scholarly journals The Impact of the Madden–Julian Oscillation on Cyclone Amphan (2020) and Southwest Monsoon Onset

2020 ◽  
Vol 12 (18) ◽  
pp. 3011
Author(s):  
Heather L. Roman-Stork ◽  
Bulusu Subrahmanyam
Keyword(s):  
Bay Of Bengal ◽  
Heat Content ◽  
Southwest Monsoon ◽  
Ocean Model ◽  
Madden Julian Oscillation ◽  
Atmospheric Conditions ◽  
Kelvin Wave ◽  
Upper Ocean Heat Content ◽  
Southeastern Arabian Sea ◽  
The Impact

Cyclone Amphan was an exceptionally strong tropical cyclone in the Bay of Bengal that achieved a minimum central pressure of 907 mb during its active period in May 2020. In this study, we analyzed the oceanic and surface atmospheric conditions leading up to cyclogenesis, the impact of this storm on the Bay of Bengal, and how the processes that led to cyclogenesis, such as the Madden–Julian Oscillation (MJO) and Amphan itself, in turn impacted southwest monsoon preconditioning and onset. To accomplish this, we took a multiparameter approach using a combination of near real time satellite observations, ocean model forecasts, and reanalysis to better understand the processes involved. We found that the arrival of a second downwelling Kelvin wave in the equatorial Bay of Bengal, coupled with elevated upper ocean heat content and the positioning of the convective phase of the MJO, helped to create the conditions necessary for cyclogenesis, where the northward-propagating branch of the MJO acted as a trigger for cyclogenesis. This same MJO event, in conjunction with Amphan, heavily contributed atmospheric moisture to the southeastern Arabian Sea and established low-level westerlies that allowed for the southwest monsoon to climatologically onset on June 1.

Investigation of the Climate Change Effects on the Mediterranean Region with the Hypothetical inclusion of the Istanbul Isthmus

2020 ◽  
Author(s):  
Elcin Tan
Keyword(s):  
Climate Change ◽  
Land Surface ◽  
Mediterranean Region ◽  
Climate Model ◽  
Wrf Model ◽  
Ocean Model ◽  
Atmospheric Conditions ◽  
Sea Level Changes ◽  
The Mediterranean ◽  
The Impact

<p>A debate on the probable Istanbul Isthmus Project that may have catastrophic impacts on our ecosystem has been recently accelerated in public, due to the fact that the approved environmental impact assessment (EIA) report of the hypothetical Istanbul Isthmus (HII) Project has recently been announced. The EIA report indicates that the assessment covers only the current conditions and the conditions that may arise during the construction of the HII. Unfortunately, The EIA report did not evaluate the climate change impact on either the Istanbul Area or Mediterranean Region after the inclusion of the HII, only the current conditions were evaluated. Therefore, the aim of this study is to investigate the impact of HII on the climate of the Mediterranean Region. The climate version of the WRF Model is utilized with 9 km resolution for the Region 12: Mediterranean (CORDEX) for the historical conditions and RCP8.5 scenarios of available climate model results from CMIP5 and CMIP6 projects. Land surface and land use maps are prepared by following the EIA report if the necessary information is included, otherwise, the current conditions are applied. The atmospheric conditions were not coupled to an Ocean Model, only the Sea Surface Temperature (SST) values of the Ocean Models are coupled to the WRF model during both historical and future simulations. The model results are evaluated in terms of temperature, precipitation, and sea-level changes. Consequently, the results indicate that the HII may decrease the resilience of the Mediterranean Region to Climate Change.</p>

The impact of northern Indian Ocean rivers on the Bay of Bengal using NEMO global ocean model

2020 ◽  
Vol 39 (3) ◽  
pp. 45-55
Author(s):  
Atul Srivastava ◽  
Anitha Gera ◽  
Imran M. Momin ◽  
Ashis Kumar Mitra ◽  
Ankur Gupta
Keyword(s):  
Indian Ocean ◽  
Bay Of Bengal ◽  
Ocean Model ◽  
Global Ocean ◽  
Northern Indian Ocean ◽  
The Impact

scholarly journals Seasonality and Regionality of the Madden–Julian Oscillation, Kelvin Wave, and Equatorial Rossby Wave

2007 ◽  
Vol 64 (12) ◽  
pp. 4400-4416 ◽  
Author(s):  
Hirohiko Masunaga
Keyword(s):  
Boundary Layer ◽  
Water Solution ◽  
Austral Summer ◽  
Longwave Radiation ◽  
Boreal Summer ◽  
Dynamical Structure ◽  
Madden Julian Oscillation ◽  
Kelvin Wave ◽  
Low Level ◽  
The Impact

