scholarly journals Surface processes in the 7 November 2014 medicane from air–sea coupled high-resolution numerical modelling

2020 ◽  
Vol 20 (11) ◽  
pp. 6861-6881 ◽  
Author(s):  
Marie-Noëlle Bouin ◽  
Cindy Lebeaupin Brossier
Keyword(s):  
Tropical Cyclones ◽  
Sea Surface ◽  
Convective Precipitation ◽  
Surface Cooling ◽  
Air Masses ◽  
Coupled Modelling ◽  
Low Level ◽  
Cold Pools ◽  
Ocean Atmosphere ◽  
The Impact

Abstract. A medicane, or Mediterranean cyclone with characteristics similar to tropical cyclones, is simulated using a kilometre-scale ocean–atmosphere coupled modelling platform. A first phase leads to strong convective precipitation, with high potential vorticity anomalies aloft due to an upper-level trough. Then, the deepening and tropical transition of the cyclone result from a synergy of baroclinic and diabatic processes. Heavy precipitation results from uplift of conditionally unstable air masses due to low-level convergence at sea. This convergence is enhanced by cold pools, generated either by rain evaporation or by advection of continental air masses from northern Africa. Back trajectories show that air–sea heat exchanges moisten the low-level inflow towards the cyclone centre. However, the impact of ocean–atmosphere coupling on the cyclone track, intensity and life cycle is very weak. This is due to a sea-surface cooling 1 order of magnitude weaker than for tropical cyclones, even in the area of strong enthalpy fluxes. Surface currents have no impact. Analysing the surface enthalpy fluxes shows that evaporation is controlled mainly by the sea-surface temperature and wind. Humidity and temperature at the first level play a role during the development phase only. In contrast, the sensible heat transfer depends mainly on the temperature at the first level throughout the medicane lifetime. This study shows that the tropical transition, in this case, is dependent on processes widespread in the Mediterranean Basin, like advection of continental air, rain evaporation and formation of cold pools, and dry-air intrusion.

scholarly journals Surface processes in the 7 November 2014 medicane from air–sea coupled high-resolution numerical modelling

2019 ◽  
Author(s):  
Marie-Noëlle Bouin ◽  
Cindy Lebeaupin Brossier
Keyword(s):  
Tropical Cyclones ◽  
Surface Processes ◽  
Convective Precipitation ◽  
Surface Cooling ◽  
Air Masses ◽  
Low Level ◽  
Cold Pools ◽  
Ocean Atmosphere ◽  
Upper Level ◽  
The Impact

Abstract. A medicane, or Mediterranean cyclone with characteristics similar to tropical cyclones, is simulated using a kilometre-scale ocean–atmosphere coupled modelling platform. A first baroclinic phase of the cyclone leads to strong convective precipitation, with high potential vorticity anomalies aloft due to an upper-level trough. The deepening and tropicalization of the cyclone is due first to the crossing of the upper-level jet, then to low-level convergence and uplift of conditionally unstable air masses by cold pools, resulting either from rain evaporation or from advection of continental air masses from North Africa. Backtrajectories show that air–sea heat exchanges warm and moisten the low-level inflow feeding the latent heat release during the mature phase of the medicane. However, the impact of ocean–atmosphere coupling on the cyclone track, intensity and lifecycle is very weak, due to a surface cooling one order of magnitude weaker than for tropical cyclones, even on the area of strong enthalpy fluxes. Isolating the influence of the surface parameters on the surface fluxes at sea during the different phases of the cyclone confirms the impact of the cold pools on the surface processes. The evaporation is controlled mainly by the sea surface temperature and wind, with a significant additional impact of the humidity and temperature at first level during the development phase. The sensible heat flux is influenced mainly by the temperature at first level throughout the whole medicane lifetime. This study shows that the tropical transition, in this case, is dependent on processes widespread in the Mediterranean Basin, like advection of continental air, rain evaporation, and dry air intrusion.

scholarly journals The Effect of Atmosphere–Ocean Coupling on the Structure and Intensity of Tropical Cyclone Bejisa in the Southwest Indian Ocean

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 688
Author(s):  
Soline Bielli ◽  
Christelle Barthe ◽  
Olivier Bousquet ◽  
Pierre Tulet ◽  
Joris Pianezze
Keyword(s):  
Tropical Cyclone ◽  
Mixed Layer ◽  
Heat Fluxes ◽  
Sea Surface ◽  
Ocean Mixed Layer ◽  
Surface Cooling ◽  
Southwest Indian Ocean ◽  
Left Hand ◽  
Sea Surface Cooling ◽  
The Impact

