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.
This paper presents the development of a historical atmospheric reanalysis OCADA along with its validations and applications.
Surface pressure observations in East and Southeast Asia, which are
newly archived and used in this study, account for 15 % of the database
in the early 20th century. OCADA is superior in representing the intensities of observed tropical cyclones in 1979-2015. OCADA reproduces several extreme precipitation events in Japan before World War II.
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 volcanic-induced stratospheric warming is smaller than expected. This paper discusses the causes of such problems and possible solutions in future reanalyses.
This paper describes a new global atmospheric reanalysis JRA-3Q
developed by Japan Meteorological Agency, focusing on the improvements
from the previous reanalysis.
The large upward imbalance in the global mean net energy flux
at the top of the atmosphere and at the surface, one of the major
problems of JRA-55, has been significantly reduced. The artificial decrease in the detection of tropical cyclones
seen in JRA-55 has been resolved by the use of a tropical cyclone bogus
generation method based on the JMA operational system. For the pre-1957 period, which is first included in Japanese
reanalyses, major typhoons, such as Typhoon Kathleen and Typhoon Marie,
are clearly represented in the mean sea level pressure field of JRA-3Q,
and the pressure fields are generally consistent with the original
weather map analyzed at that time.
It is well-known in rainfall ensemble forecasts that ensemble means suffer substantially from the diffusion effect resulting from the averaging operator. Therefore, ensemble means are rarely used in practice. The use of the arithmetic average to compute ensemble means is equivalent to the definition of ensemble means as centers of mass or barycenters of all ensemble members where each ensemble member is considered as a point in a high-dimensional Euclidean space. This study uses the limitation of ensemble means as evidence to support the viewpoint that the geometry of rainfall distributions is not the familiar Euclidean space, but a different space. The rigorously mathematical theory underlying this space has already been developed in the theory of optimal transport (OT) with various applications in data science.
In the theory of OT, all distributions are required to have the same total mass. This requirement is rarely satisfied in rainfall ensemble forecasts. We, therefore, develop the geometry of rainfall distributions from an extension of OT called unbalanced OT. This geometry is associated with the Gaussian-Hellinger (GH) distance, defined as the optimal cost to push a source distribution to a destination distribution with penalties on the mass discrepancy between mass transportation and original mass distributions. Applications of the new geometry of rainfall distributions in practice are enabled by the fast and scalable Sinkhorn-Knopp algorithms, in which GH distances or GH barycenters can be approximated in real-time. In the new geometry, ensemble means are identified with GH barycenters, and the diffusion effect, as in the case of arithmetic means, is avoided. New ensemble means being placed side-by-side with deterministic forecasts provide useful information for forecasters in decision-making.
This paper proposed new ensemble means of rainfall based on the theory of unbalanced optimal transport.
Ensemble forecast results are usually announced using ensemble
means. However, for the rainfall variable, ensemble means are rarely
used in practice due to the diffusion effect resulting from the
averaging operator, which smooths rainfall significantly. A method to calculate more meaningful ensemble means of
rainfall is proposed based on the theory of unbalanced optimal
transport. The new ensemble means are interpreted as barycenters of
rainfall distributions with respect to a new geometric distance called
the Gaussian-Hellinger distance. The new ensemble means avoid the diffusion effect as observed
in the case of arithmetic means, and open a way to reintroduce ensemble
means of rainfall back to numerical weather prediction.
The trend of strong typhoons over the recent 30 years was analyzed using Dvorak reanalysis data from 1987 to 2016 produced by Japan Meteorological Agency. The strong typhoons were defined in this study as tropical cyclones equivalent to category 4 and 5 on the Saffir-Simpson scale. The temporal homogeneity of the Dvorak reanalysis data is expected to be much better than that of best track data. Results showed no statistically significant increasing trend in strong typhoons with large inter-annual and multi-year scale variations. Meanwhile, the spatial distribution of the genesis locations of tropical cyclones, which could influence whether or not they develop into strong typhoons, varied locally during the analysis period. The changes in genesis locations may have influenced the overall trend of strong typhoons during the analysis period. The results with the new Dvorak reanalysis data highlight the need for the accumulation of high quality data over time as well as for careful interpretation of trend analysis results seen in previous studies.
In a global numerical weather prediction (NWP) modeling framework we study the implementation of Gaussian uncertainty of individual particles into the assimilation step of a localized adaptive particle filter (LAPF). We obtain a local representation of the prior distribution as a mixture of basis functions. In the assimilation step, the filter calculates the individual weight coefficients and new particle locations. It can be viewed as a combination of the LAPF and a localized version of a Gaussian mixture filter, i.e., a Localized Mixture Coefficients Particle Filter (LMCPF).
Here, we investigate the feasibility of the LMCPF within a global operational framework and evaluate the relationship between prior and posterior distributions and observations. Our simulations are carried out in a standard pre-operational experimental set-up with the full global observing system, 52 km global resolution and 106 model variables. Statistics of particle movement in the assimilation step are calculated. The mixture approach is able to deal with the discrepancy between prior distributions and observation location in a real-world framework and to pull the particles towards the observations in a much better way than the pure LAPF. This shows that using Gaussian uncertainty can be an important tool to improve the analysis and forecast quality in a particle filter framework.
This paper describes a particle filter in the global NWP at Deutscher
Wetterdienst (DWD). A particle filter (PF) in the global NWP at DWD is
proposed and evaluated its skills in comparison with the operational
system. To alleviate the degeneration, which is the largest issue in PFs
with
high-dimensional systems, several approaches are effectively
incorporated such as localization, Gaussian mixture approximation in the
prior distribution, adaptive resampling, and so on (See Section 2.3).
Since comprehensive formulations in this system are described, the
readers can totally understand its theoretical aspects.
Roles of Rossby and Gravity Waves on Circulation Associated with Tropical and Subtropical Heating
公開日: 2005/10/07 | 83 巻 4 号 p. 481-498
Yosuke KOSAKA, Yoshihisa MATSUDA
Views: 910
二層の系におけるプラネタリー波動の安定性
公開日: 2007/10/19 | 55 巻 3 号 p. 240-247
山形 俊男
Views: 510
The JRA-55 Reanalysis: General Specifications and Basic Characteristics
公開日: 2015/03/18 | 93 巻 1 号 p. 5-48
Shinya KOBAYASHI, Yukinari OTA, Yayoi HARADA, Ayataka EBITA, Masami MORIYA, Hirokatsu ONODA, Kazutoshi ONOGI, Hirotaka KAMAHORI, Chiaki KOBAYASHI, Hirokazu ENDO, Kengo MIYAOKA, Kiyotoshi TAKAHASHI
Views: 502
The JRA-3Q Reanalysis
公開日: 2024/01/18 | 102 巻 1 号 p. 49-109
Yuki KOSAKA, Shinya KOBAYASHI, Yayoi HARADA, Chiaki KOBAYASHI, Hiroaki NAOE, Koichi YOSHIMOTO, Masashi HARADA, Naochika GOTO, Jotaro CHIBA, Kengo MIYAOKA, Ryohei SEKIGUCHI, Makoto DEUSHI, Hirotaka KAMAHORI, Tosiyuki NAKAEGAWA, Taichu Y. TANAKA, Takayuki TOKUHIRO, Yoshiaki SATO, Yasuhiro MATSUSHITA, Kazutoshi ONOGI
Views: 266
Geometry of Rainfall Ensemble Means: From Arithmetic Averages to Gaussian-Hellinger Barycenters in Unbalanced Optimal Transport
公開日: 2023/12/12 | 102 巻 1 号 p. 35-47
Le DUC, Yohei SAWADA
Views: 142