2,324 research outputs found
Characteristics of gravity waves generated in a convective and a non-convective environment revealed from hourly radiosonde observation under CPEA-II campaign
Analyses of hourly radiosonde data of temperature, wind, and relative
humidity during four days (two with convection and two with no convection)
as a part of an intensive observation period in CPEA-2 campaign over Koto
Tabang (100.32° E, 0.20° S), Indonesia, are presented.
Characteristics of gravity waves in terms of dominant wave frequencies at
different heights and their vertical wavelengths are shown in the lower
stratosphere during a convective and non-convective period. Gravity waves with
periods ~10 h and ~4–5 h were found dominant near
tropopause (a region of high stability) on all days of
observation. Vertical propagation of gravity waves were seen modified near
heights of the three identified strong wind shears (at ~16, 20, and
25 km heights) due to wave-mean flow interaction. Between 17 and 21 km
heights, meridional wind fluctuations dominated over zonal wind, whereas from
22 to 30 km heights, wave fluctuations with periods ~3–5 h and
~8–10 h in zonal wind and temperature were highly associated,
suggesting zonal orientation of wave propagation. Gravity waves from
tropopause region to 30 km heights were analyzed. In general, vertical
wavelength of 2–5 km dominated in all the mean-removed (~ weekly mean)
wind and temperature hourly profiles. Computed vertical wavelength spectra
are similar, in most of the cases, to the source spectra (1–16 km height)
except that of zonal wind spectra, which is broad during active convection.
Interestingly, during and after convection, gravity waves with short
vertical wavelength (~2 km) and short period (~2–3 h)
emerged, which were confined in the close vicinity of tropopause, and were
not identified on non-convective days, suggesting convection to be the source
for them. Some wave features near strong wind shear (at 25 km height) were
also observed with short vertical wavelengths in both convective and
non-convective days, suggesting wind shear to be the sole cause of generation
and seemingly not associated with deep convection below. A drop in the
temperature up to ~4–5 K (after removal of diurnal component) was
observed at ~16 km height near a strong wind shear (~45–55 m s<sup>−1</sup> km<sup>−1</sup>) during active period of convection
Mesoscale convection system and occurrence of extreme low tropopause temperatures: observations over Asian summer monsoon region
The present study examines the process of how tropospheric air enters the
stratosphere, particularly in association with tropical mesoscale convective
systems (TMCS) which are considered to be one of the causative mechanisms
for the observation of extremely low tropopause temperature over the
tropics. The association between the phenomena of convection and the
observation of extreme low tropopause temperature events is, therefore,
examined over the Asian monsoon region using data from multiple platforms.
Satellite observations show that the area of low outgoing long wave
radiation (OLR), which is a proxy for the enhanced convection, is embedded
with high altitude clouds top temperatures (≤193 K). A detailed
analysis of OLR and 100 hPa temperature shows that both are modulated by
westward propagating Rossby waves with a period of ~15 days,
indicating a close linkage between them. The process by which the
tropospheric air enters the stratosphere may, in turn, be determined by how
the areas of convection and low tropopause temperature (LTT) i.e. <I>T</I>≤191 K
are spatially located. In this context, the relative spatial
distribution of low OLR and LTT areas is examined. Though, the locations of
low OLR and LTT are noticed in the same broad area, the two do not always
overlap, except for partial overlap in some cases. When there are multiple
low OLR areas, the LTT area generally appears in between the low OLR areas.
