On May 31, 2007, a waterspout occurred over Tokyo Bay near the Futtsu Coast, Chiba Prefecture, Japan. Based on Doppler radar observations and the field surveys, the detailed structures of the funnel and the parent cloud were revealed. The funnel diameter was about 25 m near the surface, and expanded as the altitude increased. The misocyclone had a diameter of 0.2 km and vorticity on the order of 10-1 s-1 below the cloud base. The lifetime of the funnel was about 7 minutes, while that of misocyclone was about 20 minutes. The waterspout formed over the wind shear zone, which was favorable for the formation of an anticyclonic vortex.
A simple and accurate interpolation method applicable to semi-Lagrangian advection in a spectral global atmospheric model and downscaling is presented. The derivatives required for bicubic interpolation are usually represented by finite differences. Accuracy of bicubic interpolation is found to be improved by using derivatives calculated by the spectral method. Thus, the zonal and meridional derivatives are obtained by the Fourier and Legendre transforms, respectively. The proposed method is validated with the Gaussian hill rotation tests. The semi-Lagrangian advection model with this method produces a minimal error, comparable to that of the non-interpolating semi-Lagrangian model. In order to avoid the computationally expensive Legendre transforms, semi-spectral interpolation methods using only zonal spectral derivatives are also tested. Semi-spectral interpolation is found to be as accurate as full-spectral bicubic interpolation when quintic interpolation is used in the meridional direction.
The Pacific-Japan (PJ) teleconnection pattern is one of the dominant summertime anomaly patterns of the atmospheric circulation that influence summertime weather conditions over the Far East. It is associated with anomalous cumulus convection over the tropical Northwestern Pacific. The present study compares the structure and energetics of the pattern based on four atmospheric reanalysis datasets currently available. PJ-associated vorticity anomalies are found similar among the four datasets, and so are its conversions of kinetic and available potential energy from the climatological-mean flow, confirming its characteristics as a dynamical mode of variability. In contrast, spatial distribution and strength of anomalous cumulus convection differ considerably among those datasets, and distribution of temperature anomalies also exhibits some discrepancies around the anomalous convection. Those discrepancies cause substantial differences in available potential energy generation due to anomalous cumulus convection, suggesting the potential that the diabatic heating can be as equally important in maintaining the PJ pattern as the dry processes.
Atmospheric soundings using the Vaisala RS92 radiosonde were intensively conducted during the field experiment MISMO (Mirai Indian Ocean cruise for the Study of the MJO-convection Onset) in the central and eastern equatorial Indian Ocean from October to December 2006. By comparing the RS92 relative humidity data with that from the Meteolabor Snow White (SW) chilled-mirror dew/frost-point hygrometers launched on the same ship around the local noon time, the dry bias was found to increase significantly with height. In addition, it was also revealed that the dry bias had a clear diurnal variation with its maximum at local noon and near-zero at night from the comparison of precipitable water vapor (PWV) with that derived from the shipboard Global Positioning System (GPS) data. Therefore, the dry bias of the RS92 data could be attributed to a solar radiation-induced error that was recently discussed by Vömel et al. (2007). In this study, we developed a correction scheme for the MISMO RS92 humidity data as a function of pressure and local time using SW data, and then confirmed its validity with GPS-derived PWV.
We show the near-term predictions of mean and extreme precipitation up to the year 2030 by analyzing ten-member ensemble runs with perturbed initial conditions of the MIROC model. Mean and extreme precipitation increase in high latitudes and the tropics, and decrease in the subtropics in the ensemble mean. Uncertainty due to natural variability was also examined. Most of the ten runs predict positive anomalies in high latitudes and some parts of the tropics. Changes in parts of the subtropics are uncertain due to natural variability. Thermodynamic changes mainly explain robust total increases in mean precipitation in high latitudes and the tropics. Thermodynamic changes of mean precipitation are uncertain in the subtropics, resulting in a large uncertainty in total changes. It is suggested that small signal-to-noise rations of thermodynamic changes in the subtropics are induced by regional decreases in relative humidity at lower troposphere, which counteract the effects of increased column-integrated water vapor.
