Interaction Of Tropical Cyclones Research Articles

Tracing isotope precipitation patterns across Mexico

Mexico encompasses a large spectrum of landscapes with topographic, geographic, and climatic factors interacting in a complex ecohydrological setting. For decades, isotope hydrogeological tools have been applied in Mexico using short-term or seasonal local meteoric water lines as valid input functions. Yet, a systematic evaluation of meteoric isotope characteristics is still lacking. Here we report on the spatial and temporal isotope variations of 21 precipitation monitoring stations across Mexico. Our database includes 608 monthly samples collected from 2018 to 2021 over four regions (between 5 and 2,365 m asl): the Pacific coast, the Gulf of Mexico/Caribbean Sea region, and the Central and Northern plateaus. Precipitation δ18O seasonality from the dry (winter) to the wet season (summer) was characterized by a notable W-shaped variability. Monthly precipitation amounts and δ18O compositions exhibited poor to strong linear regressions (Adj. r2<0.01 to 0.75), with inverse (positive) relationships over the northern monsoon-affected region. Low d-excess (5.1 to 9.7‰) corresponded with greater terrestrial moisture contributions (20.5%) over the arid northern regions. Moisture inputs from the Gulf of Mexico/Caribbean Sea and the Pacific Ocean were associated with near-equilibrium or greater d-excess values (8.8 to 14.3‰), respectively. The best-fit linear models for δ18O (Adj. r2 = 0.85) and δ2H (Adj. r2 = 0.88) were determined for topographic and geographical predictors, resulting in an updated high-resolution precipitation isoscape (100 m2 grid) for Mexico. Orographic barriers (-2.10‰ in δ18O/km) coupled with the interaction of tropical cyclones and cold fronts, the evolution of the North American Monsoon system, and the passage of easterly trade winds play a remarkable role in controlling the spatial isotope rainfall variability. Our findings provide a robust baseline for ecohydrological, climatic, forensic, archeological, and paleoclimate studies in North America.

Investigation of links between dynamical scenarios and particularly high impact of Aeolus on numerical weather prediction (NWP) forecasts

Abstract. Global wind profiles from the Aeolus satellite mission provide an important source of wind information for numerical weather prediction (NWP). Data assimilation experiments show large mean changes in the analysis and a significant reduction in forecast errors. At Deutscher Wetterdienst (DWD), a 3-month observing system experiment (OSE), from July 2020 to October 2020, was performed to evaluate the impact of the Aeolus horizontal line-of-sight (HLOS) wind observations in the operational data assimilation system of the ICOsahedral Nonhydrostatic (ICON) global model. To better understand the underlying dynamics leading to the overall beneficial impact, specific time periods and regions with a particularly high impact of Aeolus are investigated. In this study, we illustrate three examples of atmospheric phenomena that constitute dynamical scenarios for significant forecast error reduction through the assimilation of Aeolus: the phase shift of large-scale tropical circulation systems, namely the Quasi-Biennial Oscillation (QBO) and the El Niño–Southern Oscillation (ENSO), and the interaction of tropical cyclones undergoing extratropical transition (ET) with the midlatitude waveguide.

On the interaction of mesoscale eddies and a tropical cyclone in the Bay of Bengal

Oceanic eddies span over a wide range of sizes and affect the thermodynamic properties of water column. By modifying the thermal structure of the upper ocean, these eddies influence the air-sea heat exchange and, therefore, the strength of a tropical cyclone (TC) that passes over the eddy zone. To understand the interaction of tropical cyclone with different types of eddies (cyclonic and anticyclonic) over the Bay of Bengal (BoB) region, three idealized numerical experiments are performed using an atmosphere–ocean–wave coupled model. In these experiments, the atmospheric and wave models are forced by the realistic surface forcing (i.e. wind, pressure, heat and momentum fluxes) of the Vardah cyclone period (10–15 December 2016) in the BoB. The ocean model is initialized with three idealized conditions, i.e. horizontally constant profile of temperature and salinity throughout the model domain, idealized three-dimensional (3-D) temperature and salinity profiles in the area of 2° radius for cyclonic eddy and anticyclonic eddy. The 3-D eddy profile is placed in the path of TC Vardah track. The strength and radius of both idealized cyclonic and anticyclonic eddies are kept same. The model-simulated results of these three experiments were intercompared and it is found that the tropical cyclone interaction with an anticyclonic eddy had provided an ancillary strength to the TC by raising the tropical cyclone heat potential (TCHP) in comparison with other experiments. The utilization of coupled ocean–atmosphere–wave model had also provided a better representation of ocean–atmosphere coupled feedback processes during TC interaction with different eddies. The analysis of feedback processes depicted that the TC interaction with an anticyclonic eddy has raised the magnitude of its existing moist-static-energy comparative to the cyclonic eddy interaction case which resulted into an increase in the strength of the TC.

