The Impact of Supplemental Dropwindsonde Data on the Structure and Intensity of Tropical Storm Karen (2013) in the NCEP Global Forecast System

Abstract The impact of assimilating synoptic surveillance dropwindsonde data on the analysis and forecast of the structure and intensity of Tropical Storm Karen (2013) was examined. Data-denial experiments were conducted using the NCEP hybrid 3D ensemble–variational GSI and forecasts were made using the NCEP GFS model. The assimilation of dropwindsonde data resulted in a slightly more tilted tropical cyclone vortex, stronger vertical wind shear, and more upper-tropospheric dry air west of Karen in the initial conditions. These differences grew with time in the GFS forecasts, and resulted in a weaker and more sheared vortex by 24 h in the forecast that included the dropwindsonde data. After 24 h, the cyclone reintensified in the experiment where dropwindsonde data were excluded, likely because of moist processes in a favorable region for synoptic-scale ascent ahead of a baroclinic trough. In contrast, the forecast including the dropwindsonde data kept Karen weak and also did a better job forecasting the structure and track of Karen. These results suggest that differences in the analysis and short-term evolution of Karen and the environment due to the dropwindsonde data played a role in the longer-term structure and intensity of the cyclone, including the distribution and magnitude of associated diabatic heating. These results strongly suggest that a systematic study be undertaken to examine the impact of these data on tropical cyclone structure and intensity, since previous work has focused largely on the impact on track.

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The Contribution of Ex–Tropical Cyclone Gert (1999) toward the Weakening of a Midlatitude Cyclogenesis Event

Monthly Weather Review ◽

10.1175/2007mwr1637.1 ◽

2008 ◽

Vol 136 (6) ◽

pp. 2091-2111 ◽

Cited By ~ 7

Author(s):

Anna Agustí-Panareda

Keyword(s):

Tropical Cyclone ◽

Vertical Velocity ◽

Initial Conditions ◽

Negative Impact ◽

Positive Impact ◽

Extratropical Cyclone ◽

Synoptic Scale ◽

Extratropical Transition ◽

Peak Intensity ◽

The Impact

Abstract Tropical Cyclone Gert (1999) experienced an extratropical transition while it merged with an extratropical cyclone upstream. The upstream extratropical cyclone had started to intensify before it merged with the transitioning tropical cyclone, and it continued intensifying afterward (12 hPa in 12 h, according to the Met Office analysis). The question addressed in this paper is the following: what was the impact of the transitioning tropical cyclone on this intensification of the upstream extratropical cyclone? Until now, in the literature, tropical cyclones that experience extratropical transition have been found to have either no impact or a positive impact on the development of extratropical cyclogenesis events. The positive impact involves either a triggering of the development of the extratropical cyclone or simply a contribution to its deepening. However, the case studied here proves to have a negative impact on the developing extratropical cyclone upstream by diminishing its intensification. Forecasts are performed with and without the tropical cyclone in the initial conditions. They show that when Gert is not present in the initial conditions, the peak intensity of the cyclone upstream occurs 9 h earlier and it is 10 hPa deeper than when Gert is present. Thus, Gert acts to weaken the development by contributing to the filling of the extratropical surface low upstream. Quasigeostropic (QG) diagnostics show that the negative impact on the extratropical development is linked to the fact that the transitioning tropical cyclone interacts with a warm front inducing a negative QG vertical velocity over the developing extratropical low upstream. This interpretation is consistent with other contrasting cases in which the transitioning tropical cyclone interacts with a cold front and induces a positive QG vertical velocity over the developing low upstream, thus enhancing its development. The results are also in agreement with idealized experiments in the literature that are aimed at studying the predictability of extratropical storms. These idealized experiments yielded similar results using synoptic-scale and mesoscale vortices as perturbations on warm and cold fronts.

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Cloud-Resolving Ensemble Simulations of Mediterranean Heavy Precipitating Events: Uncertainty on Initial Conditions and Lateral Boundary Conditions

Monthly Weather Review ◽

10.1175/2010mwr3487.1 ◽

2011 ◽

Vol 139 (2) ◽

pp. 403-423 ◽

Cited By ~ 82

Author(s):

Benoît Vié ◽

Olivier Nuissier ◽

Véronique Ducrocq

Keyword(s):

