A new videosonde receiving system consisting of two receiving antennas for a set of videosonde and GPS radiosonde has been developed. The antenna for the videosondes is controlled by a GPS slave method, in which the antenna elevation and azimuth are processed every second using GPS location data obtained from a GPS radiosonde attached to the videosonde. The results of the first experimental flight conducted in Okinawa as part of a synchronized observation campaign of a C-band polarimetric radar and videosondes reveal successful reception of clear images of precipitation particles in clouds.
High-temporal measurements of the stable isotope ratio (δD) of near-surface atmospheric water vapor by an Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS)-type water vapor isotope analyzer (WVIA) were performed in Sapporo from April 2009 to June 2011. The data obtained from the WVIA was corrected by comparing the δD values with those obtained from the cold trap method and subsequent cavity ring-down spectroscopy isotopic water analysis. The δD values showed a marked seasonal cycle but showed a different seasonal cycle from that of the surface air temperature. The δD values simulated by the isotopic-incorporated Global Spectral Model showed almost the same seasonal cycle as that of observed δD values, although simulated values showed about 10‰ difference from observed values in 10-month average. It is found that the monthly mean SSTmon of the nearest sea was a better predictor for δDmon than the monthly mean air temperature. Based on the data measured by the WVIA deployed on the Oshoro-Maru of Hokkaido University, from the Sea of Okhotsk to the Pacific Ocean, we confirmed that δD of water vapor generally increased with increasing SST and the highest values of δD were almost the same as those of vapor in equilibrium with ocean liquid.
This work investigates development processes of Baiu frontal depressions (BFDs) using a reanalysis data set in June and July from 2000 to 2007. On the basis of the deepening magnitude, 140 BFDs detected in the analysis period are categorized into developed and non-developed BFDs. Developed BFDs are further classified into W-BFDs and E-BFDs; W-BFDs (E-BFDs) peak in the region west (east) of 140°E. A composite analysis and many case studies reveal that the vertical coupling between lower- and upper-level disturbances and latent heating are key factors for the development of both BFDs. It is also shown that the development processes of BFDs depend on their environmental features. Latent heating plays a more important role in the development process of W-BFDs, whose environment is characterized as a large amount of water vapor. On the other hand, it is suggested that low-level baroclinicity makes a larger contribution to the development of E-BFDs, whose environment is characterized as a larger temperature gradient.
Haze exerts a large effect on visibility reduction and has serious impacts on air quality and human health. Understanding the sources and transport of haze is of importance to improve the regional air quality and evaluate its health effects. In this study, we investigated a typical haze episode that occurred in northeast (NE) China during 4-6 November 2010 by analyzing the ground PM10 measurements from 11 monitoring sites, aerosol Lidar observations, synoptic charts, MODIS satellite imageries, and back trajectories. Our analyses suggest that the regional haze formed in the North China Plain (NCP) under stagnant conditions can be transported to NE China in ∼1-3 days across Bohai Bay and Liaodong Bay - a typical transport pathway associated with the topography of northern China. The haze episode appeared to evolve progressively from southwest to northeast in the region of NE China, in agreement with the appearance of PM10 peak values, wind patterns, MODIS images and the back trajectories of air masses. Due to the haze impact, NE China showed significantly elevated particulate matter pollution by a factor of ∼4-6 with the peak concentrations reaching ∼410 μg m-3. The results together indicate that the regional transport from the NCP has a significant contribution to the PM pollution in NE China, thus efforts to control the source emissions over the NCP would be effective to improve the air quality in NE China.
The mean features of precipitation distribution associated with tropical cyclones are evaluated as anomalies from environmental precipitation fields, in six tropical cyclone active basins, using satellite-derived daily precipitation observation. A common feature in all basins is that concentric positive precipitation anomalies extend within a 5-degree radius from the tropical cyclone center with maximum values of 70 to 100 mm day-1. These distributions are well approximated by a Gaussian curve with an e-folding radius of 2.2 to 2.8 degrees. Positive precipitation anomalies are surrounded by negative anomalies in all basins, indicating suppression of precipitation due to the tropical cyclones themselves at a large distance from the center. The negative anomalies have minimum values of -2 to -3 mm day-1 and are distributed mainly on the equatorial side of the center. Precipitation excess frequency around the tropical cyclones is also evaluated. The western North Pacific has maximum values of excess frequencies in all basins, in which the frequency for 100 mm day-1 is 26 days yr-1 and that for 200 mm day-1 is 1.8 days yr-1 within a 1-degree radius from the center. We assume that tropical cyclones in the western North Pacific have the greatest precipitation intensity.