Abstract The Madden–Julian oscillation (MJO), Kelvin wave, and equatorial Rossby (ER) wave—collectively called intraseasonal oscillations (ISOs)—are investigated using a 25-yr record of outgoing longwave radiation (OLR) measurements as well as the associated dynamical fields. The ISO modes are detected by applying bandpass filters to the OLR data in the frequency–wavenumber space. An automated wave-tracking algorithm is applied to each ISO mode so that convection centers accompanied with the ISOs are traced in space and time in an objective fashion. The identified paths of the individual ISO modes are first examined and found strongly modulated regionally and seasonally. The dynamical structure is composited with respect to the convection centers of each ISO mode. A baroclinic mode of the combined Rossby and Kelvin structure is prominent for the MJO, consistent with existing work. The Kelvin wave exhibits a low-level wind field resembling the shallow-water solution, while a slight lead of low-level convergence over convection suggests the impact of frictional boundary layer convergence on Kelvin wave dynamics. A lagged composite analysis reveals that the MJO is accompanied with a Kelvin wave approaching from the west preceding the MJO convective maximum in austral summer. MJO activity then peaks as the Kelvin and ER waves constructively interfere to enhance off-equatorial boundary layer convergence. The MJO leaves a Kelvin wave emanating to the east once the peak phase is passed. The approaching Kelvin wave prior to the development of MJO convection is absent in boreal summer and fall. The composite ER wave, loosely concentrated around the MJO, is nearly stationary throughout. A possible scenario to physically translate the observed result is also discussed.

scholarly journals Impacts of the Madden–Julian Oscillation on the Summer South China Sea Ocean Circulation and Temperature

2013 ◽  
Vol 26 (20) ◽  
pp. 8084-8096 ◽  
Author(s):  
Guihua Wang ◽  
Zheng Ling ◽  
Renguang Wu ◽  
Changlin Chen
Keyword(s):  
South China Sea ◽  
Ocean Circulation ◽  
South China ◽  
Ocean Model ◽  
Ocean Modeling ◽  
Madden Julian Oscillation ◽  
Regional Ocean Modeling System ◽  
Wind Stress Curl ◽  
China Sea ◽  
The Impact

Abstract The present study investigates the impact of the Madden–Julian oscillation (MJO) on the South China Sea (SCS) in summer with three types of models: a theoretical Sverdrup model, a 1.5-layer reduced gravity model, and a regional ocean model [Regional Ocean Modeling System (ROMS)]. Results show that the ocean circulation in the SCS has an intraseasonal oscillation responding to the MJO. During its westerly phase, the MJO produces positive (negative) wind stress curl over the northern (southern) SCS and thus induces an enhanced cyclonic (anticyclonic) circulation in the northern (southern) SCS. This not only cools sea surface temperature (SST) but also decreases (increases) subsurface temperature in the northern (southern) SCS. During its easterly phase, the MJO basically produces a reversed but weaker influence on SCS ocean circulation and temperature. Thus, the MJO can have an imprint on the summer climatology of SCS circulation and temperature. The authors' analysis further indicates that the MJO's dynamic effect associated with wind is generally more important than its thermodynamic effect in modulating the regional ocean circulation and temperature. The present study suggests that the MJO is important for summer ocean circulation and temperature in the SCS.

scholarly journals Tropical Cyclones and Transient Upper-Ocean Warming

2008 ◽  
Vol 21 (1) ◽  
pp. 149-162 ◽  
Author(s):  
Claudia Pasquero ◽  
Kerry Emanuel
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Heat Content ◽  
Ocean Model ◽  
Ocean Heat Content ◽  
Upper Ocean ◽  
Cyclone Activity ◽  
Upper Ocean Heat Content ◽  
Vertical Temperature Profile ◽  
Thermodynamic Conditions

Abstract Strong winds affect mixing and heat distribution in the upper ocean. In turn, upper-ocean heat content affects the evolution of tropical cyclones. Here the authors explore the global effects of the interplay between tropical cyclones and upper-ocean heat content. The modeling study suggests that, for given atmospheric thermodynamic conditions, regimes characterized by intense (with deep mixing and large upper-ocean heat content) and by weak (with shallow mixing and small heat content) tropical cyclone activity can be sustained. A global general circulation ocean model is used to study the transient evolution of a heat anomaly that develops following the strong mixing induced by the passage of a tropical cyclone. The results suggest that at least one-third of the anomaly remains in the tropical region for more than one year. A simple atmosphere–ocean model is then used to study the sensitivity of maximum wind speed in a cyclone to the oceanic vertical temperature profile. The feedback between cyclone activity and upper-ocean heat content amplifies the sensitivity of modeled cyclone power dissipation to atmospheric thermodynamic conditions.

