Optimal Design of a Rain Gauge Network to Improve Streamflow Forecasting

Enhanced streamflow forecasting has always been an important task for researchers and water resources managers. However, streamflow forecasting is often challenging owing to the complexity of hydrologic systems. The accuracy of streamflow forecasting mainly depends on the input data, especially rainfall as it constitutes the key input in transforming rainfall into runoff. This emphasizes the need for incorporating accurate rainfall input in streamflow forecasting models in order to achieve enhanced streamflow forecasting. Based on past research, it is well-known that an optimal rain gauge network is necessary to provide high quality rainfall estimates. Therefore, this study focused on the optimal design of a rain gauge network and integration of the optimal network-based rainfall input in artificial neural network (ANN) models to enhance the accuracy of streamflow forecasting. The Middle Yarra River catchment in Victoria, Australia was selected as the case study catchment, since the management of water resources in the catchment is of great importance to the majority of Victorians

Inter-annual variability in the dynamics and physics of the mean onset date of monsoon over Indian region

241-251From observational and statistical studies, the mean onset date of southwest monsoon for India is 1st June with standard deviation of 8 days. In view of this, the atmospheric circulation over India and neighbourhood (EQ-25oN, 50oE-90oE) for the mean onset date is studied using NCEP reanalyzed data from surface-300 hPa for three different years, i.e. (i) year 2000 having normal onset, (ii) year 1999, early onset (i.e. 25th May) and (iii) year 1997, late onset (i.e. 9th June). The influence of all dynamical and physical parameters for all the three years are discussed in the present study for understanding the dynamics and physics associated with onset conditions on 1st June

Oceanic mixed layer variations during the movement of cyclone along symmetric tracks in the Indian Ocean

111-122The understanding of significant changes in the oceanic mixed layer is important for dynamical prediction of tropical cyclone. Present study aims at examining the variations in the upper ocean parameters during the movement of tropical cyclone in northern and southern Indian Ocean, by applying 1½ layer wind driven reduced gravity ocean model. Different idealized tracks in the Bay of Bengal and their mirror images in southern hemisphere are considered, The model produced mixed layer depth, temperature and currents are compared for northern and southern hemispheric cyclone cases. Also the effect of latitude for westward moving cyclones in both the hemisphere is investigated. For this, tracks in the Arabian Sea and their counter parts in the southern hemisphere are considered. The maximum cooling found in the wake of cyclone is of the order of 3 - 4°C, which is comparable with earlier studies and observations. This significant cooling can cause weakening of the storm. This can be useful for prediction especially in the event of a cyclonic storm heading towards land and likely to make land fall. Moreover it is also seen that the mixed layer is cooled more on the right (left) of the storm track in northern (southern) hemisphere. This cooling decreases for the storms translating along higher latitudes implying the sensitivity of the latitudinal location of the storm. </span

Low level wind shear and baroclinic growth of monsoon depression scale waves

A quasi-geostrophic, linear stability analysis was carried out to find the effect of low level wind shear on the baroclinic growth of monsoon depression scale waves. The low level wind shear of the mean monsoon flow is altered by varying the surface wind, the position and the magnitude of the westerly maximum. The growth rate and phase velocity of the short unstable waves for all the cases of wind profiles are obtained. It is noticed that the growth rate and phase velocity of the depression scale waves (L≈2000 to 2500 km) are not influenced by small variations in the position or magnitude of the westerly maximum. But the growth rate of depression scale waves does depend on the average wind shear between 850-500 mb region

Seasonal variations of synoptic features over the north Indian Ocean during dipole years

75-86Recent studies found that the atmospheric circulation over the Indian Ocean region is highly influenced by the Indian Ocean Dipole (IOD) forcing. In the present study, we analyzed National Center for Environmental Prediction and National center for Atmospheric Research (NCEP-NCAR) reanalysis data to observe the IOD related variability at different pressure levels from surface to upper troposphere during the spring season. The study period (1982-2001) includes three positive IOD (1982, 1994 and 1997) and two negative IOD years (1992 and 1996). It is observed that during the spring season the variations in the lower tropospheric winds were stronger in the positive IOD years than the negative dipole mode years. Signals associated with IOD were weak over upper tropospheric fields. In order to strengthen the IOD events in the upcoming boreal autumn, the warming in the central and western Indian Ocean is necessary right from spring season onwards. The extreme western Indian Ocean (west of 60E) warming and eastern cooling are not sufficient to strengthen the dipole mode structure. Although the variations in surface wind stress is small over the central Indian Ocean during spring, it has significant effect on equatorial Wyrtki Jets and the resultant variation may occur in thermal structure of equatorial Indian Ocean in the summer monsoon period. During strong dipole mode years the seasonal variability was found to be more in various fields (surface wind, sea surface temperature, outgoing long wave radiation and surface heat flux) than weaker dipole mode years

Interannual variability in simulated circulation along east coast of India

115-120A two and a half layer reduced gravity model is used to simulate the upper layer circulation along the east coast of India. The model climatology of upper layer circulations obtained from 15 year model simulation (1977-1991) is found to be in good agreement with the observed currents. A cyclonic gyre found in June-July around 10°N in the lower layer (~60m below surface) has large interannual variability. The gyre is absent in 1982 and 1984 and is very weak in 1987. Transport anomalies computed at four sections along the coast indicate large interannual variability. The upper layer transports along some section have shown a periodicity of 5-6 years

<smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="place"> Indian Ocean dipole mode events in a simple mixed layer ocean model </smarttagtype>

294-304 A precise knowledge of sea surface temperature (SST) is very essential for climate and oceanographic studies. In this paper a simple two dimensional mixed layer ocean model and its numerical code have been developed and used to simulate the SST fields over the north Indian Ocean (20°S-25°N and 35°E-115°E) for a period of 10 years (1992-2001). The model simulated the SST variability reasonably well. The simple model could simulate the observed dipole of 1997 and 1994 very well, especially the eastern cooling. The model study showed that the interannual SST variability in the western equatorial Indian Ocean is not only due to the variability in the surface heat fluxes, but also due to the variability in wind and sea surface height (SSH). The OLR anomaly also shows positive (negative) anomaly over the negative (positive) anomalous SST region. The variability in the latent heat flux is found to be greatly influencing the SST variability in the eastern equatorial Indian Ocean. </smarttagtype