Using the Non-hydrostatic ICosahedral Atmospheric Model (NICAM) on an aqua-planet with a uniform longitudinal sea surface temperature, precipitation systems (PSs) with coarse horizontal resolutions are studied. An eastward-propagating (EP) property of the PSs is seen even though the horizontal resolution becomes coarser to 112 km, as long as the vertical stratification is kept conditionally unstable. The appearance or disappearance of the EP property is explained in comparison with mesoscale (100 km) and large-scale (1,000 km) PSs, a non-precipitation system (NPS), and a system simulated by a dry model with positive-only wave CISK heating (DP). By assuming that the height and the updraft intensity of convection are common in these systems, the turnover times of representative convections are estimated. Compared with the time scale of the equatorial beta (Tβ), where its effect essentially works and the distinct EP property appears, the turnover times of the large-scale PS and DP are longer than Tβ, producing the EP property, whereas those of the NPS and mesoscale PSs are shorter, inducing no EP property. These results are consistent with observations and model outputs (Nakazawa 1988; Nasuno et al. 2007, 2008).
Dust devil-like vortices were detected by a three-dimensional scanning coherent Doppler lidar (3D-CDL) in an urban area of Sapporo, Japan, from April 2005 to July 2007. A total of 57 strong, dust devil-like vortices with vertical vorticity exceeding 0.1 s-1 were detected in 8 days of the observation period and were associated with a convective cell (fish net) pattern of wind fields detected by the 3D-CDL. The observed vortices had both rotation senses for 7 days. However, all of 7 dust devil-like vortices were cyclonic on 4 October 2006 when cyclonic mesoscale circulation with 4.5 × 10-4 s-1 in vertical vorticity existed over the 3D-CDL observation area. This result is the observed evidence that mesoscale circulation affects rotation sense of vortices.
The effects of land reclamations in the Osaka Bay area on the climate in the Keihanshin region are investigated using a numerical model. It is observed that reclamations in Osaka Bay lead to a significant increase in the surface air temperature (SAT) over the inland during the daytime and a decrease from midnight to the morning. This indicates that reclamations increase the diurnal temperature range. The decrease in the SAT in the morning, which is in contrast to urban warming, is due to the decreased surface wind speed caused by the reclamations and is accompanied by reduced vertical heat exchange.
Over the tropics, two types of precipitation systems (PSs), super clusters (SCs) and Madden Julian Oscillation (MJO), are frequently observed, having similar meridionally symmetric structures about the equator but different eastward-propagating (EP) speeds. To investigate the reasons why these PSs exist, the dependence of the longitudinal variations of surface sea temperature (SST) is examined using a NICAM on an aqua-planet. In a longitudinally uniform-SST case, only SC-like fast-EP PSs appear. When the longitudinal variation of the SST increases, meanwhile, a stationary Walker circulation (WC) emerges and MJO-like slowly EP PSs occur on the western part of a high-SST area. It is expected in the real atmosphere that two different types of EP PSs can exist in parallel due to complex surface conditions: 1) SCs as free PSs and 2) MJOs as forced PSs. Here, free (forced) PSs mean convection, which is uncontrolled (controlled) by the longitudinal variation of the SST. It is also obtained that an asymmetric WC is produced, even though the SST variation symmetric about 180° longitude is forced. Owing to the WC, combined with the Hadley circulation, the MJO is generated and decayed locally, and westward-propagating PSs are dominantly observed in the subsidence areas of the WC.
The tephra fall caused by the eruptions at Mt. Shinmoe-dake during 26 to 27 January 2011 is simulated with Japan Meteorological Agency Non-Hydrostatic Model. The model has been improved so as to involve the tephra transport and sedimentation with four aerosol classes representing different sizes of tephra particles. The total mixing ratio and number concentration are prognosed with the advection, diffusion, and source and sink terms for each class. The simulated result on the distribution of tephra deposit shows a good agreement with observation.
This study investigated the characteristics of the rainfall associated with tropical cyclones (TCs), using the TC best-track data and daily rainfall data from 15 meteorological stations for the period 1961-2008 for the coastal region of Vietnam. In addition to investigating the TC rainfall amount, we estimated the TC rain ratio and the ratio of TC heavy rainfall days (TC_R50) and interpreted these parameters for El Niño and La Niña years. Our results show that the maximum TC rainfall occurs from July to September in the northern region, whereas the total rainfall at southern stations is mainly composed of non-TC rainfall. The TC rainfall amount is concentrated in the central region, with a peak in October-November. The TC rain ratio varies from 0 to ∼25%, showing a maximum value in the region of 16°N-18°N in September. The mid-central region of Vietnam has maximum TC_R50 ratio in September-October corresponding to its highest TC frequency in the same period. During El Niño (La Niña) years, the TC rain ratio and TC_R50 ratio in the central region show a significant decrease (increase) in October-November. The La Niña phases more strongly affect TC rainfall than the El Niño phases, particularly in central Vietnam.