Implications of these observations are also discussed. The present analysis
also shows that the horizontal mean winds have a role in the spatial
distribution of low OLR and LTT
Enhanced Room Temperature Coefficient of Resistance and Magneto-resistance of Ag-added La0.7Ca0.3-xBaxMnO3 Composites
In this paper we report an enhanced temperature coefficient of resistance
(TCR) close to room temperature in La0.7Ca0.3-xBaxMnO3 + Agy (x = 0.10, 0.15
and y = 0.0 to 0.40) (LCBMO+Ag) composite manganites. The observed enhancement
of TCR is attributed to the grain growth and opening of new conducting channels
in the composites. Ag addition has also been found to enhance intra-granular
magneto-resistance. Inter-granular MR, however, is seen to decrease with Ag
addition. The enhanced TCR and MR at / near room temperature open up the
possibility of the use of such materials as infrared bolometric and magnetic
field sensors respectively.Comment: 22 pages of Text +
Figs:comments/suggestions([email protected]
Circuits for Optical Based Line of Sight Voice Communication
We present here line of sight communication between a person and his neighbour with the help of optical signal produced by a laser torch which act as a carrier. It is therefore a wireless communication and the transmission can go up to 500 meters. We used photodiode to receive the signal at the receiver. The transmitter circuit comprises condenser microphone transistor amplifier BC547 followed by an op-amp stage built around µA741. When we give a voice signal from the mike, it converts the voice signal into the electrical signal. This electrical signal is fed to IC741 (op-amp) for amplification. The gain of the op-amp can be controlled with the help of 1-mega-ohm potentiometer. The AF output from IC is coupled to the base of a class B amplifier which, in turn, modulates the signal. The transmitter uses 5V power supply. However, the 3-volt laser torch (after removal of its battery) can be directly connected to the circuit-with the body of the torch connected to the class B. The photodiode converts the optical signal into electrical signal and again this signal is amplified using IC741 and a combination of class B push pull amplifiers. The receiver circuit uses an NPN photodiode as the light sensor that is followed by a two-stage transistor preamplifier and IC741 based audio Power amplifier. The receiver does not need any complicated alignment. Just keep the photodiode oriented towards the remote transmitter's laser point and adjust the volume control for a clear sound. The sensor must not directly face the sun
Soil Quality Parameters and Carbon Stock as Influenced by Fodder Grasses and Organic Amendments in an Alfisol of Northeastern India
Intensive tillage, cultivation along the slope, low input, minimal nutrient replacement and high rainfall are among major causes of land degradation in the north eastern hill (NEH) region (Ghosh et al. 2009). Maintaining and enhancing soil quality are crucial to sustaining agricultural productivity and environmental quality (Lal, 2004). Continuous cropping, without use of conservation-effective measures, has negative effects on the soil and environment (e.g., loss of SOC, soil erosion, water pollution). Thus, soil management methods are needed that enhance use efficiency of inputs, reduce losses and minimize adverse impacts on the environment (Bilalis et al. 2009). Perennial grasses provide year- round ground cover, which reduces run-off and soil erosion from sloping land (Ghosh et al. 2009).
Cultivation of forages in degraded and sloping lands not only supply green palatable fodders to livestocks but also rehabilitates the degraded soils by improving physico-chemical properties. Forages have strong root systems compared to field crops (such as rice, maize etc.), protect soil and improve aggregation (Ghosh et al. 2009). Soils under perennial grasses and those which are undisturbed for a long time are potential C sinks because the grasses add organic matter (OM) to soils through root growth, and decline in OM decomposition because of lack of tillage. Further, conversion of degraded cropland soils to forages and perennial grasses lead to C sequestration (Grandy and Robertson, 2007).
Thus, present investigation was conducted with the objective to assess the impact of perennial forage grasses and organic amendments on soil properties and C-sequestration potential
Growth of dense CNT on the multilayer graphene film by the microwave plasma enhanced chemical vapor deposition technique and their field emission properties
Catalyst assisted carbon nanotubes (CNTs) were grown on multilayer graphene (MLG) on copper and silicon substrates by the microwave plasma enhanced chemical vapor deposition technique. The transmission of the MLG was found to vary between 82 to 91.8% with the increase of deposition time. Scanning electron microscopy depicted that the MLG film survived at the deposition condition of CNTs with the appearance of the damaged structure due to the plasma. Growth of CNTs was controlled by adjusting the flow rates of methane gas. The density of carbon nanotubes was observed to increase with a higher supply of methane gas. It was observed that the field emission properties were improved with the increased density of CNTs on MLG. The lowest turn-on field was found to be 1.6 V mu m(-1) 1 accompanied with the highest current density of 2.8 mA cm(-2) for the CNTs with the highest density. The findings suggested that the field emission properties can be tuned by changing the density of CNTs
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