A set of numerical simulations is relied upon to evaluate the impact of air-sea interactions on the behaviour of tropical cyclone (TC) Bejisa (2014), using various configurations of the coupled ocean-atmosphere numerical system Meso-NH-NEMO. Uncoupled (SST constant) as well as 1D (use of a 1D ocean mixed layer) and 3D (full 3D ocean) coupled experiments are conducted to evaluate the impact of the oceanic response and dynamic processes, with emphasis on the simulated structure and intensity of TC Bejisa. Although the three experiments are shown to properly capture the track of the tropical cyclone, the intensity and the spatial distribution of the sea surface cooling show strong differences from one coupled experiment to another. In the 1D experiment, sea surface cooling (∼1 ∘C) is reduced by a factor 2 with respect to observations and appears restricted to the depth of the ocean mixed layer. Cooling is maximized along the right-hand side of the TC track, in apparent disagreement with satellite-derived sea surface temperature observations. In the 3D experiment, surface cooling of up to 2.5 ∘C is simulated along the left hand side of the TC track, which shows more consistency with observations both in terms of intensity and spatial structure. In-depth cooling is also shown to extend to a much deeper depth, with a secondary maximum of nearly 1.5 ∘C simulated near 250 m. With respect to the uncoupled experiment, heat fluxes are reduced from about 20% in both 1D and 3D coupling configurations. The tropical cyclone intensity in terms of occurrence of 10-m TC wind is globally reduced in both cases by about 10%. 3D-coupling tends to asymmetrize winds aloft with little impact on intensity but rather a modification of the secondary circulation, resulting in a slight change in structure.

scholarly journals Effects of Tropical Cyclones on Sea Surface Salinity in the Bay of Bengal Based on SMAP and Argo Data

Water ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 2975
Author(s):  
Huabing Xu ◽  
Rongzhen Yu ◽  
Danling Tang ◽  
Yupeng Liu ◽  
Sufen Wang ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
Bay Of Bengal ◽  
Vertical Mixing ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Ekman Pumping ◽  
Surface Salinity ◽  
Argo Data ◽  
Before And After ◽  
The Impact

This paper uses the Argo sea surface salinity (SSSArgo) before and after the passage of 25 tropical cyclones (TCs) in the Bay of Bengal from 2015 to 2019 to evaluate the sea surface salinity (SSS) of the Soil Moisture Active Passive (SMAP) remote sensing satellite (SSSSMAP). First, SSSArgo data were used to evaluate the accuracy of the 8-day SMAP SSS data, and the correlations and biases between SSSSMAP and SSSArgo were calculated. The results show good correlations between SSSSMAP and SSSArgo before and after TCs (before: SSSSMAP = 1.09SSSArgo−3.08 (R2 = 0.69); after: SSSSMAP = 1.11SSSArgo−3.61 (R2 = 0.65)). A stronger negative bias (−0.23) and larger root-mean-square error (RMSE, 0.95) between the SSSSMAP and SSSArgo were observed before the passage of 25 TCs, which were compared to the bias (−0.13) and RMSE (0.75) after the passage of 25 TCs. Then, two specific TCs were selected from 25 TCs to analyze the impact of TCs on the SSS. The results show the significant SSS increase up to the maximum 5.92 psu after TC Kyant (2016), which was mainly owing to vertical mixing and strong Ekman pumping caused by TC and high-salinity waters in the deep layer that were transported to the sea surface. The SSSSMAP agreed well with SSSArgo in both coastal and offshore waters before and after TC Roanu (2016) and TC Kyant (2016) in the Bay of Bengal.

Prediction of Tornado-Like Vortex (TLV) Embedded in the 8 May 2003 Oklahoma City Tornadic Supercell Initialized from the Subkilometer Grid Spacing Analysis Produced by the Dual-Resolution GSI-Based EnVar Data Assimilation System

2020 ◽  
Vol 148 (7) ◽  
pp. 2909-2934
Author(s):  
Yongming Wang ◽  
Xuguang Wang
Keyword(s):  
Data Assimilation ◽  
Initial Conditions ◽  
Potential Temperature ◽  
Intensity Variation ◽  
Oklahoma City ◽  
Grid Spacing ◽  
Near Surface ◽  
Low Level ◽  
Cold Pools ◽  
The Impact

