著者

Yaokun Li Yanyan Kang

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2022-013, (Released:2022-03-17)

被引用文献数

2

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The energy dispersion process of westward propagating Rossby waves in tropical easterlies are investigated in the linear nondivergent barotropic atmosphere. The variations in wave energy and amplitude along energy dispersion paths are calculated by solving the wave action conservation equation. The results suggest that a westward marching ray can form a cycle-like path near the turning latitude that is located in easterlies. Waves with shorter periods propagate between two turning latitudes, which are located in either the easterlies or westerlies and have the largest meridional propagation range. Waves with longer periods propagate between a turning latitude in westerlies and a critical latitude in easterlies. Both wave energy and amplitude can simultaneously increase to their maximum values at the turning latitudes that are located in easterlies. This implies that waves may develop significantly. Wave energy and amplitude do not always have an in-phase variation when the ray moves toward the turning latitude that is located in westerlies. The oscillating ranges of wave energy and amplitude are also limited. In this case, waves may not develop significantly.

著者

Yuhji Kuroda Miho Toryu Hiroaki Naoe

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.18, pp.47-52, 2022 (Released:2022-03-18)

参考文献数

21

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This study examined the influence of stratospheric variability on the polar winter tropospheric climate. The winter-mean tropospheric condition can be well represented by a winter-mean stratospheric index (the Polar-night Jet Oscillation (PJO) index) defined from profiles of monthly polar temperature anomalies. In winters with a positive (negative) index, the winter-mean surface pressure anomaly tends to acquire a positive (negative) pattern resembling the Arctic Oscillation (AO). This tropospheric condition tends to become a persistent polarity of the AO index throughout the winter. This tendency is also found when the PJO index for each month is used. Although the PJO index in January shows the best results, those in early winter can be used as predictors for the entire winter troposphere. Use of the PJO index for the stratospheric effect on winter troposphere is compared with that associated with the occurrence of the major stratospheric sudden warmings. The origin of the decadal variability of the index is also discussed.

著者

宮本 佳明 筆保 弘徳 和田 章義

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.100, no.1, pp.181-196, 2022 (Released:2022-02-22)

参考文献数

48

被引用文献数

6

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中心気圧が960hPaで関東地方に上陸した台風Faxai (1915)に関して、非静力学モデルを用いて格子間隔1kmでの数値シミュレーションを行なった。Faxaiは上陸まで軸対称的な構造を維持し、強風により甚大な被害をもたらした。シミュレーションの結果、上陸前後の48時間の現実的な経路・強度が再現された。計算された強度は上陸まで強く、渦の水平方向の大きさは小さかった。計算されたFaxaiの構造は、熱帯海洋上における発達した熱帯低気圧(TC)のように、軸対称的で目の壁雲が存在していた。中心付近で海面の潜熱フラックスは上陸まで300W m-2を超えていて、高度1.5-12 kmでの鉛直シアーは中緯度としては比較的弱く、9m s-1よりも低かった。 台風の環境場パラメータからポテンシャル強度(MPI)を算出した。計算されたTCの強度もベストトラックの強度も、上陸12時間前からMPIよりも大きいsuperintense状態にあった。これは、内部コア域で超傾度風化していたことによるもので、強い強度や軸対称な構造が原因と考えられる。計算されたTCは、成熟期において傾度風平衡を除いたMPIの式に必要な近似を良く満たしており、これはTCの構造が熱帯で発達したものと類似していたためと考えられる。 今回の解析から、Faxaiは、好ましい環境条件と渦構造によって強い強度を維持したと考えられる。

著者

YULIHASTIN Erma HADI Tri Wahyu ABDILLAH Muhammad Rais FAUZIAH Irineu Rakhmah NINGSIH Nining Sari

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.2022-005, (Released:2021-10-04)

被引用文献数

7

---

Early morning precipitation (EMP) events occur most frequently during January and February over the northern coast of West Java and are characterized by propagating systems originating from both inland and offshore. The initial location, direction, and speed of the propagating precipitating system determine the timing of EMP. This study explores processes that characterize such propagating precipitation systems by performing composite analysis and real-case numerical simulations of selected events using the Weather and Research Forecasting (WRF) model with a cloud-permitting horizontal resolution of 3 km. In the composite analysis, EMP events are classified according to the strength of the northerly background wind (VBG), defined as the 925-hPa meridional wind averaged over an area covering western Java and the adjacent sea. We find that under both strong northerly (SN) and weak northerly (WN) wind conditions, EMP is mainly induced by a precipitation system that propagates from sea to land. For WN cases, however, precipitating systems that propagate from inland areas to the sea also play a role. The WRF simulations suggest that mechanisms akin to cold pool propagation and advection by prevailing winds are responsible for the propagating convection that induces EMP, which also explains the dependence of EMP frequency on the strength of VBG. Based on the WRF simulations, we also discuss the roles of sea breeze and gravity waves in the initiation of convection.

