The JRA-55 Reanalysis: General Specifications and Basic Characteristics

In this paper, we present a comprehensive review of the data sources and estimation methods of 30 currently available global precipitation data sets, including gauge-based, satellite-related, and reanalysis data sets. We analyzed the discrepancies between the data sets from daily to annual timescales and found large differences in both the magnitude and the variability of precipitation estimates. The magnitude of annual precipitation estimates over global land deviated by as much as 300 mm/yr among the products. Reanalysis data sets had a larger degree of variability than the other types of data sets. The degree of variability in precipitation estimates also varied by region. Large differences in annual and seasonal estimates were found in tropical oceans, complex mountain areas, northern Africa, and some high-latitude regions. Overall, the variability associated with extreme precipitation estimates was slightly greater at lower latitudes than at higher latitudes. The reliability of precipitation data sets is mainly limited by the number and spatial coverage of surface stations, the satellite algorithms, and the data assimilation models. The inconsistencies described limit the capability of the products for climate monitoring, attribution, and model validation.

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A Review of Global Precipitation Data Sets: Data Sources, Estimation, and Intercomparisons

Editor’s note: For easy download the posted pdf of the State of the Climate for 2016 is a very low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download.

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State of the Climate in 2015

Variability Assessment and Forecasting of Renewables : A Review for Solar, Wind, Wave and Tidal Resources

Variability assessment and forecasting of renewables: A review for solar, wind, wave and tidal resources

. An earth system model has been developed at Beijing Normal University (Beijing Normal University Earth System Model, BNU-ESM); the model is based on several widely evaluated climate model components and is used to study mechanisms of ocean-atmosphere interactions, natural climate variability and carbon-climate feedbacks at interannual to interdecadal time scales. In this paper, the model structure and individual components are described briefly. Further, results for the CMIP5 (Coupled Model Intercomparison Project phase 5) pre-industrial control and historical simulations are presented to demonstrate the model's performance in terms of the mean model state and the internal variability. It is illustrated that BNU-ESM can simulate many observed features of the earth climate system, such as the climatological annual cycle of surface-air temperature and precipitation, annual cycle of tropical Pacific sea surface temperature (SST), the overall patterns and positions of cells in global ocean meridional overturning circulation. For example, the El Nino-Southern Oscillation (ENSO) simulated in BNU-ESM exhibits an irregular oscillation between 2 and 5 years with the seasonal phase locking feature of ENSO. Important biases with regard to observations are presented and discussed, including warm SST discrepancies in the major upwelling regions, an equatorward drift of midlatitude westerly wind bands, and tropical precipitation bias over the ocean that is related to the double Intertropical Convergence Zone (ITCZ).

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Description and basic evaluation of Beijing Normal University Earth System Model (BNU-ESM) version 1

The Japan Meteorological Agency (JMA) started the second Japanese global atmospheric reanalysis project named the Japanese 55-year Reanalysis (JRA-55). It covers 55 years, extending back to 1958, when the global radiosonde observing system was established. Many of the deficiencies found in the first Japanese reanalysis, the Japanese 25-year Reanalysis (JRA-25), have been improved. It aims at providing a comprehensive atmospheric dataset that is suitable for studies of climate change or multi-decadal variability, by producing a more time-consistent dataset for a longer period than JRA-25. Production of JRA-55 started in 2010, and computations for more than 16 years have been completed as of August 2011. The entire JRA-55 production will be completed in early 2013 and thereafter JRA-55 will be continued as a new JCDAS on real time basis. This paper is a brief report to introduce the JRA-55 reanalysis project. The data assimilation and prediction (DA) system used in JRA-55 is introduced and compared to that used in JRA-25. Early results of JRA-55 are presented and discussed, showing general improvements.

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The Japanese 55-year Reanalysis "JRA-55": An Interim Report

The purpose of this article is to document genesis, development and dissipation of a subsynoptic-scale typhoon-like cyclone, that caused severe weather on 13 October 2003, over the eastern part of the Kanto area. In this documentation, practically all available data obtained operationally by the Japan Meteorological Agency are used. The subtropical low of interest formed initially as a mesoscale vortex at 0000UTC 8 October over the ocean near Okinawa Island (∼26°N, 128°E), where the western end of a quasi-stationary polar front was located. The genesis region is characterized by a weak baroclinicity, and nearly saturated low-level atmosphere, with a negative Showalter Stability Index. Several mesoscale convective systems developed prior to the formation of the subtropical low in the genesis region. It is inferred that diabatic heating, by the release of latent heat in deep convection helped spin up pre-existing relative vorticity associated with the quasi-stationary polar front. In addition, an upper-level short wave trough spawned a cut-off low over the region, helping the vortex to develop into the subtropical low. When matured ∼50 h later, the subtropical low exhibited remarkable axisymmetry in the wind and thermal structures, with the diameter of 100∼200 km. The cloud pattern also displayed a cloud-free eye-like structure. After it traveled slowly northwards for four days, the subtropical low was overtaken by a synoptic scale trough, and underwent the processes known as the extratropical transition of a typhoon, while it moved towards the east. Finally, briefly discussed are similarities and dissimilarities between the present subtropical low, and hurricane-like subtropical cyclones that develop in other regions of the globe, such as the Mediterranean Sea and the central/eastern Pacific Ocean.

