GRIDDED DATA SET OF GLOBAL SURFACE FLUXES CONSTRUCTED BY SATELLITE DATA: J-OFURO V2
＊ Kunio Kutsuwada1), Masahisa Kubota1), Masatoshi Akiyama1), Shinsuke Iwasaki1) and Hiroyuki Tomita2)
1) School of Marine Science and Technology, Tokai University, Japan Tel.: +81-54-337-0196 / Fax : +81-54-336-1434
2) Kuroshio Transport and Surface Flux Group, Ocean General Circulation Observational Research Program, Institute of Observational Research for Global Change,
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Kanagawa, Japan.
E-mail: [email protected]
Abstract:
We have constructed gridded products of some parameters on the sea surface over the world ocean using satellite data. They are available as the Japanese Ocean Flux data sets with Use of Remote sensing Observation (J-OFURO) on our website. Recently, all the products were updated to improve some problems found in the previous ones, and called the J-OFURO V2. They cover almost global ocean with spatial resolutions of 1.0° x 1.0° and time resolutions of daily and monthly averages. The parameters consist of heat and momentum flux components, and other meteorological elements used in the estimations.
KEY WORDS: heat flux, momentum flux, gridded product, J-OFURO
1. INTRODUCTION
Since the exchange and transport processes of heat and momentum play important roles for controlling the global climate system, the estimations of the fluxes between the ocean and atmosphere and their transports in the oceanic and atmospheric circulations are crucial problem for understanding the mechanism of the climate system. Recent populations of products constructed by satellites and numerical models have provided detailed information on surface fluxes to us.
We have constructed data sets of surface fluxes over the global ocean mainly derived by satellite data. The data sets called Japanese Ocean Flux data sets with Use of Remote-sensing Observations (J-OFURO) have been provided to numerous scientists since 2002 (Kubota et al., 2002), and used in many climate studies. Recently, we reconstructed new data sets of surface fluxes, thereby upgrading it to version 2 (J- OFURO V2). In our new version, improvements have made in many points such as original data sources and construction procedures for the estimation of surface fluxes, compared with those in the previous version.
In this paper, we introduce the contents and impacts of
our new products.
2. DESCRIPTION OF OUR PRODUCT Our data set consists of gridded products of surface heat and momentum fluxes and some meteorological parameters used in their estimations over the global ocean. Most of them have been derived from data measured by satellite sensors. All of them have spatial resolutions of 1.0° x 1.0° and time resolutions of daily and monthly averages, and are available for users in our website: http://dtsv.scc.u-tokai.ac.jp/j-ofuro/index.
html. In the website, every user can download in different data types: netCDF with three dimension (zonal and meridional directions and time), unfor- matted binary data and formatted ASCII code data.
Further, they can view image of spatial distribution for selected parameter in selected time period and to download it as jpg format type.
2.1. Heat Flux
The products for surface heat flux were updated on April 1, 2009. This minor update was carried out to correct some problems found in the previous version.
The previous dataset is referred to as the release id ID002, together with the release id HF003 for new version.
All products cover a period from January 1988 to December 2006. The parameters consists not only of heat flux components: latent heat flux (LHF), sensible heat flux (SHF) and net heat flux (NHF) but also parameters used in their estimations: scalar wind speed at 10m height (MWND), saturated specific humidity at surface (QS) and surface air humidity at 10m height(QA).
DMSP/SSMI brightness temperature data used in our J-OFURO V2 product are supplied by the Remote Sensing Systems (RSS). Recently, the RSS released a new version of SSMI brightness temperature (V6). We recalculated Qa from this new version data for the whole period (January1988-December 2006).
Surface air specific humidity derived from DMSP/
SSMI F15 is significantly different from that derived from other sensors such as F13 and 14. Since the reason for the bias is currently under investigation, the DMSP/SSMI F15 data are removed in the calcu- lation of QA in this release. Surface air specific humidity obtained from ECMWF reanalysis was used in the previous version (J-OFURO V1) as a first guess value for optimum interpolation. However, there are serious problems associated with the tropical Pacific region those are related to the assimilation of TAO/
TRITON buoy data (see Tomita and Kubota, 2006, Fig.10). Therefore, we used the QA data derived from JRA25 as the first guess value of OIM in this release.
2.2. Momentum Flux
Original swath data by the Qscat/SeaWinds are referred to Jet Propulsion Laboratory (2001). In addition to the previous data, we use the new one which has delivered since 2006. These two products are called as Qscat/J-OFURO v1 and v2, respectively.
Details of construction procedure are the same as those in Kutsuwada (1998) and Kubota et al.(2002).
