Search Results

You are looking at 1 - 7 of 7 items for

  • Author or Editor: Y. R. Rao x
  • Refine by Access: All Content x
Clear All Modify Search
Y. R. Rao
and
C. R. Murthy

Abstract

The recently developed wavelet transform, conventional spectral, and empirical orthogonal function decompositions have been applied to the vertical temperature profiles characterized with an isolated upwelling event and several other small-scale structures. Although empirical orthogonal function provides optimal decomposition of variance, it does not reveal much information about the transition of energy to small-scale oscillations. The localized characteristics that are not detected properly in the power spectral analysis are well represented by wavelets in the frequency–time domain.

Full access
Y. R. Rao
and
C. R. Murthy

Abstract

Simultaneous measurements of Eulerian and Lagrangian currents along the north shore of Lake Ontario are analyzed to provide the mean flow properties and horizontal turbulent exchange characteristics in the coastal boundary layer (CBL). The summer coastal boundary layer is characterized by a frictional boundary layer (FBL) of a width of ∼3 km, in which shore and bottom friction affects the flow. In this regime the currents are predominantly shore parallel and persistent. The outer boundary layer also called an inertial boundary layer (IBL), typically of the order of 5–6 km wide, is a consequence of the adjustment of inertial oscillations to the lateral boundary.

During the summer season within the CBL, the current motions are associated with thermocline displacements. The eastward (westward) wind stress causes thermocline elevation (depression) causing upwelling (downwelling). The mean subsurface westward currents associated with downwelling events are typically stronger in comparison to weak eastward flow during upwelling. Further, upwelling events are characterized by reduced low frequency motion (>1 day) and significant near-inertial (∼17 h) currents. The width of the CBL decreases during upwelling and increases during downwelling. Internal waves generated by baroclinic seiches during these events have periods from 11 to 17 hours. The near-surface horizontal exchange coefficients calculated from Lagrangian measurements are higher than those from subsurface Eulerian values. Upwelling events show that the turbulent kinetic energy is higher than mean flow kinetic energy (MKE) in the CBL, and cross-shore turbulent exchange increases in the IBL. During downwelling the alongshore exchange coefficients are higher in the FBL, whereas cross-shore exchanges are higher in the IBL. Downwelling events are also characterized by increased contribution from the MKE rather than the turbulent kinetic energy.

Full access
C. R. V. Raman
,
Y. P. Rao
,
S. K. Subramanian
, and
Jose A. Maliekal

Abstract

In earlier papers it was shown that tropospheric vertical wind shear in the layer 850–200 mb decreases appreciably prior to formation of depressions in the Indian summer monsoon area. Further analysis reveals that this decrease in shear stems almost entirely from the upper troposphere between 400 mb (7.4 km) and 250 mb (10.5 km).

During the southwest monsoon period (June–September) the tropospheric wind shear over the Indian subcontinent is found to wax and wane in periods of 5–10 days in the latitudinal belt 9–27°N with an amplitude of the order of 35 m s−1 (650 mb)−1. These oscillations in wind shear thus appear to be a characteristic of the monsoon atmosphere. The phase of the shear oscillation south of about 16°N is opposite to that in the north.

Full access
I. Zurbenko
,
P. S. Porter
,
R. Gui
,
S. T. Rao
,
J. Y. Ku
, and
R. E. Eskridge

Abstract

Recognizing the need for a long-term database to address the problem of global climate change, the National Climatic Data Center has embarked on a project called the Comprehensive Aerological Reference Data Set to create an upper-air database consisting of radiosondes, pibals, surface reports, and station histories for the Northern and Southern Hemispheres. Unfortunately, these data contain systematic errors caused by changes in instruments, data acquisition procedures, etc. It is essential that systematic errors be identified and/or removed before these data can be used confidently in the context of greenhouse-gas-induced climate modification.

The purpose of this paper is to illustrate the use of an adaptive moving average filter in detecting systematic biases and to compare its performance with the Schwarz criterion, a parametric method. The advantage of the adaptive filter over traditional parametric methods is that it is less affected by seasonal patterns and trends. The filter has been applied to upper-air relative humidity and temperature data. The accuracy of locating the time at which a bias is introduced ranges from about 600 days for changes of 0.1 standard deviations to about 20 days for changes of 0.5 standard deviations.

