11 results on '"Nozomu Ohkawara"'
Search Results
2. Twenty-five years of spectral UV-B measurements over Canada, Europe and Japan: Trends and effects from changes in ozone, aerosols, clouds, and surface reflectivity
- Author
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J. Kapsomenakis, Nozomu Ohkawara, Hugo De Backer, Vitali Fioletov, Alkiviadis F. Bais, Ann R. Webb, Ilias Fountoulakis, Maria-Elissavet Koukouli, Christos Zerefos, Kaisa Lakkala, and Tomi Karppinen
- Subjects
Global and Planetary Change ,Ozone ,010504 meteorology & atmospheric sciences ,Cloud cover ,Irradiance ,Northern Hemisphere ,010501 environmental sciences ,Atmospheric sciences ,Solar irradiance ,01 natural sciences ,Aerosol ,Latitude ,chemistry.chemical_compound ,chemistry ,General Earth and Planetary Sciences ,Environmental science ,sense organs ,Absorption (electromagnetic radiation) ,0105 earth and related environmental sciences - Abstract
Spectral UV records of solar irradiance at stations over Europe, Canada, and Japan were used to study long-term trends at 307.5 nm for a 25-year period, from 1992 to 2016. Ground-based measurements of total ozone, as well as satellite measurements of the Aerosol Index, the Total Cloud Cover and the surface reflectivity were also used in order to attribute the estimated changes of the UV to the corresponding changes of these factors. The present study shows that over the Northern Hemisphere, the long-term changes in UV-B radiation reaching the Earth’s surface vary significantly over different locations, and that the main drivers of these variations are changes in aerosols and total ozone. At high latitudes, part of the observed changes may also be attributed to changes in the surface reflectivity. Over Japan, the UV-B irradiance at 307.5 nm has increased significantly by 3%/decade during the past 25 years, possibly due to the corresponding significant decrease of its absorption by aerosols. It was found that the greatest part of this increase took place before the mid-2000s. The only European station, over which UV radiation increases significantly, is that of Thessaloniki, Greece. Analysis of the clear-sky irradiance for the particular station shows increasing irradiance at 307.5 nm by 3.5%/decade during the entire period of study, with an increasing rate of change during the last decade, possibly again due to the decreasing absorption by aerosols.
- Published
- 2018
3. Optimal use of Prede POM sky radiometer for aerosol, water vapor, and ozone retrievals
- Author
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Rei Kudo, Henri Diémoz, Victor Estellés, Monica Campanelli, Masahiro Momoi, Franco Marenco, Claire L. Ryder, Osamu Ijima, Akihiro Uchiyama, Kouichi Nakashima, Akihiro Yamazaki, Ryoji Nagasawa, Nozomu Ohkawara, and Haruma Ishida
- Abstract
The Prede POM sky radiometer is a filter radiometer deployed worldwide in the SKYNET international network. A new method called, Skyrad pack MRI version 2 (MRI v2), is here presented, to retrieve aerosol properties (size distribution, real and imaginary parts of the refractive index, single-scattering albedo, asymmetry factor, lidar ratio, and linear depolarization ratio), and water vapor and ozone column concentrations from the sky radiometer measurements. MRI v2 overcomes two limitations of previous methods (Skyrad pack versions 4.2 and 5, and MRI version 1). One is the use of all the wavelengths of 315, 340, 380, 400, 500, 675, 870, 940, 1020, 1627, and 2200 nm, if available from the sky radiometers, for example, in POM-02 models. The previous methods cannot use the wavelengths of 315, 940, 1627, and 2200 nm. This enables us to provide improved estimates of the aerosol optical properties, covering almost all the wavelengths of solar radiation. The other is the use of measurements in the principal plane geometry in addition to the solar almucantar plane geometry that is used in the previous versions. The measurements in the principal plane are regularly performed, however they are currently not exploited despite being useful in the case of small solar zenith angles, when the scattering angle distribution for almucantars becomes too small to yield useful information. Moreover, in the inversion algorithm, MRI v2 optimizes the smoothness constraints of the spectral dependencies of the refractive index and size distribution, and changes the contribution of the diffuse radiances to the cost function according to the aerosol optical depth. These overcome issues with the estimation of the size distribution and single-scattering albedo in the Skyrad pack version 4.2. The scattering model used here allows for non-spherical particles, improving results for mineral dust and permitting to evaluate the depolarization ratio. An assessment of the retrieval uncertainties using synthetic measurement show that best performance is obtained when the aerosol optical depths is larger than 0.2 at 500 nm. Improvements over the Skyrad pack versions 4.2 and 5 are obtained for the retrieved size distribution, imaginary part of the refractive index, single-scattering albedo, and lidar ratio at Tsukuba, Japan, while yielding comparable retrievals of the aerosol optical depth, real part of the refractive index, and asymmetry factor. A radiative closure study using surface solar irradiances from Baseline Surface Radiation Network and the parameters retrieved from MRI v2 showed consistency, with a positive bias of the simulated global irradiance, about +24 Wm−2 (+3 %). Furthermore, the MRI v2 retrievals of the refractive index, single-scattering albedo, asymmetry factor, and size distribution have been found in agreement with integrated profiles of aircraft in-situ measurements of two Saharan dust events at the Cape Verde archipelago, during the SAVEX-D 2015 field campaign.
