Showing papers in "Sola in 2012"

A Climatological Study of Tropical Cyclone Rainfall in Vietnam

Abstract: This study investigated the characteristics of the rainfall as-sociated 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 ad-dition 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 Nino and La Nina 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 Nino (La Nina) years, the TC rain ratio and TC_R50 ratio in the central region show a significant decrease (increase) in October-November. The La Nina phases more strongly affect TC rainfall than the El Nino phases, particularly in central Vietnam.

Tephra Fall Simulation for the Eruptions at Mt. Shinmoe-dake during 26-27 January 2011 with JMANHM

Abstract: 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.

Development Processes of Baiu Frontal Depressions

Abstract: 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.

The Impact of Intraseasonal Oscillations in the Tropical Atmosphere on the Formation of Extreme Central Vietnam Precipitation

Abstract: 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.

Mean Features of Tropical Cyclone Precipitation from TRMM/3B42

Abstract: 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.

Gravity-Current Driven Transport of Haze from North China Plain to Northeast China in Winter 2010-Part I: Observations

Abstract: 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.

Eastward-Propagating Property of Large-Scale Precipitation Systems Simulated in the Coarse-Resolution NICAM and an Explanation of its Appearance

Abstract: 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).

Downscaling of Snow Cover Changes in the Late 20th Century Using a Past Climate Simulation Method over Central Japan

Abstract: 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.

Diurnal Variations of Summertime Precipitation in South Korea in 2009 Using Precipitation Reanalysis Data

Abstract: 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.

Development of a New Videosonde Observation System for In-situ Precipitation Particle Measurements

Abstract: A new videosonde receiving system consisting of two receiv- ing 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.

Why do Super Clusters and Madden Julian Oscillation Exist over the Equatorial Region

Abstract: 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.