Abstract Explicit forecasts of a tornado-like vortex (TLV) require subkilometer grid spacing because of their small size. Most previous TLV prediction studies started from interpolated kilometer grid spacing initial conditions (ICs) rather than subkilometer grid spacing ICs. The tornadoes embedded in the 8 May 2003 Oklahoma City tornadic supercell are used to understand the impact of IC resolution on TLV predictions. Two ICs at 500-m and 2-km grid spacings are, respectively, produced through an efficient dual-resolution (DR) and a single-coarse-resolution (SCR) EnVar ingesting a 2-km ensemble. Both experiments launch 1-h forecasts at 500-m grid spacing. Diagnostics of data assimilation (DA) cycling reveal DR produces stronger and broader rear-flank cold pools, more intense downdrafts and updrafts with finer scales, and more hydrometeors at high altitudes through accumulated differences between two DA algorithms. Relative differences in DR, compared to SCR, include the integration from higher-resolution analyses, the update for higher-resolution backgrounds, and the propagation of ensemble perturbations along higher-resolution model trajectory. Predictions for storm morphology and cold pools are more realistic in DR than in SCR. The DR-TLV tracks match better with the observed tornado tracks than SCR-TLV in timing of intensity variation, and in duration. Additional experiments suggest 1) the analyzed kinematic variables strongly influence timing of intensity variation through affecting both low-level rear-flank outflow and midlevel updraft; 2) potential temperature analysis by DR extends the second track’s duration consistent with enhanced low-level stretching, delayed broadening large-scale downdraft, and (or) increased near-surface baroclinic vorticity supply; and 3) hydrometeor analyses have little impact on TLV predictions.

scholarly journals Processes setting the characteristics of sea surface cooling induced by tropical cyclones

2012 ◽  
Vol 117 (C2) ◽  
pp. n/a-n/a ◽  
Author(s):  
Emmanuel M. Vincent ◽  
Matthieu Lengaigne ◽  
Gurvan Madec ◽  
Jérôme Vialard ◽  
Guillaume Samson ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
Sea Surface ◽  
Surface Cooling ◽  
Sea Surface Cooling

Cold Pool and Precipitation Responses to Aerosol Loading: Modulation by Dry Layers

2015 ◽  
Vol 72 (4) ◽  
pp. 1398-1408 ◽  
Author(s):  
Leah D. Grant ◽  
Susan C. van den Heever
Keyword(s):  
Cloud Droplet ◽  
Convective Precipitation ◽  
Cloud Base ◽  
Cold Pool ◽  
Moisture Profile ◽  
Positive Feedbacks ◽  
Low Level ◽  
Aerosol Loading ◽  
Cold Pools ◽  
Moving Storm

Abstract The relative sensitivity of midlatitude deep convective precipitation to aerosols and midlevel dry layers has been investigated in this study using high-resolution cloud-resolving model simulations. Nine simulations, including combinations of three moisture profiles and three aerosol number concentration profiles, were performed. Because of the veering wind profile of the initial sounding, the convection splits into a left-moving storm that is multicellular in nature and a right-moving storm, a supercell, which are analyzed separately. The results demonstrate that while changes to the moisture profile always induce larger changes in precipitation than do variations in aerosol concentrations, multicells are sensitive to aerosol perturbations whereas supercells are less so. The multicellular precipitation sensitivity arises through aerosol impacts on the cold pool forcing. It is shown that the altitude of the dry layer influences whether cold pools are stronger or weaker and hence whether precipitation increases or decreases with increasing aerosol concentrations. When the dry-layer altitude is located near cloud base, cloud droplet evaporation rates and hence latent cooling rates are greater with higher aerosol loading, which results in stronger low-level downdrafts and cold pools. However, when the dry-layer altitude is located higher above cloud base, the low-level downdrafts and cold pools are weaker with higher aerosol loading because of reduced raindrop evaporation rates. The changes to the cold pool strength initiate positive feedbacks that further modify the cold pool strength and subsequent precipitation totals. Aerosol impacts on deep convection are therefore found to be modulated by the altitude of the dry layer and to vary inversely with the storm organization.

scholarly journals An oceanic pathway for Madden–Julian Oscillation influence on Maritime Continent Tropical Cyclones

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Karthik Balaguru ◽  
L. Ruby Leung ◽  
Samson M. Hagos ◽  
Sujith Krishnakumar
Keyword(s):  
Numerical Model ◽  
Tropical Cyclones ◽  
Large Scale ◽  
Sea Surface ◽  
Madden Julian Oscillation ◽  
Surface Cooling ◽  
Maritime Continent ◽  
Large Scale Circulation ◽  
Model Simulations ◽  
Sea Surface Cooling