- Published
- 2020
4. Supplementary material to 'Optimal use of Prede POM sky radiometer for aerosol, water vapor, and ozone retrievals'
- Author
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Rei Kudo, Henri Diémoz, Victor Estellés, Monica Campanelli, Masahiro Momoi, Franco Marenco, Claire L. Ryder, Osamu Ijima, Akihiro Uchiyama, Kouichi Nakashima, Akihiro Yamazaki, Ryoji Nagasawa, Nozomu Ohkawara, and Haruma Ishida
- Published
- 2020
5. Supplementary material to 'Results from the 4th WMO Filter Radiometer Comparison for aerosol optical depth measurements'
- Author
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Stelios Kazadzis, Natalia Kouremeti, Henri Diémoz, Julian Gröbner, Bruce W. Forgan, Monica Campanelli, Victor Estellés, Kathleen Lantz, Joseph Michalsky, Thomas Carlund, Emilio Cuevas, Carlos Toledano, Ralf Becker, Stephan Nyeki, Panagiotis G. Kosmopoulos, Viktar Tatsiankou, Laurent Vuilleumier, Frederick M. Denn, Nozomu Ohkawara, Osamu Ijima, Philippe Goloub, Panagiotis I. Raptis, Michael Milner, Klaus Behrens, Africa Barreto, Giovanni Martucci, Emiel Hall, James Wendell, Bryan E. Fabbri, and Christoph Wehrli
- Published
- 2017
6. Results from the 4th WMO Filter Radiometer Comparison for aerosol optical depth measurements
- Author
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Stelios Kazadzis, Natalia Kouremeti, Henri Diémoz, Julian Gröbner, Bruce W. Forgan, Monica Campanelli, Victor Estellés, Kathleen Lantz, Joseph Michalsky, Thomas Carlund, Emilio Cuevas, Carlos Toledano, Ralf Becker, Stephan Nyeki, Panagiotis G. Kosmopoulos, Viktar Tatsiankou, Laurent Vuilleumier, Frederick M. Denn, Nozomu Ohkawara, Osamu Ijima, Philippe Goloub, Panagiotis I. Raptis, Michael Milner, Klaus Behrens, Africa Barreto, Giovanni Martucci, Emiel Hall, James Wendell, Bryan E. Fabbri, and Christoph Wehrli
- Abstract
This study presents the results of the 4th Filter Radiometer Comparison that was held in Davos, Switzerland, between September 28 and October 16, 2015. Thirty filter radiometers and spectroradiometers from 12 countries participated including reference instruments from global aerosol networks. The absolute differences of all instruments compared to the reference have been based on the WMO criterion defined as 95 % of the measured data has to be within 0.005 ± 0.001/m (where m is the air mass). At least 24 out of 29 instruments achieved this goal at both 500 and 865 nm, while 12 out of 17 and 13 out of 21 achieved this at 368 and 412 nm, respectively. While searching for sources of differences among different instruments, it was found that all individual differences linked to Rayleigh, NO2, ozone, water vapor calculations and related optical depths and air mass calculations were smaller than 0.01 in AOD at 500 and 865 nm. Different cloud detecting algorithms used have been compared. Ångström exponent calculations showed relatively large differences among different instruments partly because of the sensitivity of this parameter at low AOD conditions. The overall low deviations of these AOD results and the high accuracy of reference aerosol network instruments demonstrated a promising framework to achieve homogeneity, compatibility and harmonization among the different spectral AOD networks in the near-future.