Climatology of Tropical Cyclone Strikes along the Southeastern Coastline of the United States

Lindner, B.L.; Holden, W.; Neuhauser, A., and Evsich, R., 2020. Climatology of tropical cyclone strikes along the southeastern coastline of the United States. Journal of Coastal Research, 36(6), 1162–1177. Coconut Creek (Florida), ISSN 0749-0208.It has been theorized that tropical cyclones originating in or passing through the Gulf of Mexico (hereafter referred to as GOM tropical cyclones) may significantly impact communities along the Atlantic coast of the southeastern United States. To explore this hypothesis, site-specific climatologies were compiled using National Hurricane Center records of tropical cyclones that passed within 139 km of either Savannah, Georgia, or Wilmington, North Carolina, during the years 1851–2018. Return periods for tropical cyclones are longer for Savannah than for Wilmington, particularly for intense hurricanes. Intense GOM hurricanes are weakened by land interaction, which would result in longer return periods. A secondary maximum in the number of tropical storms early in hurricane season is more pronounced with proximity to the Gulf of Mexico, which is again consistent with the contribution from GOM tropical cyclones. Moreover, the percentage of tropical cyclones that passed near Savannah but did not make landfall is higher than that for Wilmington, again an indication of the significance of GOM tropical cyclones. Further evidence of the influence of GOM tropical cyclones is seen in the difference in approach angle and translational velocity between tropical storms and hurricanes. In addition, translational velocities for tropical cyclones increase with latitude, and translational velocities for tropical cyclones near either Savannah or Wilmington increase as the hurricane season progresses. Both relationships are likely due to the interaction of tropical cyclones with synoptic and planetary-scale winds. The median date for tropical cyclones has shifted earlier in recent decades for both Savannah and Wilmington, which is potentially an indication of climate change. An improved understanding of the climatology of tropical cyclones could lead to enhanced city planning, building codes, infrastructure, and resource management.

Tropical Cyclone Interaction with the Ocean: The Role of High-Frequency (Subdaily) Coupled Processes

Through tropical cyclone (TC) activity the ocean and the atmosphere exchange a large amount of energy. In this work possible improvements introduced by a higher coupling frequency are tested between the two components of a climate model in the representation of TC intensity and TC–ocean feedbacks. The analysis is based on the new Centro Euro-Mediterraneo per I Cambiamenti Climatici Climate Model (CMCC-CM2-VHR), capable of representing realistic TCs up to category-5 storms. A significant role of the negative sea surface temperature (SST) feedback, leading to a weakening of the cyclone intensity, is made apparent by the improved representation of high-frequency coupled processes. The first part of this study demonstrates that a more realistic representation of strong TC count is obtained by coupling atmosphere and ocean components at hourly instead of daily frequency. Coherently, the positive bias of the annually averaged power dissipation index associated with TCs is reduced by one order of magnitude when coupling at the hourly frequency, compared to both forced mode and daily coupling frequency results. The second part of this work shows a case study (a modeled category-5 typhoon) analysis to verify the impact of a more realistic representation of the high-frequency coupling in representing the TC effect on the ocean; the theoretical subsurface warming induced by TCs is well represented when coupling the two components at the higher frequency. This work demonstrates that an increased horizontal resolution of model components is not sufficient to ensure a realistic representation of intense and fast-moving systems, such as tropical and extratropical cyclones, but a concurrent increase in coupling frequency is required.

Main results of recent investigations into the physical mechanisms of the interaction of tropical cyclones and the ionosphere

International investigations into the correlation between tropical cyclones (TCs) and the ionosphere are associated with great difficulties in proving the influence of possible TC mechanisms on the ionosphere. In this paper, the ionospheric parameters obtained by ground-based and satellite sensing over the TC and at a certain distance from it are analyzed. This paper is a brief presentation of the main areas of research on the TC–ionosphere interaction problem by different international teams of scientists from the formulation of the problem to the present. The main conclusion of the paper is that internal gravity waves are the main factors that influence the ionosphere from the active cyclones.