Cyclone phases for 15 tropical cyclones (TCs) that made 17 landfalls in Japan during 2004-2006 are examined by using the gridded reanalysis datasets of the Japan Meteorological Agency. TCs with 9 landfalls south of 40°N from late June through early September had the structure of typical tropical cyclones, i.e., a thermally symmetric warm-core structure. TCs of 3 landfallings north of 40°N and one landfalling in western Japan in mid-June had the structure of a frontal cyclone, which suggests that the environmental baroclinicity would have contributed to the structure change of the cyclones. With the other 4 landfalls south of 40°N after mid-September, TCs were transitioning into extratropical cyclones with a thermally asymmetric warm-core structure, and were associated with significant features including frontal heavy rainfall and localized gusts related to the environmental baroclinicity. This suggests that precautions should be taken against a TC approaching Japan in mid- and late autumn associated with features different from those of a typical TC.
Five-year integrations with the Non-hydrostatic Regional Climate Model (NHRCM) are conducted to evaluate the reproducibility of the regional climate. NHRCM, with a grid interval of 10 km, is nested in the Regional Analysis data set, and a 4 km grid interval NHRCM is nested in it. NHRCM reproduces the monthly precipitation, seasonal change, and regional features well when compared to AMeDAS observations. The model also simulates the frequency of heavy precipitation well. Annual mean temperature of NHRCM exhibits a +0.8ºC bias compared to the AMeDAS observation. NHRCM also reproduces inter-annual variation of surface temperature well, especially in summer.
The source terms of the cloud condensate tendency equation are analyzed for two general circulation models to clarify the effect of model differences on the non-convective cloud response to CO2 doubling. This analysis investigates the differences in the mechanism of cloud feedback between models, which is considered a major source of uncertainty in climate change projections. The two GCMs, the Hadley Centre model and MIROC, exhibit marked differences in cloud response in the mixed-phase region: cloud in middle to low latitudes decreases in the former and increases in the latter. The source terms indicate that the difference is attributable to the condensation-evaporation response. Discussions on the inter-model variance of cloud feedback may thus be assisted by developing a better understanding and evaluation of condensation-evaporation. The difference in the cloud response is also related to the relative importance of ice sedimentation compared to other microphysical processes: the former tends to increase mixed-phase cloud while the latter tends to decrease the cloud. Physically based modeling of the relevant microphysical processes is thus considered essential for having more confidence in the simulated cloud feedback.
We investigated the diurnal variation of water vapor mixing between the atmospheric boundary layer (ABL) and the free atmosphere over the Loess Plateau in China. Water vapor and wind velocity in the troposphere were observed using a ground-based microwave radiometer and a wind profiler radar in 2005 and 2006. On sunny days in early summer, a strong vertical wind was generated in the afternoon followed by ABL development. Strong convection was enhanced when active cumulus convection developed in the afternoon. In such cases, water vapor decreased in the lower atmosphere from the early morning until late afternoon, while water vapor increased in the upper atmosphere. This finding suggests that water vapor was exchanged diurnally between the ABL and the free atmosphere. The strong convection in the ABL, which was developed by sensible heat from the land surface, played critical roles with link to cumulus convection in such vertical mixing of water vapor. Influences of other processes such as a local circulation and advection of cloud systems were also discussed.
The background error variance is modified within the Japan Meteorological Agency (JMA) global four-dimensional variational (4D-Var) data assimilation system; the impact is investigated. In the operational 4D-Var the background error variance is assumed to be constant globally at each vertical level for each variable. This study performs additional data assimilation experiments by allowing horizontal and temporal inhomogeneities in the background error variance. A new method with a similar idea to the one for the dynamic quality control is proposed in this study to account for temporal variations, i.e., flow-dependence. It turns out that the impact by the horizontal and temporal inhomogeneities is small and that including the horizontal variations does not necessarily improve the forecast. However, considering flow-dependence indicates generally positive impact.
We propose a use of high speed spherical self-organizing map (HSS-SOM) as a new visualization technique for huge climate datasets complementarily and alternatively to empirical orthogonal function (EOF) analysis. In order to reduce computational cost, we change the number and visible positions of neurons in our HSS-SOM method. This method allows us to use a large number of neurons and thus understand climate datasets better than conventional methods. We apply the HSS-SOM to a 4-times daily surface temperature dataset to check the accuracy. Then the HSS-SOM succeeds to map all data into 4 cluster regions in which each cluster region includes data of the same observational time. While 4 cluster regions are also classified by EOF analysis clearly, HSS-SOM locates several observational data points whose spatial patterns are similar to each other but observed at different time in a marginal area of different cluster regions. We also apply the HSS-SOM to a huge climatology dataset which is not classified clearly in the EOF analysis. Then the HSS-SOM classifies observational data points of similar spatial patterns in the physical space closely, while those of different spatial patterns far away. These results show HSS-SOM extracts more detailed features than the EOF, and suggest that the HSS-SOM would be a useful tool to study future climate change and its assessment.
