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Onogi, K., J. Tsutsui, H. Koide, M. Sakamoto, S. Kobayashi, H.
Hatsushika, T. Matsumoto, N. Yamazaki, H. Kamahori, K. Takahashi, S.
Kadokura, K. Wada, K. Kato, R. Oyama, T. Ose, N. Mannoji, and R.
Taira, 2007: The JRA-25 Reanalysis. J. Met. Soc. Jap., 85(3),
369-432, URL:
http://www.jstage.jst.go.jp/article/jmsj/85/3/85_369/_article.
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The Japanese 25-year Reanalysis (JRA-25) represents the first
long-term global atmospheric reanalysis undertaken in Asia. Covering
the period 1979-2004, it was completed using the Japan
Meteorological Agency (JMA) numerical assimilation and forecast
system and specially collected and prepared observational and
satellite data from many sources including the European Center for
Medium-Range Weather Forecasts (ECMWF), the National Climatic Data
Center (NCDC), and the Meteorological Research Institute (MRI) of
JMA. A primary goal of JRA-25 is to provide a consistent and
high-quality reanalysis dataset for climate research, monitoring,
and operational forecasts, especially by improving the coverage and
quality of analysis in the Asian region.
In JRA-25, three-dimensional variational (3D-Var) data assimilation
and a global spectral model were employed to produce 6-hourly
atmospheric analysis and forecast cycles. The global spectral model
was based on a 320 by 160 (~1.125 degree) Gaussian grid with T106
truncation. Vertical discretization employed a hybrid sigma-pressure
coordinate utilizing 40 levels where 0.4 hPa represents the model
top level. A predictive mass-flux Arakawa-Schubert scheme was
utilized for cumulus parameterization, and Simple Biosphere (SiB)
parameterizations for land-surface processes. Assimilated variables
include temperature, relative humidity, and surface pressure from
conventional observations, and also winds retrieved from
geostationary satellites, radiative brightness temperature from
TIROS Operational Vertical Sounder (TOVS), and precipitable water
from Special Sensor Microwave/Imager (SSM/I). Variables not directly
assimilated include daily sea surface temperature (SST) and sea ice
based on Centennial in-situ Observation-Based Estimates (COBE), and
ozone profiles based on chemical transport models constrained by
observations from Total Ozone Mapping Spectrometer (TOMS).
The JRA-25 shows marked improvement over previous reanalyses in
several notable areas, especially predicted (both 6-hourly and long
term) precipitation, with more realistic variability and fewer
spurious trends due to contamination of satellite data by volcanic
eruptions. JRA-25 is also the first reanalysis to assimilate wind
profiles around tropical cyclones deduced from best-track data,
resulting in improved tropical cyclone analysis in a global context.
In addition, low-level (stratus) cloud decks along the western
subtropical coasts of continents are also better simulated,
improving radiation budgets in these regions.
In 2006, JMA started real-time operation of the JMA Climate Data
Assimilation System (JCDAS). JCDAS employs the same system as JRA-25
and the data assimilation cycle is extended to the present time.
JRA-25 and JCDAS products will enable users to conduct climate
diagnostics with a long-term, and current, homogeneous reanalysis
dataset. The JMA has also engaged in ongoing cooperation with ECMWF
(European Center for Medium-Range Weather Forecasts) on reanalysis,
including the ECMWF CDAS (ECDAS), more commonly known as
ERA-Interim.
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