Thermodynamic structure of the atmospheric boundary layer over a coastal station in India for contrasting sky conditions during different seasons
by Sachin Philip Kakkanattu, Sanjay Kumar Mehta, D. Bala Subrahamanyam, V. Rakesh and Amit P. Kesarkar
Abstract
The thermodynamic structure of the atmospheric boundary layer for contrasting sky conditions over Chennai, a coastal station in the Indian subcontinent, is investigated through conserved variable analysis of equivalent potential temperature and specific humidity. Simultaneous radiosonde and micropulse lidar measurements undertaken in 2018 constitute the primary database in this investigation. One of the most prominent features of this analysis is a consistent occurrence of a double mixed layer structure during the clear-sky and cloudy conditions throughout the year. The occurrence frequency of the double mixing lines is higher during the pre-monsoon season compared with the winter and northeast (NE) monsoon seasons. The advection mainly dominates the formation of double mixing lines during the winter and pre-monsoon seasons. In contrast, convection and advection dominate during the southwest (SW) and NE monsoon seasons. The frequent double mixing lines over Chennai occur mainly from the restratification of the convective boundary layer (CBL) due to the sea-breeze onset and the cloud layer. Occasionally, a triple mixing line structure is also observed during the fair-weather boundary layer (FWBL) of the pre-monsoon and SW monsoon seasons. Among the 355 total observations collected during 2018, the first, second, and third mixing lines occurred 100%, 70%, and 14%, respectively. The thermal internal boundary layer (TIBL), CBL, and FWBL occur ~50%, ~97%, and ~ 30%, respectively. The first mixing line is represented by both the TIBL and CBL, and CBL and FWBL represent the second mixing line, whereas the third mixing line is represented solely by the FWBL. The first and second mixing line shows strong seasonal variations with lower altitudes during the pre-monsoon season and higher altitudes in the SW monsoon season, almost in the same phase as the CBL variation but in the opposite phase of the TIBL variations. The CBL height attains a minimum during the winter season and maximum during the SW monsoon season, while TIBL becomes minimum during the pre-monsoon and SW monsoon seasons and maximum during winter and NE monsoon seasons.
Source: https://doi.org/10.1016/j.atmosres.2023.106915
Dynamical influence of MJO phases on the onset of Indian monsoon
by S Lenka, Krushna Chandra Gouda, Rani Devi and C M Joseph
Abstract
There is a need to understand the onset of monsoon dynamics as the date of onset of monsoon (DOM) is an important parameter in framing all the policy for the imminent season like crop choice, sowing schedule, disaster management, power distribution etc It is observed that the interannual variability of the DOM in India is about 7–8 days, making it more challenge to predict this at long lead. The MJO phases are linked with the different convection centres and hence, influences the global circulation process and the rainfall. In this paper the dynamical influence of the different phases of MJO are being quantified on DOM and its progress in continental India by using the multi-source atmospheric and oceanic parameters like wind structure, outgoing longwave radiation (OLR), sea surface temperature (SST). The linkage of the active and inactive phases of MJO along with the favourable conditions for DOM is obtained by using the pentad analysis of associated parameters in different clusters for both the wet and dry phases of MJO along with the strength for the period 1980–2018. Also the dynamics are studied for the early, normal and late onset years separately to understand the relation better. It is inferred that the wet (dry) phase leads to early (late) monsoon onset over Kerala (MOK) in India. To address the progress of monsoon the DOM in Rajasthan (MOR) is considered and the rainfall anomalies during MOK-MOR period are linked to the MJO phases. It is inferred that the wet MJO phase with negative OLR anomaly triggers the fast progress of monsoon over India. This understanding will surely help operational researchers and the NWP modellers for improving the methodologies for the advanced and accurate prediction of DOM.
Source: https://iopscience.iop.org/article/10.1088/2515-7620/acde3a
A case study on multiple self-interactions of MSTID bands: New insights
by Dipjyoti Patgiri, Rahul Rathi, Virendra Yadav, Sumanta Sarkhel, Dibyendu Chakrabarty, Subarna Mondal, M.V. Sunil Krishna, Arun K. Upadhayaya, Chiranjeevi G. Vivek, Suresh Kannaujiya, Surendra Sunda
Abstract
In this study, we report a special event of nighttime southwestward propagating medium scale traveling ionospheric disturbances (MSTIDs) observed in O(1D) 630.0 nm airglow images from an all-sky imager at Hanle (32.7°N, 78.9°E; Mlat. ∼ 24.1°N), Leh Ladakh, India on a geomagnetically quiet (Ap = 7) night of 15 September 2018. The time sequence of airglow images unveiled two dynamic interactions between multiple dark bands of MSTID. Following the first interaction, one of the interacting bands decayed possibly due to the entrance of plasma from the ambient higher plasma density region. Shortly after this interaction, the other interacting dark band was involved in the second interaction with a third dark band which resulted in the co-alignment of the two interacting bands. Following this co-alignment, one of the bands started rotating prominently that led to further separation of these two co-aligned bands. These changes in the MSTID phase fronts (bands) are explained based on the development of the polarization electric fields arising out of the interactions. This investigation combines the all-sky 630.0 nm airglow imaging observations with TEC maps constructed, for the first time over the Indian sector, from 67 Global Navigation Satellite System (GNSS) measurements to capture the MSTID over this region. The investigation reveals a few important features of self-interactions of MSTID bands over the geomagnetic low-mid latitude transition region which is important to assess their impact over low latitudes.
Impact of different land use data on WRF model short range forecasts during pre-monsoon and monsoon seasons in India
by P. Ipsita, V. Rakesh, Randhir Singh and G.N. Mohapatra
Abstract
This study focuses to analyse the impact of land use changes on short range weather forecasts over Indian region. Weather Research and Forecasting (WRF) model simulation experiments are conducted by using land use data from Moderate Resolution Imaging Spectroradiometer (MODIS) and Indian Space Research Organization (ISRO) satellites for pre-monsoon and monsoon season. MODIS 2001 land use is used in control (CNT) experiment and updated land use with recent urban class from MODIS (EXP1) and ISRO (EXP2) for the year 2019 is used to generate model lower boundary conditions in other two experiments. Quantitative error measures and skill score computed for rainfall forecast showed that model skill is better with the use of realistic recent land use data from MODIS and ISRO during pre-monsoon and monsoon period. Extreme Dependency Index score computed also revealed that model skill in predicting extreme rare rainfall events is improved with recent landuse data. Model simulated surface meteorological variables and profiles at lower levels also found to be improved with the inclusion of realistic land use class from MODIS and ISRO. Between the two experiments, the one which used ISRO based land use showed larger improvement particularly during the monsoon season.
Source: https://doi.org/10.1016/j.uclim.2023.101558
Why is the Indian summer monsoon in CFSv2 hypersensitive to moisture exchange with the Pacific Ocean?
by Priyanshi Singhai, Arindam Chakraborty, Kavirajan Rajendran & Sajani Surendran
- Annual and seasonal trends in actual evapotranspiration over different meteorological sub-divisions in India using satellite-based data
- The synergistic effect of climatic factors on malaria transmission: a predictive approach for northeastern states of India
- 3-D Crustal structure in Kumaon–Garhwal Himalaya using joint inversion of receiver functions and surface wave group velocity
- Trends of seasonal and annual rainfall of semi-arid districts of Karnataka, India: application of innovative trend analysis approach
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