Characteristics of springtime cyclones with heavy rainfall in Japan are examined. Heavy rain episodes are obtained from the upper five percent of an area-averaged daily rainfall in the mainland Japan for the period 1982-2009. For heavy rain episodes, the cyclogenesis area shifts westward. The primary path of cyclones, locates along the south coast of Japan, displaces northward from the climatological path and that of the moderate rain episodes. Maximum developments of cyclones are frequently observed over the East China Sea and western Japan near the oceanic frontal zone. A composite analysis of heavy rain episodes exhibits that a lower tropospheric ridge covers Japan two days before a heavy rain date (Day -2). The ridge, which locates to the east of the trough, amplifies and extends meridionally with eastward progress until Day 0. As the eastward migration of the trough and ridge, poleward moisture flux is enhanced between the trough and ridge systems. In moderate rain episodes, amplification of trough and ridge systems and associated poleward moisture flux are rather weak for the period around Day 0. Enhanced poleward moisture flux due to the amplification of both trough and ridge may cause early development and northward shift of cyclones.
The UV/Vis/near infrared spectrometer SCIAMACHY on board the European ENVISAT satellite is the only one instrument which enables quantitative total column retrieval of atmospheric carbon monoxide (CO) with high sensitivity to the lower troposphere. Although the general selection of SCIAMACHY observations are the measurements with effective cloud fractions below 20%, due to much higher albedo of clouds compared to ground surface, the remaining effects of clouds can still be large (even up to 100%). Since inaccurate corrections will lead to a wrong interpretation of the results, the accurate cloud correction is essential; in this paper we applied a cloud correction scheme which explicitly considers the cloud fraction, cloud top height and surface albedo of individual observations. In this paper, the sensitivity of cloud effect is described and the difference between corrected and uncorrected result is studied.
Future climate change around Japan was projected with a non-hydrostatic regional climate model with a 5-km grid spacing. The future surface air temperature, averaged over all of Japan, is projected at the 99% confidence level to rise about 3°C in each month of the year. Diurnal temperature ranges are projected to increase in many areas, especially over plains on the Pacific Ocean side in February, as the warming rates of minimum temperatures are small as compare to other areas. This is due to that minimum soil temperatures of just below 0°C occur with high frequency in both the present and future climates, because they are constrained by the heat of solidification. Storm tracks are projected to approach the Japan Archipelago in February, leading to a remarkable increase in precipitation along the Pacific coast of Japan. The annual occurrence frequency of heavy precipitation is also projected to increase. The maximum snow depth is projected to decrease almost everywhere, but the changes will be small in high mountains and in northern Japan.
The present study examined the atmospheric circulations leading to the extraordinary heavy precipitation event that occurred in central Vietnam during 2-5 October 2010. Results from an analysis of data from the Japan Meteorological Agency Climate Data Assimilation System (JCDAS) showed that the combined effects of a westward-propagating synoptic-scale tropical disturbance from the western Pacific and the eastward propagation of a strong active phase of the Madden Julian Oscillation (MJO) from the Indian Ocean were the primary causes. Investigation of MJO activities during the wet season in the region for the 30 years from 1981 to 2010 revealed that the intraseasonal oscillations in the tropical atmosphere are an important factor in the formation of extreme precipitation events in central Vietnam.
We focus on the dramatic decrease in the snow cover on the Japan Sea side of Central Japan in the late 20th century. Using a regional climate model, a control experiment (CTL) was conducted, and it accurately simulated the dramatic decrease in maximum snow depth (SNDmax) between the 1980s and the 1990s. We then conducted a pseudo climate simulation (PCS) in the 1990s, which assumes the mean atmospheric fields in the 1990s and the perturbation from the mean atmospheric fields in the 1980s. The PCS method is expected to evaluate only the impacts of changes in the mean atmospheric fields on the snow cover changes. The PCS simulates the decreases in SNDmax over the coastal area, which are comparable to the changes simulated by the CTL. On the other hand, changes in SNDmax are negligible in the PCS over the mountainous area, where the slight increases in SNDmax are simulated by the CTL. Therefore, the changes in the mean atmospheric fields, especially, the mean temperature rise, are main factors of the snow cover decrease over the coastal area, while changes in both the mean atmospheric fields and the perturbation contribute to the snow cover changes over the mountainous area.