scholarly journals Impacts of Idealized Air–Sea Coupling on Madden–Julian Oscillation Structure in the Superparameterized CAM

2011 ◽  
Vol 68 (9) ◽  
pp. 1990-2008 ◽  
Author(s):  
James J. Benedict ◽  
David A. Randall
Keyword(s):  
Deep Convection ◽  
Ocean Model ◽  
Surface Fluxes ◽  
Convective Heating ◽  
Madden Julian Oscillation ◽  
Kelvin Wave ◽  
Coupled Simulation ◽  
Wave Response ◽  
Community Atmosphere Model ◽  
Anomalous Surface

Abstract Air–sea interactions and their impact on intraseasonal convective organization are investigated by comparing two 5-yr simulations from the superparameterized Community Atmosphere Model version 3.0 (SP-CAM). The first is forced using prescribed sea surface temperatures (SSTs). The second is identical except that a simplified oceanic mixed-layer model is used to predict tropical SST anomalies that are coupled to the atmosphere. This partially coupled simulation allows SSTs to respond to anomalous surface fluxes. Implementation of the idealized slab ocean model in the SP-CAM results in significant changes to intraseasonal convective variability and organization. The more realistic treatment of air–sea interactions in the coupled simulation improves many aspects of tropical convection on intraseasonal scales, from the relationships between precipitation and SSTs to the space–time structure and propagation of the Madden–Julian oscillation (MJO). This improvement is associated with a more realistic convergence structure and longitudinal gradient of SST relative to MJO deep convection. In the uncoupled SP-CAM, SST is roughly in phase with the MJO convective center and the development of the Kelvin wave response and boundary layer convergence east of the convective center is relatively weak. In the coupled SP-CAM, maxima in SST lead maxima in MJO convection by cycle. Coupling produces warmer SSTs, a stronger Kelvin wave response, enhanced low-level convergence, and increased convective heating ahead (east) of the MJO convective center. Convective development east of the MJO precipitation center is more favorable in the coupled versus the uncoupled version, resulting in more realistic organization and clearer eastward propagation of the MJO in the coupled SP-CAM.

Variability of Intraseasonal Oscillations and Synoptic Signals in Sea Surface Salinity in the Bay of Bengal

2019 ◽  
Vol 32 (20) ◽  
pp. 6703-6728 ◽  
Author(s):  
Corinne B. Trott ◽  
Bulusu Subrahmanyam ◽  
Heather L. Roman-Stork ◽  
V. S. N. Murty ◽  
C. Gnanaseelan
Keyword(s):  
Soil Moisture ◽  
River Runoff ◽  
Bay Of Bengal ◽  
Southwest Monsoon ◽  
Ocean Model ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Surface Salinity ◽  
Intraseasonal Oscillations ◽  
Salinity Data

Abstract Intraseasonal oscillations (ISOs) significantly impact southwest monsoon precipitation and Bay of Bengal (BoB) variability. The response of ISOs in sea surface salinity (SSS) to those in the atmosphere is investigated in the BoB from 2005 to 2017. The three intraseasonal processes examined in this study are the 30–90-day and 10–20-day ISOs and 3–7-day synoptic weather signals. A variety of salinity data from NASA’s Soil Moisture Active Passive (SMAP) and the European Space Agency’s (ESA’s) Soil Moisture and Ocean Salinity (SMOS) satellite missions and from reanalysis using the Hybrid Coordinate Ocean Model (HYCOM) and operational analysis of Climate Forecast System version 2 (CFSv2) were utilized for the study. It is found that the 30–90-day ISO salinity signal propagates northward following the northward propagation of convection and precipitation ISOs. The 10–20-day ISO in SSS and precipitation deviate largely in the northern BoB wherein the river runoff largely impacts the SSS. The weather systems strongly impact the 3–7-day signal in SSS prior to and after the southwest monsoon. Overall, we find that satellite salinity products captured better the SSS signal of ISO due to inherent inclusion of river runoff and mixed layer processes. CFSv2, in particular, underestimates the SSS signal due to the misrepresentation of river runoff in the model. This study highlights the need to include realistic riverine freshwater influx for better model simulations, as accurate salinity simulation is mandatory for the representation of air–sea coupling in models.

