scholarly journals AN ANALYSIS OF MONTHLY AND SYNOPTIC SCALE VARIATION OF RADIO REFRACTIVE INDEX DURING PRE-MONSOON AND MONSOON ONSET PHASE

MAUSAM ◽  
2022 ◽  
Vol 63 (3) ◽  
pp. 508-510
Author(s):  
V.K. MINI ◽  
S.R.PRABHAKARAN NAYAR
Keyword(s):  
Refractive Index ◽  
Monsoon Onset ◽  
Synoptic Scale ◽  
Onset Phase ◽  
Scale Variation

scholarly journals On the Detection of Onset and Activity of the Indian Summer Monsoon Using GPS RO Refractivity Profiles

2013 ◽  
Vol 141 (6) ◽  
pp. 2096-2106 ◽  
Author(s):  
V. V. M. Jagannadha Rao ◽  
M. Venkat Ratnam ◽  
Y. Durga Santhi ◽  
M. Roja Raman ◽  
M. Rajeevan ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Arabian Sea ◽  
Active Phase ◽  
Monsoon Onset ◽  
Tropospheric Temperature ◽  
Sudden Increase ◽  
Atmospheric Conditions ◽  
Good Relation ◽  
Onset Phase

Abstract Global positioning system (GPS) radio occultation (RO) data available during 2001–10 have been used to examine the variations in the refractivity during the onset of Indian summer monsoon (ISM) over the east Arabian Sea (5°–15°N, 65°–75°E). An enhancement of 5–10 N-units in the refractivity is observed around 4.8 km (~600 hPa) a few days (9.23 ± 3.6 days) before onset of the monsoon over Kerala, India. This is attributed to moisture buildup over the Arabian Sea during the monsoon onset phase. A sudden increase (1.5–2 K) in mean upper-tropospheric temperature at the time of onset and during the active phase of the monsoon is attributed to convective activity and the release of latent heat. On the day of monsoon onset over Kerala, an appreciable dip in the refractivity is observed that persisted for 1–3 days followed by an enhancement in refractivity with the active phase of the monsoon. An arbitrary value of 128 N-units difference between 4.8 km (~600 hPa) and 16 km (~100 hPa) coupled with a dip in refractivity on the day of monsoon arrival might give an indication of clear transition of atmospheric conditions and the detection of monsoon onset. Further, a good relation is also found between the activity of monsoon and variability in the refractivity.

Synoptic-scale variation of δ 18O in summer monsoon rainfall at Lijiang, China

2006 ◽  
Vol 51 (23) ◽  
pp. 2897-2904 ◽  
Author(s):  
Hongxi Pang ◽  
Yuanqing He ◽  
Aigang Lu ◽  
Jingdong Zhao ◽  
Baoying Ning ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Monsoon Rainfall ◽  
Summer Monsoon Rainfall ◽  
Synoptic Scale ◽  
Scale Variation

Tropical Cyclones over the Arabian Sea during the monsoon onset phase

2021 ◽  
Author(s):  
Shreyas Dhavale ◽  
Milind Mujumdar ◽  
M.K. Roxy ◽  
Vineet Kumar Singh
Keyword(s):  
Tropical Cyclones ◽  
Arabian Sea ◽  
Monsoon Onset ◽  
Onset Phase

scholarly journals Contrasting movement of wind based equatorial trough and equatorial cloud zone over Indian southern peninsula and adjoining Bay of Bengal during the onset phase of northeast monsoon

MAUSAM ◽  
2021 ◽  
Vol 58 (1) ◽  
pp. 33-48
Author(s):  
Y. E. A. RAJ ◽  
R. ASOKAN ◽  
P. V. REVIKUMAR
Keyword(s):  
Bay Of Bengal ◽  
Tamil Nadu ◽  
Southwest Monsoon ◽  
Monsoon Onset ◽  
Northeast Monsoon ◽  
Peninsular India ◽  
Zonal Winds ◽  
The North ◽  
Latitudinal Position ◽  
Onset Phase

ABSTRACT. The northeast monsoon sets in over southern parts of peninsular India after the retreat of southwest monsoon and in association with the southward movement of equatorial trough. The INSAT satellite imageries scrutinised during the past several years revealed that the cloud bands at the time of northeast monsoon onset moved from south Bay into the southern peninsula, a feature that contrasts with the north to south movement of the equatorial trough. The paper investigates this aspect based on a dataset of lower level upper winds of the peninsula, rainfall data and INSAT OLR data for the 20 year period 1981–2000. The super epoch profiles of zonal winds, latitudinal position of equatorial trough with reference to northeast monsoon onset dates have been derived and studied. The region with OLR values less than 230 W/m2 was defined as the equatorial cloud zone and the movement of northern limit of ECZ was studied based on the normal pentad OLR data and also the superposed epoch profiles. From these analysis it has been established that at the time of northeast monsoon onset, the wind based equatorial trough moves south of Comorin whereas the cloud zone in the Bay of Bengal moves from south to north. Reasons for the occurrence of such a contrasting feature have been ascribed to features such as decreasing strength of lower level easterlies from north to south over coastal Tamil Nadu, reversal of temperature gradient between Chennai and Thiruvananthapuram at the time of onset and the dynamics of 40-day oscillation. The northeast monsoon activity over coastal Tamil Nadu has been found to be negatively correlated with the low level zonal winds over the coast, the degree of relation decreasing from north to south and also from October to December. Based on the results derived in the study and also the other known features of northeast monsoon a thematic model of northeast monsoon onset listing the events that precede and succeed the onset has been postulated.