Initial Transient Response of an Intensifying Baroclinic Wave to Increases in Cloud Droplet Number Concentration

Abstract Ensemble simulations of an idealized baroclinic wave were conducted with the WRF Model to investigate the effects of increased cloud droplet number concentration (DNC) on the development of the wave. Statistically significant differences between experiments where the DNC was doubled and the control experiments were identified for an initial transient period before the cyclone enters the stage of rapid intensification. Doubling of the DNC increases total cloud water in the model, lowers the cloud level, and enhances latent heating to the east of the surface low, which strengthens the midtropospheric ridge. Subsequent changes in dry dynamical processes [e.g., advection of potential vorticity (PV)] as a result of the ridge strengthening lead to the deepening of the trough and ultimately produce a mild yet statistically significant strengthening of the baroclinic wave as a result of the DNC doubling. Piecewise PV inversion further confirms the critical role that latent heating change plays in strengthening the midtropospheric ridge. Also discussed are the distinctions between aerosol–tropical cyclone interaction and aerosol–extratropical cyclone interaction.

Remote impact of North Atlantic hurricanes on the Mediterranean during episodes of intense rainfall in autumn 2012

Autumn is the most favourable season for tropical cyclones to undergo extratropical transition and interact with the midlatitude flow over the North Atlantic. Autumn is also the season when intense rainfall over the Mediterranean is often triggered by Rossby wave breaking. The impact of tropical cyclones on downstream wave breaking is investigated here during three episodes of intense rainfall which were the target of HyMeX (Hydrological cycle in Mediterranean eXperiment) in autumn 2012. Five‐day simulations of hurricanes Leslie, Rafael and Sandy were performed with the Meso‐NH model in a domain encompassing the North Atlantic and the Mediterranean. Control simulations were compared to simulations in which the hurricanes were filtered out from the initial conditions. In each case, the hurricane locally impeded the forward progression of an upstream trough, then reintensified as an extratropical cyclone during the wrap‐up of the trough. The local impact of Leslie and Rafael on the midlatitude flow quickly propagated downstream along a polar jet and amplified Rossby wave breaking but decreased the intensity of the forecast precipitation over the Mediterranean. The local impact of Sandy propagated downstream along a subtropical jet in addition to the polar jet and resulted in a weak impact of the forecast precipitation on the Mediterranean. This study suggests that the interaction of tropical cyclones with the midlatitude flow over the western North Atlantic may be considered a perturbation to, rather than a source of, downstream wave breaking.

Upper ocean response to the passage of two sequential typhoons

Abstract. The atmospheric wind stress forcing and the oceanic response are examined for the period between 15 September 2008 and 6 October 2008, during which two typhoons – Hagupit and Jangmi – passed through the same region of the western Pacific at Saffir–Simpson intensity categories one and three, respectively. A three-dimensional oceanic mixed layer model is compared against the remote sensing observations as well as high-repetition Argo float data. Numerical model simulations suggested that magnitude of the cooling caused by the second typhoon, Jangmi, would have been significantly larger if the ocean had not already been influenced by the first typhoon, Hagupit. It is estimated that the temperature anomaly behind Jangmi would have been about 0.4 °C larger in both cold wake and left side of the track. The numerical simulations suggest that the magnitude and position of Jangmi's cold wake depends on the precursor state of the ocean as well as lag between typhoons. Based on sensitivity experiments we show that temperature anomaly difference between "single typhoon" and "two typhoons" as well as magnitude of the cooling strongly depends on the distance between them. The amount of kinetic energy and coupling with inertial oscillations are important factors for determining magnitude of the temperature anomaly behind moving typhoons. This paper indicates that studies of ocean–atmosphere tropical cyclone interaction will benefit from denser, high-repetition Argo float measurements.

Simple kinematic models for the environmental interaction of tropical cyclones in vertical wind shear

Abstract. A major impediment to the intensity forecast of tropical cyclones (TCs) is believed to be associated with the interaction of TCs with dry environmental air. However, the conditions under which pronounced TC-environment interaction takes place are not well understood. As a step towards improving our understanding of this problem, we analyze here the flow topology of a TC immersed in an environment of vertical wind shear in an idealized, three-dimensional, convection-permitting numerical experiment. A set of distinct streamlines, the so-called manifolds, can be identified under the assumptions of steady and layer-wise horizontal flow. The manifolds are shown to divide the flow around the TC into distinct regions. The manifold structure in our numerical experiment is more complex than the well-known manifold structure of a non-divergent point vortex in uniform background flow. In particular, one manifold spirals inwards and ends in a limit cycle, a meso-scale dividing streamline encompassing the eyewall above the layer of strong inflow associated with surface friction and below the outflow layer in the upper troposphere. From the perspective of a steady and layer-wise horizontal flow model, the eyewall is well protected from the intrusion of environmental air. In order for the environmental air to intrude into the inner-core convection, time-dependent and/or vertical motions, which are prevalent in the TC inner-core, are necessary. Air with the highest values of moist-entropy resides within the limit cycle. This "moist envelope" is distorted considerably by the imposed vertical wind shear, and the shape of the moist envelope is closely related to the shape of the limit cycle. In a first approximation, the distribution of high- and low-θe air around the TC at low to mid-levels is governed by the stirring of convectively modified air by the steady, horizontal flow. Motivated by the results from the idealized numerical experiment, an analogue model based on a weakly divergent point vortex in background flow is formulated. The simple kinematic model captures the essence of many salient features of the manifold structure in the numerical experiment. A regime diagram representing realistic values of TC intensity and vertical wind shear can be constructed for the point-vortex model. The results indicate distinct scenarios of environmental interaction depending on the ratio of storm intensity and vertical-shear magnitude. Further implications of the new results derived from the manifold analysis for TCs in the real atmosphere are discussed.