Analyses of precipitation amounts and surface winds observed at weather stations were conducted to investigate the effect of the topography on the snowfall distribution in Niigata. The topographic effect on the precipitation, particularly in the Niigata plain, has not been well discussed although Akiyama (1981a, 1981b) discussed the relationship between the snowfall distribution in Niigata and the synoptic scale condition. Using an empirical orthogonal function analysis, the winter precipitation distribution from 1988 to 2007 in Niigata was categorized as plain-type (P-type) and mountain-type (M-type). The P-type precipitation occurs under an upper trough over the Sea of Japan. The synoptic westerly wind, brought by the lower trough near the Japan Islands, and the deep convective mixed layer will be responsible for the precipitation in the plains of Niigata and Hokuriku. In addition, the Noto Peninsula and the mountain range to the east of the Hokuriku area seem to play an dynamical role in the precipitation in the Niigata plain. The M-type precipitation occurs under the upper trough over Japan. The synoptic scale condition brings northwesterly wind, which causes a topographic updraft at the mountain slope, resulting in precipitation dominated in the Niigata mountain range.
In this paper, the calculation of eddy covariance flux is reevaluated with newly-emerged capability of the wavelet transform. It is demonstrated that the wavelet transform clearly revealed the cospectral gap that separates turbulent and mesoscale motions with the data collected over a rice and a larch forest. It is also shown that the computed eddy covariance flux is insensitive to the method of decomposition of the turbulent fluctuation from the mean when averaging time is set at around the cospectral gap location. Therefore, information on the gap location removes the ambiguity in the calculation of eddy covariance flux.
The air temperature distribution and airflow field in an actual urban street canyon were clarified through intensive observations. The 2-D distribution of temperature and wind was clarified on a N-S vertical cross section of the E-W-oriented street canyon. A steady single vortex, approximately equal to the size of the canyon, was frequently observed. A rather distinct vortex was observed when the ambient winds above the canyon were high and their direction was transverse to the canyon. Thermally unstable stratification also contributed to the formation of the distinct vortex. The vortex airflow advected the cold air mass, which was produced by the shade due to the buildings, upwind of the ambient wind above the canyon.
Cloud types of tropical upper-tropospheric stratiform clouds (UTSCs) were estimated using split-window brightness temperatures (TB) measured by a geostationary satellite. For non-precipitating high clouds, cloud-top heights were estimated. Observation-based estimation tables in terms of 10.8 µm TB (T11) and the difference between T11 and 12 µm TB (ΔT = T11 - T12) were presented using ship-borne cloud radar measurements conducted during three months in the tropical warm-pool region. After defining the cloud types and cloud-top height using radar measurements, their detectabilities were shown as the function of T11 and ΔT. The detectability of non-precipitating UTSCs is higher in regions with T11 between 220 and 275 K and higher ΔT. Surface precipitation is more detectable in regions with low T11 and small ΔT. The estimated cloud-top height of non-precipitating UTSCs tends to rise with decreasing T11 and increasing ΔT. The variation in the cloud-top estimates with ΔT reached a few kilometers at T11 of ∼250 K.
The results of a T213L250 gravity wave (GW) resolving general circulation model (GWR-GCM) are used to constrain the GW source spectra of a non-orographic GW drag parameterization (GWDP) proposed by Hines. In this study, the following two constraints were placed on Hines’s GWDP: 1) the launch level at which GW source spectra are specified, and 2) the GW-source spectra, that is, the seasonally varying geographical and azimuthal distribution of GW momentum flux and horizontal wind amplitude. Considering the importance of the lateral propagation of GWs, which is ignored in Hines’s GWDP, the GW source spectra are prescribed using information from the GWR-GCM at 70 hPa, where the GWs have already propagated laterally some distance from their source regions. The GW-source spectra have significant geographical variations and anisotropy, reflecting source distribution and the effects of critical level filtering due to the background flows. Although the effects of the lateral propagation and intermittency of GWs are ignored, a T42L80 chemistry coupled climate model using the GWDP with the constraints developed in this study realistically reproduced the meridional structures of the zonal wind jets in the stratosphere and mesosphere.
