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\begin{document}

\title{Effect of Atmospheric River in Generating Extreme Precipitation in
Meghalaya on June 2022}



\author[1]{Ahmed  Hossain}%
\affil[1]{Affiliation not available}%


\vspace{-1em}



  
  \date{May 17, 2024}


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\subsection*{}

{\label{851263}}

\subsection*{Introduction}

{\label{174365}}

Atmospheric River (AR) is a long, narrow stream of water vapor that
moves in the earth's atmosphere and carries abound moisture from the
mid-latitude, engendering extreme rainfall upon landfall (Ralph et al.,
2006). According to Zhu \& Newell, (1998), around 90\% of the largest
rainfall events in the world have been followed by ARs. Furthermore,
recent research shows the relevance of AR in occurring extreme
precipitation in South East Asia, especially in the Bay of Bengal Region
(Yang et al., 2018). Hence, the role of AR in generating extreme
rainfall in Meghalaya is necessary for a better understanding of flash
floods in the North Eastern (NE) region of Bangladesh.

The NE region of Bangladesh is exposed to regular flash floods because
of the rapid rainfall-runoff response from the extreme precipitation in
Meghalaya. On June 2022, this region experienced one of the most
devastating floods, more than 70\% of the Sylhet and Sunamganj district
went under water, as the aftermath of the heaviest rainfall in the last
102 years in Mawsynram, Meghalaya in conjunction with the existing water
in the floodplain due to the flash flood in the previous month. ~

Therefore, this study illustrates the contribution of AR in generating
the extreme precipitation in the Meghalaya region on June 2022 that
created enormous flooding in the NE region of Bangladesh.

\subsection*{Methodology}

{\label{662736}}

To analyze the contribution of AR in the extreme rainfall event in
Meghalaya on June 2022, the Vertically integrated Northward and Eastward
Water Vapor Flux or Integrated Vapor Transport (IVT) in Meridian and
Zonal direction data are collected from the European Center of Medium
Range Weather Forecasts (ECMWF) ERA-5 Reanalysis data of June 2022 with
an interval of 6 hours. Secondly, the extreme rainfall days have been
identified from gauge station rainfall data from the Indian
Meteorological Department (IMD). After that, the presence of AR will be
detected by calculating the magnitude of IVT and identifying the
geometric Criteria of AR (Length and area of AR, Length to Width ratio,
and the direction of the IVT front)(Xu et al., 2020) from the collected
data. Finally, the identified AR for June 2022 will be compared with the
extreme rainfall timeline to determine the contribution of AR to this
extreme rainfall. The conceptual framework of the study is provided in
Figure 1.

\par\null\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Picture3/Picture3}
\caption{{Conceptual Framework of the Study
{\label{204140}}%
}}
\end{center}
\end{figure}

\subsection*{Results and Discussions}

{\label{234614}}

\subsection*{Analysis of the Atmospheric
River}

{\label{443906}}

The AR analysis indicates that an AR made landfall in the NE region of
India on 15 June at 12 AM provided in Figure 2 where the moisture
movement had been initiated from the Arabian Sea and the moisture front
traveled across Northern India. Additionally, the IVT front persisted
for 72 hours as a form of AR where the length of the front decreased.
Later, the available moisture in the North Eastern India intensified by
the supply of Moisture from Bay of Bengal during 16 to 18 June.
Consequently, Indian Meteorological Department (IMD) recorded the
extreme rainfall from 15 June in the North Indian region where Mawsynram
and Cherapunjee received the heaviest rainfall on 17 June, around 1000
mm. Therefore, the presence of AR before the extreme rainfall from 14 to
17 June indicated the moisture from AR movement had a significant role
in this extreme precipitation.

\par\null\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Picture13-imageonline-co-merged(1)/Picture13-imageonline-co-merged(1)}
\caption{{Magnitude and Direction of IVT for (a) 14 June (b) 15 June, (c) 16 June,
and (d) 17 June, and Identification of AR
{\label{176423}}%
}}
\end{center}
\end{figure}

\par\null

\subsection*{Climatic Drivers influencing the formation of
AR}

{\label{558997}}

The initiation of the monsoon season in the Indian South Continent
occurs in May, peaking in the region during the month of June. In order
to distinguish between the monsoon onset and the formation of
Atmospheric River, we evaluated the impact of the Low-Level Jet (LLJ) on
the development of AR. Figure 3 displays the Wind Speed and Geopotential
Height at a 500 hPa level for the time period of 15 June 12 AM in both
2021 and 2022. During the onset of the monsoon season, there is a
movement of strong winds from the Indian Ocean into the Bay of Bengal in
mid-June. This movement results in the provision of moisture in India
and Bangladesh, as illustrated in Figure 3 (a) for the year 2021, when
the AR was not formed. In contrast, Figure 3 (b) depicts the observation
of a prominent high-velocity wind jet in 2022, which traverses the
Northern area of India and extends towards the Pacific Ocean,
encompassing Bangladesh and the neighboring nations. This jet
facilitates the rapid movement of moisture in a narrow corridor,
resulting in the formation of an Atmospheric River on 15 June 2022.

\par\null\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Picture19-imageonline-co-merged/Picture19-imageonline-co-merged}
\caption{{Wind Speed and Geopotential Height of (a) 2021 and (b) 2022 at 15 June
12 AM
{\label{272240}}%
}}
\end{center}
\end{figure}

\subsection*{Conclusion}

{\label{234553}}

Extreme precipitation in Meghalaya region creates enormous and rapid
flash floods in the downstream of the Meghna basin. The record breaking
rainfall on 17 June engender massive flooding the downstream especially
in Sylhet and Sunamganj district. Analysis results show that there had
been a landfall of AR in the North Indian Region on 15 June indicating
the significant contribution of AR in generating extreme rainfall in
these regions. Further studies have become indispensable to understand
the dynamics of AR linked with extreme precipitation in this region.~

\subsection*{References}

{\label{559207}}

Ralph, F. M., Neiman, P. J., Wick, G. A., Gutman, S. I., Dettinger, M.
D., Cayan, D. R., \& White, A. B. (2006). Flooding on California's
Russian River: Role of atmospheric rivers. \emph{Geophysical Research
Letters}, \emph{33}(13), 3--7. https://doi.org/10.1029/2006GL026689

Xu, G., Ma, X., Chang, P., \& Wang, L. (2020). Image-processing-based
atmospheric river tracking method version 1 (IPART-1).
\emph{Geoscientific Model Development}, \emph{13}(10), 4639--4662.
https://doi.org/10.5194/gmd-13-4639-2020

Yang, Y., Zhao, T., Ni, G., \& Sun, T. (2018). Atmospheric rivers over
the Bay of Bengal lead to northern Indian extreme rainfall.
\emph{International Journal of Climatology}, \emph{38}(2), 1010--1021.
https://doi.org/10.1002/joc.5229

Zhu, Y., \& Newell, R. E. (1998). A proposed algorithm for moisture
fluxes from atmospheric rivers. \emph{Monthly Weather Review},
\emph{126}(3), 725--735.

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