Boundary Conditions ◽

Case Studies ◽

Short Range ◽

Initial Conditions ◽

Ensemble Prediction ◽

Lateral Boundary ◽

Synoptic Scale ◽

Lateral Boundary Conditions ◽

Convective Scale ◽

The Impact

Abstract This study assesses the impact of uncertainty on convective-scale initial conditions (ICs) and the uncertainty on lateral boundary conditions (LBCs) in cloud-resolving simulations with the Application of Research to Operations at Mesoscale (AROME) model. Special attention is paid to Mediterranean heavy precipitating events (HPEs). The goal is achieved by comparing high-resolution ensembles generated by different methods. First, an ensemble data assimilation technique has been used for assimilation of perturbed observations to generate different convective-scale ICs. Second, three ensembles used LBCs prescribed by the members of a global short-range ensemble prediction system (EPS). All ensembles obtained were then evaluated over 31- and/or 18-day periods, and on 2 specific case studies of HPEs. The ensembles are underdispersive, but both the probabilistic evaluation of their overall performance and the two case studies confirm that they can provide useful probabilistic information for the HPEs considered. The uncertainty on convective-scale ICs is shown to have an impact at short range (under 12 h), and it is strongly dependent on the synoptic-scale context. Specifically, given a marked circulation near the area of interest, the imposed LBCs rapidly overwhelm the initial differences, greatly reducing the spread of the ensemble. The uncertainty on LBCs shows an impact at longer range, as the spread in the coupling global ensemble increases, but it also depends on the synoptic-scale conditions and their predictability.

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Experimental Tropical Cyclone Forecasts Using a Variable-Resolution Global Model

Monthly Weather Review ◽

10.1175/mwr-d-15-0159.1 ◽

2015 ◽

Vol 143 (10) ◽

pp. 4012-4037 ◽

Cited By ~ 21

Author(s):

Colin M. Zarzycki ◽

Christiane Jablonowski

Keyword(s):

High Resolution ◽

Tropical Cyclone ◽

Initial Conditions ◽

Weather Prediction ◽

Horizontal Resolution ◽

Hurricane Sandy ◽

Track Forecast ◽

Time Step ◽

Variable Resolution ◽

The Impact

Abstract Tropical cyclone (TC) forecasts at 14-km horizontal resolution (0.125°) are completed using variable-resolution (V-R) grids within the Community Atmosphere Model (CAM). Forecasts are integrated twice daily from 1 August to 31 October for both 2012 and 2013, with a high-resolution nest centered over the North Atlantic and eastern Pacific Ocean basins. Using the CAM version 5 (CAM5) physical parameterization package, regional refinement is shown to significantly increase TC track forecast skill relative to unrefined grids (55 km, 0.5°). For typical TC forecast integration periods (approximately 1 week), V-R forecasts are able to nearly identically reproduce the flow field of a globally uniform high-resolution forecast. Simulated intensity is generally too strong for forecasts beyond 72 h. This intensity bias is robust regardless of whether the forecast is forced with observed or climatological sea surface temperatures and is not significantly mitigated in a suite of sensitivity simulations aimed at investigating the impact of model time step and CAM’s deep convection parameterization. Replacing components of the default physics with Cloud Layers Unified by Binormals (CLUBB) produces a statistically significant improvement in forecast intensity at longer lead times, although significant structural differences in forecasted TCs exist. CAM forecasts the recurvature of Hurricane Sandy into the northeastern United States 60 h earlier than the Global Forecast System (GFS) model using identical initial conditions, demonstrating the sensitivity of TC forecasts to model configuration. Computational costs associated with V-R simulations are dramatically decreased relative to globally uniform high-resolution simulations, demonstrating that variable-resolution techniques are a promising tool for future numerical weather prediction applications.

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A Balanced Tropical Cyclone Test Case for AGCMs with Background Vertical Wind Shear

Monthly Weather Review ◽

10.1175/mwr-d-14-00366.1 ◽

2015 ◽

Vol 143 (5) ◽

pp. 1762-1781 ◽

Cited By ~ 4

Author(s):

Fei He ◽

Derek J. Posselt ◽

Colin M. Zarzycki ◽

Christiane Jablonowski

Keyword(s):

Tropical Cyclone ◽

Wind Shear ◽

General Circulation ◽

Vertical Wind Shear ◽

Circulation Model ◽

Background Field ◽

Vertical Wind ◽

Intensity Change ◽

Test Case ◽

The Impact

Abstract This paper presents a balanced tropical cyclone (TC) test case designed to improve current understanding of how atmospheric general circulation model (AGCM) configurations affect simulated TC development and behavior. It consists of an analytic initial condition comprising two independently balanced components. The first provides a vortical TC seed, while the second adds a planetary-scale zonal flow with height-dependent velocity and imposes background vertical wind shear (VWS) on the TC seed. The environmental flow satisfies the steady-state hydrostatic primitive equations in spherical coordinates and is in balance with other background field variables (e.g., temperature, surface geopotential). The evolution of idealized TCs in the test case framework is illustrated in 10-day simulations performed with the Community Atmosphere Model, version 5.1.1 (CAM 5.1.1). Environmental wind profiles with different magnitudes, directions, and vertical inflection points are applied to ensure that the technique is robust to changes in the VWS characteristics. The well-known shear-induced intensity change and structural asymmetry in tropical cyclones are well captured. Sensitivity of TC evolution to small perturbations in the initial vortex is also quantitatively addressed to validate the numerical robustness of the technique. It is concluded that the enhanced TC test case can be used to evaluate the impact of model choice (e.g., resolution, physical parameterizations) on the simulation and representation of TC-like vortices in AGCMs.

