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  1. AU="Ettammal, S."
  2. AU=Cook Jack
  3. AU="Narayan Mohanta"
  4. AU="Gruber, Marion F"
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  8. AU="Sarjanoja, E (Länsi-Pohja Central Hospital)"
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  1. Conference proceedings ; Online: A survey of Mixed Rossby-gravity waves and quantification of their association with extratropical disturbances

    Keshri, S. / Ettammal, S.

    XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)

    2023  

    Abstract: In this study we have conducted a survey of Mixed Rossby-Gravity (MRG) wave events in the upper troposphere and quantified their association with intrusions of extratropical disturbances from 1979-2019. MRG events are identified by projecting equatorial ...

    Abstract >In this study we have conducted a survey of Mixed Rossby-Gravity (MRG) wave events in the upper troposphere and quantified their association with intrusions of extratropical disturbances from 1979-2019. MRG events are identified by projecting equatorial meridional winds at 200 hPa onto the meridional structure of theoretical MRG waves. 2390 MRG events are identified and majority (61%) of them occurred during May-October months, and 65% of the activity occurred over the central-east Pacific and Atlantic Ocean. Not only frequency of occurrence but also amplitude, wavenumber and trapping scale of MRG events are found to exhibit a clear seasonality. MRG events associated with intrusions of extratropical disturbances are identified when potential vorticity on 350K isentropic surface at 15° latitude exceeds 1 PVU in vicinity of MRG events. We find that 37% of MRG events are intrusion MRG events and majority (88%) of such events occurred over central-east Pacific and Atlantic Ocean. It is also noteworthy that nearly 70% of such intrusions occurred in the winter Hemisphere where the westerly wind ducts are well developed. Over central-east Pacific during Northern Hemispheric (NH) winter, it is observed that amplitude of intrusion MRG events are larger and have larger meridional extent compared to non-intrusion MRG events. They also exhibit similar spatial scale as extratropical disturbances implying that resonant interactions may be a primary mechanism for genesis of MRG events. During NH summer, on the other hand, MRG events are primarily triggered by convective processes and extratropical disturbances may be instrumental in amplifying their amplitude.
    Subject code 551
    Language English
    Publishing country de
    Document type Conference proceedings ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  2. Conference proceedings ; Online: Major Factors governing the trends and interannual variability in the occurrences of Mixed Rossby-Gravity Wave events

    Na, M. / Keshri, S. / Ettammal, S.

    XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)

    2023  

    Abstract: Mixed Rossby-Gravity (MRG) waves are westward propagating synoptic scale equatorial disturbances, which play a crucial role in the formation of tropical cyclones and tropical depressions. They constitute a significant part of various modes of tropical ... ...

    Abstract Mixed Rossby-Gravity (MRG) waves are westward propagating synoptic scale equatorial disturbances, which play a crucial role in the formation of tropical cyclones and tropical depressions. They constitute a significant part of various modes of tropical variability, like Madden-Julian Oscillation (MJO) and Quasi-Biennial Oscillation. This study investigates the trends and Inter Annual Variability (IAV) in the occurrence of upper tropospheric MRG events using ERA-I reanalysis data for the period 1979-2018. The MRG events are identified by projecting the 200hpa meridional winds onto the theoretical spatial structure of MRG waves. A steady increasing trend is observed in the MRG events, which is contributed by the MRG events associated with intrusion of extratropical disturbances. Possible factors governing the observed trend and IAV in MRG events are El-Nino Southern Oscillation (ENSO), MJO and extratropical forcing. The MRG events over the central and eastern Pacific contribute maximum to IAV. ENSO explains about 25% of IAV and exhibits a positive correlation with non-intrusion MRG events and a negative correlation with intrusion MRG events. These observations have been investigated by exploring the properties of the westerly duct at 200hPa and Outgoing Longwave Radiation during El-Nino and La-Nina years over the central-eastern Pacific. The convectively active state of MJO over the western Pacific explains 20% of IAV. The antisymmetric heating with respect to the equator, associated with MJO, enhances non-intrusion MRG events by forbidding the intrusion of extratropical disturbances through subtropical easterlies. The increasing trend in the intrusion of extratropical disturbances explains the observed trend in MRG events.
    Subject code 551
    Language English
    Publishing country de
    Document type Conference proceedings ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

    Full text online

    More links

    Kategorien

    Inter-library loan at ZB MED

    Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.

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