M. C. R. Kalapureddy

Identification of aerosol type over the Arabian Sea in the premonsoon season during the Integrated Campaign for Aerosols, Gases and Radiation Budget (ICARB)

A discrimination of the different aerosol types over the Arabian Sea (AS) during the Integrated Campaign for Aerosols, Gases and Radiation Budget (ICARB-06) is made using values of aerosol optical depth (AOD) at 500 nm (AOD500) and A ngstrA¶m exponent (I±) in the spectral band 340-1020 nm (I±340-1020). For this purpose, appropriate thresholds for AOD500 and I±340-1020 are applied. It is shown that a single aerosol type in a given location over the AS can exist only under specific conditions while the presence of mixed aerosols is the usual situation. Analysis indicates that the dominant aerosol types change significantly in the different regions (coastal, middle, and far) of AS. Thus the urban/industrial aerosols are mainly observed in coastal AS, the desert dust particles occur in the middle and northern AS, while clear maritime conditions mainly occur in far AS. Spectral AOD and A ngstrA¶m exponent data were analyzed to obtain information about the adequacy of the simple use of the A ngstrA¶m exponent and spectral variation of a for characterizing the aerosols. Using the least squares method, I± is calculated in the spectral interval 340-1020 nm along with the coefficients a1 and a2 of the second-order polynomial fit to the plotted logarithm of AOD versus the logarithm of wavelength. The results show that the spectral curvature can effectively be used as a tool for their discrimination, since the fine mode aerosols exhibit negative curvature, while the coarse mode particles exhibit positive curvature. The correlation between the coefficients a1 and a2 with the A ngstrA¶m exponent, and the atmospheric turbidity, is further investigated.

Characteristics of Rain Integral Parameters during Tropical Convective, Transition, and Stratiform Rain at Gadanki and Its Application in Rain Retrieval

Abstract In the present study the characteristics of rain integral parameters during tropical convective (C), transition (T), and stratiform (S) types of rain are studied with the help of Joss–Waldvogel disdrometer (JWD), L-band, and very-high-frequency wind profilers at Gadanki (13.5°N, 79.20°E). The classifications of three regimes are made with the help of an L-band wind profiler. For rain rate R < 10 mm h−1 larger drops are found in S type of rain relative to C and T rain, and for R ≥ 10 mm h−1 larger drops are found in convective rain. Empirical relations are developed for Dm–R, Dm–Z, N*0–R, Z–R, and Z/Dm–R by fitting the power-law equations. Event to event, no systematic variation of the coefficients and exponents could be found for Z–R and Z/Dm–R relations during the three types of rain. Overall, the C and S events are found to be number controlled, and T events are size controlled. During C type of rain, bigger mean raindrops are found during the presence of strong updrafts. During S type of rain,...

Mobile Lidar Profiling of Tropical Aerosols and Clouds

Abstract Lidar profiling of atmospheric aerosols and clouds in the lower atmosphere has been in progress at the Indian Institute of Tropical Meteorology (IITM), Pune (18°32′N, 73°52′E, 559 m MSL), India, for more than two decades. To enlarge the scope of these studies, an eye-safe new portable dual polarization micropulse lidar (DPMPL) has been developed and installed at this station. The system utilizes a diode-pumped solid-state (DPSS) neodymium–yttrium–aluminum–garnet (Nd:YAG) laser second harmonic, with either parallel polarization or alternate parallel and perpendicular polarization, as a transmitter and a Schmidt–Cassegrain telescope, with a high-speed detection and data acquisition and processing system, as a receiver. This online system in real-time mode provides backscatter intensity profiles up to about 75 km at every minute in both parallel and perpendicular polarization channels, corresponding to each state of polarization of the transmitted laser radiation. Thus, this versatile lidar system i...

Time evolution of monsoon low-level jet observed over an Indian tropical station during the peak monsoon period from high-resolution Doppler wind lidar measurements

Doppler wind lidar measurements of horizontal winds at an Indian tropical station, Mahbubnagar (16.73°N, 77.98°E, 445u2009m above mean sea level), were used to investigate the time evolution of the monsoon low-level jet (MLLJ) during the southwest monsoon season. Vertical profiles of zonal wind in the altitude range of 100 to 3000u2009m above surface (at every 50u2009m height interval and 5u2009min time averaged) obtained during the period 25 July to 23 August 2011 are considered for the analysis. The zonal winds in the altitude up to 3000u2009m above ground are predominantly westerly throughout the period and on almost all the days there is a westerly wind speed maximum around 500u2009m above ground during nighttime. Soon after local sunrise, the core of this wind speed maximum (jet) gets lifted up and by afternoon, the westerly wind maximum is shifted to a higher altitude of 2000u2009m–2500u2009m without much change in its magnitude. Analysis of the high-resolution lidar data strongly indicates that the same nocturnal LLJ seems to be moving up and evolving into a daytime westerly MLLJ reported in several previous studies. Wind speed and direction derived from the wind lidar agree reasonably well with simultaneously observed GPS upper air sounding wind measurements. Further analysis shows that the time-height evolution of the jet core is closely associated with daytime convection and boundary layer growth. The presence of clouds over the region seems to inhibit this type of time evolution.

