@article{chaichitehrani_he_2024, title={Investigation of ocean environmental variables and their variations associated with major Loop Current eddy-shedding events in the Gulf of Mexico}, volume={213}, ISSN={["1879-0100"]}, DOI={10.1016/j.dsr2.2023.105354}, abstractNote={The eddy kinetic energy (EKE) variability associated with 26 major Loop Current eddies (LCEs) in the Gulf of Mexico from 1994 through 2019 was investigated. We employed 3D multivariate observation-based ARMOR3D monthly ocean analyses of salinity, temperature, and geostrophic velocity field data. In addition, we used ERA5 wind data, the fifth generation of the European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric global climate reanalysis, to analyze internal and external forcing processes affecting the evolution of these LCEs. The energy analysis was performed to understand the role of barotropic (BT) and baroclinic (BC) instabilities and their associated energy conversion mechanisms in EKE generation. Our results suggest that BT instabilities are the primary source of EKE variability in the upper water column of the LC system. Furthermore, BT was positively correlated with Yucatan Channel (YC) transport during these major LCE shedding events. YC transport plays a significant role in energy conversion from mean kinetic energy to EKE, Loop Current growth, and generation of LCEs. BC instability was inversely correlated with buoyancy frequency, and a decrease in stratification triggers the development of BC instability, which favors eddy shedding. An eddy shedding index (ESI) was developed to quantify EKE evolution. Major LCE shedding occurs when ESI ≥0.46.}, journal={DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY}, author={Chaichitehrani, Nazanin and He, Ruoying}, year={2024}, month={Feb} }
 @article{chaichitehrani_li_xu_hestir_allahdadi_2023, title={Sediment dynamics over a dredge pit during summer fair weather conditions: A numerical study for Sandy Point, west flank of the Mississippi River}, volume={269}, ISSN={["1873-5258"]}, DOI={10.1016/j.oceaneng.2022.113473}, abstractNote={A coupled Flow-Wave-Sediment model was used to study hydrodynamics, sedimentation, and bottom boundary layer (BBL) dynamics over the Sandy Point Dredge Pit (SPDP; a potential sand mining site in the Louisiana shelf, northern Gulf of Mexico) during fair weather summer conditions (July and August 2015). The Delft3D modeling system on a curvilinear computational grid with spatial resolution between 10 m and 2.8 km was used. The flow, wave, and sediment transport models were evaluated using water level, current speed, wave parameters, and sediment concentration. During this period, the wind over the Louisiana shelf is characterized as low energy with the prevailing direction from southeast to the southwest, which corresponds to small wave heights (Hs < 1.2 m) and small wave periods (Tm < 4 s). The relatively shorter waves resuspended sediments only in very shallow areas along the Mississippi Birdfoot Delta. Simulations with and without the SPDP showed that the presence of the pit could decrease the speed of surface currents by as much as 19%, while its effect on wave characteristics was minor. The northward current produced by the prevailing winds transported the discharged sediments from the Mississippi River contributed 60% of the sedimentation over the SPDP. Sediment re-suspension inside the BBL of the SPDP occurred during the days that more energetic waves propagated over the shelf. As a result, sediments from the Mississippi River significantly increased the sediment concentration near the bottom of and throughout the water column above the SPDP.}, journal={OCEAN ENGINEERING}, author={Chaichitehrani, Nazanin and Li, Chunyan and Xu, Kehui and Hestir, Erin L. and Allahdadi, Mohammad Nabi}, year={2023}, month={Feb} }