Increasing incidence of Arabian Sea cyclones during the monsoon onset phase: Its impact on the robustness and advancement of Indian summer monsoon

2021 ◽  
pp. 105915
Author(s):  
P.P. Baburaj ◽  
S. Abhilash ◽  
C.S. Abhiram Nirmal ◽  
A.V. Sreenath ◽  
K. Mohankumar ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Arabian Sea ◽  
Monsoon Onset ◽  
Onset Phase

scholarly journals Simulation of the Indian summer monsoon onset-phase rainfall using a regional model

2015 ◽  
Vol 33 (9) ◽  
pp. 1097-1115 ◽  
Author(s):  
C. V. Srinivas ◽  
D. Hari Prasad ◽  
D. V. Bhaskar Rao ◽  
R. Baskaran ◽  
B. Venkatraman
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Onset Time ◽  
India Meteorological Department ◽  
Regional Model ◽  
Monsoon Onset ◽  
Scale Model ◽  
Wave Radiation ◽  
Climate Zones ◽  
Onset Phase

Abstract. This study examines the ability of the Advanced Research WRF (ARW) regional model to simulate Indian summer monsoon (ISM) rainfall climatology in different climate zones during the monsoon onset phase in the decade 2000–2009. The initial and boundary conditions for ARW are provided from the NCEP/NCAR Reanalysis Project (NNRP) global reanalysis. Seasonal onset-phase rainfall is compared with corresponding values from 0.25° IMD (India Meteorological Department) rainfall and NNRP precipitation data over seven climate zones (perhumid, humid, dry/moist, subhumid, dry/moist, semiarid and arid) of India to see whether dynamical downscaling using a regional model yields advantages over just using large-scale model predictions. Results show that the model could simulate the onset phase in terms of progression and distribution of rainfall in most zones (except over the northeast) with good correlations and low error metrics. The observed mean onset dates and their variability over different zones are well reproduced by the regional model over most climate zones. It has been found that the ARW performed similarly to the reanalysis in most zones and improves the onset time by 1 to 3 days in zones 4 and 7, in which the NNRP shows a delayed onset compared to the actual IMD onset times. The variations in the onset-phase rainfall during the below-normal onset (June negative) and above-normal onset (June positive) phases are well simulated. The slight underestimation of onset-phase rainfall in the northeast zone could be due to failure in resolving the wide extent of topographic variations and the associated multiscale interactions in that zone. Spatial comparisons showed improvement of pentad rainfall in both space and quantity in ARW simulations over NNRP data, as evident from a wider eastward distribution of pentad rainfall over the Western Ghats, central and eastern India, as in IMD observations. While NNRP under-represented the high pentad rainfall over northeast, east and west coast areas, the ARW captured these regional features showing improvement upon NNRP reanalysis, which may be due to the high resolution (30 km) employed. The onset-phase rainfall characteristics during the contrasting ISM of 2003 and 2009 are well simulated in terms of the variations in the strength of low-level jet (LLJ) and outgoing long-wave radiation (OLR).

scholarly journals A meteorological and chemical overview of the DACCIWA field campaign in West Africa in June–July 2016

2017 ◽  
Vol 17 (17) ◽  
pp. 10893-10918 ◽  
Author(s):  
Peter Knippertz ◽  
Andreas H. Fink ◽  
Adrien Deroubaix ◽  
Eleanor Morris ◽  
Flore Tocquer ◽  
...  
Keyword(s):  
West Africa ◽  
Biomass Burning ◽  
Urban Pollution ◽  
Monsoon Onset ◽  
Boreal Summer ◽  
Deep Penetration ◽  
Study Region ◽  
Field Campaign ◽  
Low Level ◽  
Onset Phase