A self-consistent mechanistic model is considered for the response of the South China Sea (SCS) monsoon to the remote forcing. The feedback parameters are evaluated by using an atmospheric general circulation model (AGCM) control run, AGCM sensitivity experiments, and observation data of the NCEP reanalysis and ICOADS sea surface temperature (SST). Zonal wind anomaly induced over SCS from the surrounding weather system without any effect from SCS precipitation anomaly is regarded as the remote forcing for SCS monsoon. The remote forcing directly affects SCS monsoon variability through the water vapor transport and Convective-Wind-Evaporation (CWE), and indirectly through the reduction of SST. The effect of the activated zonal wind induced-reduction of SST is much smaller than that of CWE and plays a role in suppressing SCS precipitation. This result suggests that the SST reduction contributes to stabilize the monsoon variability over SCS in summer through local air-sea coupling. On the other hand, present study also suggests that monsoon precipitation contribute to reduce SST through the change in the local circulation.
Interannual rainfall variability over northwestern Jawa, Indonesia and its relation to the Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO) events were investigated using daily rainfall data for 1973-2008. IOD events clearly influence interannual rainfall variation in the dry season (May-October) in northwestern Jawa. Drought conditions during the dry season occur in conjunction with simultaneous development of positive IOD and El Niño events, whereas wet conditions tend to appear in negative IOD (with or without La Niña) rather than single La Niña events. During positive (negative) IOD years, cooler (warmer) sea surface temperature (SST) surrounds the maritime continent and large-scale divergence (convergence) and lower (higher) atmospheric water vapor content are observed. These conditions tend to suppress (induce) rainfall in northwestern Jawa. On the other hand, interannual rainfall variation in the rainy season (November-April) is not closely related to ENSO/IOD, but rainfall tends to be abundant in “neutral” (non-ENSO/IOD) years. This may be influenced by Northern Hemisphere winter monsoon strength and/or northerly (cold) surges. Furthermore, decreasing trends are detected for rainfall amounts and number of rainy days in the rainy season.
Global warming projection experiments were conducted using a 20-km mesh global atmospheric model, focusing on the near future (2015-2039, 25 years) change in the rain band of East Asian summer monsoon. In the present-day climate simulations (1979-2003, 25 years), observed historical sea surface temperature (SST)s are given to the models. For the near future and the future (2075-2099, 25 years) climate, A1B emission scenario is assumed. To assess the uncertainty of climate change projections, we performed ensemble simulations with the 60-km resolution model combining four different SSTs and three atmospheric initial conditions. Projections by the 20-km and 60-km models consistently show the increase of July precipitation over Japan, but magnitude of change and level of statistical significance in the near future are smaller than those in the future. The near future projections suggest the delay in the termination of rainy season over Japan, although this delay is less evident and less robust compared with that in the future. We confirmed that the near future climate is located approximately midway between the present-day climate and the future climate, mainly because forcing by greenhouse gases in the near future is also located midway between the present-day climate and the future climate.
The relationship between the strong wind and land cover in dust source regions and the Asian dust event over Japan (ADE) was analyzed using the weather reports and coverage of the Normalized Differential Vegetation Index (NDVI) derived from the MODIS-Terra reflectance products during the spring (March to May) of 2000 to 2011. The target area for the dust source area in northeast Asia was defined as 35°N to 45°N and 100°E to 115°E as with Kimura (2012), with reference to past results (Iwasaka et al. 2009; Lim and Chun 2006; Shao and Dong 2006; Sun et al. 2001). The annual change in the number of ADE agreed well with the Dust Storm Frequency (DSF) in the target area (R2 = 0.549). Strong wind has significant effect on ADE (R2 = 0.538), and coverage of NDVI ranging from 0.05 to 0.2 (bare land or bare land with less vegetation) and that of NDVI over 0.2 (vegetation surface reducing dust outbreaks) in April and May are also related to the number of ADE. The coverage of bare land or bare land surface with less vegetation decreased by 4%; in contrast, vegetation surface reducing dust outbreaks increased 4% in the 12 years from 2000 to 2011. Increasing trend of vegetation corresponded to the decreasing trend in ADE (R2 = 0.359).
In September 2011, catastrophic landslide disasters triggered by record-breaking rainfall due to Typhoon 1112 (Talas) caused enormous damage in the Kii Peninsula, Japan. We analyzed cumulative event rainfall, maximum hourly rainfall intensity, Soil Water Index (SWI), and Normalized SWI (NSWI) for 30 landslide events occurring in Nara Prefecture. The first two parameters are classical variables used for landslide hazard assessment. SWI represents the theoretical soil water content calculated by using a hydrological model, while NSWI is normalized SWI divided by the largest value over the past ten years (2001-2010) at the location. The distributions of the cumulative event rainfall, maximum hourly rainfall intensity, and SWI do not well correspond to landslide locations; p-values obtained from Wilcoxon rank-sum tests between landslide and non-landslide cells were 0.98, 0.95, and 0.91 for these distributions, respectively. However, landslides occurred in an area where the maximum NSWI was high (p-value < 0.01). Heavy rainfall occurs frequently in the eastern part of the Kii Peninsula where the mean annual precipitation is higher than 3800 mm. That is, in regions of frequent rainfall, the relative value of NSWI (in comparison with historical records) is more useful than the other rainfall variables for landslide hazard assessment.