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- 2017
7. Validation of 10-year SAO OMI Ozone Profile (PROFOZ) product using ozonesonde observations
- Author
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Tristan J. Hall, Bertrand Calpini, Bogumil Kois, Roeland Van Malderen, René Stübi, Marion Marchand, Marc Allaart, Masatomo Fujiwara, Thierry Leblanc, Anne M. Thompson, M.B. Tully, Richard Querel, Everette Joseph, Françoise Posny, Ghassan Taha, Kai Yang, Zhaonan Cai, Giovanni Laneve, Michael J. Newchurch, Manvendra K. Dubey, Gary A. Morris, Hugo De Backer, Rinus Scheele, Xiong Liu, Jacquelyn C. Witte, Kenneth R. Minschwaner, Nozomu Ohkawara, Ankie Piters, Kelly Chance, Shin-Ya Ogino, Margarita Yela, Ninong Komala, Emilio Cuevas-Agulló, H. B. Selkirk, Sophie Godin-Beekmann, Guanyu Huang, Manuel Cupeiro, Valérie Thouret, Holger Vömel, Russell C. Schnell, Gerrie Coetzee, Pawan K. Bhartia, Masato Shiotani, Gérard Ancellet, Otto Schrems, Bryan J. Johnson, Gert König-Langlo, Rigel Kivi, F. J. Schmidlin, Peter von der Gathen, P. Skrivankova, David W. Tarasick, Henry E. Fuelberg, Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University [Cambridge]-Smithsonian Institution, Department of Atmospheric and Oceanic Science [College Park] (AOSC), University of Maryland [College Park], University of Maryland System-University of Maryland System, NASA Goddard Space Flight Center (GSFC), Royal Netherlands Meteorological Institute (KNMI), TROPO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Payerne Aerological Station, Federal Office of Meteorology and Climatology MeteoSwiss, South African Weather Service (SAWS), Izaña Atmospheric Research Center (IARC), Agencia Estatal de Meteorología (AEMet), National Meteorological Service [Ushuaia], Institut Royal Météorologique de Belgique [Bruxelles] (IRM), Los Alamos National Laboratory (LANL), Department of Earth, Ocean and Atmospheric Science [Tallahassee] (FSU | EOAS), Florida State University [Tallahassee] (FSU), Faculty of Environmental Earth Science [Sapporo], Hokkaido University [Sapporo, Japan], STRATO - LATMOS, ESRL Global Monitoring Laboratory [Boulder] (GML), NOAA Earth System Research Laboratory (ESRL), National Oceanic and Atmospheric Administration (NOAA)-National Oceanic and Atmospheric Administration (NOAA), Atmospheric Sciences Research Center (ASRC), University at Albany [SUNY], State University of New York (SUNY)-State University of New York (SUNY), Finnish Meteorological Institute (FMI), Institute of Meteorology and Water Management - National Research Institute (IMGW - PIB), Indonesian National Institute of Aeronautics and Space (LAPAN), Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung (AWI), Earth Observation Satellite Images Applications Laboratory (EOSIAL), Università degli Studi di Roma 'La Sapienza' = Sapienza University [Rome], Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Department of Physics [Socorro], New Mexico Institute of Mining and Technology [New Mexico Tech] (NMT), St. Edward's University, Department of Atmospheric Science [Huntsville], University of Alabama in Huntsville (UAH), Department of Coupled Ocean-Atmosphere-Land Processes Research (DCOP), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Global Environment and Marine Department [Tokyo], Japan Meteorological Agency (JMA), Laboratoire de l'Atmosphère et des Cyclones (LACy), Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Météo France, Observatoire des Sciences de l'Univers de La Réunion (OSU-Réunion), Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR), National Institute of Water and Atmospheric Research [Lauder] (NIWA), Universities Space Research Association (USRA), Research Institute for Sustainable Humanosphere (RISH), Kyoto University [Kyoto], Czech Hydrometeorological Institute (CHMI), Environment and Climate Change Canada, Laboratoire d'aérologie (LAERO), Centre National de la Recherche Scientifique (CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées, Australian Bureau of Meteorology [Melbourne] (BoM), Australian Government, Earth Observing Laboratory [Boulder] (EOL), National Center for Atmospheric Research [Boulder] (NCAR)-University Corporation for Atmospheric Research (UCAR), Science Systems and Applications, Inc. [Lanham] (SSAI), Instituto Nacional de Técnica Aeroespacial (INTA), Harvard University-Smithsonian Institution, Institut Royal Météorologique de Belgique [Bruxelles] - Royal Meteorological Institute (IRM), Università degli Studi di Roma 'La Sapienza' = Sapienza University [Rome] (UNIROMA), Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Météo-France, Kyoto University, Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), and Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)
- Subjects
Atmospheric Science ,010504 meteorology & atmospheric sciences ,Cloud cover ,0211 other engineering and technologies ,02 engineering and technology ,01 natural sciences ,Latitude ,Troposphere ,Ozone layer ,lcsh:TA170-171 ,Stratosphere ,021101 geological & geomatics engineering ,0105 earth and related environmental sciences ,validation ,Ozone Monitoring Instrument ,[PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph] ,[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere ,lcsh:TA715-787 ,Anomaly (natural sciences) ,OMI ,lcsh:Earthwork. Foundations ,ozone ,lcsh:Environmental engineering ,Trace gas ,13. Climate action ,Climatology ,Environmental science - Abstract