Abstract. In June and July 2016 the Dynamics–Aerosol–Chemistry–Cloud Interactions in West Africa (DACCIWA) project organised a major international field campaign in southern West Africa (SWA) including measurements from three inland ground supersites, urban sites in Cotonou and Abidjan, radiosondes, and three research aircraft. A significant range of different weather situations were encountered during this period, including the monsoon onset. The purpose of this paper is to characterise the large-scale setting for the campaign as well as synoptic and mesoscale weather systems affecting the study region in the light of existing conceptual ideas, mainly using objective and subjective identification algorithms based on (re-)analysis and satellite products. In addition, it is shown how the described synoptic variations influence the atmospheric composition over SWA through advection of mineral dust, biomass burning and urban pollution plumes.The boreal summer of 2016 was characterised by Pacific La Niña, Atlantic El Niño and warm eastern Mediterranean conditions, whose competing influences on precipitation led to an overall average rainy season. During the relatively dusty pre-onset Phase 1 (1–21 June 2016), three westward-propagating coherent cyclonic vortices between 4 and 13° N modulated winds and rainfall in the Guinea coastal area. The monsoon onset occurred in connection with a marked extratropical trough and cold surge over northern Africa, leading to a breakdown of the Saharan heat low and African easterly jet and a suppression of rainfall. During this period, quasi-stationary low-level vortices associated with the trough transformed into more tropical, propagating disturbances resembling an African easterly wave (AEW). To the east of this system, moist southerlies penetrated deep into the continent. The post-onset Phase 2 (22 June–20 July 2016) was characterised by a significant increase in low-level cloudiness, unusually dry conditions and strong northeastward dispersion of urban pollution plumes in SWA as well as rainfall modulation by westward-propagating AEWs in the Sahel. Around 12–14 July 2016 an interesting and so-far undocumented cyclonic–anticyclonic vortex couplet crossed SWA. The anticyclonic centre had its origin in the Southern Hemisphere and transported unusually dry air filled with aged aerosol into the region. During Phase 3 (21–26 July 2016), a similar vortex couplet slightly farther north created enhanced westerly moisture transports into SWA and extraordinarily wet conditions, accompanied by a deep penetration of the biomass burning plume from central Africa. Finally, a return to more undisturbed monsoon conditions took place during Phase 4 (27–31 July 2016). The in-depth synoptic analysis reveals that several significant weather systems during the DACCIWA campaign cannot be attributed unequivocally to any of the tropical waves and disturbances described in the literature and thus deserve further study.

scholarly journals A meteorological and chemical overview of the DACCIWA field campaign in West Africa in June–July 2016

2017 ◽  
Author(s):  
Peter Knippertz ◽  
Andreas H. Fink ◽  
Adrien Deroubaix ◽  
Eleanor Morris ◽  
Flore Tocquer ◽  
...  
Keyword(s):  
West Africa ◽  
Biomass Burning ◽  
Urban Pollution ◽  
Monsoon Onset ◽  
Boreal Summer ◽  
Study Region ◽  
Field Campaign ◽  
Low Level ◽  
Onset Phase ◽  
Pollution Plumes

Abstract. In June and July 2016 the Dynamics–Aerosol–Chemistry–Cloud Interactions in West Africa (DACCIWA) project organised a major international field campaign in southern West Africa (SWA) including measurements from three inland ground supersites, urban sites in Cotonou and Abidjan, radiosondes and three research aircraft. A significant range of different weather situations was encountered during this period, including the monsoon onset. The purpose of this paper is to characterise the large-scale setting for the campaign as well as synoptic and mesoscale weather systems affecting the study region in the light of existing conceptual ideas, mainly using objective and subjective identification algorithms based on (re-) analysis and satellite products. In addition, it is shown how the described synoptic variations influence the atmospheric composition over SWA through advection of mineral-dust, biomass-burning and urban-pollution plumes. The boreal summer of 2016 was characterised by Pacific La Niña, Atlantic El Niño and warm eastern Mediterranean conditions, whose competing influences on precipitation led to an overall average rainy season. During the relatively dusty pre-onset Phase 1 (1–21 June 2016), three westward propagating coherent cyclonic vortices between 4 and 13° N modulated winds and rainfall in the Guinea coastal area. The monsoon onset occurred in connection with a marked extratropical trough and cold surge over northern Africa, leading to a breakdown of the Saharan heat low and African easterly jet and a suppression of rainfall. During this period, quasi-stationary low-level vortices associated with the trough transformed into more tropical, propagating disturbances resembling an African easterly wave (AEW). To the east of this system, moist southerlies penetrated deep into the continent. The post-onset Phase 2 (22 June–20 July 2016) was characterised by a significant increase of low-level cloudiness, unusually dry conditions and strong northeastward dispersion of urban pollution plumes in SWA as well as rainfall modulation by westward propagating AEWs in the Sahel. Around 12–14 July 2016 an interesting and so-far undocumented cyclonic-anticyclonic vortex couplet crossed SWA. The anticyclonic centre had its origin in the southern hemisphere and transported unusually dry air filled with aged aerosol into the region. During Phase 3 (21–26 July 2016), a similar vortex couplet slightly farther north created enhanced westerly moisture transports into SWA and extraordinarily wet conditions, accompanied by a deep penetration of the biomass-burning plume from central Africa. Finally, a return to more undisturbed monsoon conditions took place during Phase 4 (27–31 July 2016). The in-depth synoptic analysis reveals that several significant weather systems during the DACCIWA campaign cannot be attributed unequivocally to any of the tropical waves and disturbances described in the literature, and thus deserve further study.

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