In this paper, the main wind erosion factors influencing dust emission are analyzed by using the observed data from the gobi and oasis sites of ADEC (Aeolian Dust Experiment on Climate impact) Project in Dunhuang station in Northwest China, and the dust emission rate over the two different land surfaces are calculated by using Shao’s dust emission model. The results indicate that the threshold friction velocity over the non-ploughed cropland is larger than that over the gobi desert, while after spring ploughing, it is smaller. Dust emission rate over the ploughed cropland is largest, which is hundreds of times larger than that over the gobi desert. Over the non-ploughed cropland, dust emission rate is less than that over the ploughed cropland, but larger than that over the gobi desert, while when the friction velocity is larger than 0.8 ms−1 it is close or equal to that over the ploughed cropland.
The favorable environmental low-level wind condition under which band-shaped rainfall systems form around Kyushu Island, located in the western part of Japan, was statistically examined using upper-air sounding data at Kagoshima and meteorological radar data. The representative rainbands extending northeastward from the Koshikijima Islands (the Koshikijima line), and the Nagasaki Peninsula (the Nagasaki line), are discussed in this study. The favorable conditions for their formation and maintenance are that the southwesterly low-level wind field persists for longer than 12 hours, and that the wind speed at an 850 hPa level is between 5 m s−1 and 25 m s−1. When the Koshikijima line stagnates for a long time to cause heavy rainfall, other disturbances are usually found around the Koshikijima Islands. Meanwhile, the Nagasaki line forms more frequently than the Koshikijima line, and it often stagnates for a long time without other disturbance.
Remote influences of El Nino-Southern Oscillation (ENSO) on tropical Atlantic sea surface temperature (SST) are examined using reanalysis and in-situ observational datasets. During both the warm and cold events of ENSO, latent heat flux anomalies are the major mechanism for SST anomalies over the Caribbean Sea. Results from a linear decomposition of the latent heat flux anomalies indicate that the anomalous air-sea difference in specific humidity (Δq´) is the dominant term in January, one month after the ENSO’s mature phase. Since anomalies of SST and saturation specific humidity at the sea surface are still small in January, Δq´ is due mostly to changes in specific humidity in the lower atmosphere. Changes in surface air humidity and temperature, and their relationship to temperature variability in the upper troposphere during ENSO warm events are discussed.
In this paper impacts of nss-sulfate, sea-salt and organic particles on microphysical properties of marine cloud are investigated, using a mutil-component size-resolving aerosol model. Numerical results show that the number and type of cloud condensation nuclei (CCN) depend on panicle physical and chemical properties (size distribution, chemical composition) of particles, and on environmental conditions (updrafts or supersaturation). Sea-salt particles play a critical role in cloud microphysical processes. Due to its large radius, sea-salt particles are activated into cloud drops in the initial cloud development. Sea-salt activation decreases supersaturation by consuming water vapor and suppresses nss-sulfate activation. Nss-sulfate indirect forcing may be overestimated in some conditions (such as updraft is low), because of the presence of sea-salt particles. Soluble organic components decrease maximum supersaturation, and lead to a decrease of cloud drops activated at the case of a high nss-sulfate and a high updraft velocity. Nss-sulfate CCN account for most variations of the cloud optical depth (COD). Sea-salt increases COD in the case of low nss-sulfate, but decreases COD when nss-sulfate concentration is high. The organic component enhances this influence of sea-salt on COD.
Measurements of soil water content, relative humidity ofsoil air, and soil temperature in surface soil at 0.01 m and 0.05 m depths were carried out at a gobi site near Qira in the southern part of the Taklimakan Desert, China from the end of March 2001 to April 2004. By calibrating Time Domain Reflectometry (TDR) sensors at the site, the applicability of TDR sensors for use in natural hyper-arid conditions was shown. In the wetting process, soil water infiltrated in the liquid phase, while the soil water was in the vapor phase during the drying process. As the first step of the drying process, the surface ground at both depths rapidly and thoroughly dried by evaporation due to the daytime soil temperature increase. As the second step, the soil water evaporated predominantly from the shallower depth. However, because of the supply of water vapor from deeper soil, saturated conditions continued at 0.01 m depth. As the third step, the surface ground gradually dried, repeated diurnal variations in humidity of soil air resulted from the decreased supply ofwater vapor from deeper soil. Once soil water was supplied in the soil at the gobi site, soil water and water vapor of soil air at 0.05 m depth were not easy to remove.
By using the observational data collected by the C-band Doppler radar which was located at the Green Island off the southeast coast of Taiwan, as well as the offshore island airport and ground weather stations, this article focuses on the mesoscale analysis of inner and outer rainband features of Typhoon Otto (1998), before and after affected by the Central Mountain Range (CMR) which exceeds 3000 m in elevation while the storm was approaching Taiwan in the northwestward movement. While the typhoon was over the open ocean and moved north-northwestward in speed of 15 km/h, its eyewall was not well organized. The rainbands, separated from the inner core region and located at the first and second quadrants relative to the moving direction of typhoon, were embedded with active convections. The vertical cross sections along the radial showed that the outer rainbands tilted outward and were more intense than the inner ones. As the typhoon system gradually propagated to the offshore area near the southeast coast of Taiwan, the semi-elliptic eyewall was built up at the second and third quadrants. Moreover, the strength of the eyewall became more intense compared with the outer rainbands, and the maximum wind axis was quite parallel to the vertical orientation of radar reflectivity in the eyewall. After the detailed streamline analysis, it indicated that the eyewall was enhanced by the confluence between the westerly flow, triggered by the farther outer circulation of the storm around the Taiwan Island, and the northwesterly flow near the inner circulation of the storm itself. Also, the left quadrant in the lower portion (below 2 km in altitude) possessed stronger Doppler velocity than that in the right quadrant, and the upper portion (above 2.0 km) had the opposite mode. This reverse phenomenon of Doppler wind in the lower portion of the typhoon became more pronounced while the storm was getting closer to the mountain. The estimated typhoon center below 1.5 km in altitude had a slower propagating speed due to the orographical blocking and corner effects, and the storm entity suggested a distorted appearance in the lower portion.