We used ozone (O3) and carbon monoxide (CO) measurements conducted at Rishiri Island, a remote surface site located in northern Japan to characterize impacts of boreal forest fires in Siberia on photochemical O3 formation. Hourly O3 observations during severe fire seasons in 1998, 2002, and 2003 were examined based on large enhancement in the CO mixing ratios and backward trajectories. In total, we identified sixteen episodes impacted by Siberian biomass burning. Correlations of O3 to CO in individual plumes were significant in eight wildfire plumes. The relative enhancement of O3 to CO quantified in these fire plumes ranged from slightly negative to up to ∼0.4, depending on episodes. Two episodes in 2002 and 2003 suggested that O3 formation in wildfire-polluted plumes was comparable to the magnitude typically observed in industrially-polluted air masses from the Asian continent. Possible physical, chemical, and biogeochemical factors leading to different O3 to CO ratios were presented.
Water shortage has been a serious problem for a long time in many countries and areas in the world. In Japan, a research programme is now in progress to sophisticate the cloud seeding techniques to enhance the snowfall in the catchment of dams located downwind the Echigo Mountains. We conducted the long-term numerical experiments through two winters, using a high resolution meso-scale model, in order to evaluate how frequently the suitable situations for cloud seeding appeared in this region. As a result, the opportunities appeared in one-third of the total cases concerned here. In addition, it was attempted to estimate the seeding effect on the surface snowfall in the focused dam catchment. It was found that the surface snowfall enhancement was expected to be more than 200 mm, if the cloud seeding was conducted in all preferable cases through the winter when we had a record little snowfall.
This study focuses on the reproducibility of the climatic change in the early summer rainfall in East Asia (Mei-yu rainband) by the Pseudo Climate Simulation (PCS) using a regional climate model. In the PCS, the lateral boundary condition is given by the composite of six hourly reanalysis data and the difference between two decadal climate means. The daily variation on the lateral boundary of the PCS is similar to that of the control hindcast in one decade, but its climate is the same as the other decadal mean. The PCS accurately reproduces the change in the Mei-yu rainband over Southern China between the 1960s and the 1990s, suggesting that the climatic features of the Mei-yu rainband are controlled by the climatic change in a large-scale circulation. The PCS reduces the uncertainty caused by the interannual variability in case of the downscaling of global warming projected by the General Circulation Models (GCMs) even if the number of sample years is the same as that in the conventional dynamical downscaling. The PCS can also exclude model biases in the present climatology reproduced by each GCM.
In this study, Multi-Center Grand Ensembles (MCGEs) were constructed by combining five operational medium-range ensemble forecasts: CMC, ECMWF, JMA, NCEP, and UKMO with equal weights and no bias correction. The forecast performance of the MCGEs relative to the ECMWF ensemble, having the best forecast performance in the world, was investigated using the seasonal Root Mean Square Error (RMSE) and the Ranked Probability Score (RPS) for 500 hPa geopotential height over the Northern Hemisphere (20°N-90°N) from December 2006 to November 2007. It was found in the deterministic and probabilistic verifications that the MCGEs generally outperformed the ECMWF ensemble at least in the medium forecast range (day 6-9) for all seasons. The improvements in the RMSE and the RPS are several percentage points. These are almost comparable with the rate of improvement in a single-center ensemble forecast during the latest few years.
The appearance frequency of clouds with much cloud water and less precipitating water, which significantly influences cloud seeding to increase rainfall, is examined from the simulation results of a cloud-resolving model with a horizontal resolution of 1 km. The area of Shikoku Island, located in western Japan, was analyzed in the 2007 Baiu season. In this study, target clouds are judged using the threshold values of the vertically accumulated total amount of rainwater, snow and graupel (TRSG) less than 1.0 mm and that of cloud water exceeding 0.5 mm. Moreover, the available total rainfall amount is roughly estimated by vertically accumulating cloud water for TRSG < 1.0 mm. Between May and July 2007, target clouds appear at a rate of 6.4% in average over the central area of Shikoku Island. Even in June 2007 when observed rainfall amount was less than 50% of the 10-year mean value published by the Japan Meteorological Agency, the cloud appearance rate of 7.6% is comparable with that in July when rainfall reached the 10-year mean value. The diurnal variation of the appearance rate of target clouds is also examined. In June, target clouds appear at a higher rate (∼12%) in the afternoon. Moreover, available total rainfall amount of about 200 mm is estimated over the central area of Shikoku Island for three months.
