San Francisco to near Japan (30∘ N, 145∘ E) via Honolulu, we estimated the component of the heat transport variation caused by change in the southward interior geostrophic flow of the North Pacific subtropical gyre in the top 700 m layer during 1993–2012. The volume transport-weighted temperature (TI) is strongly dependent on the season. The anomaly of TI from the mean seasonal variation, whose standard deviation is 0.14∘C, was revealed to be caused mainly by change in the volume transport in a potential density layer of 25.0−25.5σ𝜃. The anomaly of TI was observed to vary on a decadal or shorter, i.e., quasi-decadal (QD), timescale. The QD-scale variation of TI had peaks in 1998 and 2007, equivalent to the reduction in the net heat transport by 6 and 10 TW, respectively, approximately 1 year before those of sea surface temperature (SST) in the warm pool region, east of the Philippines. This suggests that variation in TI affects the warm pool SST through modification of the heat balance owing to the entrainment of southward transported water into the mixed layer.

An estimation of degradation of VISSR visible sensors aboard GMS-3, GMS-4, and GMS-5

The rates of degradation of VISSR (Visible and Infrared Spin Scan Radiometer) visible radiometers on three GMS-series satellites, GMS-3, GMS-4 and GMS-5, were estimated from 1987 to 2000 by a simple method in which the long-term behaviour of the higher end of brightness was used as a calibration target. The sensitivity of GMS-3/VIS was found to have decreased by about 3.5% per year during March 1987 through to December 1989. GMS-4/VIS appeared to have deteriorated steadily at a similar rate as GMS-3/VIS except in the first five months when quicker degradation is thought to have occurred. The degradation rate of GMS-5/VIS was estimated to be about 1.1% per year, which is nearly one-third of the preceding two satellites. The results are compared with the vicarious calibration by ISCCP (International Satellite Cloud Climatology Project). Both results agree in general degrading tendency for GMS-3 and GMS-4 visible channels, but the deterioration was likely more constant than ISCCP shows. The most distinct difference is that GMS-5/VIS seems to have also been degraded in the present investigation though ISCCP shows an increase of sensitivity.