著者

Haruka Sasaki Tatsuo Motoi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2022-011, (Released:2022-03-03)

被引用文献数

3

---

Previous studies suggested that increases in ocean heat content result in strengthening of tropical cyclone (TC) and causing the associated disasters. In the western North Pacific (WNP), acceleration of increasing rates of tropical cyclone heat potential (TCHP: ocean heat content above 26°C from the surface) in the TC rapidly intensifying (RI: a 24-h intensity change of ≥ 30 kt) zone may have contributed to increases in TC intensity. However, there is no research on the relation of the acceleration of increasing rates to the variations in TCHP in a climatological view, differently from the relation to decadal variations such as Pacific Decadal Oscillation (PDO). This study focused on the relation of the variations in TCHP anomalies (TCHPA) to RITCs over the past six decades. Although the annual mean TCHPA in the global ocean was not accelerated, the TCHPA accelerated recently in the late 1990s over the RI zone particularly in fall (October–December) in the WNP. The acceleration of the increase in TCHPA was possibly explained by the intensification of trade wind-driven ocean general circulation and the combination of the linear trend of TCHPA with PDO phase change.

著者

Yasumitsu Maejima Takuya Kawabata Hiromu Seko Takemasa Miyoshi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.18, pp.25-32, 2022 (Released:2022-03-07)

参考文献数

35

被引用文献数

6

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This study investigates a potential impact of a rich phased array weather radar (PAWR) network covering Kyushu, Japan on numerical weather prediction (NWP) of the historic heavy rainfall event which caused a catastrophic disaster in southern Kumamoto on 4 July 2020. Perfect-model, identical-twin observing system simulation experiments (OSSEs) with 17 PAWRs are performed by the local ensemble transform Kalman filter (LETKF) with a regional NWP model known as the Scalable Computing for Advanced Library and Environment-Regional Model (SCALE-RM) at 1-km resolution. The nature run is generated by running the SCALE-RM initialized by the Japan Meteorological Agency (JMA) mesoscale model (MSM) analysis at 1800 JST 3 July 2020, showing sustained heavy rainfalls in southern Kumamoto on 4 July. Every 30-second synthetic reflectivity and radial winds are generated from the nature run at every model grid point below 20-km elevation within 60-km ranges from the 17 PAWRs. Two different control runs are generated, both failing to predict the heavy rainfalls in southern Kumamoto. In both cases, assimilating the PAWR data improves the heavy rainfall prediction mainly up to 1-hour lead time. The improvement decays gradually and is lost in about 3-hour lead time likely because the large-scale Baiu front dominates.

著者

Hirokazu Endo Akio Kitoh Ryo Mizuta

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2022-010, (Released:2022-03-01)

被引用文献数

1

---

Future changes in extreme precipitation over the western North Pacific and East Asia (WNP-EA) are investigated using a 20 km mesh atmospheric general circulation model (AGCM). Time-slice simulations are performed under low- and high-emission scenarios using different spatial patterns of changes in sea surface temperature. In the WNP-EA region, future changes in the climatological mean of the annual maximum 1 day precipitation total (Rx1d) are characterized by a large meridional variation, where the higher the latitude, the greater the rate of increase in Rx1d, although this pattern is not so clear under the low emission scenario. This feature probably results from a combination of two factors: a greater warming in high latitudes and a decrease in tropical cyclone (TC) frequency in the subtropics. The future changes in Rx1d climatology for the 20 km AGCM show a marked difference in comparison with those of the lower-resolution AGCM and conventional climate models. Part of this discrepancy may come from differences in model resolution through representation of TCs, suggesting that coarse-resolution models may have some systematic bias in future projections of extreme precipitation in the WNP-EA region.

