scholarly journals Lightning in Eastern North Pacific Tropical Cyclones: A Comparison to the North Atlantic

2015 ◽  
Vol 144 (1) ◽  
pp. 225-239 ◽  
Author(s):  
Stephanie N. Stevenson ◽  
Kristen L. Corbosiero ◽  
Sergio F. Abarca
Keyword(s):  
Tropical Cyclones ◽  
North Atlantic ◽  
North Pacific ◽  
Wind Shear ◽  
Inner Core ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Intensity Change ◽  
The North ◽  
The North Atlantic

Abstract As global lightning detection has become more reliable, many studies have analyzed the characteristics of lightning in tropical cyclones (TCs); however, very few studies have examined flashes in eastern North Pacific (ENP) basin TCs. This study uses lightning detected by the World Wide Lightning Location Network (WWLLN) to explore the relationship between lightning and sea surface temperatures (SSTs), the diurnal cycle, the storm motion and vertical wind shear vectors, and the 24-h intensity change in ENP TCs during 2006–14. The results are compared to storms in the North Atlantic (NA). Higher flash counts were found over warmer SSTs, with 28°–30°C SSTs experiencing the highest 6-hourly flash counts. Most TC lightning flashes occurred at night and during the early morning hours, with minimal activity after local noon. The ENP peak (0800 LST) was slightly earlier than the NA (0900–1100 LST). Despite similar storm motion directions and differing vertical wind shear directions in the two basins, shear dominated the overall azimuthal lightning distribution. Lightning was most often observed downshear left in the inner core (0–100 km) and downshear right in the outer rainbands (100–300 km). A caveat to these relationships were fast-moving ENP TCs with opposing shear and motion vectors, in which lightning peaked downmotion (upshear) instead. Finally, similar to previous studies, higher flash densities in the inner core (outer rainbands) were associated with nonintensifying (intensifying) TCs. This last result constitutes further evidence in the efforts to associate lightning activity to TC intensity forecasting.

New Probabilistic Forecast Models for the Prediction of Tropical Cyclone Rapid Intensification

2011 ◽  
Vol 26 (5) ◽  
pp. 677-689 ◽  
Author(s):  
Christopher M. Rozoff ◽  
James P. Kossin
Keyword(s):  
Logistic Regression ◽  
North Atlantic ◽  
North Pacific ◽  
North Pacific Ocean ◽  
Vertical Wind Shear ◽  
Intensity Change ◽  
Rapid Intensification ◽  
The North ◽  
Skill Scores ◽  
The North Atlantic

Abstract The National Hurricane Center currently employs a skillful probabilistic rapid intensification index (RII) based on linear discriminant analysis of the environmental and satellite-derived features from the Statistical Hurricane Intensity Prediction Scheme (SHIPS) dataset. Probabilistic prediction of rapid intensity change in tropical cyclones is revisited here using two additional models: one based on logistic regression and the other on a naïve Bayesian framework. Each model incorporates data from the SHIPS dataset over both the North Atlantic and eastern North Pacific Ocean basins to provide the probability of exceeding the standard rapid intensification thresholds [25, 30, and 35 kt (24 h)−1] for 24 h into the future. The optimal SHIPS and satellite-based predictors of rapid intensification differ slightly between each probabilistic model and ocean basin, but each set of optimal predictors incorporates thermodynamic and dynamic aspects of the tropical cyclone’s environment (such as vertical wind shear) and its structure (such as departure from convective axisymmetry). Cross validation shows that both the logistic regression and Bayesian probabilistic models are skillful relative to climatology. Dependent testing indicates both models exhibit forecast skill that generally exceeds the skill of the present operational SHIPS-RII and a simple average of the probabilities provided by the logistic regression, Bayesian, and SHIPS-RII models provides greater skill than any individual model. For the rapid intensification threshold of 25 kt (24 h)−1, the three-member ensemble mean improves the Brier skill scores of the current operational SHIPS-RII by 33% in the North Atlantic and 52% in the eastern North Pacific.

scholarly journals Observation of Jet Stream Winds during NAWDEX and Characterization of Systematic Meteorological Analysis Errors

