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The pulsed, beamwidth-limited atmospheric radar suffers from a finite resolution volume, making it difficult to resolve the small-scale irregularity structure of refractive index (or clear-air turbulence) in the scattering region. Multireceiver and multi-frequency imaging techniques were thus proposed to improve the spatial resolution of the measurements in the finite resolution volume. The middle and upper atmosphere radar (MUR; 34.85° N, 136.10° N) possesses the capabilities of 5 frequencies, ranging from 46 MHz to 47 MHz, and up to 25 receivers to carry out the imaging techniques. In this paper, we exhibit the three-dimensional (3-D) radar imaging utilizing five frequencies and 19 receivers of the MUR. The Capon method was employed for the process of imaging, and examinations of a wavy layer and turbulent structures were made, in which the spatial weighting effect on the imaging were mitigated beforehand. Information such as echo center and structure morphology in the resolution volume was then extracted. For example, the location distribution of echo centers could imply the traveling orientation of the wavy layer, which was correspondent with horizontal wind direction. Such information of wavy layer structure was more difficult to disclose without removal of the spatial weighting effect. This paper demonstrates an advanced application of 3-D radar imaging to some practical atmospheric phenomena. [ABSTRACT FROM AUTHOR]

In this study we have used wind observation data from the mesosphere and lower thermosphere (MLT) region, obtained from meteor radar measurements in São João do Cariri (7.4° S, 36.5° W) from July 2004 to December 2008 and in Cachoeira Paulista (22.7° S, 45.0° W) from January 2002 to July 2006 and from September 2007 to November 2008. From the spectral analysis it was possible to identify the presence of planetary-scale oscillations in the hourly winds for the two latitudes and to study their transient character, which allowed elaboration of a climatology of planetary oscillation signatures. Planetary waves with periods near 2-days, 6-7 days, and 16 days were focussed on in this study. The quasi-2-day waves in the meteoric winds showed a seasonal cycle, with intense amplitudes occurring after the austral summer solstice and extending until the end of the season. The vertical wavelengths of the 2- day wave over Cachoeira Paulista were larger than those at São João do Cariri. A possible modulation of the quasi-2- day wave amplitudes by the quasi-biennial oscillation (QBO) has been observed only at São João do Cariri. The 6-7 day oscillations presented more intense amplitudes during August-November but were present with lower amplitudes during March-April at both sites. The 6-7 day vertical wavelengths over São João do Cariri were larger than at Cachoeira Paulista. The 6-7 day amplitudes exhibited intra-seasonal and annual behavior, however, there was no clear evidence of QBO modulation. The 16-day oscillations showed a seasonal cycle at São João do Cariri, with amplifications from austral spring to mid-summer and weaker amplitudes from autumn until early winter, however, there was no clear seasonality over Cachoeira Paulista. The 16-day vertical wavelengths have assumed values of λz ~45-85 km over both sites. 16-day wave amplitudes at the two sites showed different long-term behaviors. [ABSTRACT FROM AUTHOR]

Using a fully nonlinear two-dimensional (2-D) numerical model, we simulated gravity waves (GWs) breaking and their contributions to the formation of large winds and wind shears in the mesosphere and lower thermosphere (MLT). An eddy diffusion coefficient is used in the 2-D numerical model to parameterize realistic turbulent mixing. Our study shows that the momentum deposited by breaking GWs accelerates the mean wind. The resultant large background wind increases the GW's apparent horizontal phase velocity and decreases the GW's intrinsic frequency and vertical wavelength. Both the accelerated mean wind and the decreased GW vertical wavelength contribute to the enhancement of wind shears. This, in turn, creates a background condition that favors the occurrence of GW instability, breaking, and momentum deposition, as well as mean wind acceleration, which further enhances the wind shears. We find that GWs with longer vertical wavelengths and faster horizontal phase velocity can induce larger winds, but they may not necessarily induce larger wind shears. In addition, the background temperature can affect the time and height of GW breaking, thus causing accelerated mean winds and wind shears. [ABSTRACT FROM AUTHOR]

During the passage of typhoon Kujira in April 2003 near to the northeast of Taiwan, atmospheric radar at Chung-Li (24°58N, 121°11E) was continuously operated. The data collected from profiler radar was used to investigate the impact of typhoon on generating waves and other atmospheric disturbances. Result showed that the typhoon and the associated wind disturbances can generate atmospheric waves with varied periodicity even when the core was far away from the land. The waves were quite prominent when the core was closer to the mountain. Observations show that these waves propagate vertically upward for many kilometers and getting trapped in higher altitudes. The radar reflectivity at the tropopause during the event showed that stable layer structure was very weak. Further, the enhancement in ozone measurement at the ground level was observed when the typhoon was near to radar site. [ABSTRACT FROM AUTHOR]

