Search

A historical atmospheric reanalysis from 1850 to 2015 was performed using an atmospheric general circulation model assimilating surface pressure observations archived in international databases, with perturbed observational sea surface temperatures as a lower boundary condition. Posterior spread during data assimilation provides quantitative information on the uncertainty in the historical reanalysis. The reanalysis reproduces the evolution of the three-dimensional atmosphere close to those of the operational centers. Newly archived surface pressure observations greatly reduced the uncertainties in the present reanalysis over East Asia in the early 20th century. A scheme for assimilating tropical cyclone tracks and intensities was developed. The scheme was superior to the present several reanalyses in reproducing the intensity close to the observations and the positions. The reanalysis provides possible images of atmospheric circulations before reanalyses with full-scale observations become available, and opportunities for investigating extreme events that occurred before World War II. Incorporating dynamical downscaling with a regional model that includes detailed topography and sophisticated physics is an application of historical reanalysis to reveal the details of past extreme events. Some examples of past heavy rainfall events in Japan are shown using a downscaling experiment, together with dense rainfall observations over the Japanese islands. [ABSTRACT FROM AUTHOR]

Tropical cyclone (TC) induced precipitation (TCP) over Japan is evaluated with the rain gauge observation based gridded dataset APHRO_JP. The TC-influenced frequency reaches a maximum in the Nansei Islands and decreases monotonically with latitude. On the other hand, the distribution of TCP indicates different characteristics from the one of TC-influenced frequency. The largest annual TCP, 500 mm yr-1 or more, occurs over eastern Kyushu (E-Kyushu), southern Shikoku (S-Shikoku), and the eastern Kii peninsula (E-Kii), where it accounts for 15% or more of the total precipitation. The maximum daily TCP amounts to 200 mm d-1 in those three areas, which are all located on the eastern side of Japan and correspond to eastward or southeastward topographic inclines. A significant relationship is found between the amount of annual TCP and topographic incline, and the large amount of TCP concentrates in the eastward or the southeastward inclines. The extreme daily TCP once every 50 years is also evaluated. The extreme daily TCP is estimated to be 500 mm d-1 comparable to the climatological annual TCP in E-Kyushu, S-Shikoku, and E-Kii. These three areas appear to be the most hazardous part of Japan in terms of TCP. [ABSTRACT FROM AUTHOR]

This study investigates the quality of the Japanese 55-year Reanalysis (JRA-55), which is the second global reanalysis constructed by the Japan Meteorological Agency (JMA), by comparing it with other reanalyses and observational datasets. Improvements were found in the representation of atmospheric circulation on an isentropic surface and in the consistency of momentum budget based on the mass-weighted isentropic zonal mean method. The representation of climate variability in several regions was also examined. In the tropics, the frequencies of high spatial correlations with precipitation, which were estimated using the Tropical Rainfall Measuring Mission Multisatellite Precipitation Analysis, are clearly higher in JRA-55 than in JRA-25. The results indicate that JRA-55 generally improved the representations of phenomena on a wide range of space-time scales, such as equatorial waves, and transient eddies in the storm track regions, compared with JRA-25 during the satellite era. Moreover, JRA-55 improved the temporal consistency compared with the older reanalyses throughout the reanalysis period. In the stratosphere, we found larger discrepancies between reanalyses for the extra-tropical stratosphere during the Southern Hemisphere (SH) winter. Comparisons with radiosonde temperature revealed that JRA-55 has a smaller bias in temperature than the other reanalyses in the extra-tropical SH winter before 1979. Some issues in JRA-55 were also identified. The amplitude of equatorial waves and Madden-Julian oscillation in JRA-55 are weaker than in the other reanalyses. JRA-55 shows unrealistic strong cooling in South America and Australia, although the spatial distribution of the long-term temperature trends in JRA-55 is the closest to an observational dataset of global historical surface temperature. [ABSTRACT FROM AUTHOR]

The Japan Meteorological Agency (JMA) has developed the third Japanese global atmospheric reanalysis, the Japanese Reanalysis for Three Quarters of a Century (JRA-3Q). The objective of JRA-3Q is to improve quality in terms of issues identified in the previous Japanese 55-year Reanalysis (JRA-55) and to extend the reanalysis period further into the past. JRA-3Q is based on the TL479 version of the JMA global Numerical Weather Prediction (NWP) system as of December 2018 and uses results of developments in the operational NWP system, boundary conditions, and forcing fields achieved at JMA since JRA-55. It covers the period from September 1947, when Typhoon Kathleen brought severe flood damage to Japan, and uses rescued historical observations to extend its analyses backwards in time about 10 years earlier than JRA-55. This paper describes the data assimilation system, forecast model, observations, boundary conditions, and forcing fields used to produce JRA-3Q as well as the basic characteristics of the JRA-3Q product. The initial quality evaluation revealed major improvements from JRA-55 in the global energy budget and representation of tropical cyclones (TCs). One of the major problems in JRA-55--global energy imbalance with excess upward net energy flux at the top of the atmosphere and at the surface--has been significantly reduced in JRA-3Q. Another problem--a trend of artificial weakening of TCs--has been resolved through the use of a method that generates TC bogus based on the JMA operational system. There remain several problems such that the volcanic-induced stratospheric warming is smaller than expected. This paper discusses the causes of such problems and possible solutions in future reanalyses. [ABSTRACT FROM AUTHOR]

As an additional product of the Japanese 55-year Reanalysis (JRA-55) project, a new global atmospheric reanalysis product, named JRA-55CHS, is under construction. It utilizes quarterdegree sea-surface temperature (SST) as lower-boundary condition with the same data assimilation system as the JRA-55 Conventional (JRA-55C), into which no satellite data is assimilated. The SST data can resolve steep SST gradients along the western boundary currents (WBCs), which are not necessarily well represented in many of the other atmospheric reanalysis products, including the JRA-55C. The present paper briefly documents basic performance of the JRA-55CHS, through comparing it with the JRA-55C and satellite observations in focusing on the major WBC regions. In the JRA-55CHS, mesoscale atmospheric structures along the WBCs are well reproduced in their climatological-mean fields as captured in the satellite observations. Their interannualto decadal-scale variations associated with SST variations are also reasonably reproduced. The corresponding atmospheric features are less obvious in the JRA-55C owing to smoother SST prescribed. Furthermore, comparison between the two reanalysis products reveals that the influence of frontal-scale SST distributions can reach into the middle and upper troposphere, especially in summer. The JRA-55CHS will be useful for deepening our understanding of the nature of midlatitude frontal-scale air-sea interactions. [ABSTRACT FROM AUTHOR]