Stratosphere Troposphere (ST) Radars are emerging as powerful tools for Atmospheric Research in recent years around the world. They have immense applications in studies in Meteorology, Cloud Physics, Thunderstorms, Convections, Atmospheric Electricity, Climate Change, Environmental Physics, Civil aviation, communications, etc.
Continuous information available from ST Radar is highly useful to the aviation. Cochin International Airport is just 14 km away from CUSAT campus. Cochin Airport can very well use the ST Radar information for the prediction of thunderstorms, fog, convective clouds, and heavy rainfall cases in the airport area. This can forecast severe weather conditions, thereby avert aircraft accidents. Indian Navy can also use the radar derived atmospheric conditions for their helicopter operations and training.
Science Engineering Research Board (SERB), Department of Science and Technology, Government of India, has sanctioned this 5-year funding under its Intensification of Research in High Priority Area (IRHPA) scheme for the developing of basic research in Atmospheric Science and improving the forecast skill. This state-of-art and sophisticated Radar is designed and developed to operate successfully for the next 25-30 years.
Kerala is the land of Monsoons. In fact the first burst of the southwest monsoon over the Indian subcontinent takes place over Kerala. The timely onset, optimum duration and reasonable strength of the southwest monsoon are of vital importance to the life and economy not only of our Country but the entire South Asian region. Monsoon touches the state in June and remains there till September though not much difference in temperature can be felt.
Cochin (Kochi), the Queen of the Arabian Sea, is situated on the south west coast of Indian peninsula. Cochin is located near to the central part of the Kerala State, around 10º N and 76º E. Kerala constitutes a natural and unique geographic unit. It is a land of oval mountains, verdant valleys, evergreen forests, cascading waterfalls and palm-fringed lagoons.
The location of Cochin is highly significant to understand and timely predict the variability and the characteristics features of monsoon onset, intensification, break and withdrawal phases of India summer monsoon, which is highly relevant to proper planning for the agriculture, hydro-electrical power generation, economy and industrial sector of our State, in particular.
Wind Profiler Radar
A wind profiler is a sensitive Doppler radar, designed to point (nearly) vertically and to respond to fluctuations of the refractive index of the (clear) air. The fluctuations of the refractive index are due to turbulence, and turbulence on the scale of half the radar wavelength (Bragg scattering) gives a strong signal. However, the emitted signal is also sensitive to particles such as hydrometeors (rain, snow, hail), cloud droplets, and insects. Insects, birds, and airplanes are also possible targets, but their signal can be removed fairly well. The horizontal wind is measured by oblique beams in orthogonal directions (e.g. east and north). The beams are tilted 15 to 30 degrees from the zenith, and the Doppler shifts of the echoes in each direction are compared to determine the wind speed and direction. Just as a Doppler radar, a wind profiler measures radar reflectivity and radial velocity of its echo, amongst other less important variables.
Wind profilers operate in various frequencies. A VHF wind profiler (50 MHz or 6 m) measures wind profiles between 2 and 16, occasionally 20 km AGL, but the antenna occupies 2 soccer fields (100 x 100m). An example is the Mesosphere, Stratosphere Troposphere (MST) Radar at Tirupati, India. The Indian MST Radar is a highly sensitive VHF phased array radar operating at 53 MHz with a peak power aperture product of 3 x 1010 Wm2. The phased array consists of 1024 crossed three-element Yagi antennas occupying an area of 130m x 130m. The higher the frequency, the smaller the antenna, the smaller the turbulent flow scale that is resolved, the higher the resolution close to the radar, but the higher the attenuation.The present ST radar at Cochin will operate at 205 MHz (1.5 m) Frequency, which measures, zonal, meridional and vertical winds up to a height of about 20 km, at very high resolution in both time and vertical levels continuously for 24 hours in a day. This frequency is not much used world- wide, because this frequency band lies in the television broadcasting in USA and other countries. Advantage of this frequency band is that highly reliable wind measurement is possible in the entire tropospheric heights and lower stratospheric levels. A similar ST Radar is already installed in ARIES, Nainital, which will also be in operation soon.