著者

Eigo Tochimoto Satoshi Iizuka Tadayasu Ohigashi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.18A, no.Special_Edition, pp.1-7, 2022 (Released:2022-02-11)

参考文献数

24

被引用文献数

5

---

The influence of an upper-level trough on a Baiu frontal depression (BFD) that caused a heavy rainfall event in southern Kyushu, Japan, on July 4, 2020, was examined using numerical simulations with and without the upper-level trough. The numerical simulation with the upper-level trough (CNTL) reproduced a reasonable well-developed BFD and heavy rainfall in southern Kyushu. Conversely, the numerical simulation without the upper-level trough (NOUT) produced a weaker BFD and notable southward rainfall shift compared with the situation in the CNTL. The weaker BFD for the NOUT was due to weaker convection than that of the CNTL over mainland China. Thus, strong convection over mainland China was essential for the formation and development of the BFD that caused heavy rainfall in southern Kyushu. Additional sensitivity experiments, in which the strength of the upper-level potential vorticity anomalies was reduced to 75, 50, and 25% of the CNTL, showed that the spatial rainfall distribution shifted southward and resulted in a change in precipitation amounts in southern Kyushu because of the weakening of the BFD.

著者

Kazuto Takemura Hitoshi Mukougawa Yuhei Takaya Shuhei Maeda

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.18, pp.19-24, 2022 (Released:2022-02-11)

参考文献数

18

---

Seasonal predictability of summertime Asian jet deceleration near Japan is examined using monthly mean data of hindcasts based on an operational seasonal prediction system of the Japan Meteorological Agency. Interannual variabilities of the Asian jet deceleration averaged during July–August are generally well predicted with moderate to high forecast skill starting from initial months from January to June. The seasonal predictability of the Asian jet deceleration in specific years is, by contrast, limited with large forecast errors. An inter-member regression analysis for the forecast errors of the Asian jet deceleration using ensembles shows that the forecast errors of the Asian jet are associated with those of the Asian jet deceleration near Japan. Furthermore, the forecast errors of El Niño Southern Oscillation (ENSO)-related excessive upper-tropospheric divergence near Southeast Asia can account for the errors of the northward shifted Asian jet. The above-mentioned results indicate that more accurate seasonal prediction of ENSO can further improve the seasonal prediction skill of the Asian jet deceleration and summer climate near Japan.

著者

Chiaki Kobayashi Shuhei Maeda Yuki Kanno Toshiki Iwasaki

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.18, pp.1-7, 2022 (Released:2022-01-29)

参考文献数

18

被引用文献数

1

---

We examine the relationship between the record-warm winter (DJF) 2019/2020 over East Asia and the extremely weak hemispheric circulation anomaly. During this period, the polar cold-air mass (PCAM) flux over East Asia was the weakest on record since the DJF 1958/1959 due to the weak Siberian High. The zonal averaged surface temperature over the Northern Hemisphere mid-latitudes in DJF 2019/2020 was the highest since DJF 1958/1959 and was linked to the weakest PCAM flux at the mid-latitudes. The zonal mean field during this period was characterized by weak stationary waves, weak wave activity as diagnosed by Eliassen-Palm flux, and, to balance with this, record-weak extratropical direct meridional circulation (EDC). The weak EDC corresponded to weaker-than-normal meridional heat exchange and was consistent with warm anomalies in the Northern Hemisphere mid-latitudes, since the lower branch of EDC corresponds to zonally averaged cold air outflow. In addition, the statistical relationship also indicates the EDC intensity is negatively correlated with the surface temperature anomaly over East Asia.

著者

Ju-Young Shin Kyu Rang Kim Yong Hee Lee

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2022-007, (Released:2022-01-26)

---

Determining the thresholds for risk assessment is critical for the successful implementation of thermal health warning systems. A risk assessment methodology with multiple thresholds must be developed to provide detailed warning information to the public and decision makers. This study developed a new methodology to identify multiple thresholds for different risk levels for heat or cold wave events by considering simultaneously impact on public health. A new objective function was designed to optimize segmented Poisson regression, which relates public health to temperature indicators. Thresholds were identified based on the values of the objective functions for all threshold candidates. A case study in identifying thresholds for cold and heat wave events in Seoul, South Korea, from 2014 to 2018, was conducted to evaluate the appropriateness of the proposed methodology. Daily minimum or maximum air temperature, mortality, and morbidity data were used for threshold identification and evaluation. The proposed methodology can successfully identify multiple thresholds to simultaneously represent different risk levels. These thresholds show comparable performance to those using the relative frequency approach.