2020 ◽  
Vol 148 (7) ◽  
pp. 2889-2907 ◽  
Author(s):  
Andreas Schäfler ◽  
Ben Harvey ◽  
John Methven ◽  
James D. Doyle ◽  
Stephan Rahm ◽  
...  
Keyword(s):  
Wind Speed ◽  
North Atlantic ◽  
Wind Shear ◽  
Forecast Error ◽  
Vertical Wind Shear ◽  
Weather Forecast ◽  
Vertical Wind ◽  
Jet Stream ◽  
The North ◽  
The North Atlantic

Abstract Observations across the North Atlantic jet stream with high vertical resolution are used to explore the structure of the jet stream, including the sharpness of vertical wind shear changes across the tropopause and the wind speed. Data were obtained during the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) by an airborne Doppler wind lidar, dropsondes, and a ground-based stratosphere–troposphere radar. During the campaign, small wind speed biases throughout the troposphere and lower stratosphere of only −0.41 and −0.15 m s−1 are found, respectively, in the ECMWF and Met Office analyses and short-term forecasts. However, this study finds large and spatially coherent wind errors up to ±10 m s−1 for individual cases, with the strongest errors occurring above the tropopause in upper-level ridges. ECMWF and Met Office analyses indicate similar spatial structures in wind errors, even though their forecast models and data assimilation schemes differ greatly. The assimilation of operational observational data brings the analyses closer to the independent verifying observations, but it cannot fully compensate for the forecast error. Models tend to underestimate the peak jet stream wind, the vertical wind shear (by a factor of 2–5), and the abruptness of the change in wind shear across the tropopause, which is a major contribution to the meridional potential vorticity gradient. The differences are large enough to influence forecasts of Rossby wave disturbances to the jet stream with an anticipated effect on weather forecast skill even on large scales.

Tropical Cyclone Intensity Estimation in the North Atlantic Basin Using an Improved Deviation Angle Variance Technique

2012 ◽  
Vol 27 (5) ◽  
pp. 1264-1277 ◽  
Author(s):  
Elizabeth A. Ritchie ◽  
Genevieve Valliere-Kelley ◽  
Miguel F. Piñeros ◽  
J. Scott Tyo
Keyword(s):  
Root Mean Square ◽  
North Atlantic ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Mean Square ◽  
Deviation Angle ◽  
The North ◽  
Variance Technique ◽  
The North Atlantic

Abstract This paper describes results from an improvement to the objective deviation angle variance technique to estimate the intensity of tropical cyclones from satellite infrared imagery in the North Atlantic basin. The technique quantifies the level of organization of the infrared cloud signature of a tropical cyclone as an indirect measurement of its maximum wind speed. The major change described here is to use the National Hurricane Center’s best-track database to constrain the technique. Results are shown for the 2004–10 North Atlantic hurricane seasons and include an overall root-mean-square intensity error of 12.9 kt (6.6 m s−1, where 1 kt = 0.514 m s−1) and annual root-mean-square intensity errors ranging from 10.3 to 14.1 kt. A direct comparison between the previous version and the one reported here shows root-mean-square intensity error improvements in all years with a best improvement in 2009 from 17.9 to 10.6 kt and an overall improvement from 14.8 to 12.9 kt. In addition, samples from the 7-yr period are binned based on level of intensity and on the strength of environmental vertical wind shear as extracted from Statistical Hurricane Intensity Prediction Scheme (SHIPS) data. Preliminary results suggest that the deviation angle variance technique performs best at the weakest intensity categories of tropical storm through hurricane category 3, representing 90% of the samples, and then degrades in performance for hurricane categories 4 and 5. For environmental vertical wind shear, there is far less spread in the results with the technique performing better with increasing vertical wind shear.

scholarly journals Normalized Convective Characteristics of Tropical Cyclone Rapid Intensification Events in the North Atlantic and Eastern North Pacific

2018 ◽  
Vol 146 (4) ◽  
pp. 1133-1155 ◽  
Author(s):  
Michael S. Fischer ◽  
Brian H. Tang ◽  
Kristen L. Corbosiero ◽  
Christopher M. Rozoff
Keyword(s):  
Tropical Cyclone ◽  
North Atlantic ◽  
North Pacific ◽  
Forecast Skill ◽  
Passive Microwave ◽  
Intensity Change ◽  
Rapid Intensification ◽  
Brightness Temperatures ◽  
The North ◽  
The North Atlantic

