著者
SUI Chung-Hsiung SATOH Masaki SUZUKI Kentaroh
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2020-024, (Released:2020-03-01)

Precipitation efficiency (PE) is a useful concept for estimating precipitation under a given environmental condition. PE is used in various situations in meteorology: to evaluate severe precipitation associated with a single storm event; as a parameter of cumulus convective parameterization; and to separate clouds and precipitation in climate projection studies. PE has been defined in several ways. In this review, we start with definitions of PE from microscopic and macroscopic perspectives, and provide estimates of PE based on observational and modeling approaches. Then, we review PE in shallow and organized deep convective systems that provide either a conceptual framework or physical constraints on representations of convection in models. Specifically, we focus on the roles of PE in cloud-radiative feedbacks to climate variability. Finally, we argue the usefulness of PE for investigating cloud and precipitation changes in climate projection studies.
著者
NAKAMURA Yuhi MIYAKAWA Tomoki SATOH Masaki
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2020-046, (Released:2020-06-02)

From 9 to 11 September 2015, the Kanto and Tohoku regions of Japan experienced an extremely heavy rainfall event. The synoptic-scale field was characterized by two typhoons, Etau (T1518) and Kilo (T1517). After Etau made landfall in the Tokai region and transformed into an extra-tropical cyclone over the Sea of Japan, meridionally oriented rain bands persisted over the Kanto region for about 12 hours and caused heavy rainfall, particularly over the Tochigi prefecture. During this time, Kilo approached the eastern ocean of the Kanto region. In this study, we examine the role of Kilo in this event by conducting numerical experiments using a stretched version of the Nonhydrostatic Icosahedral Atmospheric Model configured with a minimum grid interval of about 5.6 km. The control experiment reproduced intense rain bands around the same period and place as the observed event, although they were not reproduced in an experiment with a longer lead time. Sensitivity experiments were conducted in which Kilo was weakened by removing moisture in its central region with a longer lead time. In contrast to the expectation that reduced moisture would lead to a weaker typhoon and hence weaker rain, the sensitivity experiment reproduced the rain band with realistic location but 5 % less precipitation than the control experiment. Furthermore, this experiment indicated that precipitation over the outer band of Etau, which covers the Kanto region, increased by 10 % compared to the control experiment. We found that a southeasterly wind induced by a high-pressure ridge between Kilo and the Kanto region played a greater role in supplying moisture to the Kanto region than the strong easterly wind produced by the pressure gradient between Kilo and the Okhotsk high. In this case, weaker Kilo resulted in enhanced northwestward moisture flux associated with the ridge, thereby inducing heavier rainfall over the Kanto region.
著者
JINNO Takuya MIYAKAWA Tomoki SATOH Masaki
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2019-017, (Released:2018-12-07)
被引用文献数
1

In August 2016, a monsoon gyre persisted over the western North Pacific and was associated with the genesis of multiple devastating tropical cyclones. A series of hindcast simulations was performed using the nonhydrostatic icosahedral atmospheric model (NICAM) to reproduce the temporal evolution of this monsoon gyre. The simulations initiated at dates during the mature stage of the monsoon gyre successfully reproduced its termination and the subsequent intensification of the Bonin high, while the simulations initiated before the formation and during the developing stage of the gyre failed to reproduce subsequent gyre evolution even at a short lead time. These experiments further suggest a possibility that the development of the Bonin high is related to the termination of the monsoon gyre. High predictability of the termination is likely due to the predictable mid-latitudinal signals that intensify the Bonin high.
著者
OHNO Tomoki NODA Akira T. SATOH Masaki
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2020-054, (Released:2020-07-20)

The impacts of the saturation adjustment type approach to sub-grid-scale (SGS) ice clouds in a turbulent closure scheme on the high clouds and their response to global warming were investigated based on the radiative–convective equilibrium experiments (RCEs). This was motivated by the fact that the time scale of ice condensation is several orders of magnitude longer than that for liquid water. The RCEs were conducted with uniform sea surface temperatures over the spherical domain for the Earth's radius without rotation using an explicit cloud microphysics and a non-hydrostatic icosahedral atmospheric model. This study revealed that suppressing the phase change effect associated with the SGS ice condensation on the buoyancy of the SGS turbulence could cause approximately a 20 % reduction of the total high cloud covers and a significantly different response of high cloud amounts to global warming due to the change in static stability near high clouds, which leads to weaker vertical heat transport at a sub-grid scale there. Since the typical value of the time scale of the ice-phase cloud is much longer than that for liquid water and the ice supersaturation is in general, using the saturation adjustment type approach for SGS ice clouds could lead to an overestimation of the effect of ice condensation for the turbulent mixing and model biases in simulations with both cloud resolving models and general circulation models. The present result underlines the critical nature of the treatment of SGS ice clouds in turbulence schemes which reflects a realistic ice condensation time scale not only for a better representation of high clouds in the current climate but for an improved projection of changes of high clouds due to global warming.
著者
ROH Woosub SATOH Masaki
出版者
(公社)日本気象学会
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2018-002, (Released:2017-09-29)
被引用文献数
1

As an alternative approach to the previous multisensor satellite evaluation method of cloud system resolving models, a method is presented using combined infrared and microwave channels for precipitation clouds in cloud system resolving models over the ocean. This method determines characteristics of cloud-top temperatures and ice scatterings for clouds using infrared 11-μm and microwave high frequencies (89.0 GHz) brightness temperatures (TBs). The threshold of the TB at low frequencies (18.7 GHz) is also used to identify precipitation regions. This method extends the previous approach via the wider swath of the passive microwave sensor and sensitivities to ice clouds compared to the previous Tropical Rainfall Measuring Mission (TRMM)-based analysis method using the narrower coverage of the Precipitation Radar. The numerical results of the non-hydrostatic icosahedral atmospheric model (NICAM) with two cloud microphysics schemes are evaluated over the tropical open ocean using this method. The intensities of the scatterings in the two simulations at 89.0 GHz are different due to the parameterizations of the snow and graupel size distributions. A bimodal size distribution of the snow improved the underestimation of the TBs at 89.0 GHz. These results have a similar structure to the joint histograms of cloud-top temperatures and precipitation-top heights in the previous method: the overestimated intensity of scattering and the frequencies of high precipitation-top heights above 12 km in the control experiment. We find that the change in the snow size distribution in the cloud microphysics scheme can lead to better agreements of simulated TBs at 89.0 GHz with observations. We further investigate impacts of non-spherical assumptions for snow using a satellite simulator. The effect of a non-spherical shape of snow in the radiative transfer model causes a smaller change of TBs at 89.0 GHz compared to the difference between the TBs of the two simulations without non-spherical assumptions.