Advantages of ST Radar
Stratosphere-Troposphere (ST) Radar is the most powerful and versatile wind- profiling instrument. The traditional method of measuring the wind is to track the movement of a radiosonde – an instrumented, helium-filled, meteorological balloon – as it rises up through the atmosphere. However, radiosondes are rarely launched at intervals of less than 6 hours and so can only be used to provide information about the large-scale weather patterns.
By contrast, the ST radar is operated on a continuous basis and provides measurements of the wind every few minutes. The data consequently provides unique opportunities for atmospheric research. Its major advantages over other conventional observational methods are:
- Continuous operation and measurement
- No intrusion into the space being sampled
- Low labour costs for measurements
- High altitude coverage
- Operation in high wind
- Operation in high acoustic noise environments
- Industrial process and thereby pollution control by real-time monitoring of the local atmospheric environment
- Meteorological research; etc.
Applications of ST Radar
There is increasing evidence that stratospheric processes influence the tropospheric circulation across a wide range of timescales. On intra-seasonal timescales, observations show that anomalies of the Northern Hemisphere wintertime stratospheric circulation frequently precede persistent changes to the tropospheric circulation. This may be useful in improving the predictability of the troposphere on time scales of the order of several weeks.
The tropical stratosphere plays a major role in the intra-seasonal and interannual variability of the tropospheric circulations, especially over the Asian summer monsoon region. The tropospheric circulation may also be linked to the stratosphere on longer timescales. It has been found that stratospheric forcings in relationship with ozone depletion, volcanic aerosols, or the quasi-biennial oscillation exhibit a signature in surface climate. Such a coupling may be important for more realistic simulations of anthropogenic climate change in relationship with secular changes of greenhouse gases.
Relevance of Stratospheric Research:
- The stratosphere is the transition region, which interacts with the weather systems in the dense lower atmosphere and the richly ionized thin upper atmosphere.
- The decrease in stratospheric ozone and increase in the tropospheric ozone is a major concern in studies on climate change and variability.
- The study of stratosphere troposphere interactions is significantly important to understand the climate variability.
- Stratospheric changes can affect the climate in a quite complex way through radiative and dynamical interactions with the troposphere.
- There is also the possibility that changes in ozone could lead to changes in the stratospheric distribution of wind and temperature and thus affect the dynamical interactions between the troposphere and stratosphere.
Origin of the Program
To investigate the influence of stratosphere and upper troposphere on the underlying monsoon circulation over the Indian subcontinent, Government of India, Ministry of Science and Technology has given sanction and identified Cochin University of Science and Technology (CUSAT) to install Stratosphere Troposphere Wind Profiler Radar (ST Radar) to study horizontal and vertical circulation pattern, interaction and coupling of the lower, middle and upper levels in the troposphere as well as the radiatively sensitive stratosphere.
A detailed spatial and temporal variability of the circulation pattern is expected to provide interesting results for a better understanding on the onset, active, and break phases of the monsoon as well as its interannual and intra-seasonal variability. These observational evidences can also be assimilated in the numerical monsoon forecasting models to get a better forecasting.
• To study the characteristics of summer monsoon and its dynamics
• To search for the possible causes of monsoon variability
• To understand the monsoon low level jet and its association with monsoon activity
• To study the characteristics of Tropical Esterly Jetstream in the upper troposphere and its linkage with monsoon activity
• To monitor, analyze and modeling of Tropical mesoscale convective systems
• To study the Orographic Forcing by the Western Ghats and the Generation of Wave Activity
• To investigate the characteristics of Extreme Rainfall Events and its synoptic and mesoscale features
• To study the role of Stratospheric QBO on Tropospheric Circulation
• To study the moisture transport from troposphere to stratosphere and understand the Stratosphere Troposphere Exchange processes
• To understand the role of tropical tropopause on the interaction between upper troposphere and lower stratosphere
• To comprehend the characteristics of orographically induced gravity waves and their role in Stratosphere troposphere coupling