JMSJ, 2015, Vol. 93, No. 1 (February)
Kobayashi et al. (2015)
Kobayashi, S., Y. Ota, Y. Harada, A. Ebita, M. Moriya, H. Onoda, K. Onogi, H. Kamahori, C. Kobayashi, H. Endo, K. Miyaoka, and K. Takahashi, 2015: The JRA-55 Reanalysis: General specifications and basic characteristics. J. Meteor. Soc. Japan, 93, 5-48.
http://dx.doi.org/10.2151/jmsj.2015-001 Graphical Abstract
- The Japan Meteorological Agency (JMA) conducted the second Japanese global atmospheric reanalysis, called the Japanese 55-year Reanalysis or JRA-55. It covers the period starting in 1958, when regular radiosonde observations began on a global basis. JRA-55 is the first comprehensive reanalysis that has covered the last half-century since the European Centre for Medium-Range Weather Forecasts 45-year Reanalysis (ERA-40), and is the first one to apply four-dimensional variational analysis to this period.
- JRA-55 has been produced with the TL319 version of JMA’s operational data assimilation system as of December 2009, which was extensively improved since the Japanese 25-year Reanalysis (JRA-25). It also uses many newly available and improved past observations. The resulting reanalysis products are considerably better than the JRA-25 product (Fig. 1).
- Two major problems of JRA-25 were a cold bias in the lower stratosphere, which has been diminished, and a dry bias in the Amazon basin, which has been mitigated.
- The temporal consistency of temperature analysis has also been considerably improved compared to previous reanalysis products (Fig. 2).
Sekiyama et al. (2015)
Sekiyama, T. T., M. Kunii, M. Kajino, and T. Shimbori, 2015: Horizontal resolution dependence of atmospheric simulations of the Fukushima nuclear accident using 15-km, 3-km, and 500-m grid models. J. Meteor. Soc. Japan, 93, 49-64.
http://dx.doi.org/10.2151/jmsj.2015-002 Graphical Abstract
- There was a large difference in the surface wind field between the 15-km grid resolution and the other (3-km and 500-m) grid resolutions. The 15-km grid model could not reproduce Fukushima’s mountainous topography in detail (Fig. 1).
- The 15-km grid models could not represent the blockage of the 137Cs plume, which unnaturally spread out through the Naka-dori valley. In contrast, the 3-km and 500-m grid models successfully replicated the blockage along the valley (Fig. 2).
- It is illogical to use low-resolution atmospheric models to assess the Fukushima nuclear accident when a regional analysis is needed. Meanwhile, it is reasonable to use a 3-km grid model instead of high-resolution models due to the similarities between the 3-km and 500-m grid simulations.
Kwon et al. (2015)
Kwon, S., G. W. Lee, and G. Kim, 2015: Rainfall estimation from an operational S-band dual-polarization radar: Effect of radar calibration. J. Meteor. Soc. Japan, 93, 65-79.
http://dx.doi.org/10.2151/jmsj.2015-005 Graphical Abstract
- The calibration biases of ZH are calculated by using the self-consistency constraint between ZH and specific differential phase shift (KDP). This procedure is performed every 2.5 min. The biases are varied from -3.3 dB to 0.8 dB during the period between July 2010 to October 2011
- The ZDR calibration biases are obtained by two methods: 1) vertically pointing measurements, and 2) comparison of observed data with the average ZH-ZDR relationship derived from disdrometric data. The ZDR biases are varied from 0.25 dB to 0.7 dB and both methods show similar results. This ZH-ZDR technique can be applied for a volume scan and does not require a special scan.
- The verification of rainfall estimation is performed by applying 1) average ZH and ZDR calibration biases for the entire period, and 2) adaptive calibration biases that vary each rain event. The application of adaptive calibration biases is more effective for R(ZH,ZDR) and R(ZH, ξDR) than for R(ZH), indicating necessity of frequent calibration of ZH and ZDR. (Fig. 1).
Zhao et al. (2015)
Zhao, H., X. Jiang, and L. Wu, 2015: Modulation of Northwest Pacific tropical cyclone genesis by the intraseasonal variability. J. Meteor. Soc. Japan, 93, 81-97.
http://dx.doi.org/10.2151/jmsj.2015-006 Graphical Abstract
- A majority of TC geneses over the WNP is found to occur during the period when both of these two modes are active (Fig.1), suggesting a joint influence of these two ISV modes on TC genesis over the WNP.
- Modulation of TC genesis over the WNP by the two leading ISV modes can be well depicted by the genesis potential index (GPI) (Fig.2).
