scholarly journals Evolution of GLM-Observed Total Lightning in Hurricane Maria (2017) during the Period of Maximum Intensity

2018 ◽  
Vol 146 (6) ◽  
pp. 1641-1666 ◽  
Author(s):  
Alexandre O. Fierro ◽  
Stephanie N. Stevenson ◽  
Robert M. Rabin
Keyword(s):  
Inner Core ◽  
Surface Wind ◽  
Outer Region ◽  
Low Frequency ◽  
Surface Wind Speed ◽  
Major Hurricane ◽  
Complex Relationships ◽  
Total Lightning ◽  
Rate Ratios ◽  
Correlation Statistics

Total lightning data obtained from the Geostationary Lightning Mapper (GLM) were analyzed to present a first glimpse of relationships with intensity variations and convective evolution in Hurricane Maria (2017). The GLM has made it possible, for the first time, to analyze total lightning within a major hurricane for a long period, far from ground-based detection networks. It is hoped that these observations could enlighten some of the complex relationships existing between intensity fluctuations and the distribution of electrified convection in these systems. Prior to rapidly intensifying from a category 1 to category 5 storm, Maria produced few inner-core flashes. Increases in total lightning in the inner core ( r ≤ 100 km) occurred during both the beginning and end of an intensification cycle, while lightning increases in the outer region (100 < r ≤ 500 km) occurred earlier in the intensification cycle and during weakening. Throughout the analysis period, the largest lightning rates in the outer region were consistently located in the southeastern quadrant, a pattern consistent with modeling studies of electrification within hurricanes. Lightning in the inner core was generally tightly clustered within a 50-km radius from the center and most often found in the southeastern portion of the eyewall, which is atypical. Bootstrapped correlation statistics revealed that the most robust and systematic relationship with storm intensity was obtained for inner-core lightning and maximum surface wind speed. A brief comparison between flash rates from GLM and a very low-frequency ground-based network revealed that not all lightning peaks are seen equally, with hourly flash-rate ratios between both systems sometimes exceeding two orders of magnitude.

Effect of a Low-frequency Vortex on the Size of Typhoon Lan (2017)

2020 ◽  
Author(s):  
Mengyuan Ma ◽  
Tim Li
Keyword(s):  
Large Scale ◽  
Surface Wind ◽  
Radial Profile ◽  
Outer Region ◽  
Wrf Model ◽  
Low Frequency ◽  
Vertical Wind Shear ◽  
Surface Wind Speed ◽  
Tangential Wind ◽  
Set Up

AbstractTyphoon Lan (2017) was one of the largest tropical cyclone (TC) in the western North Pacific (WNP), and it was developed in a low-frequency (10-90-day filtered) large-scale cyclonic vortex environment. The physical mechanism responsible for the TC unusual size was investigated through idealized numerical experiments with the Weather Research and Forecasting (WRF) model. Sensitivity experiments showed that the low-frequency cyclonic circulation played an important role in modulating the TC size through the following three processes. Firstly, it weakened the background vertical wind shear and provided a favorable condition for a more rapid growth of Lan. Secondly, it strengthened a vorticity aggregation process through enhanced background vorticity. As a result, a stronger and more organized TC core was quickly set up, which strengthened the TC intensity and expanded its size. Thirdly, it enhanced the total surface wind speed and surface latent heat flux, strengthening convective instability in the outer region through increased moisture. The development of the outer rain band expanded the radial profile of diabatic heating, leading to greater low-level inflow and tangential wind acceleration in the outer region and thus a large TC size.

Intensification of Tilted Tropical Cyclones Over Relatively Cool and Warm Oceans in Idealized Numerical Simulations

2021 ◽  
Author(s):  
David A. Schecter
Keyword(s):  
Relative Humidity ◽  
Tropical Cyclones ◽  
Inner Core ◽  
Structural Parameters ◽  
Deep Convection ◽  
Surface Wind ◽  
Vertical Wind Shear ◽  
Surface Wind Speed ◽  
Cloud Resolving Model ◽  
Complete Alignment