AbstractWhile the Madden–Julian Oscillation (MJO) has been shown to affect tropical cyclones (TCs) worldwide through its modulation of large-scale circulation in the atmosphere, little or no role for the ocean has been identified to date in this influence of MJO on TCs. Using observations and numerical model simulations, we demonstrate that MJO events substantially impact TCs over the Maritime Continent (MC) region through an oceanic pathway. While propagating across the MC region, MJO events cause significant sea surface cooling with an area-averaged value of about 0.35 ± 0.12 °C. Hence, TCs over the MC region immediately following the passage of MJO events encounter considerably cooler sea surface temperatures. Consequently, the enthalpy fluxes under the storms are reduced and the intensification rates decrease by more than 50% on average. These results highlight an important role played by the ocean in facilitating MJO-induced sub-seasonal variability in TC activity over the MC region.

scholarly journals A Hydrodynamical Atmosphere/Ocean Coupled Modeling System for Multiple Tropical Cyclones

Atmosphere ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 869
Author(s):  
Ghassan J. Alaka ◽  
Dmitry Sheinin ◽  
Biju Thomas ◽  
Lew Gramer ◽  
Zhan Zhang ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
Sea Surface ◽  
Intensity Change ◽  
Coupling Scheme ◽  
Sea Surface Temperatures ◽  
Improvement Program ◽  
Surface Temperatures ◽  
Skill Scores ◽  
Basin Scale ◽  
The Impact

The goal of this paper is to introduce a new multi-storm atmosphere/ocean coupling scheme that was implemented and tested in the Basin-Scale Hurricane Weather Research and Forecasting (HWRF-B) model. HWRF-B, an experimental model developed at the National Oceanic and Atmospheric Administration (NOAA) and supported by the Hurricane Forecast Improvement Program, is configured with multiple storm-following nested domains to produce high-resolution predictions for several tropical cyclones (TCs) within the same forecast integration. The new coupling scheme parallelizes atmosphere/ocean interactions for each nested domain in HWRF-B, and it may be applied to any atmosphere/ocean coupled system. TC forecasts from this new hydrodynamical modeling system were produced in the North Atlantic and eastern North Pacific from 2017–2019. The performance of HWRF-B was evaluated, including forecasts of TC track, intensity, structure (e.g., surface wind radii), and intensity change, and simulated sea-surface temperatures were compared with satellite observations. Median forecast skill scores showed significant improvement over the operational HWRF at most forecast lead times for track, intensity, and structure. Sea-surface temperatures cooled by 1–8 °C for the five HWRF-B case studies, demonstrating the utility of the model to study the impact of the ocean on TC intensity forecasting. These results show the value of a multi-storm modeling system and provide confidence that the multi-storm coupling scheme was implemented correctly. Future TC models within NOAA, especially the Unified Forecast System’s Hurricane Analysis and Forecast System, would benefit from the multi-storm coupling scheme whose utility and performance are demonstrated in HWRF-B here.

Interannual variability in the sea surface cooling induced by tropical cyclones in the South China Sea

2021 ◽  
Vol 40 (11) ◽  
pp. 70-78
Author(s):  
Juan Ouyang ◽  
Chunhua Qiu ◽  
Zhenhui Yi ◽  
Dongxiao Wang ◽  
Danyi Su ◽  
...  
Keyword(s):  
South China Sea ◽  
Interannual Variability ◽  
Tropical Cyclones ◽  
South China ◽  
The South China Sea ◽  
Sea Surface ◽  
The South ◽  
Surface Cooling ◽  
China Sea ◽  
Sea Surface Cooling

Influence of Assimilating CYGNSS Ocean Surface Wind Data on Tropical Cyclone Analyses and Predictions

2020 ◽  
Author(s):  
Bachir Annane ◽  
Mark Leidner ◽  
Ross Hoffman ◽  
Feixiong Huang ◽  
James Garrisson
Keyword(s):  
Tropical Cyclones ◽  
Surface Wind ◽  
Ocean Surface ◽  
Convective Precipitation ◽  
Weather Research And Forecasting ◽  
Wind Speeds ◽  
Ocean Surface Winds ◽  
Ocean Surface Wind ◽  
The Impact ◽  
Hwrf Model

<div> <div><em>For the analysis and forecasting of tropical cyclones, the main benefits of data from the CYGNSS constellation of satellites are the increased revisit frequency compared with polar-orbiting satellites and the ability to provide ocean surface wind observations through convective precipitation. Consequently, CYGNSS delivers an improved capability to observe the structure and evolution of ocean surface winds in and around tropical cyclones. This study quantifies the impact of assimilating CYGNSS delay-Doppler maps, CYGNSS retrieved wind speeds and derived CYGNSS wind vectors on 6-hourly analyses and 5-day forecasts of developing tropical cyclones, using the 2019 version of NOAA's operational Hurricane Weather Research and Forecasting (HWRF) model.</em></div> </div>

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