The transport process of a severe Asian dust storm event generated in the Gobi Desert during 30-31 March 2007 was examined by several datasets. Results clearly showed that this storm was transported eastward to the northwest Pacific and southeastward to the China seas. Dust particles were deposited in the Yellow Sea accompanied by precipitation on 31 March 2007 and the average deposition flux at an offshore region in the Yellow Sea was 0.56 g m-2 d-1. After 4 days of dust passage over this offshore region, a phytoplankton bloom event appeared on 3 April 2007 and continued until 4-6 April 2007. When compared to non-dust year in 2005, the initial timing of the bloom in 2007 was about 18 days earlier than that in 2005 and peak chlorophyll a concentration in 2007 was 45% higher than that in 2005. Similar results were found in the dust storm cases in 2004 and 2006. Results indicated that besides increased SST, PAR, and nutrients accumulated in winter from strong mixing, dust input may play important roles in spring bloom in the dust years. That provided evidence of biotic response to natural fertilization caused by dust deposition.
Two adjacent shear lines accompanied by wind gusts exceeding 20 m s-1 passed over the Shonai region on the Japan Sea coast during a moderate cold-air outbreak on 12 December 2010. The structure of the shear lines were examined using simulation results and observational data including high-frequency upper-air soundings. Simulation results revealed that cold-airmass outflow from the Eurasian Continent had a split-flow pattern due to the blocking effect of the Changbai Mountains. One is from the south side of the mountains (SCF), and the other is from the north side (NCF). NCF also has two streams: a shallow southward-meandering flow on the south and a slightly deeper straight flow on the north. A shallow shear line was formed between SCF and the shallow southward-meandering flow of NCF. The deeper straight flow of NCF sharply formed another shear line on the north at around 1-km height with SCF. This result implies that the shear lines accompanied by wind gusts on the Japan Sea coast during a cold-air outbreak have various structures and that the horizontal wind shear a little above the surface could cause surface wind gusts.
To estimate contributions of water vapor (WV), carbon dioxide (CO2), and clouds to longwave radiation, surface downward longwave irradiance (DLI) was evaluated by comparing observations with values calculated using data from vertical profiles of WV and clouds obtained from radiosonde observations at five Baseline Surface Radiation Network (BSRN) sites. The observed DLI was reproduced by calculation with an accuracy of 3.9 ± 4.4 W m-2 for clear-sky conditions at all sites, but the accuracy was -7.7 ± 8.6 W m-2 for overcast conditions. The individual contributions of WV, CO2, and clouds to DLI were evaluated by removing these factors one by one from the normal condition including all of the factors (removal method) and by removing all factors except for one particular factor (addition method). The results indicate that the contributions of WV and clouds are relatively large, whereas the contribution of CO2 is relatively small.
Mineral dust aerosols from the Taklimakan desert can be elevated to high altitude and transported long distances, thus affecting the Earth's climate. A numerical simulation was conducted to elucidate the seasonal characteristics of dust elevated from the Taklimakan desert. The global land area was divided into the western (including the Taklimakan desert) and eastern region of China and Mongolia (including the Gobi desert), and the other regions so that the relative contributions of mineral dust from the Taklimakan and Gobi deserts to the global dust budget could be identified. The lifetime of the simulated dust aerosols from the Taklimakan desert (2.1 days) was longer than that of aerosols from the Gobi Desert (1.5 days). Simulated dust emission increased in March, peaked in April to May, and decreased from June to September, which is a seasonal variation pattern consistent with the observed Taklimakan dust storm frequency. The simulated Taklimakan dust concentration in the upper troposphere was higher than that of the Gobi dust, suggesting that Taklimakan dust tends to be transported to higher altitudes. It is also suggested that the Taklimakan dust is trapped in the Asian summer anticyclone and partly contributes to the formation of the Asian tropopause aerosol layer during summer.