 @article{allahdadi_li_chaichitehrani_2023, title={Stratification Breakdown by Fall Cold Front Winds over the Louisiana Shelf in the Northern Gulf of Mexico: A Numerical Experiment}, volume={11}, ISSN={["2077-1312"]}, DOI={10.3390/jmse11030673}, abstractNote={Cold fronts are meteorological phenomena that impact the northern Gulf of Mexico, mostly between the fall and spring seasons. On average, they pass the region every 3–7 days, with a duration ranging between 24 and 74 h. In the present study, a high-resolution FVCOM model with an unstructured mesh was used to simulate the effect of the fall cold front winds on water column mixing over the Louisiana shelf, which is often stratified in the summer, leading to hypoxia. Numerical experiments were conducted for October 2009, a period with five consecutive cold front events. Winds from an offshore station forced the model, while climatological temperature/salinity profiles prepared by NOAA for September were used for model initialization. The model performance was evaluated by comparing it with the surface current measurements at two offshore stations, and the results showed a good agreement between the model results and observations. Shelf mixing and stratification were investigated through examining the simulated sea surface temperature as well as the longitudinal and cross-shelf vertical sections. Simulation results showed a significant effect on shelf mixing, with the mixed layer depth increasing from the initial values of 5 m to 25 m at the end of simulation at different parts of the shelf, with maximum mixed layer depths corresponding to the peak of cold fronts. The buoyancy frequency, Richardson number, and the average potential energy demand (APED) for mixing the water column were used to quantify the stratification at two selected locations over the shelf. Results showed that all these parameters almost continuously decreased due to mixing induced by cold front wind events during this time. At the station off the Terrebonne Bay with a water depth of 20 m, the water column became fully mixed after three of the cold front events, with Richardson numbers smaller than 0.25 and approaching zero. This continued mixing trend was also proven by obtaining a decreasing trend of APED from 100 to 5 kg/m.s2 with several close to zero energy demand values.}, number={3}, journal={JOURNAL OF MARINE SCIENCE AND ENGINEERING}, author={Allahdadi, Mohammad Nabi and Li, Chunyan and Chaichitehrani, Nazanin}, year={2023}, month={Mar} }
 @article{allahdadi_li_chaichitehrani_2022, title={Numerical Experiments of Temperature Mixing and Post-Storm Re-Stratification over the Louisiana Shelf during Hurricane Katrina (2005)}, volume={10}, ISSN={["2077-1312"]}, DOI={10.3390/jmse10081082}, abstractNote={Studying mixing and re-stratification during and after hurricanes have important implications for the simulation of circulation and bio-geochemical processes in oceanic and shelf waters. Numerical experiments using FVCOM on an unstructured computational mesh were implemented to study the direct effect of hurricane winds on the mixing and temperature redistribution of the stratified Louisiana shelf during Hurricane Katrina (2005), as well as the post-storm re-stratification timescale. The model was forced by Katrina’s wind stress obtained from a combination of H-Wind database and NCEP model. The climatological profiles of temperature and salinity for August (the month in which Katrina occurred) from the world ocean atlas (WOA, 2013) were used as the pre-storm conditions over the shelf. Model results for sea surface temperature (SST) and mixed layer depth (MLD) were validated versus SST data from an optimally interpolated satellite product, and the MLD was calculated from the heat budget equation of the mixed layer. Model results were used to examine the temporal and spatial responses of SST and MLD over the shelf to Katrina. Results showed that intense mixing occurred within 1–1.1 RMW (RMW is the radius of maximum wind for Katrina), with turbulent mixing as the dominant mixing force for regions far from the eye, although upwelling was an important contributor to modulating SST and MLD. During the peak of Katrina and for the shelf regions severely affected by the hurricane wind, three distinct temperature zones were formed across the water column: an upper mixed layer, a transition zone, and a lower upwelling zone. Shelf re-stratification started from 3 h to more than two weeks after the landfall, depending on the distance from the track. The mixing during Hurricane Katrina affected the seasonal summertime hypoxic zone over the Louisiana shelf and likely contributed to the water column re-oxygenation.}, number={8}, journal={JOURNAL OF MARINE SCIENCE AND ENGINEERING}, author={Allahdadi, Mohammad Nabi and Li, Chunyan and Chaichitehrani, Nazanin}, year={2022}, month={Aug} }
