Intriguing Aspects of the Monsoon Low-Level Jet over Peninsular India Revealed by High-Resolution GPS Radiosonde Observations

Raman, M. Roja; Ratnam, M. Venkat; Rajeevan, M.; Rao, V. Ramgopal; Rao, S. Vijaya Bhaskara

doi:10.1175/2011jas3611.1

Cited by 29 publications

(12 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Previous studies have emphasized the need for high spatial–temporal resolution data for analysis of the diurnal cycle of monsoon (Roja Raman et al ., ). In this respect, the availability of high resolution downscaled WRF winds enables to study the diurnal evolution of low‐level winds.…”

Section: Resultsmentioning

confidence: 97%

Variability of monsoon low‐level jet and associated rainfall over India

Viswanadhapalli

Dasari

Dwivedi

et al. 2019

Intl Journal of Climatology

View full text Add to dashboard Cite

The structure and climatology of the monsoon low‐level jet (MLLJ) is studied based on dynamically downscaled simulations over a 37‐year period (1980–2016) using the Weather Research Forecasting (WRF) model. The simulations are conducted by adopting a continuous initialization method with daily re‐initializations using ERA‐Interim data as initial and boundary conditions. Validation of the downscaled fields with radiosonde data shows that the model has reasonable skill in reproducing MLLJ characteristics. Analysis of the simulations suggests that the MLLJ exhibits systematic diurnal variation: maximum winds of the synoptically induced large‐scale monsoon jet occur during the daytime, and the orographic channelled winds through the mountains of East Africa, Hejaz, and Western Ghats in the night‐time. These diurnal changes in monsoon winds modulate the moisture convergence process and the associated evolution of rainfall over India. Seasonal and monthly climatology of monsoon winds shows that the model accurately reproduces the spatial pattern of winds and slightly overestimates (2–3 m/s) the mean monthly winds over the Bay of Bengal and Arabian Seas. Analysis of wind variability and the trends using 37 years simulations suggests that the MLLJ exhibits an increasing trend in wind speed on both seasonal and monthly scales, except for August which shows a decreasing trend. The weakening of the MLLJ in August has a profound influence on the number of monsoon depressions forming over the Bay of Bengal (which are decreasing), and on the number of break days (which are increasing) and associated precipitation reduction over the central Indian region.

show abstract

Section: Resultsmentioning

confidence: 97%

Variability of monsoon low‐level jet and associated rainfall over India

Viswanadhapalli

Dasari

Dwivedi

et al. 2019

Intl Journal of Climatology

View full text Add to dashboard Cite

show abstract

“…The Somali low-level jet stream is the location of permanent region of MI during the month of July. The spatial distribution of monsoon low-level jet stream (Roja Raman et al, 2011) reveals that the centre of the core is seen around 13 • N and 60 • E and strong shear exists between 850 and 700 hPa. Strong surface winds of the southwest monsoon produce an Ekman transport perpendicular to the wind flow with strong upwelling in the region which in turn brings the cool water from the deeper layers to surface.…”

Section: Contrasting Behaviour Of MI Between the Was And Easmentioning

confidence: 99%

Characteristics of monsoon inversions over the Arabian Sea observed by satellite sounder and reanalysis data sets

et al. 2016

View full text Add to dashboard Cite

Abstract. Monsoon inversion (MI) over the Arabian Sea (AS) is one of the important characteristics associated with the monsoon activity over Indian region during summer monsoon season. In the present study, we have used 5 years (2009-2013) of temperature and water vapour measurement data obtained from satellite sounder instrument, an Infrared Atmospheric Sounding Interferometer (IASI) onboard MetOp satellite, in addition to ERA-Interim data, to study their characteristics. The lower atmospheric data over the AS have been examined first to identify the areas where MIs are predominant and occur with higher strength. Based on this information, a detailed study has been made to investigate their characteristics separately in the eastern AS (EAS) and western AS (WAS) to examine their contrasting features. The initiation and dissipation times of MIs, their percentage occurrence, strength, etc., has been examined using the huge database. The relation with monsoon activity (rainfall) over Indian region during normal and poor monsoon years is also studied. WAS T values are ∼ 2 K less than those over the EAS, T being the temperature difference between 950 and 850 hPa. A much larger contrast between the WAS and EAS in T is noticed in ERA-Interim data set vis-à-vis those observed by satellites. The possibility of detecting MI from another parameter, refractivity N, obtained directly from another satellite constellation of GPS Radio Occultation (RO) (COSMIC), has also been examined. MI detected from IASI and Atmospheric Infrared Sounder (AIRS) onboard the NOAA satellite have been compared to see how far the two data sets can be combined to study the MI characteristics. We suggest MI could also be included as one of the semipermanent features of southwest monsoon along with the presently accepted six parameters.

show abstract

“…The most notable similarity between the regions in which MLPSs and AEWs occur is that they are characterized by strong jets that exhibit strong easterly vertical shear (›u/›z , 0) (Burpee 1972;Roja Raman et al 2009, 2011, although the depth of these jets differs in their respective regions. Because of this shear and the deep convection that is observed in association with these systems, it was thought that a variant of baroclinic instability that is modified by deep convection could explain their growth (Mass 1979;Salvekar et al 1986;Krishnakumar et al 1992).…”

Section: Introductionmentioning

confidence: 99%

Interactions between Water Vapor, Potential Vorticity, and Vertical Wind Shear in Quasi-Geostrophic Motions: Implications for Rotational Tropical Motion Systems

Adames

2021

Journal of the Atmospheric Sciences

View full text Add to dashboard Cite

A linear two-layer model is used to elucidate the role of prognostic moisture on quasi-geostrophic (QG) motions in the presence of a mean thermal wind (). Solutions to the basic equations reveal two instabilities that can explain the growth of moist QG systems. The well-documented baroclinic instability is characterized by growth at the synoptic scale (horizontal scale of ~1000 km) and systems that grow from this instability tilt against the shear. Moisture-vortex instability —an instability that occurs when moisture and lower-tropospheric vorticity exhibit an in-phase component— exists only when moisture is prognostic. The instability is also strongest at the synoptic scale, but systems that grow from it exhibit a vertically-stacked structure. When moisture is prognostic and is easterly, baroclinic instability exhibits a pronounced weakening while moisture vortex instability is amplified. The strengthening of moisture-vortex instability at the expense of baroclinic instability is due to the baroclinic () component of the lower-tropospheric flow. In westward-propagating systems, lower-tropospheric westerlies associated with an easterly advect anomalous moisture and the associated convection towards the low-level vortex. The advected convection causes the vertical structure of the wave to shift away from one that favors baroclinic instability to one that favors moisture-vortex instability. On the other hand, a westerly reinforces the phasing between moisture and vorticity necessary for baroclinic instability to occur. Based on these results, it is hypothesized that moisture-vortex instability is an important instability in humid regions of easterly such as the South Asian and west African monsoons.

show abstract

Intriguing Aspects of the Monsoon Low-Level Jet over Peninsular India Revealed by High-Resolution GPS Radiosonde Observations

Cited by 29 publications

References 17 publications

Variability of monsoon low‐level jet and associated rainfall over India

Variability of monsoon low‐level jet and associated rainfall over India

Characteristics of monsoon inversions over the Arabian Sea observed by satellite sounder and reanalysis data sets

Interactions between Water Vapor, Potential Vorticity, and Vertical Wind Shear in Quasi-Geostrophic Motions: Implications for Rotational Tropical Motion Systems

Contact Info

Product

Resources

About