Abstract: This study explores the inevitable role of wind parameters such as wind speed, wind convergence and wind vorticity in the long range transport and distribution of aerosols in the winter time atmosphere over the Bay of Bengal (BoB) during the campaign Winter ICARB. MODIS observed aerosol optical depth (AOD), with an excellent agreement with ship borne Microtops AOD, was found to increase over the BoB particularly, in the eastern parts during the course of the campaign. The influence of atmospheric circulation on this increase is examined using the wind field from NCEP reanalysis and computed wind convergence and vorticity for first and second halves (FH and SH) of the campaign along with a back trajectory analysis using HYSPLIT transport and dispersion model. While surface winds over the BoB remained nearly the same throughout the campaign denying the possibility of enhancement in marine aerosol generation, the higher altitude winds altered significantly in SH providing a channel for aerosol transport from the Indian landmass to the BoB in addition to the increased forest fire contribution from south Asia. This suggested mechanism is supported by CALIPSO aerosol extinction profiles over the eastern BoB and the surrounding land masses. Fine particle dominance in MODIS AOD and diminished correlation between ship borne AOD and surface aerosol mass measurements during SH corroborate this inference by indicating the presence of elevated aerosol layers, which can contribute substantially to the radiative effects of the earth–atmosphere system. This study throws light on the importance of wind convergence and vorticity in the investigations on the long range transport and spatial distribution of aerosols. [Copyright &y& Elsevier]

Based on in-situ time series data from an array of temperature sensors and an acoustic Doppler current profiler on the continental shelf of the northwestern South China Sea, a sequence of internal solitary waves (ISWs) were observed during the passage of tropical storm Washi in the summer of 2005, which provided a unique opportunity to investigate the ISW response to the tropical cyclone. The passing tropical storm is found to play an important role in affecting the stratification structure of the water column, and consequently leading to significant variability in the propagating features of the ISWs, such as the polarity reversal and amplitude variations of the waves. The response of the ISWs to Washi can be divided into two stages, direct forcing by the strong wind (during the arrival ofWashi) and remote forcing via the nearinertial internal waves induced by the tropical storm (after the passage of Washi). The field observations as well as a theoretical analysis suggest that the variations of the ISWs closely coincide with the changing stratification structure and shear currents in accompanied by the typhoon wind and nearinertial waves. This study presents the first observations and analysis of the ISW response to the tropical cyclone in the South China Sea. [ABSTRACT FROM AUTHOR]

Information on the aerosol intensive properties like Single Scattering Albedo (SSA) and asymmetry parameter are very limited, particularly over the peninsular India, though extensive reports are available on the aerosol bulk properties. In view of the importance of these parameters in evaluating the aerosol radiative forcing, we present for the first time the temporal variation in SSA with measurements on aerosol absorption and scattering coefficients over Visakhapatnam (17.72° N, 83.32° E; located on the east coast of India) for the year 2007. The inferred SSA was in the range of 0.65 and 0.9 with an annual mean of 0.76±0.013 and with a probable value of 0.80, indicating a marginal atmospheric warming over the region. The mixed layer contribution to column Aerosol Optical depth is found to be 35% in summer while it is well above 35% in winter, indicating the confinement of aerosol within the boundary layer during winter. The asymmetry parameter which represents the angular scattering in radiative forcing estimation is found to be around 0.65±0.1 for the location. The day to day variability in SSA is found to be well correlated with the variations in surface BC mass concentrations and/or the relative dominance of the fine/coarse mode aerosol. The results are discussed in light of the aerosol physical and optical properties and the asymmetry parameter. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents the results of in situ observations related to Arctic clouds where possible ice-multiplication via stellar-crystal fragmentation processes is discussed. The microphysical and morphological cloud-parameters are derived from airborne measurements performed with a Cloud Particle Imager (CPI). One principal idea of this study is to demonstrate the potential of the CPI as an instrumental means to access the controversial topic of natural and instrumental crystal break-ups, and the importance of human over automated software for ice crystal classification. For the particular cloud flight of May 20th in 2004, a minimum of 18% of all observed fragmented stellar crystals have been identified as resulting from a natural fragmentation process (indication for possibly subsequent growth and/or lack of a fresh break-up line), therefore contributing to the ice-multiplication in the clouds. In other words, up to 82% of the fragmented crystals still may have experienced break-up by the CPI instrument itself. The performed simulation study for crystal break-up shows quite good agreement between the outcome of a simplest model and the experimental data. [Copyright &y& Elsevier]

Abstract: A new model of blue jets as a lightning-related phenomenon is proposed. A blue jet consists of the bi-leader, whose top part is seen on photos as a “trunk of a tree”, and is capped at the topside of the leader by its streamer zone. The latter is shown as tall and narrow branches of “the tree”. It is shown that the time independent fractal blue jet model does not provide an adequate description of blue jets and streamer zone of a leader. It ignores an important fact of the fast loss of the streamer channel conductivity due to the electron attachment to the oxygen. The top streamer branches were born mostly prior to the bottom branches not as result of branching, but formed by the leader tip. It was shown that due to transfer of the high potential of the edge of the thundercloud by the leader, long streamers of blue jets can be sustained by moderate cloud charge. The streamer length is estimated along with the height at which the streamers can reach the ionosphere. The propagation of a streamer in the atmosphere of exponentially falling density N and in the self-consistent electric field of the streamer zone was computed. It was found that the critical external field E S required for unlimited streamer growth satisfies the similarity law E S/N⋍const. The similarity law was numerically studied in a wide range of N. [Copyright &y& Elsevier]