 @article{chaichitehrani_allahdadi_li_2022, title={Simulation of Low Energy Waves during Fair-Weather Summer Conditions in the Northern Gulf of Mexico: Effect of Whitecapping Dissipation and the Forcing Accuracy}, volume={13}, ISSN={["2073-4433"]}, DOI={10.3390/atmos13122047}, abstractNote={Simulating WAves Nearshore (SWAN) on a structured grid over the Louisiana shelf in the northern Gulf of Mexico is used to evaluate the performance of three different classes of formulations for quantifying wind input and whitecapping dissipation. The formulations include Komen based on the mean spectral parameters, Westhuysen based on the saturation concept of the wave groups, and the most recent observation-based physics package ST6. The evaluation was implemented for two summer months (July and August 2015) to assess these formulations for a low wave energy period. The modeling area consists of the Louisiana inner shelf with the offshore open boundary located beyond the continental shelf. The model was forced using the spatially variable Climate Forecast System Reanalysis (CFSR) wind field and wave parameters obtained from the NOAA’s WAVEWATCH-III (WWIII) model along the open boundaries. Simulated wave parameters and spectra regarding each formulation were evaluated and compared with measured wave data at NDBC stations; comparisons showed that the most appropriate formulation for the simulation of low energy waves for the study area to be ST6. The e performance of each whitecapping formulation was described by examining 1D/2D spectra and the source term balance at different met-ocean conditions during the simulation period. It was also shown that the inaccuracies in the input wind field and boundary conditions can substantially contribute to the model inaccuracy.}, number={12}, journal={ATMOSPHERE}, author={Chaichitehrani, Nazanin and Allahdadi, Mohammad Nabi and Li, Chunyan}, year={2022}, month={Dec} }
 @article{isaie moghaddam_allahdadi_ashrafi_chaichitehrani_2021, title={Coastal system evolution along the southeastern Caspian Sea coast using satellite image analysis: response to the sea level fall during 1994-2015}, volume={14}, ISBN={1866-7538}, DOI={10.1007/s12517-021-07106-2}, number={9}, journal={ARABIAN JOURNAL OF GEOSCIENCES}, author={Isaie Moghaddam, Ehsan and Allahdadi, Mohammad Nabi and Ashrafi, Ali and Chaichitehrani, Nazanin}, year={2021}, month={May} }
 @article{koohestani_allahdadi_chaichitehrani_2021, title={Oceanic Response to Tropical Cyclone Gonu (2007) in the Gulf of Oman and the Northern Arabian Sea: Estimating Depth of the Mixed Layer Using Satellite SST and Climatological Data}, volume={9}, ISSN={["2077-1312"]}, DOI={10.3390/jmse9111244}, abstractNote={The category 5-equivalent tropical Cyclone Gonu (2007) was the strongest cyclone to enter the northern Arabian Sea and Gulf of Oman. The impact of this cyclone on the sea surface temperature (SST) cooling and deepening of the mixed layer was investigated herein using an optimally interpolated (OI) cloud-free sea surface temperature (SST) dataset, climatological profiles of water temperature, and data from Argo profilers. SST data showed a maximum cooling of 1.7–6.5 °C during 1–7 June 2007 over the study area, which is similar to that of slow- to medium-moving cyclones in previous studies. The oceanic heat budget equation with the assumptions of the dominant turbulent mixing effect was used to establish relationships between SST and mixed layer depth (MLD) for regions that were directly affected by cyclone-induced turbulent mixing. The relationships were applied to the SST maps from satellite to obtain maps of MLD for 1–7 June, when Gonu was over the study area. Comparing with the measured MLD from Argo data showed that this approach estimated the MLDs with an average error of 15%, which is an acceptable amount considering the convenience of this approach in estimating MLD and the simplifications applied in the heat budget equation. Some inconsistencies in calculating MLD were attributed to use of climatological temperature profiles that may not have appropriately represented the pre-cyclone conditions due to pre-existing cold/warm core eddies. Estimation of the diapycnal diffusion that quantified the turbulent mixing across the water column showed consistent temporal and spatial variations with the calculated MLDs.}, number={11}, journal={JOURNAL OF MARINE SCIENCE AND ENGINEERING}, author={Koohestani, Kamran and Allahdadi, Mohammad Nabi and Chaichitehrani, Nazanin}, year={2021}, month={Nov} }