S INDIRA RANI
Articles written in Journal of Earth System Science
Volume 129 All articles Published: 12 October 2020 Article ID 0209 Research article
Observing System Experiments (OSEs) were conducted to analyze the impact of assimilation of Megha-Tropique’s (MT) Sounder for Probing Vertical Profiles of Humidity (SAPHIR) radiances on the simulation of tracks and intensity of three tropical cyclones (Kyant, Vardah, and Maarutha) formed over the Bay of Bengal during 2016–2017 North Indian Ocean cyclone period. National Centre for Medium Range Weather Forecast (NCMRWF) Unified Model (NCUM) Hybrid-4DVAR assimilation and forecast system was used for the OSEs. Assimilation of SAPHIR radiances produced an improvement of 9% and 12%, respectively, in the cyclones’ central sea level pressure (CSLP) and the maximum sustained wind (MSW), while an improvement of 38% was seen in the cyclone tracks within the forecast lead time of 120 hrs. Initial assessment shows that the improvement in the cyclone intensity is due to the assimilation of the unique surface peaking channel of SAPHIR (channel-6), whereas the improvement in the cyclone track is due to the assimilation remaining five channels of SAPHIR. Thus, the assimilation of SAPHIR radiances in the NCUM system showed improvement in both intensity and track of the cyclones over the Bay of Bengal; however, more cyclone cases over different ocean basins have to be analyzed to make a robust conclusion. This study specifies the importance of similar microwave humidity instruments in the same frequency range for the detailed exploration of cyclone track and structure.
$\bullet$ Impact of SAPHIR humidity channel information in the NCMRWF Hybrid-4DVar assimilation and forecast system is analysed through Observing system experiments (OSEs)
$\bullet$ Assimilation of SAPHIR humidity information improved both track and intensity of the cyclones compared to the control experiment, and the improvement is visible upto a lead time of 5 days
$\bullet$ It is noted that the improvement in the cyclone intensity simulation is due to the assimilation of the lowest peaking channel of the SAPHIR, while the track improvement is contributed by other channels as well.
$\bullet$ This study underlines the importance of SAPHIR like instruments in the low earth orbiting satellites with frequent revisit time to explore the features of cyclones.
Volume 130 All articles Published: 12 May 2021 Article ID 0089 Research Article
Wind observations are critical for the better atmospheric analysis for Numerical Weather Prediction (NWP), particularly over the tropics. High-resolution direct wind observations are essential for defining smaller scales and deeper atmospheric structures. Recently launched Aeolus satellite delivers wind profiles that mostly satisfy these requirements, suitable for NWP assimilation. The main product from Aeolus is the horizontally projected Line of Sight wind component, a single component of wind, approximately zonal in nature over the tropics and more meridional over the Polar region, and the main limitation of this observation. Observing system experiments are conducted with the assimilation of individual components of radiosonde and pilot balloon winds to assess the impact of a single component of wind compared to the assimilation of full wind vector in the NCMRWF global assimilation and forecast system. Denial of the zonal component of wind in the assimilation system produced a larger observation increment (observation – model background) in the meridional wind than the full vector assimilation. In contrast, the observation increment of the zonal wind remains nearly the same, even after removing the meridional wind component from the assimilation system. Assimilation of both zonal and meridional components produced changes in the analysis fields of various meteorological variables; however, the zonal component plays a significant role in the tropics. Both wind components play an important role in controlling the humidity field, whereas only zonal components of wind impact the temperature field in the upper troposphere and lower stratosphere. Though the full vector wind assimilation produces a larger impact in the forecast fields of various meteorological variables, the zonal component has more impact than the meridional component. Verification of analysis and forecast wind against the satellite-derived atmospheric motion vectors clearly show the importance of both the horizontal components of winds in the lower troposphere. In contrast, the zonal component of wind alone has a high impact on the upper troposphere and lower stratosphere.
Volume 130 All articles Published: 20 November 2021 Article ID 0235 Research article
INSAT-3DR is the latest geostationary satellite launched by the Indian Space Research Organization (ISRO) as
a continuation to the INSAT-3D, for enhanced meteorological observations. National Centre for Medium Range Weather
Forecasting (NCMRWF) receives INSAT-3DR Atmospheric Motion Vectors (AMVs) through Global Telecommunication System
(GTS) along with the AMVs from other satellites. The INSAT-3DR AMVs are validated against the
Volume 131 All articles Published: 9 May 2022 Article ID 0114 Research article
Operational forecasting of tropical cyclone (TC) track and intensity in the India Meteorological Department (IMD) relies more and more on the numerical weather prediction (NWP) model guidance from national and international agencies particularly, on the medium range (24–120 h). Any improvement in TC forecasts by the NWPmodels enhances the operational forecaster’s confidence and capability. The real-time information from the National Centre for Medium Range Weather Forecasting (NCMRWF) global NWP model (NCUM-G) is routinely used by operational forecasters at IMD as model guidance. The present study documents the improved skill of NCUM-G in forecasting the North Indian Ocean (NIO) TCs during 2015–2019, based on a collection of 1810 forecasts involving 22 TC cases. The study highlights three significant changes in the modelling system during the recent five years, namely (i) increased grid resolution from 17 to 12 km, (ii) use of hybrid 4D-Var data assimilation (DA), and (iii) increased volume of assimilated data. The study results indicate a consistent improvement in the NCUM-G model forecasts during the premonsoon (April–May,AM)and post-monsoon (October–December,OND)TCseasons. In addition to a 44% reduction in the initial position error, the study also reports a statistically significant decrease in the direct position error (DPE) and error in the intensity forecast, resulting in a forecast gain of 24 hrs. Comparing NWP models with IMDs official track error shows that NCUM-G and ECMWF model forecasts feature lower DPE than IMD in 2019, particularly at higher (96, 108, and 120 h) lead times.
Volume 131, 2022
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