著者

Eigo Tochimoto Satoshi Iizuka Tadayasu Ohigashi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.18A-001, (Released:2022-01-25)

被引用文献数

5

---

The influence of an upper-level trough on a Baiu frontal depression (BFD) that caused a heavy rainfall event in southern Kyushu, Japan, on July 4, 2020, was examined using numerical simulations with and without the upper-level trough. The numerical simulation with the upper-level trough (CNTL) reproduced a reasonable well-developed BFD and heavy rainfall in southern Kyushu. Conversely, the numerical simulation without the upper-level trough (NOUT) produced a weaker BFD and notable southward rainfall shift compared with the situation in the CNTL. The weaker BFD for the NOUT was due to weaker convection than that of the CNTL over mainland China. Thus, strong convection over mainland China was essential for the formation and development of the BFD that caused heavy rainfall in southern Kyushu. Additional sensitivity experiments, in which the strength of the upper-level potential vorticity anomalies was reduced to 75, 50, and 25% of the CNTL, showed that the spatial rainfall distribution shifted southward and resulted in a change in precipitation amounts in southern Kyushu because of the weakening of the BFD.

著者

松野 太郎

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.44, no.1, pp.25-43, 1966 (Released:2008-05-27)

参考文献数

10

被引用文献数

1371 1997

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コリオリの力が働かなくなる赤道近辺での大規模運動の特性を理論的に検討してみた。自由表面をもった単層の流体-いわゆる発散順圧モデル-について線型化された運動方程式を扱い東西方向に動く自由波動の解を求めると,一定のスケールに対して3つの解が得られた。これらは振動数解の形(圧力及び運動の場)から夫々東向きおよび西向きの慣性重力波およびロスビー波であることがわかる.但し南北スケール最小のものに関してはその区別は明瞭でなく一方の型から他方の型に連続的にかわる。ロスビー波に相当する解は風と圧力の関係が高緯度でほぼ地衡風的であるごと,および赤道近くで特異なふるまいをするのが特徴である。次に同じモデル熱冷源に相当するものとして東西に周期的なmass source,sinkを与え,定常解と求めた。熱源に相当する所は低圧になるが赤道で分断され,赤道のごく近くはやや逆センスになり,これに伴って高緯度と逆向きの強い流れが生ずることが分った。

著者

Chih-Chien Chang Shu-Chih Yang Stephen G. Penny

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2022-006, (Released:2022-01-20)

被引用文献数

2

---

A regional hybrid gain data assimilation (HGDA) system is newly developed using Weather Research and Forecasting model (WRF). The WRF-HGDA augments an ensemble-based Kalman filter (WRF-LETKF) with information from the variational analysis system (WRF-3DVAR) by combining their gain matrices. The performance of WRF-HGDA is evaluated by assimilating the GNSS radio occultation (RO) observations from the FORMOSAT-3/COSMIC (FS3/C) and the FORMOSAT-7/COSMIC2 (FS7/C2) under an Observing System Simulation Experiment (OSSE) framework. The results demonstrate that the variational correction improves the WRF-LETKF, with the equal-weighted WRF-HGDA outperforming its component DA systems in the moisture and wind fields when only conventional observations are assimilated. Assimilating additional RO data from FS7/C2 further improves the WRF-LETKF and WRF-HGDA systems. Although the variational correction for the mid-level temperature causes degradation in the WRF-HGDA analysis, this can be alleviated by adjusting the combination weight to include more flow-dependent information in WRF-HGDA at these levels. Further tuning of the static background error covariance used in WRF-3DVAR also brings some improvement in the WRF-HGDA wind analysis. Our results imply that a well-tuned variational system is critical for the accuracy of the regional HGDA analysis.

著者

Kazuto Takemura Hitoshi Mukougawa Yuhei Takaya Shuhei Maeda

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2022-004, (Released:2022-01-13)

---

Seasonal predictability of summertime Asian jet deceleration near Japan is examined using monthly mean data of hindcasts based on an operational seasonal prediction system of the Japan Meteorological Agency. Interannual variabilities of the Asian jet deceleration averaged during July–August are generally well predicted with moderate to high forecast skill starting from initial months from January to June. The seasonal predictability of the Asian jet deceleration in specific years is, by contrast, limited with large forecast errors. An inter-member regression analysis for the forecast errors of the Asian jet deceleration using ensembles shows that the forecast errors of the Asian jet are associated with those of the Asian jet deceleration near Japan. Furthermore, the forecast errors of El Niño Southern Oscillation (ENSO)-related excessive upper-tropospheric divergence near Southeast Asia can account for the errors of the northward shifted Asian jet. The above-mentioned results indicate that more accurate seasonal prediction of ENSO can further improve the seasonal prediction skill of the Asian jet deceleration and summer climate near Japan.