These products cover the almost world ocean (60°N-80°S) with spatial resolution of 1° x 1° grid and with the time resolution of one day.
In our new product, the original surface wind data (QuikSCAT/SeaWinds) have been updated. These data are provided by Jet Propulsion Laboratory (JPL). The latest version of L2B data known as P286 is used instead of v24, which is used in the previous version.
For more details on P286, please visit the website of PO.DACC in JPL (http://podaac.jpl. nasa.gov/).
All products cover a period from August 1999 to December 2008. The parameters consists not only of momentum flux components: scalar momentum flux (TAU), zonal momentum flux (TAUX) and meridional momentum flux (TAUY) but also parameters used for their estimations: scalar wind speed at 10m height (WND), zonal wind speed at 10m Height (UWND) and meridional wind speed at 10m Height (VWND).
In our surface momentum flux products (momen- tum flux and 10-m wind speed), the original swath data (Level 2B) of the Qscat/SeaWinds were renewed.
The swath data, provided by the NASA Physical Oceanography Distributed Active Archive Center (PO.DAAC) at the Jet Propulsion Laboratory, are based on the new algorithm involving the following three improvements: flagging for rain contamination, performance at high wind speeds, and supply of level 2 data with high spatial resolution (12.5 km) (See PODAAC website http://podaac.jpl. nasa.gov/). In our new products (ver. 2), the zonal and meridional com- ponents (vector averages) and the scalar average for every 1° x 1° grid are available for 10-m wind and surface momentum flux (wind stress). The updated data files are named as MF001, and distinguished from their previous ones named as MF_QSCAT.
3. VALIDATION OF GRIDDIED PRODUCTS Reliabilities have been verified by comparisons with in-situ measurements mainly obtained by moored buoys on open ocean (Tomita and Kubota, 2006;
Kasahara et al., 2003; Kutsuwada et al., 2004). In those validation studies, we use time series of surface wind and other parameters at moored buoys in open ocean region. An example is the Kuroshio Extension Observatory (KEO) buoy, which has deployed at 144.5°E, 32.3°N on June 2004 by the NOAA/Pacific Marine Environmental Laboratory (PMEL; chief scientist: Dr. Meghan Cronin). Using wind data on each 10 minute, we convert into 10-meter winds and calculate daily-averaged wind stress using the new version (LKB-3) of the procedure depending upon atmospheric stability (Liu et al., 1979).
We also use data set by the Numerical Weather Pre- diction (NWP) model which has been supplied by the National Center for Environmental Predic tion- National Center for Atmospheric Research (NCEP/
NCAR) reanalysis (Kalnay et al., 1996). It has temporal and spatial resolutions of 6 hours and 2.5°x 2.5°, respectively. We use two products: one is the 6-hourly wind stress supplied by NCEP, and the other is calculated from each 6-hourly wind using the drag coefficient based on Large and Pond (1982). In comparisons with other products, we calculate daily-averaged wind stress. Further, two versions of products has been available. These are referred to as NRA-2, while the old version as NRA-1.
Their reliabilities have been verified by compari- sons with in-situ measurements mainly obtained by moored buoys on open ocean (Kasahara et al., 2003;
Kutsuwada et al., 2004), and it has been revealed that the Qscat product has relatively high reliability compared with numerical weather prediction (NWP) products (NCEP-1 & 2). Validation study was also made for the open ocean region of the mid- and high-latitudes where there had been few moored buoys using the Kuroshio Extension Observatory (KEO) buoy (Kutsuwada et al., 2006).
Results of the validation for wind and wind-stress and sensible heat flux are shown in Table 1 and 2 as statistical values and Fig. 1 and 2 as time series.
Similar validation studies are made in the tropical Pacific region and coastal region around the American continent using Tropical Atmosphere Ocean (TAO) and National Data Buoy Center (NDBC), respectively, buoys.
Acknowledgements
This study was carried out, in part, under the Category 7 MEXT RR2002 Project for Sustainable Coexistence of Human, Nature and the Earth. Also Parts of this study were financially supported by the Japan Aerospace Exploration Agency.
References
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Table 1. Statistics for wind and wind-stress between KEO and satellite-derived wind and wind-stress data
Table 2. Statistics for turbulent heat fluxes between KEO and other products (Tomita et al., 2009)
Fig.1 Time series of zonal components of wind speeds measured at KEO buoy and derived by gridded products by satellite (Qscat) and numerical model(NRA-1,2) at the buoy location.
Fig.2. Time series of latent heat flux calculated by surface meteorological parameters measured at KEO buoy (black line) and one (red line) at its nearest grid in our J-OFURO products.