We validate the Ozone Monitoring Instrument (OMI) Ozone Profile (PROFOZ) product from October 2004 through December 2014 retrieved by the Smithsonian Astrophysical Observatory (SAO) algorithm against ozonesonde observations. We also evaluate the effects of OMI row anomaly (RA) on the retrieval by dividing the dataset into before and after the occurrence of serious OMI RA, i.e., pre-RA (2004–2008) and post-RA (2009–2014). The retrieval shows good agreement with ozonesondes in the tropics and midlatitudes and for pressure ∼ 50 hPa after applying OMI averaging kernels to ozonesonde data. The MBs of the stratospheric ozone column (SOC, the ozone column from the tropopause pressure to the ozonesonde burst pressure) are within 2 % with SDs of ∼ 50 hPa. The SOC MBs increase up to 3 % with SDs as great as 6 % and the TOC SDs increase up to 30 %. The comparison generally degrades at larger solar zenith angles (SZA) due to weaker signals and additional sources of error, leading to worse performance at high latitudes and during the midlatitude winter. Agreement also degrades with increasing cloudiness for pressure > ∼ 100 hPa and varies with cross-track position, especially with large MBs and SDs at extreme off-nadir positions. In the tropics and midlatitudes, the post-RA comparison is considerably worse with larger SDs reaching 2 % in the stratosphere and 8 % in the troposphere and up to 6 % in TOC. There are systematic differences that vary with latitude compared to the pre-RA comparison. The retrieval comparison demonstrates good long-term stability during the pre-RA period but exhibits a statistically significant trend of 0.14–0.7 % year−1 for pressure
- Published
- 2017
8. Is global dimming and brightening in Japan limited to urban areas?
- Author
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Katsumasa Tanaka, Atsumu Ohmura, Doris Folini, Martin Wild, and Nozomu Ohkawara
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13. Climate action ,11. Sustainability - Abstract
Observations worldwide indicate secular trends of all-sky surface solar radiation on decadal time scale, termed global dimming and brightening. Accordingly, the observed surface radiation in Japan generally shows a strong decline till the end of the 1980s and then a recovery toward around 2000. Because a substantial number of measurement stations are located within or proximate to populated areas, one may speculate that the observed trends are strongly influenced by local air pollution and are thus not of large-scale significance. This hypothesis poses a serious question as to what regional extent the global dimming and brightening are significant: Are the global dimming and brightening truly global phenomena, or regional or even only local? Our study focused on 14 meteorological observatories that measured all-sky surface solar radiation, zenith transmittance, and maximum transmittance. On the basis of municipality population time series, historical land use maps, recent satellite images, and actual site visits, we concluded that eight stations had been significantly influenced by urbanization, with the remaining six stations being left pristine. Between the urban and rural areas, no marked differences were identified in the temporal trends of the aforementioned meteorological parameters. Our finding suggests that global dimming and brightening in Japan occurred on a large scale, independently of urbanization.
- Published
- 2016
9. Aerosol impact on the brightening in Japan
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Akihiro Uchiyama, Osamu Ijima, Sachio Ohta, Nozomu Ohkawara, and Rei Kudo
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Atmospheric Science ,Radiometer ,Ecology ,Single-scattering albedo ,Paleontology ,Soil Science ,Forestry ,Forcing (mathematics) ,Aquatic Science ,Oceanography ,Solar irradiance ,Atmospheric sciences ,eye diseases ,Aerosol ,Atmosphere ,stomatognathic diseases ,Geophysics ,Space and Planetary Science ,Geochemistry and Petrology ,Earth and Planetary Sciences (miscellaneous) ,Environmental science ,sense organs ,Earth-Surface Processes ,Water Science and Technology - Abstract
[1] The long-term changes in aerosol optical depth (AOD) and single scattering albedo (SSA) at 0.75 μm from the 1970s to the 2000s at 14 sites in Japan were estimated from the direct and diffuse irradiances measured by ground-based broadband radiometers under clear-sky conditions. Noticeable changes in AOD and SSA were seen: AOD decreased by 0.02, and SSA increased by 0.21. The ratio of surface solar irradiance to solar irradiance at the top of the atmosphere under clear-sky conditions, calculated from the estimated AOD and SSA, showed apparent brightening of +0.05, of which +0.01 was attributed to a decrease of AOD and +0.04 to an increase of SSA. The cloud forcing of the surface solar irradiance, estimated as the difference between the surface solar irradiance measured under cloudy-sky conditions and that under clear-sky conditions, showed no significant trend. These findings suggest that the brightening in Japan has been caused by changes in aerosol optical properties, especially SSA, rather than by cloud changes.