We examined the composite seasonal evolution of atmospheric convection over the tropical western North Pacific and northern Indian Ocean during April-August, following the wintertime warm, cold ENSO events, and neutral cases. It was found that the warm (cold) wintertime ENSO events correspond to three times of anomalous convection suppressions (enhancements) in the South China Sea and tropical western North Pacific, separately in April and May, in middle and late June, and in late July and August. The total seasonal evolution and its annual cycle component exhibit nonlinear responses to the different ENSO phases. The annual cycle, and 30-60-day oscillations, all contribute to this ENSO-related seasonal evolution. The phases of composite 30-60-day oscillations for the different ENSO phases were further examined. We found the out-of-phase feature of summertime 30-60-day oscillations in convection over the tropical western North Pacific, between the warm ENSO cases and cold or neutral cases in the preceding winter. The phase of the composite oscillations for the warm cases is three or four pentads lagged to that for the cold and neutral cases. The phase-locking feature of 30-60-day oscillations shown by previous studies is essentially contributed by the cold and neutral cases. Over the northern Indian Ocean, in contrast, the phase of composite oscillations for the warm cases is similar to that for the neutral cases, and is about ten days lagged to that for the cold cases. These features of ENSO-related phase of 30-60-day oscillations are explained by the annual cycle of local zonal winds. The 30-60-day oscillations appear to be more closely phase-locked to the annual cycle of zonal winds, which is substantially influenced by the ENSO phase in the preceding winter, than they are phase-locked to the calendar annual cycle.
An eye-safe airborne coherent Doppler lidar system has been developed at the National Institute of Information and Communications Technology (NICT). This system can also be used at ground level and ground-based experiments were made to evaluate the system performance at the NICT Wakkanai radio observatory. The obtained wind profiles were compared with those measured by radiosondes launched at the Wakkanai local meteorological observatory, and by a VHFR system installed by NICT near the Wakkanai airport. Although the volume measured by the coherent Doppler lidar system differed spatially and temporally from those by the radiosonde and the NICT VHF radar system, the wind profiles observed by the coherent Doppler lidar system agreed well with those observed by other instruments. The wind velocities obtained through the full correlation analysis of the VHF radar system were a little smaller than those from the coherent Doppler lidar system, which is consistent with previous statistical results for the VHF radar system. The ground-based results showed that the standard deviations of wind velocity estimates in the laser pulse accumulation seemed to approach a constant value under the real atmospheric conditions, and that the lower limit of the signal-to-noise ratio for the reliable estimate of the wind velocity decreases with the laser pulse accumulation. The ground-based experiments showed that the coherent Doppler lidar system is a reliable system for wind-related research.
Numerical experiments are performed for Typhoon Flo (T9019), which was the subject of an international model intercomparison (COMPARE III). The model used is a mesoscale-convection-resolving model. A global objective analysis (GANAL) data produced by JMA is used as an initial condition, and the initial time is 00 UTC 14 September 1990. The horizontal grid size is taken to be 5/36 degrees (about 15 km) in the fine-mesh area of a triply-nested grid model. Mesoscale structure of the simulated typhoon is studied in detail. Cloud water and rainwater fields are compared with satellite images. In the first 12 hours, the predicted rainwater field is quite different from that suggested from satellite images, mainly because the initial field is latently stable in the typhoon area. Latent instability is created by strong surface winds. Later in the integration, the rainfall patterns exhibit several important features in the satellite images. The simulated 6-hour accumulated rainfall between 48 and 54 hours is compared with some simulations from COMPARE. Rainfall amounts in the inner area of the typhoon, and in the tropics, appear to be better simulated. It is also shown that the time change of latent instability distribution is an important measure to explain how the rainfall distribution during this period is realized. Comparison of the wind fields at 200 hPa indicates great differences among the models. The structure of simulated rainbands is examined in some detail. It is shown that the model simulates rainbands of four types, with respect to locations of updraft/downdraft and the cold pool relative to the rainwater field, and whether the inflow into the rainband is on the concave edge or the convex edge. Behavior of mesoscale organized convection, which constitutes the rainband, is also examined. These results suggest that even a model with a coarse grid size of about 15 km can describe important features of the mesoscale structure of tropical cyclones.
Cloud microphysical propenies derived from satellite data during December 2000 and April 2001, Asian Atmospheric Particulate Environment Change Studies (APEX) Intensive Observational Period (IOP), are compared with ground and aircraft measurements. The target clouds are marine stratus and stratocumulus. They appeared over the Amami-Oshima Island, and off the south coast of Kyushu island. The principal goals of the comparison are to understand the characteristics of data obtained from each observing platform, and investigate the potentiality ofsynergistic use of multi platform data. The liquid water paths obtained from satellite (MODIS) observation by using the GLI cloud retrieval algorithm were compared with the ground-based measurements (microwave radiometer). The correlation co-eflicient and the root mean square error between ground and satellite liquid water path was 0.87 and 61.9 g/m2. The satellite-retrieved cloud effective radius agreed with those from the aircraft measurements (FSSP) around the top of the cloud.