Radar observations of tropical cyclones over the Indian Seas

ABSTRACT. A review is presented of the radar observation of tropical cyclones in the Indian seas. The use of radar in operational cyclone tracking and forecasting as well as the knowledge gained from radar observations of the structure, wind and rainfall distribution and motion of cyclones are discussed. In the context of the expected introduction of operational Doppler ra1ars in India, the future prospects in the use of radar for operations and research are outlined. Some important areas where our understanding of cyclones can be improved by studies with radar in conjunction with other observations are listed.

Sources and transport pathways of precipitating waters in cold-season deep North Atlantic cyclones

Extratropical cyclones are responsible for a large share of precipitation at mid-latitudes and they profoundly impact the characteristics of the water cycle. In this study, we use the ERA5 reanalysis and a cyclone tracking scheme combined with a Lagrangian diagnostic to identify the sources of moisture precipitating close to the center of 676 deep North Atlantic cyclones in winters 1979 to 2018. Moisture uptakes occur pre-dominantly in originally cold and dry air heated over the North Atlantic, in particular, over the warm waters of the Gulf Stream, whereas more remote sources from land or the subtropics are less important. Analysing the dynamical environment of moisture uptakes, we find that moisture precipitating during the cyclone intensification phase originates in the pre-cyclone environment in the cold sectors of preceding cyclones and the cyclone-anticyclone interaction zone. These moisture sources are linked to the cyclone’s ascent regions via the so-called feeder airstream, a north-easterly cyclone-relative flow that arises due to the cyclone propagation exceeding the advection by the low-level background flow. During the decay phase more and more of the moisture originates in the cyclone’s own cold sector. Consequently, the residence time of precipitating waters in cyclones is short (median of ≈ 2 days) and transport distances are typically less than the distance travelled by the cyclone itself. These findings emphasize the importance of pre-conditioning by surface fluxes in the pre-cyclone environment for the formation of precipitation in cyclones, and suggest an important role for the hand-over of moisture from one cyclone to the next within a storm track.

Changes in cyclone circulation and storm tracks under different future climate scenarios

<p>Extratropical cyclones have the potential to cause large damages across the mid-latitudes. Future climate change is projected to have a large impact on the location of the storm tracks, and the frequency of these cyclones, however the sign and magnitude of these responses has been uncertain for regions near the end of the storm tracks in previous coupled and idealized modelling studies.</p><p> </p><p>Through the use of a Lagrangian cyclone tracking method we quantify changes in the storm tracks for both summer and winter seasons in both hemispheres for four future climate scenarios using a number of CMIP6 models. A cyclone compositing technique is employed to identify changes in cyclone circulation for the strongest cyclones in the lower, middle, and upper troposphere. We identify an intensification of the cyclone circulation in all seasons, apart from NH summer, where a weakening is detected. Cyclone size is also projected to increase, with a widening of the pressure and wind fields.</p><p> </p><p>These results have significant implications from a socio-economic perspective. Despite a projected decrease in cyclone numbers, an increase in severity may lead to more drastic windstorms and larger impacts across heavily populated regions of the mid-latitudes.</p>

An Overview of the Extratropical Storm Tracks in CMIP6 Historical Simulations

The representation of the winter and summer extratropical storm tracks in both hemispheres is evaluated in detail for the available models in phase 6 of the Coupled Model intercomparison Project (CMIP6). The state of the storm tracks from 1979 to 2014 is compared to that in ERA5 using a Lagrangian objective cyclone tracking algorithm. It is found that the main biases present in the previous generation of models (CMIP5) still persist, albeit to a lesser extent. The equatorward bias around the SH is much reduced and there appears to be some improvement in mean biases with the higher-resolution models, such as the zonal tilt of the North Atlantic storm track. Low-resolution models have a tendency to underestimate the frequency of high-intensity cyclones with all models simulating a peak intensity that is too low for cyclones in the SH. Explosively developing cyclones are underestimated across all ocean basins and in both hemispheres. In particular the models struggle to capture the rapid deepening required for these cyclones. For all measures, the CMIP6 models exhibit an overall improvement compared to the previous generation of CMIP5 models. In the NH most improvements can be attributed to increased horizontal resolution, whereas in the SH the impact of resolution is less apparent and any improvements are likely a result of improved model physics.