On the interaction of tropical cyclones with each other and with different atmospheric structures

The paper deals with the investigation of the interaction of tropical cyclones (TC) of the Atlantic and Pacific oceans with each other and with the polar front on the basis of computations using the mesoscale numerical ETA-model. The process of the interaction is demonstrated of TC Man-yi with the polar front accompanied by the distortion of vorticity circle and its consolidation with the vorticity zone of the polar front as well as by the formation of a convective “tail” interacting with the frontal zone. It is shown how one can define the beginning of this interaction, the moment of the potential trajectory turn, and the interaction process between a pair of tropical cyclones using the sea level pressure and vorticity fields. The transformation of the kinetic energy field at the isobaric surface of 850 hPa can serve as an indicator of the energy transfer between the cyclones. The influence of islands on the hurricane Gustav resulting in certain changes in the structure of vorticity, wind speed and kinetic energy fields is considered.

Diagnosis of the interaction of tropical cyclones

At present the mutual influence of tropical cyclones (TCs) has been investigated to a much lesser extent than the cyclones themselves. Most frequently, such investigations are restricted to the study of the influence of the interaction of two TCs on their motion. However, actually, the mutual influence of TCs is much more diverse. For example, each cyclone alters the state of the medium (in particular, decreases the heat store of the upper ocean layer), i.e., affects the subsequent cyclones. Under conditions of a limited energy resource of the medium, cyclones, existing simultaneously, “compete,” to a degree, with each other. These and other similar circumstances have made it practical to consider tropical cyclones and the environment as interdependent elements of a complex open system. This study considers two versions of nonlinear models describing the interaction of TCs with the upper ocean layer and with one another similarly to a number of well-known and verified models of synergetics (interaction of populations, dynamics of optical quantum generators). It is shown that the models reproduce some very important qualitative features of the evolution of TC intensity.

On the interaction of tropical‐cyclone‐scale vortices. IV: Baroclinic vortices

AbstractThe binary interaction of tropical cyclones is investigated using a three‐dimensional primitive‐equation model. The extended anticyclonic circulations in the upper troposphere merge at very large vortex‐separation distances. For the cyclonic component in the lower troposphere, we find three fundamental modes of interaction separated by two critical separation distances: a mutual approach separation (MAS) and a mutual merger separation (MMS). We suggest that failure to identify these modes may have caused some confusion in interpreting previous baroclinic interaction studies.The MAS delineates vortices that approach each other from those that move on divergent orbits. The approach phase consists of steady radial movement and gradual acceleration, with deformation of the outer vorticity structure of each vortex but little change to their cores. In contrast to barotropic studies, the MAS is much larger than the radius at which the potential‐vorticity gradient of each vortex changes sign. Vortex tilting associated with the vertical shear of the azimuthal winds from the opposing vortex and secondary circulations associated with diabatic heating increases the mutual vortex attraction. The presence of an earth‐vorticity gradient reduces this attraction slightly, but also introduces considerable sensitivity to vortex orientation. When all physical processes are included, we find an MAS of around 1000 km with a scatter of several hundred km, which agrees well with observational studies.Approach occurs with little change in the vortex cores until they reach the MMS. Merger then occurs very rapidly, usually within several hours, and follows that described in parts II and III for barotropic vortices. The MMS is approximately three times the equivalent vortex‐patch radius for the cyclones; it is slightly reduced by diabatic heating, but it is largely independent of the earth‐vorticity gradient. The vortices experience a slight weakening during the approach and initial merger stages. However, with diabatic heating, rapid intensification follows merger; such intensification may have implications for rapid development of tropical cyclones.