The relationship between tropical cyclone (TC) convective characteristics and TC intensity change is explored using infrared and passive microwave satellite imagery of TCs in the North Atlantic and eastern North Pacific basins from 1989 to 2016. TC intensity change episodes were placed into one of four groups: rapid intensification (RI), slow intensification (SI), neutral (N), and weakening (W). To account for differences in the distributions of TC intensity among the intensity change groups, a normalization technique is introduced, which allows for the analysis of anomalous TC convective characteristics and their relationship to TC intensity change. A composite analysis of normalized convective parameters shows anomalously cold infrared and 85-GHz brightness temperatures, as well as anomalously warm 37-GHz brightness temperatures, in the upshear quadrants of the TC are associated with increased rates of TC intensification, including RI. For RI episodes in the North Atlantic basin, an increase in anomalous liquid hydrometeor content precedes anomalous ice hydrometeor content by approximately 12 h, suggesting convection deep enough to produce robust ice scattering is a symptom of, rather than a precursor to, RI. In the eastern North Pacific basin, the amount of anomalous liquid and ice hydrometeors increases in tandem near the onset of RI. Normalized infrared and passive microwave brightness temperatures can be utilized to skillfully predict episodes of RI, as the forecast skill of RI episodes using solely normalized convective parameters is comparable to the forecast skill of RI episodes by current operational statistical models.

scholarly journals Structural and Intensity Changes of Hurricane Bret (1999). Part I: Environmental Influences

2008 ◽  
Vol 136 (11) ◽  
pp. 4320-4333 ◽  
Author(s):  
Alexander Lowag ◽  
Michael L. Black ◽  
Matthew D. Eastin
Keyword(s):  
Wind Shear ◽  
Inner Core ◽  
Critical Role ◽  
Heat Content ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Mean Values ◽  
The North ◽  
Intensity Changes ◽  
Environmental Prediction

Abstract Hurricane Bret underwent a rapid intensification (RI) and subsequent weakening between 1200 UTC 21 August and 1200 UTC 22 August 1999 before it made landfall on the Texas coast 12 h later. Its minimum sea level pressure fell 35 hPa from 979 to 944 hPa within 24 h. During this period, aircraft of the National Oceanic and Atmospheric Administration (NOAA) flew several research missions that sampled the environment and inner core of the storm. These datasets are combined with gridded data from the National Centers for Environmental Prediction (NCEP) Global Model and the NCEP–National Center for Atmospheric Research (NCAR) reanalyses to document Bret’s atmospheric and oceanic environment as well as their relation to the observed structural and intensity changes. Bret’s RI was linked to movement over a warm ocean eddy and high sea surface temperatures (SSTs) in the Gulf of Mexico coupled with a concurrent decrease in vertical wind shear. SSTs at the beginning of the storm’s RI were approximately 29°C and steadily increased to 30°C as it moved to the north. The vertical wind shear relaxed to less than 10 kt during this time. Mean values of oceanic heat content (OHC) beneath the storm were about 20% higher at the beginning of the RI period than 6 h prior. The subsequent weakening was linked to the cooling of near-coastal shelf waters (to between 25° and 26°C) by prestorm mixing combined with an increase in vertical wind shear. The available observations suggest no intrusion of dry air into the circulation core contributed to the intensity evolution. Sensitivity studies with the Statistical Hurricane Intensity Prediction Scheme (SHIPS) model were conducted to quantitatively describe the influence of environmental conditions on the intensity forecast. Four different cases with modified vertical wind shear and/or SSTs were studied. Differences between the four cases were relatively small because of the model design, but the greatest intensity changes resulted for much cooler prescribed SSTs. The results of this study underscore the importance of OHC and vertical wind shear as significant factors during RIs; however, internal dynamical processes appear to play a more critical role when a favorable environment is present.