Global warming projection experiments were conducted using a 20-km mesh global atmospheric model (the 20-km model), focusing on the change in the rain band of the East Asian summer monsoon (the Baiu rain band in Japan). To quantify the dependence of the projected change on the sea surface temperature (SST) prescribed to the 20-km model, we have taken different SSTs given by the two Atmospheric-Ocean General Circulation Model (AOGCM)s of MRI-CGCM2.3.2 and MIROC(hires). In the future climate simulations, the Intergovermental Panel on Climate Change (IPCC) A1B emission scenario was assumed. The future climate simulations show that precipitation and its intensity increase over the Yangtze River valley of China and Western Japan. The termination of the Baiu season tends to be delayed until August. These changes were consistently found in the simulations regardless of different SSTs.
Inverse modeling of Asian dust was performed using MODIS coarse-mode aerosol optical thickness (AOT) and a regional adjoint dust model. The a posteriori AOT shows better agreement with the MODIS AOT and OMI Aerosol index (AI). Independent validation with the NIES Lidar network shows that the inversion leads to a significant improvement and reduces root mean squares of differences by 29-32% at Seoul, Matsue, and Toyama. The inversion results show considerably greater dust emissions over the Gobi Desert and Mongolia. Especially, optimized emissions are estimated as 8.1 Tg (352% of the a priori) for 29 March and 19.5 Tg (325%) for 30 March. Comparison with inversion results using NIES Lidar (Yumimoto et al. 2008) shows consistency with our a posteriori dust emissions which underscores the feasibility of dust inversion with satellite optical observations, and encourages combined inversion that assimilates the Lidar extinction coefficient (vertical profiles) and MODIS AOT (horizontal distribution) concurrently. However, the a posteriori results might reflect effects of air pollutants from highly industrialized regions, which might contaminate the assimilated results. Further quality control of the input for the data assimilation is necessary in future studies.
Volcanic clouds from the eruption of Jebel at Tair (south-central Red Sea, Yemen) on 30th September 2007 were observed by ground based lidar at Nagoya, Japan, and also by the space borne lidar CALIOP. The cloud was found as a non-depolarized cloud layer in the upper troposphere by ground based Mie/Depolarization lidar. By tilted lidar observations from ground it was demonstrated that these clouds were not composed of ice particles. Clouds with similar characteristics were also observed by CALIOP. Some evidence confirmed their origin to be the said eruption. The estimated total mass of the cloud particles by lidar-observed data coincides with the estimated sulfuric acid oxidized from SO2 included in the volcanic cloud observed by Aura satellite. All of the clouds were observed at altitudes lower than the cold point tropopause for a week after the eruption. Since then parts of the clouds were observed in the stratosphere, indicating transport from the troposphere to the stratosphere.
The present paper investigates the relationship between the skin sea surface temperature (SSTskin) and the precipitable water (PW) observed over the tropical Indian Ocean. PW is derived from a shipborne Global Positioning System (GPS). Composite diurnal variations indicate that the increase of PW and radar echo coverage (rainfall) in the daytime correspond to the large SSTskin rise during the undisturbed period (The PW increase is statistically significant at 90% level). The surface fluxes calculated using the bulk flux algorithm are too small to account for the observed increase of PW, while the bulk flux agrees with the directly measured eddy flux.
A procedure to correct the reflectivity data from multiple radars is proposed. The TRMM/PR (Tropical Rainfall Measurement Mission satellite/Precipitation Radar) is used as the standard calibrator. The data from a disdrometer is also used to account for the effects of rain attenuation at short wavelengths. The procedure is evaluated in the case of oceanic rain observed in MISMO (Mirai Indian Ocean cruise for the Study of the MJO-convection Onset), in which two radars were deployed; a C-band shipborne radar and an X-band ground-based radar. On the C-band radar, the traditional corrections for the factors such as rain attenuation, second-trip echos, shadows by obstacles, and noise, result in reflectivity data which closely matches that of the TRMM/PR. For the X-band radar, iterative matching to the TRMM/PR worked effectively to correct the reflectivity, with the aid of the disdrometer data to reflect the attenuation by the rain in the vicinity of the radar. The corrected reflectivity from both radars well matches that of TRMM/PR with negligible biases and reduced deviations.