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Evolution of a Typhoon-Like Subtropical Low Causing Severe Weather over the Kanto Area on 13 October 2003

On 7-8 April, 2008, a sub-synoptic scale cyclone traveled eastward over the sea south of the Japan Islands. Heavy precipitation and high winds caused severe damages in the regions along the passage of the cyclone. In order to describe the structure of the cyclone and understand processes underlying its evolution, operationally observed meteorological data and numerical model output are analyzed. The result reveals that the cyclone fits a class of subtropical low (abbreviated as SL). The SL is basically a vortex that is characterized by the following features: It is accompanied by heavy precipitation and typhoon force winds (wind speed exceeding 17 m s-1), is on the meso-α scale, has contours of nearly axisymmetric surface isobars without a cold front nor a warm front, has potential temperature higher than the surrounding atmosphere around the vortex center and exhibits a cloud-free “eye”. The sea surface temperature is below 26°C.The SL under study was initiated beneath the exit region of an upper-level straight jet that became collocated with the region marked by increasing diffluence in the 300 hPa geopotential height field immediately downstream of the trough axis. While propagating over the sea south of the Japan Islands, the incipient low evolved into a meso-α scale, typhoon-like vortex. It is speculated that the intensification of the vortex was caused by latent heat released in deep convections.In terms of vorticity at low levels, the vortex reached its peak activity about 30 hours after it was born. Since then, the vortex started loosing its axisymmetric structure. A region of high vorticity began to develop at the east side of the vortex, corresponding to the development of a bent-back warm front. The T-born type frontal structure similar to the third stage of evolution in the Shapiro and Kayser’s midlatitude cyclone model eventually emerged. In the decaying stage of evolution, the spiral pattern of a potential vorticity streamer was observed, followed by formation of the spiral cloud pattern. Thus, as a distinct weather system, the concept of the SL may be broadened to include not only an intense subsynoptic-scale vortex but also a frontal system that develops at the later stage.

Initiation and Evolution of a Subtropical Low Observed near the Japan Islands

The purpose of this article is to report the result of our effort to uncover the nature, and possible cause(s), of the high wind that was responsible for some human and property damage in the morning of 2 March 2003 in Yaita city, Totigi prefecture. Our approach is through the analysis of observed data and all data used are conventional. It is found that the damage-causing high wind was a foehn-like downslope wind, which occurred when a bomb-class midlatitude cyclone passed over the Kanto area, and Yaita city was situated on the lee side of the mountain range in the strong northwesterly flow in the back side of the cyclone. The unique feature of the present high wind event is that it was followed by another foehn-like episode, in that surface temperature was higher and dewpoint temperature was lower than in the preceding foehn, while the wind was less violent. It is concluded, through the analysis of the precipitation field, that the first foehn was wet (thermodynamic), whereas the second foehn was dry (dynamic). Further, in our quest to understand why the surface air was warmer and dryer in the second foehn, it is found that, by the time of the commencement of the second foehn, the region of the unusually strong mid-level descending motion, representing the dry intrusion, had approached the Kanto area and this helped bring down the air possessing high potential temperature and low mixing ratio into the downslope wind in the second foehn. Finally, it is pointed out that a well-defined low-level jet was present in the northwesterly flow behind the cyclone center and the strong wind associated with the low level jet was instrumental in the present foehn event. Thus, presented here are documentations showing the sequence of events associated with successive foehn formations, that occurred in a quite limited local area but was intimately linked with the evolution and structure of a synoptic-scale midlatitude cyclone.

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Ryoji Kumabe

Papers

The Japanese 55-year Reanalysis "JRA-55": An Interim Report

Evolution of a Typhoon-Like Subtropical Low Causing Severe Weather over the Kanto Area on 13 October 2003

Initiation and Evolution of a Subtropical Low Observed near the Japan Islands

A Foehn Event Enhanced by the Synoptic Scale Dry Intrusion