Seasonal forecasting of intense tropical cyclones over the North Atlantic and the western North Pacific basins

2016 ◽  
Vol 47 (9-10) ◽  
pp. 3063-3075 ◽  
Author(s):  
Woosuk Choi ◽  
Chang-Hoi Ho ◽  
Chun-Sil Jin ◽  
Jinwon Kim ◽  
Song Feng ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
North Atlantic ◽  
North Pacific ◽  
Western North Pacific ◽  
Seasonal Forecasting ◽  
The North ◽  
The North Atlantic

scholarly journals A Statistical Analysis of the Effects of Vertical Wind Shear on Tropical Cyclone Intensity Change over the Western North Pacific

2015 ◽  
Vol 143 (9) ◽  
pp. 3434-3453 ◽  
Author(s):  
Yuqing Wang ◽  
Yunjie Rao ◽  
Zhe-Min Tan ◽  
Daria Schönemann
Keyword(s):  
North Pacific ◽  
Wind Shear ◽  
Western North Pacific ◽  
Deep Layer ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Intensity Change ◽  
Low Level ◽  
Typhoon Season ◽  
Translational Speed

Abstract The effect of vertical wind shear (VWS) between different pressure levels on TC intensity change is statistically analyzed based on the best track data of tropical cyclones (TCs) in the western North Pacific (WNP) from the Joint Typhoon Warning Center (JTWC) and the ECMWF interim reanalysis (ERA-Interim) data during 1981–2013. Results show that the commonly used VWS measure between 200 and 850 hPa is less representative of the attenuating deep-layer shear effect than that between 300 and 1000 hPa. Moreover, the authors find that the low-level shear between 850 (or 700) and 1000 hPa is more negatively correlated with TC intensity change than any deep-layer shear during the active typhoon season, whereas deep-layer shear turns out to be more influential than low-level shear during the remaining less active seasons. Further analysis covering all seasons exhibits that a TC has a better chance to intensify than to decay when the deep-layer shear is lower than 7–9 m s−1 and the low-level shear is below 2.5 m s−1. The probability for TCs to intensify and undergo rapid intensification (RI) increases with decreasing VWS and increasing sea surface temperature (SST). TCs moving at slow translational speeds (less than 3 m s−1) intensify under relatively weaker VWS than TCs moving at intermediate translational speeds (3–8 m s−1). The probability of RI becomes lower than that of rapid decaying (RD) when the translational speed is larger than 8 m s−1. Most TCs tend to decay when the translational speed is larger than 12 m s−1 regardless of the shear condition.

Are Tropical Cyclones Less Effectively Formed by Easterly Waves in the Western North Pacific than in the North Atlantic?

2008 ◽  
Vol 136 (11) ◽  
pp. 4527-4540 ◽  
Author(s):  
Tsing-Chang Chen ◽  
Shih-Yu Wang ◽  
Ming-Cheng Yen ◽  
Adam J. Clark
Keyword(s):  
Tropical Cyclones ◽  
North Atlantic ◽  
North Pacific ◽  
Western North Pacific ◽  
Monsoon Trough ◽  
Easterly Waves ◽  
The North ◽  
Easterly Wave ◽  
Monsoon Gyre ◽  
The North Atlantic

Abstract It has been observed that the percentage of tropical cyclones originating from easterly waves is much higher in the North Atlantic (∼60%) than in the western North Pacific (10%–20%). This disparity between the two ocean basins exists because the majority (71%) of tropical cyclogeneses in the western North Pacific occur in the favorable synoptic environments evolved from monsoon gyres. Because the North Atlantic does not have a monsoon trough similar to the western North Pacific that stimulates monsoon gyre formation, a much larger portion of tropical cyclogeneses than in the western North Pacific are caused directly by easterly waves. This study also analyzed the percentage of easterly waves that form tropical cyclones in the western North Pacific. By carefully separating easterly waves from the lower-tropospheric disturbances generated by upper-level vortices that originate from the tropical upper-tropospheric trough (TUTT), it is observed that 25% of easterly waves form tropical cyclones in this region. Because TUTT-induced lower-tropospheric disturbances often become embedded in the trade easterlies and resemble easterly waves, they have likely been mistakenly identified as easterly waves. Inclusion of these “false” easterly waves in the “true” easterly wave population would result in an underestimation of the percentage of easterly waves that form tropical cyclones, because the TUTT-induced disturbances rarely stimulate tropical cyclogenesis. However, an analysis of monsoon gyre formation mechanisms over the western North Pacific reveals that 82% of monsoon gyres develop through a monsoon trough–easterly wave interaction. Thus, it can be inferred that 58% (i.e., 82% × 71%) of tropical cyclones in this region are an indirect result of easterly waves. Including the percentage of tropical cyclones that form directly from easterly waves (∼25%), it is found that tropical cyclones formed directly and indirectly from easterly waves account for over 80% of tropical cyclogeneses in the western North Pacific. This is more than the percentage that has been documented by previous studies in the North Atlantic.