Intertropical convergence zone (ITCZ) occasionally breaks down to simultaneously form several tropical cyclones mainly due to barotropic instability of the zonal flow. This process is called ITCZ breakdown and is thought to be one of the mechanisms for a tropical cyclogenesis in the central and eastern Pacific. In the present paper, an idealized numerical simulation is performed by a non-hydrostatic meso-scale model on an f-plane at 10°N, and a detailed energy budget analysis of the ITCZ breakdown and associated genesis of tropical cyclones is made for the first time. A sea surface temperature (SST) forcing is used to generate an ITCZ-like structure in the atmosphere. This “ITCZ” starts to undulate mainly due to barotropic instability of the lower tropospheric zonal flow, and two vortices are formed in the present experiment. These vortices merge while mutually rotating anti-clockwise, and end up with a single tropical cyclone. The central pressure and maximum wind speed reach under 950 hPa and over 45 m s-1, respectively. An energy budget analysis shows that the barotropic instability is mainly responsible for the genesis and initial intensification of the two vortices, but cumulus heating rapidly takes over to contribute to the genesis of the tropical cyclone.
Simultaneous observations of cumulonimbi by a Ka-band Doppler radar (KaDR) and an X-band polarimetric Doppler radar (MP-X) were performed during the summer of 2011 in the Kanto region, Japan to study the process of cumulonimbus initiation and development. A cumulonimbus developed up to 12 km above sea level (ASL) in the mountainous western part of the Kanto region on the morning of 18 August 2011, and its initiation and development were observed by the two radars. A misoscale convective echo which was newly detected in an RHI or PPI scan and developed vertically (RHI scan) or spatially (PPI scan) was labeled as a ‘new misoscale convective echo’ (NMCE). In the developing stage (DS), NMCEs occurred one after another, and the echo top height and maximum reflectivity of each individual echo gradually increased. In the first half of the DS, the NMCEs appeared between 2 and 5 km ASL. In contrast, in the second half of the DS, the NMCEs' appearance height stepped up to between 5 and 12 km ASL. These results suggest that the ascent of NMCE appearance height is one of the key factors in the prediction of deep convection, which later causes localized heavy rainfall.
One-year meteorological radar observations (from November 2006 to October 2007) over a region from the west coast of central Sumatera (Sumatra) through the Mentawai Strait (about 130-km width) to Siberut Island were analyzed, and modulation of rainfall diurnal cycle (DC) in the region by the Madden-Julian oscillation (MJO) was studied. The DC peaked in the afternoon over Sumatera and Siberut islands, and in the nighttime/early morning over Mentawai Strait between the islands. Over the strait, offshore (westward) migration of the DC peak was distinct when the MJO active phase was propagating eastward over the Indian Ocean, whereas the migration was indistinct after the active phase passed over Sumatera. When the MJO active phase was propagating eastward over the eastern Indian Ocean, the DC was amplified, and daily rainfall maximum tended to appear over western Sumatera including the strait. The DC peak originating from Sumatera reached Siberut, and the DC over Siberut had an additional, stronger rainfall peak after midnight.
In the diagnosis of mass-weighted isentropic zonal mean (MIM), the mean- meridional circulation has a strong extratropical direct (ETD) cell in the northern- hemispheric winter, which turns from downward to equatorward around 45°N and isentropic zonal mean pressure of 850 hPa. The January mean equatorward flow in the extratopical lower troposphere is almost in balance with Eliassen-Palm (E-P) flux divergence for both climatology and interannual variability. This means that the zonal mean equatorward flow in the extratropical lower troposphere is the wave-induced circulation as well as the poleward flow in the stratosphere is. The interannual variation of January mean mass stream functions at (45°N, 850 hPa) positively (negatively) correlates with the zonal mean temperature in the lower troposphere north (south) of about 45°N, respectively. This is consistent with a simple thermodynamic consideration that the strong ETD circulation adiabatically warms up the lower troposphere due to the descending flow in the higher latitudes but cools it down due to the heat advection by the equatorward flow in the middle latitudes (∼35°N).
Atmospheric aerosol particles play an important role in climate change by scattering and absorbing solar radiation. To quantify the direct influence of aerosols on the atmospheric radiation balance, a detailed understanding of the complex refractive index (RI) for a variety of aerosols is required. The wavelength dependence of the RI values for secondary organic aerosols (SOAs) generated during the ozonolysis and photooxidation of α-pinene, which is a major biogenic volatile organic compound (BVOC), was investigated using a photoacoustic soot spectrometer (PASS) and a cavity ring-down spectrometer (CRDS). The real part of the RI values for SOAs generated from both ozonolysis and photooxidation was found to lie between 1.4 and 1.5 at 405, 532, and 781 nm, and to slightly increase with decreasing wavelength. Additionally, the imaginary part of the RI values for these SOAs was found to be negligible (< 0.003) at all of the wavelengths studied (405, 532, and 781 nm). The obtained complex RI values were also compared with values reported in the literature and the chemical properties of the SOAs, which were measured using a high resolution time-of-flight aerosol mass spectrometer (H-ToF-AMS).