Inter-comparison of wind profiles in the tropical boundary layer remotely sensed from GPS radiosonde and Doppler wind lidar

Winds play a very important role in the dynamics of the lower atmosphere, and there is a need to obtain vertical distribution of winds at high spatio-temporal resolution for various observational and modelling applications. Profiles of wind speed and direction obtained at two tropical Indian stations using a Doppler wind lidar during the Indian southwest monsoon season were inter-compared with those obtained simultaneously from GPS upper-air sounding (radiosonde). Mean wind speeds at Mahbubnagar (16.73° N, 77.98° E, 445 m above mean sea level) compare well in magnitude for the entire height range from 100 m to 2000 m. The mean difference in wind speed between the two techniques ranged from −0.81 m s−1 to +0.41 m s−1, and the standard deviation of wind speed differences ranged between 1.03 m s−1 and 1.95 m s−1. Wind direction by both techniques compared well up to about 1200 m height and then deviated slightly from each other at heights above, with a standard deviation in difference of 19°–48°. At Pune (18○32′ N, 73○51′ E, 559 m above mean sea level), wind speed by both techniques matched well throughout the altitude range, but with a constant difference of about 1 m s−1. The root mean square deviation in wind speed ranged from 1.0 to 1.6 m s−1 and that in wind direction from 20° to 45°. The bias and spread in both wind speed and direction for the two stations were computed and are discussed. The study shows that the inter-comparison of wind profiles obtained by the two independent techniques is very good under conditions of low wind speeds, and they show larger deviation when wind speeds are large, probably due the drift of the radiosonde balloon away from the location.

Lidar remote sensing of the mixed layer height over a tropical urban Indian station

Mixed layer is an important parameter which controls meteorological conditions in the lower atmosphere. Transport and diffusion of pollutants in the lower atmosphere is highly dependant on the structure of the planetary boundary layer, one important feature of which is the height of the well-mixed layer. In the present study, continuous wave, bistatic argon ion lidar-derived scattered signal strength from different heights in the lower troposphere over Pune (18˚ 32′ N, 73˚ 51′ E, 559 m above mean sea level), India during the period April 2007–January 2008 has been recorded remotely and by employing simple statistical tools, the mixed layer height (MLH) and transition layer thickness (TLT) have been estimated. The results show that sufficient mixing of atmospheric constituents such as aerosols exists in the boundary layer in the post-sunset hours during the summer season, enabling estimation of MLH and TLT. On the other hand, during winter months as mixing ceases/weakens by late evening hours, the mixed layer depth is either low or not easily discernible. In view of the importance of mixed layer depth information for various atmospheric applications, the remote sensing tool used and the simple methodology followed here seem promising.

A case study on large-scale dynamical influence on bright band using cloud radar during the Indian summer monsoon

The present study is a first of its kind attempt in exploring the physical features (e.g., height, width, intensity, duration) of tropical Indian bright band using a Ka-band cloud radar under the influence of large-scale cyclonic circulation and attempts to explain the abrupt changes in bright band features, viz., rise in the bright band height byxa0~xa0430xa0m and deepening of the bright band by about 300xa0m observed at around 14:00 UTC on Sep 14, 2016, synoptically as well as locally. The study extends the utility of cloud radar to understand how the bright band features are associated with light precipitation, ranging from 0 to 1.5xa0mm/h. Our analysis of the precipitation event of Sep 14–15, 2016 shows that the bright band above (below) 3.7xa0km, thickness less (more) than 300xa0m can potentially lead to light drizzle of 0–0.25xa0mm/h (drizzle/light rain) at the surface. It is also seen that the cloud radar may be suitable for bright band study within light drizzle limits than under higher rain conditions. Further, the study illustrates that the bright band features can be determined using the polarimetric capability of the cloud radar. It is shown that an LDR value of −xa022xa0dB can be associated with the top height of bright band in the Ka-band observations which is useful in the extraction of the bright band top height and its width. This study is useful for understanding the bright band phenomenon and could be potentially useful in establishing the bright band-surface rain relationship through the perspective of a cloud radar, which would be helpful to enhance the cloud radar-based quantitative estimates of precipitation.