In order to study changes in the regional climate in the vicinity of Japan during the summer rainy season due to global warming, preliminary experiments by a semi-cloud resolving non-hydrostatic model with a horizontal resolution of 5 km (NHM-5km) are conducted from June to October between 2002 and 2006 using 20-km horizontal grid operational regional analysis data of Japan Meteorological Agency (JMA) as the initial and boundary conditions. The total precipitation amount and appearance frequency for daily precipitation amount simulated by the NHM-5km show notable agreement with those of the surface observation data of Automated Meteorological Data Acquisition System (AMeDAS) of JMA. The temporal and spatial characteristics of maximum daily precipitation amounts (MDPs) from June to October also agree well with the observational results. The regional largest values among MDPs (R-MDPs) for 6 regions of the Japanese Islands are also estimated for the simulation results of the nearest grid points for each AMeDAS station and the AMeDAS observations. Those comparisons conclude the high performance of the NHM-5km for the reproducibility of MDPs and R-MDPs, which are highly related to extreme events.
The relationship between precipitation and elevation in the present climate, reproduced by the Non-hydrostatic Regional Climate Model (NHRCM), is compared with observation to examine how well the model expresses the effect of topography. The comparison is carried out in the central region of Japan during June and July. Both reproduced and observed precipitation increases with elevation over the whole calculation domain, though the correlation is low. The correlation becomes very high when the observation points are classified into river systems. The correlation in the model is low for river systems where the correlation is also low in the observation data. The correlation in both the observation data and NHRCM becomes high in river systems where the correlation is low if they are classified in more detail. The characteristic that precipitation increases with elevation becomes clear through appropriate classification of the area. The rate of increase is different in each region. The relationship between precipitation and elevation is well reproduced in NHRCM.
The characteristics of the anomalous winter climate around Japan in December 2005, including abnormally heavy snowfall, were analyzed from the viewpoint of interannual variation using reanalysis data for 50 years. The anomalous snowfall near the Sea of Japan in 2005 is attributed to an anomalous air-mass modification over the Sea of Japan, the large changes of thermodynamic characteristics due to the warmth of the Sea of Japan. Thermodynamic budget analyses showed that the air-mass modification in December 2005 over the Sea of Japan was the strongest in more than 40 years. Air-mass modification over the Sea of Japan was strongly related with a large-scale atmospheric north-south dipole pattern consisting of a northern high covering Siberia and a southern low covering a wide area of Japan in the 500 hPa height field in the positive phase (SJ pattern). In addition, the local SST variability during late autumn was significantly related to air-mass modification. However, the Arctic Oscillation was not significantly correlated with the air-mass modification over the Sea of Japan on an interannual timescale.
We analyzed tropospheric column ozone (TCO) observed by the GOME-1 (Global Ozone Monitoring Experiment; European Space Agency, 1995) and ozonesondes to determine the spatiotemporal variation in TCO over East Asia from 1996 to 2003. An enhanced TCO belt (E-TCO belt) was observed at approximately 35°N throughout the year. The E-TCO belt moved northward from winter to summer and southward from summer to winter, strongly suggesting connection with the seasonal variation of meteorological conditions. The large enhancement of TCO found over central China in summer suggests that there is significant outflow of ozone from that region. This study presents the first satellite-derived comprehensive picture of the TCO spatiotemporal variation over East Asia, which has not been obtained from limited ground-based measurements.
The impact of chemical production and transport on diurnal ozone behavior in June 2006 at a mountainous site (Mt. Tai) in North China Plain (NCP) was studied by regional chemical transport coupled with a process analysis and a tagged tracer method. The observed diurnal variation in the morning minimum-afternoon maximum was reproduced well. The results showed that regional transport contributed ∼60 ppbv to “background” ozone, with no significant diurnal variations (< 7 ppbv), while the chemistry (∼25 ppbv) in the surrounding region (an area of 150,000 km2) which demonstrated an afternoon-maximum explained the causes of diurnal ozone behavior. The process analysis also suggested that in-situ chemistry accounted for most of the increase in ozone from morning to mid-afternoon (rather than the ozone concentration itself), with a minor contribution from vertical transport. A comparison was conducted between Mt. Tai and a mountainous site in Japan (Happo) to determine the regional variability in photochemistry and transport over Eastern Asia. The results showed that photochemical activities around Mt. Tai were stronger than those around Happo, where dynamic processes, rather than in-situ chemistry, played a dominant role in the diurnal behavior of ozone at midnight (0:00-3:00 local time (LT) and at the maxima-minima before noon (11:00 LT).