Full access
S. T. Rao
,
I. G. Zurbenko
,
R. Neagu
,
P. S. Porter
,
J. Y. Ku
, and
R. F. Henry

This paper describes the characteristic space and time scales in time series of ambient ozone data. The authors discuss the need and a methodology for cleanly separating the various scales of motion embedded in ozone time series data, namely, short-term (weather related) variations, seasonal (solar induced) variations, and long-term (climate–policy related) trends, in order to provide a better understanding of the underlying physical processes that affect ambient ozone levels. Spatial and temporal information in ozone time series data, obscure prior to separation, is clearly displayed by simple laws afterward. In addition, process changes due to policy or climate changes may be very small and invisible unless they are separated from weather and seasonality. Successful analysis of the ozone problem, therefore, requires a careful separation of seasonal and synoptic components.

The authors show that baseline ozone retains global information on the scale of more than 2 months in time and about 300 km in space. The short-term ozone component, attributable to short-term weather and precursor emission fluctuations, is highly correlated in space, retaining 50% of the short-term information at distances ranging from 350 to 400 km; in time, short-term ozone resembles a Markov process with 1-day lag correlations ranging from 0.2 to 0.5. The correlation structure of short-term ozone permits highly accurate predictions of ozone concentrations up to distances of about 600 km from a given monitor. These results clearly demonstrate that ozone is a regional-scale problem.

Full access
Pankajakshan Thadathil
,
Prasad Thoppil
,
R. R. Rao
,
P. M. Muraleedharan
,
Y. K. Somayajulu
,
V. V. Gopalakrishna
,
Raghu Murtugudde
,
G. V. Reddy
, and
C. Revichandran

Abstract

The formation mechanisms of the barrier layer (BL) and its seasonal variability in the Arabian Sea (AS) are studied using a comprehensive dataset of temperature and salinity profiles from Argo and other archives for the AS. Relatively thick BL of 20–60 m with large spatial extent is found in the central-southwestern AS (CSWAS), the convergence zone of the monsoon wind, during the peak summer monsoon (July–August) and in the southeastern AS (SEAS) and northeastern AS (NEAS) during the winter (January–February). Although the BL in the SEAS has been reported before, the observed thick BL in the central-southwestern AS during the peak summer monsoon and in the northeastern AS during late winter are the new findings of this study. The seasonal variability of BL thickness (BLT) is closely related to the processes that occur during summer and winter monsoons. During both seasons, the Ekman processes and the distribution of low-salinity waters in the surface layer show a dominant influence on the observed BLT distributions. In addition, Kelvin and Rossby waves also modulate the observed BL thickness in the AS. The relatively low salinity surface water overlying the Arabian Sea high-salinity water (ASHSW) provides an ideal ground for strong haline stratification in the CSWAS (during summer monsoon) and in NEAS (during winter monsoon). During summer, northward advection of equatorial low-salinity water by the Somali Current and the offshore advection of low-salinity water from the upwelling region facilitate the salinity stratification that is necessary to develop the observed BL in the CSWAS. In the SEAS, during winter, the winter monsoon current (WMC) carries less saline water over relatively high salinity ambient water to form the observed BL there. The winter West India Coastal Current (WICC) transports the low-salinity water from the SEAS to the NEAS, where it lies over the subducted ASHSW leading to strong haline stratification. Ekman pumping together with the downwelling Kelvin wave in the NEAS deepen the thermocline to cause the observed thick BL in the NEAS.

Full access
P. C. S. Devara
,
P. E. Raj
,
K. K. Dani
,
G. Pandithurai
,
M. C. R. Kalapureddy
,
S. M. Sonbawne
,
Y. J. Rao
, and
S. K. Saha

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 is expected to play a vital role not only in atmospheric aerosol and cloud physics research and environmental monitoring but also in weather and climate modeling studies of the impact of radiative forcing on the earth–atmosphere radiation balance and hydrological cycle. This paper provides a detailed description of Asia’s only lidar facility and presents initial observations of space–time variations of boundary layer structure from experiments carried out during winter 2005/06.

Full access