scholarly journals Objective Identification of Annular Hurricanes

2008 ◽  
Vol 23 (1) ◽  
pp. 17-28 ◽  
Author(s):  
John A. Knaff ◽  
Thomas A. Cram ◽  
Andrea B. Schumacher ◽  
James P. Kossin ◽  
Mark DeMaria
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
North Atlantic ◽  
North Pacific ◽  
Probability Of Detection ◽  
Linear Discriminant ◽  
The North ◽  
The North Atlantic ◽  
Special Algorithm ◽  
Central North Pacific

Abstract Annular hurricanes are a subset of intense tropical cyclones that have been shown in previous work to be significantly stronger, to maintain their peak intensities longer, and to weaken more slowly than average tropical cyclones. Because of these characteristics, they represent a significant forecasting challenge. This paper updates the list of annular hurricanes to encompass the years 1995–2006 in both the North Atlantic and eastern–central North Pacific tropical cyclone basins. Because annular hurricanes have a unique appearance in infrared satellite imagery, and form in a specific set of environmental conditions, an objective real-time method of identifying these hurricanes is developed. However, since the occurrence of annular hurricanes is rare (∼4% of all hurricanes), a special algorithm to detect annular hurricanes is developed that employs two steps to identify the candidates: 1) prescreening the data and 2) applying a linear discriminant analysis. This algorithm is trained using a dependent dataset (1995–2003) that includes 11 annular hurricanes. The resulting algorithm is then independently tested using datasets from the years 2004–06, which contained an additional three annular hurricanes. Results indicate that the algorithm is able to discriminate annular hurricanes from tropical cyclones with intensities greater than 84 kt (43.2 m s−1). The probability of detection or hit rate produced by this scheme is shown to be ∼96% with a false alarm rate of ∼6%, based on 1363 six-hour time periods with a tropical cyclone with an intensity greater than 84 kt (1995–2006).

scholarly journals Climate Changes of Atlantic Tropical Cyclone Formation Derived from Twentieth-Century Reanalysis

2013 ◽  
Vol 26 (22) ◽  
pp. 8995-9005 ◽  
Author(s):  
Ruifang Wang ◽  
Liguang Wu
Keyword(s):  
Global Warming ◽  
North Atlantic ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
The United States ◽  
Tropical Atlantic ◽  
The North ◽  
The Caribbean ◽  
The North Atlantic ◽  
Twentieth Century Reanalysis

Abstract Whereas some studies linked the enhanced tropical cyclone (TC) formation in the North Atlantic basin to the ongoing global warming, other studies attributed it to the warm phase of the Atlantic multidecadal oscillation (AMO). Using the National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory (ESRL) Twentieth Century Reanalysis (20CR) dataset, the present study reveals the distinctive spatial patterns associated with the influences of the AMO and global warming on TC formation in the North Atlantic basin. Two leading empirical orthogonal function (EOF) patterns are identified in the climate change of TC formation on time scales longer than interannual. The first pattern is associated with the AMO and its spatial pattern shows the basin-scale enhancement of TC formation during the AMO positive phase. The second pattern is associated with global warming, showing enhanced TC formation in the east tropical Atlantic (5°–20°N, 15°–40°W) and reduced TC formation from the southeast coast of the United States extending southward to the Caribbean Sea. In the warm AMO phase, the basinwide decrease in vertical wind shear and increases in midlevel relative humidity and maximum potential intensity (MPI) favor the basinwide enhancement of TC formation. Global warming suppresses TC formation from the southeast coast of the United States extending southward to the Caribbean Sea through enhancing vertical wind shear and reducing midlevel relative humidity and MPI. The enhanced TC formation in the east tropical Atlantic is due mainly to a local increase in MPI or sea surface temperature (SST), leading to a close relationship between the Atlantic SST and TC activity over the past decades.

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