Multidecadal changes in ENSO properties in the recharge oscillator conceptual model

2020 ◽  
Author(s):  
Lander R. Crespo ◽  
Belen Rodriguez-Fonseca ◽  
Irene Polo ◽  
Noel Keenlyside ◽  
Dietmar Dommenget
Keyword(s):  
Lead Time ◽  
Southern Oscillation ◽  
Heat Content ◽  
Ocean Heat Content ◽  
Water Volume ◽  
Upper Ocean ◽  
Upper Ocean Heat Content ◽  
Discharge Mechanism ◽  
The Impact ◽  
Observational Record

<p><span>We use a simple conceptual recharge oscillator model for the tropical Pacific to identify multidecadal changes in El Niño-Southern Oscillation (ENSO) statistics and dynamics during the observational record. The model, defined by only two variables, sea surface temperature (SST) and warm water volume (WWV), is fitted to the observations for the period 1901-2010. The variability of ENSO has increased during the 20<sup>th</sup> century. The model simulates similar changes in variance of SST and WWV. The cross-correlation between SST and WWV also shows significant changes during the observational record. From the 1970s onwards, both observations and model output show that the SST drives WWV anomalies with a lead-time of 10 months and the WWV feedbacks onto the SST with a lead-time of about 8 months. The latter is reminiscent of a recharge-discharge mechanism of the upper ocean heat content. Before the 1970s only the impact of SST on WWV, through implied wind changes, is observed and is reproduced by the model. The periodicity of ENSO has also changed; ENSO has become more frequent changing from a 7-yr periodicity in the beginning of 20<sup>th</sup> century to a 5-yr periodicity in the recent decades. We find that the full recharge-discharge mechanism of the equatorial upper ocean heat content that characterizes the dynamics of the ReOsc model is only observed from the 1970s onwards and is likely to be a consequence of a stronger observed coupling between WWV and SST and of the leading role of the thermocline feedback. The</span><span> degrading quality in the observations for earlier periods can also partly explain the decadal changes in the ENSO interactions. We find that the Atlantic Multidecadal Variability and global warming can partly explain the observed and simulated multidecadal changes in ENSO properties.</span></p>

scholarly journals Role of Horizontal Advection of Seasonal-Mean Moisture in the Madden–Julian Oscillation: A Theoretical Model Analysis

2016 ◽  
Vol 29 (17) ◽  
pp. 6277-6293 ◽  
Author(s):  
Fei Liu ◽  
Bin Wang
Keyword(s):  
Theoretical Model ◽  
Warm Pool ◽  
Eastern Pacific ◽  
Madden Julian Oscillation ◽  
Kelvin Wave ◽  
Horizontal Advection ◽  
Pacific Warm Pool ◽  
Zonal Advection ◽  
Central Eastern ◽  
The Impact

Abstract The impact of horizontal advection of seasonal-mean moisture (SMM) on Madden–Julian oscillation (MJO) dynamics is investigated here using a theoretical model that includes moisture advection processes. The zonal advection of SMM with an eastward gradient is found to produce planetary-scale instability and promote slow eastward propagation corresponding to an intraseasonal periodicity. This is because the SMM advection by an anomalous easterly of the Kelvin waves generates a moisture source to the east of precipitation, which favors eastward propagation and unstable growth. On the other hand, the advection of SMM with a westward gradient results in a westward-propagating unstable mode. For a realistic SMM distribution, the simulated eastward propagation is enhanced over the Indo-Pacific warm pool, while the westward propagation prevails over the central-eastern Pacific. In contrast to the zonal advection of SMM, the meridional advection of SMM only affects short waves and leaves planetary waves nearly unaffected. The effect of zonal advection of SMM suggests an important mechanism for explaining the eastward propagation and growth of the MJO over the Indo-Pacific warm pool when the SMM increases eastward. However, this mechanism alone produces unrealistic Kelvin wave–like structure and strong westward propagation in the central-eastern Pacific; both disagree with observations. These caveats, however, can be remitted if the planetary boundary layer (PBL) moisture convergence feedback is included, which couples the Kelvin wave and the Rossby wave via precipitation heating, producing a realistic horizontal structure and also substantially suppressing the unrealistically growing, westward-propagating mode in the central-eastern Pacific.

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