- Published
- 2012
10. ON THE VERTICAL PROFILES OF LONG WAVE RADIATION AT SYOWA STATION IN ANTARCTICA
- Author
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Masaatsu, MIYAUCHI, Nozomu, OHKAWARA, Meteorological College, and Yamagata Local Meteorological Observatory
- Abstract
Vertical profiles of long wave radiation have been measured with radiometersonde since 1966 at Syowa Station in Antarctica. The measurements have been carried out mainly from March to October of each year. Much data have been stored but most have not been analyzed or evaluated. Here the data from 1966 to 1988 were analyzed for respective sky conditions : cloudless, overcast and all conditions. The upward fluxes at the 100 mb and 850 mb levels, and the downward fluxes at those levels in each month, are discussed, and also the budgets of radiative flux in the atmosphere and at the ground surface for all three conditions are discussed. All downward and upward measured fluxes and those calculated are compared for cloudless conditions. The downward fluxes show good agreement with each other on average. But there are discrepancies in the case of upward flux. It can be inferred that the discrepancies might be caused by setting the ground surface temperature equal to the surface air temperature in calculation, and by the temperature change of the ground surface over location that the radiometersonde observed. There are 6 types of radiometersonde used which are basically almost the same as each other. Discrepancies among vertical profiles of the flux measured with each type are discussed by comparing with those obtained by theoretical calculations concerning only the downward flux for cloudless conditions. Generally the vertical profiles of flux measured with each type of radiometersonde agree well with those calculated except for one type.
- Published
- 1992
11. Japanese 25-year reanalysis (JRA-25)
- Author
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Nozomu Ohkawara
- Subjects
Meteorological reanalysis ,Geography ,Data assimilation ,Meteorology ,Precipitable water ,Climatology ,Microwave radiometer ,Radiance ,Geostationary orbit ,Precipitation ,Tropical cyclone - Abstract
A long term global atmospheric reanalysis Japanese 25-year Reanalysis (JRA-25) which covers from 1979 to 2004 was completed using the Japan Meteorological Agency (JMA) numerical assimilation and forecast system. This is the first long term reanalysis undertaken in Asia. JMA's latest numerical assimilation system, and observational data collected as much as possible, were used in JRA-25 to generate a consistent and high quality reanalysis dataset to contribute to climate research and operational work. One purpose of JRA-25 is to enhance to a high quality the analysis in the Asian region. 6-hourly data assimilation cycles were performed and produced 6-hourly atmospheric analysis and forecast fields with various kinds of physical variables. The global model used in JRA-25 has a spectral resolution of T106 (equivalent to a horizontal grid size of around 120km) and 40 vertical layers with the top level at 0.4hPa. For observational data, a great deal of satellite data was used in addition to conventional surface and upper air data. Atmospheric Motion Vector (AMV) data retrieved from geostationary satellites, brightness temperature (TBB) data from TIROS Operational Vertical Sounder (TOVS), precipitable water retrieved from radiance of microwave radiometer from orbital satellites and some other satellite data were assimilated with 3-dimensional variational method (3DVAR). Many advantages have been found in the JRA-25 reanalysis. Firstly, forecast 6-hour global total precipitation in JRA-25 performs well, distribution and amount are properly represented both in space and time. JRA-25 has the best performance compared to other reanalysis with respect to time series of global precipitation over many years, with few unrealistic variations caused by degraded quality of satellite data due to volcanic eruptions. Secondly, JRA-25 is the first reanalysis which assimilated wind profiles surrounding tropical cyclones retrieved from historical best track information; tropical cyclones were analyzed correctly in all the global regions. Additionally, low-level cloud along the subtropical western coast of continents is forecast very accurately, and snow depth analysis is also good.
- Published
- 2006
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