- Further investigations indicate that while in general, the low-level absolute vorticity and mid-level relative humidity are the two most important factors affecting WNP TC genesis, relative roles of the four GPI factors tend also to be dependent on the ISV phases (Fig.2).
- Changes in occurrence of major stratospheric sudden warmings (MSSWs) for Northern winter with El Niño/Southern Oscillation (ENSO) and Quasi-Biennial Oscillation (QBO) are investigated using the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data for 56 years.
- La Niña (LA) and El Niño (EL) phases of the ENSO are defined using the NINO3.4 index. Easterly and westerly phases of the QBO are classified with a 0 m/s threshold of the equatorial zonal wind at 50 hPa.
- Our results reveal complex changes in the MSSW probability with both ENSO and QBO (Fig. 1). When the QBO is in a westerly phase, the MSSW probability increases with the ENSO sea-surface temperature condition in the eastern equatorial Pacific, i.e., from LA, through neutral (NT), to EL years. When the QBO is easterly, the probability significantly increases for LA years than for NT years, whereas the probability is not significantly different between NT and EL years.
- A characteristic feature is the high MSSW probability for the LA and QBO easterly winters, which is consistent with strengthened stationary wave with zonal wavenumber 1 compared to the climatology (Fig. 2).
Cho et al. (2015)
Cho, E., H. Moon, and M. Choi, 2015: First assessment of the Advanced Microwave Scanning Radiometer 2 (AMSR2) soil moisture contents in northeast Asia. J. Meteor. Soc. Japan, 93, 117-129.
http://dx.doi.org/10.2151/jmsj.2015-008 Graphical Abstract
- The temporal patterns of the AMSR2 were roughly associated with the in situ soil moisture measurements with some intermittent striking values. Normalizing and filtering methods were applied for the comparison between them with less systematic differences.
- Based on triple collocation, the error estimation showed that the AMSR2 data had a larger error than the in situ and Global Land Data Assimilation System (GLDAS) soil moisture values (Fig.1).
- The spatial distribution of the soil moisture anomaly which used the average soil moisture during the studied period (July 2012 to October 2012) was compared with the spatial distribution of the precipitation that were obtained from the Tropical Rainfall Measuring Mission (TRMM) 3B43 (Fig. 2). The spatial distribution of the AMSR2 soil moisture anomaly and precipitation were found to be moderately well correlated.
Notes and Correspondence
Isono et al. (2015)
Isono, J., and K. Ueno, 2015: Diurnal variations of surface wind speed observed in the mountainous area of central Japan during sunny summer days. J. Meteor. Soc. Japan, 93, 131-141.
http://dx.doi.org/10.2151/jmsj.2015-003 Graphical Abstract
- Surface wind speed anomalies during fair weather in the summer in central Japan, including data at Automated Meteorological Data Acquisition System (AMeDAS) and mountain station data above 2000 m above the mean sea level (a.s.l.) archived by an inter-university cooperative project, showed remarkable diurnal differences depending on the elevations (Fig. 1).
- Nocturnal enhancement of wind speeds at representative mountaintop stations appeared with prevailing Pacific Highs in synoptic pressure patterns, but it did not always appear in the same day and the absolute nocturnal wind speed varied day by day.
- The degree of concavity was not clearly related to the wind speed anomaly, and the degree of convexity was linearly related to the wind speed anomaly at a scale of approximately 10 km.
Orikasa et al. (2015)
Orikasa, N., and M. Murakami, 2015: Ice crystal shapes in midlatitude cirrus clouds derived from hydrometeor videosonde (HYVIS) observations. J. Meteor. Soc. Japan, 93, 143-155.
http://dx.doi.org/10.2151/jmsj.2015-004 Graphical Abstract
- The frequencies of occurrence of ice crystal habits in midlatitude cirrus clouds that were primarily associated warm or stationary fronts within synoptic-scale lows are investigated, using the balloonborne hydrometeor videosonde (HYVIS) observations.
- The predominant types were single bullets at temperatures ranging from –60° to –20°C: Plate-type crystals were dominant at temperatures warmer than –20°C, whereas column or bullet rosette crystals became dominant at temperatures colder than –60°C (Fig. 1).
- Size and temperature dependencies of shape-sensitive parameters, such as area ratio or aspect ratio are examined in each six classified crystal type. The area ratio decreased with increasing dimension was apparent for all the crystal types.
- A comparison of the area ratio of each crystal type between this study and previous studies shows the different size dependency (Fig. 2), which results in 10-80% overestimation of vertically integrated cross-sectional area through the conventional relationships reported in a previous study.