著者

ROH Woosub SATOH Masaki HOHENEGGER Cathy

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.2021-070, (Released:2021-08-24)

被引用文献数

12

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We intercompared the cloud properties of the DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains (DYAMOND) simulation output over the Atlantic Ocean. The domain averaged outgoing long-wave radiation (OLR) is relatively similar across the models, but the net shortwave radiation at the top of the atmosphere (NSR) shows large differences among the models. The models capture the triple modes of cloud systems corresponding to shallow, congestus, and high clouds, even though their partition in these three categories is strongly model dependent.The simulated height of the shallow and congestus peaks is more robust than the peak of high clouds, whereas cloud water content exhibits larger intermodel differences than cloud ice.  Furthermore, we investigated the resolution dependency of the vertical profiles of clouds for NICAM (Nonhydrostatic ICosahedral Atmospheric Model), ICON (Icosahedral Nonhydrostatic), and IFS (Integrated Forecasting System). We found that the averaged mixing ratio of ice clouds consistently increased with finer grid spacing. Such a consistent signal is not apparent for the mixing ratio of liquid clouds for shallow and congestus clouds. The impact of the grid spacing on OLR is smaller than on NSR and also much smaller than the intermodel differences.

著者

Bjorn STEVENS Masaki SATOH

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.99, no.6, pp.1393-1394, 2021 (Released:2021-12-24)

参考文献数

10

著者

Mizuki Konagaya Teruo Ohsawa Takaya Inoue Toshinari Mito Hideki Kato Kazuhiro Kawamoto

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17, pp.234-238, 2021 (Released:2021-12-18)

参考文献数

13

被引用文献数

1

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To develop offshore wind energy, we investigated nearshore wind conditions, notably the land–sea contrast, using the coastal area of Mutsu-Ogawara, Aomori Prefecture as a case study. We found that wind conditions were substantially different between onshore (MT-A1) and offshore (MT-B) sites, even when the latter were only 1.5 km apart. The mean wind speed at 55 m above sea level at MT-B was higher than that at the onshore site by up to 20% monthly and 12% annually. For winds from the landward side, the Iref value (turbulence intensity at a mean wind speed of 15 m/s) at MT-B was 37% lower than that at MT-A1. Because such high wind speeds and low turbulence conditions are preferable for the operation of wind turbines, an offshore wind farm would have advantageous wind conditions, even if placed close to the coastline. Moreover, we found that the land–sea contrast is caused not only by mechanical factors, such as roughness length, but also by thermodynamic factors such as seasonal variations of atmospheric stability over land and sea.

著者

Yoshifumi Ota Miho Sekiguchi Yousuke Sato

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17, pp.228-233, 2021 (Released:2021-12-16)

参考文献数

19

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A three-dimensional (3D) atmospheric radiative transfer (RT) model based on the Monte Carlo method was developed to evaluate the cloud-resolving radiation budget. The simulation data of stratocumulus (open and closed cell types) stimulated by a large eddy simulation model were used to obtain a detailed cloud field dataset at different spatial resolutions between 100 m and 1 km orders. By applying the 3D RT model offline to a multiscale cloud field dataset, the 3D distribution and magnitude of the solar radiative heating rate were estimated for each spatial resolution. The results showed that the magnitude of the local solar radiative heating effect significantly changes in the range of spatial resolution between 100 m and 1 km. The solar radiative heating rate can reach 6 K/hr locally in the case of the spatial resolution at 100-m order, whereas it is approximately 1 K/hr at most in the case of the spatial resolution at 1-km order. However, the domain-averaged values of the solar radiative heating rates were almost invariant at different spatial resolutions. The results indicate that a radiation scheme for the cloud-resolving model needs to be constructed while considering spatial resolutions, along with cloud parameterization.

著者

MURAKAMI Masataka

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.2019-009, (Released:2018-11-05)

被引用文献数

5

---

A large amount of snowfall caused by snow clouds over the Sea of Japan sometimes severely affects social and economic activities in Japan. Therefore, snow clouds, which form and develop mainly over the ocean and bring heavy snowfall to populated coastal plains, have long been intensively studied from the perspective of disaster prediction and prevention. Most studies have analyzed data acquired by aerological, meteorological satellite, and radar observations, or have conducted numerical simulations. Because of the difficulties involved in accessing cloud systems over the ocean, however, few in situ observation data have been available, and up until the middle 1990s, many problems remained unsolved or their analysis and simulation results remained unvalidated. Here, knowledge gained from instrumented aircraft observations made from the middle 1990s through the early 2000s is reviewed, in particular with regard to the development of a convectively mixed boundary layer and the inner structures of longitudinal-mode cloud bands, Japan-Sea polar-air mass convergence zone cloud bands, and a polar low. Unsolved problems relating to the inner structures and precipitation mechanisms of snow clouds and the expected contributions of aircraft observations to further progress in these areas of atmospheric science are also briefly discussed.