Abstract A cloud resolving model is used to examine the intensification of tilted tropical cyclones from depression to hurricane strength over relatively cool and warm oceans under idealized conditions where environmental vertical wind shear has become minimal. Variation of the SST does not substantially change the time-averaged relationship between tilt and the radial length scale of the inner core, or between tilt and the azimuthal distribution of precipitation during the hurricane formation period (HFP). By contrast, for systems having similar structural parameters, the HFP lengthens superlinearly in association with a decline of the precipitation rate as the SST decreases from 30 to 26 °C. In many simulations, hurricane formation progresses from a phase of slow or neutral intensification to fast spinup. The transition to fast spinup occurs after the magnitudes of tilt and convective asymmetry drop below certain SST-dependent levels following an alignment process explained in an earlier paper. For reasons examined herein, the alignment coincides with enhancements of lower–middle tropospheric relative humidity and lower tropospheric CAPE inward of the radius of maximum surface wind speed rm. Such moist-thermodynamic modifications appear to facilitate initiation of the faster mode of intensification, which involves contraction of rm and the characteristic radius of deep convection. The mean transitional values of the tilt magnitude and lower–middle tropospheric relative humidity for SSTs of 28-30 °C are respectively higher and lower than their counterparts at 26 °C. Greater magnitudes of the surface enthalpy flux and core deep-layer CAPE found at the higher SSTs plausibly compensate for less complete alignment and core humidification at the transition time.

A Coupled-Pixel Model (CPM) Atmospheric Retrieval Algorithm for High-Resolution Imagers

2015 ◽  
Vol 32 (10) ◽  
pp. 1866-1879 ◽  
Author(s):  
Mary Morris ◽  
Christopher S. Ruf
Keyword(s):  
Wind Speed ◽  
Rain Rate ◽  
Microwave Radiometer ◽  
Surface Wind ◽  
Low Frequency ◽  
Surface Wind Speed ◽  
Retrieval Algorithm ◽  
Single Column ◽  
Simplifying Assumptions ◽  
Cross Track

AbstractLow-frequency passive microwave observations allow for oceanic remote sensing of surface wind speed and rain rate from spaceborne and airborne platforms. For most instruments, the modeling of contributions of rain absorption and reemission in a particular field of view is simplified by the observing geometry. However, the simplifying assumptions that can be applied in most applications are not always valid for the scenes that the airborne Hurricane Imaging Radiometer (HIRAD) regularly observes. Collocated Stepped Frequency Microwave Radiometer (SFMR) and HIRAD observations of Hurricane Earl (2010) indicate that retrieval algorithms based on the usual simplified model, referred to here as the decoupled-pixel model (DPM), are not able to resolve two neighboring rainbands at the edge of HIRAD’s swath. The DPM does not allow for the possibility that a single column of atmosphere can affect the observations at multiple cross-track positions. This motivates the development of a coupled-pixel model (CPM) that is developed and tested in this paper. Simulated observations as well as HIRAD’s observations of Hurricane Earl (2010) are used to test the CPM algorithm. Key to the performance of the CPM algorithm is its ability to deconvolve the cross-track scene, as well as unscramble the signatures of surface wind speed and rain rate in HIRAD’s observations. While the CPM approach was developed specifically for HIRAD, other sensors could employ this method in similar complicated observing scenarios.

scholarly journals Estimating Tropical Cyclone Integrated Kinetic Energy with the CYGNSS Satellite Constellation

2017 ◽  
Vol 56 (1) ◽  
pp. 235-245 ◽  
Author(s):  
Mary Morris ◽  
Christopher S. Ruf
Keyword(s):  
Tropical Cyclone ◽  
Kinetic Energy ◽  
Tropical Cyclones ◽  
Measurement Errors ◽  
Inner Core ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Satellite System ◽  
Insurance Companies ◽  
High Temporal Resolution

AbstractThe Cyclone Global Navigation Satellite System (CYGNSS) constellation is designed to provide observations of surface wind speed in and near the inner core of tropical cyclones with high temporal resolution throughout the storm’s life cycle. A method is developed for estimating tropical cyclone integrated kinetic energy (IKE) using CYGNSS observations. IKE is calculated for each geographically based quadrant out to an estimate of the 34-kt (1 kt = 0.51 m s−1) wind radius. The CYGNSS-IKE estimator is tested and its performance is characterized using simulated CYGNSS observations with realistic measurement errors. CYGNSS-IKE performance improves for stronger, more organized storms and with increasing number of observations over the extent of the 34-kt radius. Known sampling information can be used for quality control. While CYGNSS-IKE is calculated for individual geographic quadrants, using a total-IKE—a sum over all quadrants—improves performance. CYGNSS-IKE should be of interest to operational and research meteorologists, insurance companies, and others interested in the destructive potential of tropical cyclones developing in data-sparse regions, which will now be covered by CYGNSS. The CYGNSS-IKE product will be available for the 2017 Atlantic Ocean hurricane season.