Surface meteorological observations indicate that the diurnal cycle of rainfall over Siberut Island is characterized by dual maxima in the afternoon and after midnight, with the minima in the early morning and evening. The GPS-derived precipitable water (PW) over the island shows similar dual maxima in the afternoon and near midnight. The incident solar radiation during the morning hours is still sufficiently intense to generate local circulations on the island and to induce large diurnal variation of PW in the afternoon on days with daytime rain and days with nighttime rain. Meanwhile, a great increase of PW during the evening to nighttime is observed on days with nighttime rain. The results suggest a possibility that the increase of moisture during nighttime over Siberut Island, which is probably caused by the transport of water vapor from Sumatra Island, play a major role in formation of the nighttime rainfall over the island.
An intense rainfall system that developed on the west coast of India caused heavy rain in excess of 900 mm at Santa Cruz, a suburb of Mumbai, on 26 July 2005. This system was simulated by the non-hydrostatic model (NHM) of the Japan Meteorological Agency (JMA), using the global analysis data of JMA as the initial condition. A maximum rainfall amount exceeding 1,100 mm in 17 hours was obtained by the simulation with a horizontal resolution of 5 km. The detailed structure of the rainfall system at the intense rain stage was investigated by NHM with a horizontal resolution of 1 km. The rain was mainly caused by a humid westerly flow near the surface, which overrode a cold pool near the mountain range. A dry southwesterly flow at the height of 2.51 km enhanced the cold pool. Another low-level humid westerly flow entered the rainfall system from the north and formed a thick humid northerly flow that reinforced the rainfall. Sensitivity experiments were conducted to investigate the influences of the mountain range, water vapor of the airflow north of the system, and the dry westerly flow. The results supported the proposed structure of the heavy rainfall system.
Statistical verification of short term numerical weather prediction (NWP) experiments using the Japan Meteorological Agency (JMA) non-hydrostatic model (NHM) and the advanced research WRF (the weather research and forecasting model), referred to as WRF-ARW, was conducted around Japan and Southeast Asia. Two seasons (July 2007 and January 2008) that include typical weather systems in each region were selected for the verification. The results of the verification were compared between the two models with the same initial/boundary conditions, the same domain size (3000 km × 3000 km), and the same horizontal resolution (20 km). Forecast results were verified by the surface precipitation estimated by satellites and vertical profiles based on sonde observations. The threat scores for precipitation around Japan determined by the two models are almost the same. In the rainy season (July 2007), they are not far from the typical values for summer determined by the JMA operational mesoscale model. WRF tends to predict more rain than NHM and the bias scores of NHM are closer to unity than those of WRF-ARW in most precipitation intensity ranges. In the Southeast Asia region, the threat scores of the two models are only about half of those for the rainy season in Japan. In the dry season (July 2007), the threat scores determined by WRF are slightly better than those by NHM, while in the rainy season (January 2008) NHM is slightly better than WRF-ARW for weak to moderate rains. Statistical scores against sonde are of almost the same magnitude, though the root mean square errors for wind of NHM are slightly better than those of WRF-ARW.
This study has investigated climatological features of Meiyu/Baiu frontal depressions (MBFDs) by identifying and tracing MBFDs from the past 12-year surface weather charts. With apparent interannual variability, an average of 22.5 MBFDs per year are found. There is a tendency for more MBFDs to form around Yangtze and Huaihe River Basins and to the south or southeast of the Japan Islands. Meanwhile, more MBFDs form in nocturnal and morning hours per day. More than half of MBFDs that pass over Japan originate from China. MBFDs commonly propagate from west to east and many MBFDs passing over Japan tend to be long lived. Finally, the analyzed statistical characteristics of MBFDs are discussed based on previous studies.
An aircraft observation was conducted over the East China Sea to reveal detailed distributions of wind and moisture around the Baiu frontal zone. Using a numerical simulation, the structure of the Baiu frontal zone was examined and four airstreams around the zone were identified: northeasterly, west-southwesterly, and southwesterly along the Baiu frontal cloud zone, as well as southwesterly along the oceanic zone. Each airstream had different characteristics of stratification. These differences and the convergence of the airstreams resulted in two different rainfall areas: a weak and wide rainfall area in the northern part of the cloud zone, and an intense and narrow rainfall area in the southern part.
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