P. Kishore

MF radar observations of mean winds and tides over Poker Flat, Alaska (65.1° N, 147.5° W)

Abstract. MF radar wind measurements in the mesosphere and lower thermosphere over Poker Flat, Alaska (65.1° N, 147.5° W) are used to study the features of mean winds and solar tides. Continuous observation with the newly installed radar is in progress and in the present study we have analyzed a database of the first 27 months (October 1998–December 2000) of observation. The observed mean wind climatology has been compared with previous measurements and the latest empirical model values (HWM93 model). Similarly, the tidal characteristics are described and compared with the Global Scale Wave Model (GSWM00). The mean wind characteristics observed are fairly consistent with previous wind measurements by the Poker Flat MST radar. The main feature of the zonal circulation is the annual variation with summer westward flow and winter eastward flow. The annual mean zonal wind has a west-ward motion at altitudes below 90 km. The annual mean meridional circulation has mainly southward motion at 70–100 km. There is very good agreement between the radar zonal winds and the HWM93 model winds. Comparison of the meridional winds shows some discrepancy. Analysis of two years of data indicated that the year-to-year consistency is preserved in the mean circulation in the mesosphere. Tidal characteristics observed are also consistent with previous measurements. Semidiurnal tides have the largest amplitudes in summer while the weakest amplitude is observed during the winter months. The vertical wavelength is longer during the summer season compared to the winter season. Comparison with the GSWM00 produces mixed results. There is reasonable agreement between the observed and modeled phases. Diurnal tide amplitudes are comparable in magnitude with that of the semidiurnal tide. Seasonal variation is less evident in the amplitudes. Comparison of the observed tidal parameters with the GSWM00 reveals some agreement and discrepancies. Key words. Meteorology and atmospheric dynamics (climatology; middle atmosphere dynamics; waves and tides)

Tidal structure and variability in the mesosphere and lower thermosphere over Yamagawa and Wakkanai

Abstract Observations of winds in the mesosphere and lower thermosphere (MLT) measured at Yamagawa (31.2°N, 130.6°E) and Wakkanai (45.4°N, 141.7°E) are used to study the structure/variability of solar semidiurnal and diurnal tides. MF radar observations over these sites were recently started by the Communications Research Laboratory, Tokyo, Japan. A database of 3–4 years has been used in the present analysis. The tidal features are discussed, and these are compared with the results from other similar mid-latitude sites. The semidiurnal and diurnal tides are also compared with a recent tidal model. The analysis on semidiurnal tides indicates that the variations over these sites seem to have reasonable similarities. Generally, at both locations the semidiurnal tidal amplitudes have the values in the range 5– 15 m / s . Although seasonal variations in the semidiurnal tide amplitude are not clearly seen, the multi-year average indicates that the maximum amplitude is observed in August/September at both sites. The summer season is characterized by a large vertical wavelength, while the winter season has a comparatively smaller vertical wavelength. Comparison of the observed semidiurnal tide amplitude and phase parameters, and the Global Scale Wave Model (GSWM-98) outputs is generally not satisfactory and confirms the need for further effort in the development of a more realistic model. Diurnal tide amplitude at Yamagawa and Wakkanai shows significant differences in their strengths. The amplitude is consistently larger in Yamagawa. Phase structure shows a better agreement between the sites. Again, comparison of the observed tidal parameters and the GSWM-98 values is generally not good. However, the overall assessment is that the comparison is better in the case of diurnal tides than that of semidiurnal tides. The best comparison result is observed for the diurnal tidal phase. The interannual variability observed in both the semidiurnal and diurnal tides is larger in the Yamagawa data compared to the Wakkanai data. The semidiurnal and diurnal tidal phases around 90 km generally exhibit a bimodal state with the phase being almost constant near the summer (June) and winter (December) solstices, and making rapid transitions in the equinoxes. The duration of the constant phase is longer in the summer solstice than in the winter solstice.

MF radar observations of mean winds over Yamagawa (31.2°N, 130.6°E) and Wakkanai (45.4°N, 141.7°E)

Abstract Continuous MF radar measurements of mesospheric mean winds are in progress at the observatories in Yamagawa (31.2°N, 130.6°E) and Wakkanai (45.4°N, 141.7°E). The observations at Yamagawa and Wakkanai were started in August 1994 and September 1996, respectively. The real-time wind data are used for the study of major large scale dynamic features of the middle atmosphere such as mean winds, tides, planetary waves, and gravity waves, etc. In the present study of mean winds, we have utilized the data collected until June 1999, which include the simultaneous observation period of little more than two and a half years, for the two sites. The database permits us to draw conclusions on the characteristics of mean winds and to compare the mean wind structure over these sites. The mean prevailing zonal winds at both sites are dominated by westward/eastward motions in summer/winter seasons below 90 km. Meridional circulation at meteor heights is generally southward during most times of the year and it extends to lower mesospheric heights during summer also. The summer westward jet at Wakkanai is consistently stronger than those at Yamagawa. However, the winter eastward winds have identical strength at both locations. Meridional winds also show larger values at Wakkanai. The mean wind climatology has been examined and compared with the MU radar observations over Shigaraki (34.9°N, 136.1°E). The paper also presents the results of the comparison between the MF radar winds and the latest empirical model values (HWM93 model) proposed by Hedin et al. (1996. Journal of Atmospheric and Terrestrial Physics 58, 1421–1447). Hodograph analyses of mean winds conducted for the summer and winter seasons show interesting similarities and discrepancies.

Historical and Projected Surface Temperature over India during the 20 th and 21 st century

Surface Temperature (ST) over India has increased by ~0.055 K/decade during 1860–2005 and follows the global warming trend. Here, the natural and external forcings (e.g., natural and anthropogenic) responsible for ST variability are studied from Coupled Model Inter-comparison phase 5 (CMIP5) models during the 20th century and projections during the 21st century along with seasonal variability. Greenhouse Gases (GHG) and Land Use (LU) are the major factors that gave rise to warming during the 20th century. Anthropogenic Aerosols (AA) have slowed down the warming rate. The CMIP5 projection over India shows a sharp increase in ST under Representative Concentration Pathways (RCP) 8.5 where it reaches a maximum of 5 K by the end of the 21st century. Under RCP2.6 emission scenarios, ST increases up to the year 2050 and decreases afterwards. The seasonal variability of ST during the 21st century shows significant increase during summer. Analysis of rare heat and cold events for 2080–2099 relative to a base period of 1986–2006 under RCP8.5 scenarios reveals that both are likely to increase substantially. However, by controlling the regional AA and LU change in India, a reduction in further warming over India region might be achieved.

Tumor Identification in CT Medical Images using Semi Automatic Active Contour Models

of nerves occurs when an external force traumatically injures the nerves which cause a host of physical, cognitive and behavioral effects can range from complete recovery or permanent disability or death. The delineation of the trauma in brain, abdomen and lungs is a challenging task due to variations in shapes and image quality. In this method we present a semi automatic method for extracting the damage of nerves in brain, abdomen and lung from cardiac CT images, in which all the nerves are located sequentially. Each nerve is detected by first identifying the injuries and then segmenting the damaged part. To this end, the damaged nerve is localized by utilizing its geometric features obtained on-line from a CT image. After that, a variational region-growing model is employed to extract the damages. In particular, the location of the nerves damage is determined using via active contour model on the surface of the nerves. This extracts the damage of the nervous system and determines the exact accuracy of the damage is demonstrated by experimental results.