Cyclones density and characteristics in different reanalyses dataset over South America

<p>Cyclones developing over and at the eastern coast of South America impact extreme events over the region. Understanding the present climate is crucial to assess future extremes tendencies, which are important for engineering constructions over the southeast Brazil basin. To evaluate these systems in climate change scenarios it is important to study their preferred region of formation and trajectories in the present climate. Therefore, in this study we tracked cyclones in a period from 1979 to 2018 (present climate) using different reanalyses dataset (CFSR, ERA-Interim and ERA5), pointing out the main cyclogenetic regions affecting South America and discussing the main differences between the different dataset. As a preliminary result, the cyclone tracking shows a higher number of systems in CFSR than in ERA-Interim, which would be explained by the finer resolution of CFSR.  Annually, this difference is about 6%, and seasonally, the difference is smaller in summer (3.5%) and similar (~7%) for the other seasons. The reanalyses identify basically the same four cyclogenetic regions, however, there are differences in the density center position. Other features as lifetime, intensity, traveled distance, and wind extremes associated with the cyclones will be also discussed.</p>

Significance of Wind-Pressure Relation during Bay of Bengal Cyclones

Cyclone is a natural disaster that blows Over Bay of Bengal (BoB) and makes masses of devastation. Assessment of its characteristics and prediction of its mobility are extremely difficult tasks. Wind and pressure are the most significant factors that decide cyclone genesis, propagation and intensity. Physical understanding of the relation between two significant parameters during cyclone is very complicated and is elusive through modelling and prediction. Data sourced from International Best Track Archive for Climate Stewardship (IBTrACS) were analyzed to know wind and pressure relation and cyclone tracking. Cyclone spatial wind pattern is determined using the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). Analysis shows that wind and pressure are related inversely and is complex in nature. Spatial analysis using MERRA-2 demonstrates asymmetric wind pattern. IBTrACS data (from 2005 to 2016) show the majority of the cyclone intensity is concentrated on north-eastern side of BoB which fact could be attributed to high subsurface heat storage. Inter comparison of different cyclones during the period 2005-2016 was also made and found in support of the wind pressure relation.

Best Practices for Increasing Data Return: Case Study From Indian Ocean Observation Network

Sustained real-time ocean observation systems using moored data buoys are vital for understanding ocean dynamics and variability, which are essential for improving oceanographic services including weather prediction, ocean state forecast, cyclone tracking, tsunami monitoring, and climate change studies. This paper describes the significant rapid restoration techniques implemented to increase the availability of the Indian Ocean observation networks over the past two decades. The efforts have helped in achieving availability of 97.9%, 82.3%, and 98.7% for the meteorological sensors, subsea surface oceanographic sensors, and tsunami buoy network, respectively.

Segmentation of Tropical Cyclone Eye using Satellite Infrared Images

The tropical cyclones are destructive weather systems and are known for their devastating effects during landfall. Cyclone tracking is one of the important tasks for the meteorologist. The eye of the tropical cyclone is the most remarkable feature. The eye of the cyclone is the roughly circular area extending over 30 - 65 km in diameter. The deepest convection is found around the eyewall for some tens of kilometers. The eye grows deeper when the cyclone becomes heavy and the winds speed grows high. In this study, the data from the 1995 - 2016 of the CIRA imagery for the tropical cyclone of the Bay of Bengal basin is analyzed and the model is developed to determine the eye of the cyclone. The segmented eye features are fed into the Rule Based Classifier which classifies the tropical cyclone images based on the presence and absence of the eye.