In Mongolia, drought is one of the most serious meteorological disasters, causing large direct and indirect livestock losses. In this study, we assessed the influence of climate change on future drought risk in Mongolia by simulating vegetation processes. Our simulation considered uncertainty in future climate projection by running offline a modified version of the process-based vegetation model Sim-CYCLE, forced by adjusted climate projection data with a simple scaling method. The scaling factors representing each of the 24 Phase 3 Coupled Model Intercomparison Project (CMIP3) models were obtained from the magnitude of the changes in summer temperature and precipitation from 1940-59 to 2080-99, and multiplied by the projection of MIROC3.2 medium-resolution version, one of the CMIP3 participants. We analyzed the Special Report on Emissions Scenarios (SRES) A1B and A2 scenarios, and the results showed a robust increase in the future August leaf area index (LAI), which is the indicator of summer drought and also the most important variable in estimating livestock loss by winter disasters, and a decrease in the drought (low LAI) frequency across the range of all CMIP3 models under both scenarios.
A new dust observation site was built in Tsogt-Ovoo, which is located in the northern Gobi Desert in Mongolia, to clarify wind erosion processes. Ten dust events were detected from March 24 to May 4, 2012. Strong winds (greater than 20 m s-1 at an altitude of 3 m) blew predominantly from the west. Clear relationships among wind speed, saltation and particulate matter concentrations less than 10 μm (PM10) were detected. A transition in the wind speed threshold for saltation was observed at Julian day (JD) 111 (April 20); before JD 111, the threshold was 14.0 m s-1, but it decreased to 8.8 m s-1 after JD 111. We discuss the reason for this threshold discontinuity, focusing on the ground surface conditions. It is hypothesized that this discontinuity is caused by the destruction of the surface soil aggregation.
The performance of the pseudo-global-warming downscaling (PGWDS) method is tested by comparison with the assumed true climate (ATC), which is a downscaling using a general circulation model (GCM) output data directly. The PGWDS is a simple way to downscale for a future climate using current weather data of a GCM added by the long-term mean difference between the present and the future climate projected by a GCM. The verification focuses on the East Asia during the rainy season of June. A significant change in the 30-year averaged monthly precipitation is found around the rain band in the future in both downscaling methods. Between the experiments of the PGWDS and the ATC, no significant differences in temperature and precipitation can be seen except for limited small areas. The findings indicate that the PGWDS has a highly potential to the reliable downscaling of the future climate. In smaller downscaling domains, however, the differences in precipitation increase remarkably near the upstream side of the lateral boundaries. The choice of the downscaling area is a critical issue for accuracy.
Analyzing outputs of seven climate models participating in the fifth phase of the Climate Model Intercomparison Project, this study performs multi-model projection of tropical cyclone (TC) genesis frequency over the Western North Pacific basin, with an emphasis on the spatial contrast. By evaluating reproducibility of the spatio-temporal distribution of the genesis frequency, we select five models to perform the multi-model projection. All five models and multi-model ensemble project eastward shift of the Main Development Region (MDR) of TCs located around the Philippines. This is probably caused by changes in dynamical environmental conditions such as lower-tropospheric relative vorticity and vertical shear of horizontal wind. Projected changes in the activity of tropical depression-type disturbances, which are candidates for seeds of TCs, may also contribute to the eastward shift. These projections are basically consistent with earlier results that Yokoi and Takayabu (2009) obtained from outputs of a previous generation of climate model experiments. In addition, this study projects increases in the genesis frequency over a region east of Taiwan and the South China Sea, which are inconsistent with Yokoi and Takayabu (2009).
To improve short-term (i.e., less than one hour) forecasting, a cell-tracking algorithm was applied to meso-γ-scale convective systems (MγCSs). Composite surface rainfall data derived from an X-band multiparameter radar and operational C-band radars of the Japan Meteorological Agency (JMA) were used as initial data and the Algorithm for the Identification and Tracking Convective Cells (AITCC) was used to estimate the movement vectors of MγCSs. The results demonstrate that the cell-tracking system improves forecasting of hourly rainfall compared with conventional pattern-matching extrapolation, especially for quasi-stationary rainfall systems such as back-building storms.