Dependence of Superintensity of Tropical Cyclones on SST in Axisymmetric Numerical Simulations

2020 ◽  
Vol 148 (12) ◽  
pp. 4767-4781
Author(s):  
Yuanlong Li ◽  
Yuqing Wang ◽  
Yanluan Lin ◽  
Rong Fei
Keyword(s):  
Numerical Simulations ◽  
Tropical Cyclones ◽  
North Atlantic ◽  
Diabatic Heating ◽  
Surface Wind ◽  
Outer Region ◽  
Surface Wind Speed ◽  
Convective Activity ◽  
The North ◽  
Atmospheric Sounding

AbstractThis study revisits the superintensity of tropical cyclones (TCs), which is defined as the excess maximum surface wind speed normalized by the corresponding theoretical maximum potential intensity (MPI), based on ensemble axisymmetric numerical simulations, with the focus on the dependence of superintensity on the prescribed sea surface temperature (SST) and the initial environmental atmospheric sounding. Results show a robust decrease of superintensity with increasing SST regardless of being in experiments with an SST-independent initial atmospheric sounding or in those with the SST-dependent initial atmospheric soundings as in nature sorted for the western North Pacific and the North Atlantic. It is found that the increase in either convective activity (and thus diabatic heating) in the TC outer region or theoretical MPI or both with increasing SST could reduce the superintensity. For a given SST-independent initial atmospheric sounding, the strength of convective activity in the TC outer region increases rapidly with increasing SST due to the rapidly increasing air–sea thermodynamic disequilibrium (and thus potential convective instability) with increasing SST. As a result, the decrease of superintensity with increasing SST in the SST-independent sounding experiments is dominated by the increasing convective activity in the TC outer region and is much larger than that in the SST-dependent sounding experiments, and the TC intensity becomes sub-MPI at relatively high SSTs in the former. Due to the marginal increasing tendency of convective activity in the TC outer region, the decrease of superintensity in the latter is dominated by the increase in theoretical MPI with increasing SST.

In-Orbit Performance of the Constellation of CYGNSS Hurricane Satellites

2019 ◽  
Vol 100 (10) ◽  
pp. 2009-2023 ◽  
Author(s):  
Christopher Ruf ◽  
Shakeel Asharaf ◽  
Rajeswari Balasubramaniam ◽  
Scott Gleason ◽  
Timothy Lang ◽  
...  
Keyword(s):  
Wind Speed ◽  
Tropical Cyclones ◽  
Dynamic Range ◽  
Surface Wind ◽  
Low Frequency ◽  
Surface Wind Speed ◽  
Satellite System ◽  
Low Earth Orbit ◽  
Current Status ◽  
Temporal Sampling

AbstractThe NASA Cyclone Global Navigation Satellite System (CYGNSS) constellation of eight satellites was successfully launched into low Earth orbit on 15 December 2016. Each satellite carries a radar receiver that measures GPS signals scattered from the surface. Wind speed over the ocean is determined from distortions in the signal caused by wind-driven surface roughness. GPS operates at a sufficiently low frequency to allow for propagation through all precipitation, including the extreme rain rates present in the eyewall of tropical cyclones. The spacing and orbit of the satellites were chosen to optimize frequent sampling of tropical cyclones. In this study, we characterize the CYGNSS ocean surface wind speed measurements by their uncertainty, dynamic range, sensitivity to precipitation, spatial resolution, spatial and temporal sampling, and data latency. The current status of each of these properties is examined and potential future improvements are discussed. In addition, examples are given of current science investigations that make use of the data.

scholarly journals Assimilation of Himawari-8 Imager Radiance Data with the WRF-3DVAR system for the prediction of Typhoon Soulder

2020 ◽  
Author(s):  
Dongmei Xu ◽  
Aiqing Shu ◽  
Zhankui Zhang
Keyword(s):  
Inner Core ◽  
Surface Wind ◽  
Three Dimensional ◽  
Surface Wind Speed ◽  
Background Field ◽  
Japan Meteorological Agency ◽  
Near Surface ◽  
Frequency Space ◽  
Geostationary Meteorological Satellite ◽  
Typhoon Season