The Thermal and Near-infrared Sensor for Carbon Observation Fourier Transform Spectrometer (TANSO-FTS) on board the Greenhouse Gases Observing Satellite (GOSAT) simultaneously observes column abundances and profiles of CH4 in the same field of view, from the shortwave infrared (SWIR) and thermal infrared (TIR) bands, respectively. We compared CH4 column-averaged dry-air mole fractions (XCH4) derived from the SWIR band, XCH4 calculated from the TIR CH4 profiles, and XCH4 calculated from the CH4 data obtained over Guam airport by commercial aircraft. The difference between the SWIR-XCH4 and aircraft XCH4 values (SWIR - aircraft) was −8 ppbv on average, and the 1σ standard deviation was 10 ppbv. The average difference between the TIR-XCH4 and aircraft XCH4 values (TIR - aircraft) was −5 ppbv, and the 1σ standard deviation was 15 ppbv. The ranges of uncertainties in the calculated aircraft XCH4 values were estimated to be 9, 3, and 2 ppbv, which came from stratospheric CH4 assumption, tropopause height determination, and meteorological dataset used, respectively. Both the SWIR- and TIR-XCH4 values agreed within 0.5% of the aircraft XCH4 values, demonstrating that the GOSAT CH4 data are both valid and consistent with each other over the tropical ocean.
Mechanisms of cloud feedback for marine boundary layer clouds in GCMs (General Circulation Models) to the sea surface temperature increase, which can depend on parameterization, were investigated using single column model version of a GCM with two different low cloud schemes. Both schemes showed negative cloud feedbacks and they were attributed to the increase of the liquid water path (LWP) with the future climate forcing for stratocumulus and stratus. The mechanisms of the LWP increase in the two schemes were investigated respectively through simple numerical experiments. The experimental results imply that in the first scheme, the increase of saturation specific humidity due to the temperature increase in the future climate forcing contributes to the negative cloud feedback through the parameterization determining in-cloud cloud water content (CWC). The results also imply that the increase of latent heat flux in the future climate contributes to increased LWP and hence negative cloud feedback in the other scheme.
Diurnal variations of Korean summertime (June-August) precipitation in 2009 were investigated using hourly National Institute of Meteorological Research/Korea Meteorological Administration (NIMR/KMA) Forecast Research Laboratory (FRL) precipitation data that had high spatial (5 km by 5 km grid distance) and temporal (1 h) resolutions. Using the techniques of multiresolution analysis and Incomplete Gamma Function, NIMR/KMA FRL precipitation reanalysis data are produced from the observations of about 680 Automatic Weather Systems and reflectivity data from 10 radars over South Korea. Three dominant modes of diurnal variations in 2009 summer precipitation over South Korea were indentified via the cyclostationary EOF (CSEOF) technique. Nocturnal precipitation maxima were the result of rain band enhancement from instability due to radiative cooling at the cloud top during the nighttime. This precipitation over the central region of South Korea strengthened and moved rapidly southeastward during the nighttime and then dissipated in the southern coast area of Korea by mid morning. Over the north-central region of South Korea, the daytime prevailing precipitation was nearly stationary from early morning to late afternoon. The precipitation over the southern coastal periphery of Korea also moved slowly eastward from midnight to mid afternoon.
The appearance frequency and types of clouds suitable for cloud seeding in summer were investigated using operationally available data, such as Multi-functional Transport Satellite and radar-AMeDAS precipitation data. This survey was conducted in Shikoku, Japan, as part of a preparation phase for a weather modification project. From the viewpoint of drought-prevention measures (i.e., to secure water resources), the appearance frequencies of probably seedable clouds in the warm season (May through September) did not differ greatly between wet or dry months (17-18%). ‘Warm clouds’ suitable for hygroscopic seeding and ‘cold clouds’ suitable for glaciogenic seeding appeared almost equally in the warm season. During drought periods in mid-summer, the appearance frequency of probably seedable clouds that formed due to local circulation induced by solar radiation tended to be high in late afternoon. Seeding these clouds could be an instantaneously effective way to mitigate drought damage.
A pair of 20-year simulations by two different versions of MIROC (Model for Interdisciplinary Research on Climate) was examined by using a standardized set of Madden-Julian Oscillation (MJO) diagnostics. One of the major differences between version 4 (MIROC4) and version 5 (MIROC5) of MIROC is the cumulus parameterization scheme. MIROC4 uses a prognostic Arakawa-Schubert scheme, whereas MIROC5 uses the Chikira scheme. MIROC5 reproduced the MJO better than MIROC4: a stronger signal in the wavenumber-frequency diagram, a slower and more noticeable eastward movement in the lag-correlation plot, and a better phase relationship between outgoing longwave radiation and zonal winds. To investigate the impact of mid-tropospheric humidity on cumulus development in MIROC5, the atmosphere-only version of MIROC5 was used for a series of sensitivity runs, each with different entrainment parameter values. The entrainment parameter settings significantly influenced the simulated MJO. Large-scale cloud systems tended to move westward with smaller entrainment parameter values, accompanied by a pair of rotations with quasi-symmetry about the equator in the lower troposphere, whereas eastward movements were faster, with larger entrainment parameter values.
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