Abstract. Himawari-8 is a new generation geostationary meteorological satellite launched by Japan Meteorological Agency (JMA). It carries the Advanced Himawari imager (AHI) onboard, which can continuously monitor high-impact weather events with high frequency space and time. The assimilation of AHI was implemented with the framework of the mesoscale numerical model WRF and its three-dimensional variational assimilation system (3DVAR) for the analysis and prediction of typhoon Soudelor in the Pacific Typhoon season in 2015. The effective assimilation of AHI Imager data in tropical cyclone with rapid intensify development has been realized. The results show that after assimilating the AHI imager data under clear sky conditions, the typhoon position in the background field in the model is effectively corrected compared with the control experiment without AHI data. It is found that assimilation of AHI imager data is able to improve the analyses of the water vapor and wind in typhoon inner-core region. The analyses and forecast of the typhoon minimum sea level pressure, the maximum near-surface wind speed, and the typhoon track are further improved．

scholarly journals Impact of CYGNSS Ocean Surface Wind Speeds on Numerical Simulations of a Hurricane in Observing System Simulation Experiments

2017 ◽  
Vol 34 (2) ◽  
pp. 375-383 ◽  
Author(s):  
Shixuan Zhang ◽  
Zhaoxia Pu ◽  
Derek J. Posselt ◽  
Robert Atlas
Keyword(s):  
Numerical Simulations ◽  
Inner Core ◽  
System Simulation ◽  
Surface Wind ◽  
Ocean Surface ◽  
Surface Wind Speed ◽  
Surface Fluxes ◽  
Hurricane Track ◽  
Ocean Surface Wind ◽  
The Impact

AbstractThe NASA Cyclone Global Navigation Satellite System (CYGNSS) was launched in late 2016. It will make available frequent ocean surface wind speed observations throughout the life cycle of tropical storms and hurricanes. In this study, the impact of CYGNSS ocean surface winds on numerical simulations of a hurricane case is assessed with a research version of the Hurricane Weather Research and Forecasting Model and a Gridpoint Statistical Interpolation analysis system in a regional observing system simulation experiment framework. Two different methods for reducing the CYGNSS data volume were tested: one in which the winds were thinned and one in which the winds were superobbed.The results suggest that assimilation of the CYGNSS winds has great potential to improve hurricane track and intensity simulations through improved representations of the surface wind fields, hurricane inner-core structures, and surface fluxes. The assimilation of the superobbed CYGNSS data seems to be more effective in improving hurricane track forecasts than thinning the data.

scholarly journals Relationships between Electrification and Storm-Scale Properties Based on Idealized Simulations of an Intensifying Hurricane-Like Vortex

2018 ◽  
Vol 75 (2) ◽  
pp. 657-674 ◽  
Author(s):  
Alexandre O. Fierro ◽  
Edward R. Mansell
Keyword(s):  
Inner Core ◽  
Outer Region ◽  
Significant Negative Correlation ◽  
Linear Increase ◽  
Lightning Flash ◽  
Linear Relationships ◽  
Pressure Trace ◽  
Scale Properties ◽  
Correlation Statistics ◽  
Ice Water

AbstractThis study investigates relationships between storm-scale properties and the electrification and lightning of two simulations of an intensifying idealized tropical cyclone (TC) using the cloud-resolving Collaborative Model for Multiscale Atmospheric Simulation (COMMAS). To produce an intensifying storm, an initial weak TC is subjected to a linear increase in sea surface temperature.As the TC intensifies, lightning flash rates increase in both the inner core (r ≤ 100 km) and outer region (100 &lt; r ≤ 300 km). As time progresses, lightning in the outer region gradually decreases, while the inner-core lightning remains relatively steady. Bootstrapped correlation statistics using 1000 random samples between the pressure trace and time series of lightning rates shows a statistically significant negative correlation between inner-core lightning and TC intensification. Lightning rates in the outer bands were found to lag minimum surface pressure by 12 h.The increases in lightning in both the inner core and outer region coincided well with increases in 0.5 g kg−1 graupel and 5 m s−1 updraft volumes in each respective region. Correlation statistics with selected kinematic and microphysical variables known to be associated with lightning in thunderstorms, such as the ice water path, integrated updraft volume, and graupel volume, revealed that their increase in the inner core indicated an ongoing deepening, similar to the lightning. Trends in these proxy variables in the outer bands were also found to lag TC intensification by 12 h.Overall, the best linear relationships with lightning in either the inner core or the outer region were obtained with the 0.5 g kg−1 graupel volume and total graupel mass.

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