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The Impact of Dropwindsonde Data from the THORPEX Pacific Area Regional Campaign and the NOAA Hurricane Field Program on Tropical Cyclone Forecasts in the Global Forecast System

Monthly Weather Review ◽

10.1175/2011mwr3634.1 ◽

2011 ◽

Vol 139 (9) ◽

pp. 2689-2703 ◽

Cited By ~ 23

Author(s):

Sim D. Aberson

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

Initial Conditions ◽

Unexpected Result ◽

Cyclone Track ◽

East Pacific ◽

Global Impacts ◽

The Impact ◽

Pacific Area ◽

Taiwan Region

Four aircraft released dropwindsondes in and around tropical cyclones in the west Pacific during The Observing System Research and Predictability Experiment (THORPEX) Pacific Area Regional Campaign (T-PARC) in 2008 and the Dropwindsonde Observations for Typhoon Surveillance near the Taiwan Region (DOTSTAR); multiple aircraft concurrently participated in similar missions in the Atlantic. Previous studies have treated each region separately and have focused on the tropical cyclones whose environments were sampled. The large number of missions and tropical cyclones in both regions, and additional tropical cyclones in the east Pacific and Indian Oceans, allows for the global impact of these observations on tropical cyclone track forecasts to be studied. The study shows that there are unintended global consequences to local changes in initial conditions, in this case due to the assimilation of dropwindsonde data in tropical cyclone environments. These global impacts are mainly due to the spectral nature of the model system. These differences should be small and slightly positive, since improved local initial conditions should lead to small global forecast improvements. However, the impacts on tropical cyclones far removed from the data are shown to be as large and positive as those on the tropical cyclones specifically targeted for improved track forecasts. Causes of this unexpected result are hypothesized, potentially providing operational forecasters tools to identify when large remote impacts from surveillance missions might occur.

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Joint Impact of Forecast Tendency and State Error Biases in Ensemble Kalman Filter Data Assimilation of Inner-Core Tropical Cyclone Observations

Monthly Weather Review ◽

10.1175/mwr-d-12-00211.1 ◽

2013 ◽

Vol 141 (9) ◽

pp. 2992-3006 ◽

Cited By ~ 12

Author(s):

Tomislava Vukicevic ◽

Altuğ Aksoy ◽

Paul Reasor ◽

Sim D. Aberson ◽

Kathryn J. Sellwood ◽

...

Keyword(s):

Tropical Cyclone ◽

Data Assimilation ◽

Inner Core ◽

Systematic Errors ◽

Secondary Circulation ◽

Short Term ◽

Background Error ◽

High Resolution Data ◽

Boundary Layer Dynamics ◽

The Impact

Abstract In this study the properties and causes of systematic errors in high-resolution data assimilation of inner-core tropical cyclone (TC) observations were investigated using the Hurricane Weather Research and Forecasting (HWRF) Ensemble Data Assimilation System (HEDAS). Although a recent study by Aksoy et al. demonstrated overall good performance of HEDAS for 83 cases from 2008 to 2011 using airborne observations from research and operational aircraft, some systematic errors were identified in the analyses with respect to independent observation-based estimates. The axisymmetric primary circulation intensity was underestimated for hurricane cases and the secondary circulation was systematically weaker for all cases. The diagnostic analysis in this study shows that the underestimate of primary circulation was caused by the systematic spindown of the vortex core in the short-term forecasts during the cycling with observations. This tendency bias was associated with the systematic errors in the secondary circulation, temperature, and humidity. The biases were reoccurring in each cycle during the assimilation because of the inconsistency between the strength of primary and secondary circulation during the short-term forecasts, the impact of model error in planetary boundary layer dynamics, and the effect of forecast tendency bias on the background error correlations. Although limited to the current analysis the findings in this study point to a generic problem of mutual dependence of short-term forecast tendency and state estimate errors in the data assimilation of TC core observations. The results indicate that such coupling of errors in the assimilation would also lead to short-term intensity forecast bias after the assimilation for the same reasons.

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The Impact of Airborne Doppler Aerosol Wind (DAWN) Lidar Wind Profiles on Numerical Simulations of Tropical Convective Systems during the NASA Convective Processes Experiment (CPEX)

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-19-0123.1 ◽

2020 ◽

Vol 37 (4) ◽

pp. 705-722 ◽

Cited By ~ 1

Author(s):

Zhiqiang Cui ◽

Zhaoxia Pu ◽

G. David Emmitt ◽

Steven Greco

Keyword(s):

Data Assimilation ◽

Initial Conditions ◽

Three Dimensional ◽

Tropical Storm ◽

Convective System ◽

Spatiotemporal Resolution ◽

Convective Systems ◽

Convective Processes ◽

Wind Profiles ◽

The Impact

AbstractHigh-spatiotemporal-resolution airborne Doppler Aerosol Wind (DAWN) lidar profiles over the Caribbean Sea and Gulf of Mexico region were collected during the NASA Convective Processes Experiment (CPEX) field campaign from 27 May to 24 June 2017. This study examines the impact of assimilating these wind profiles on the numerical simulation of moist convective systems using an Advanced Research version of the Weather Research and Forecasting (WRF) Model (WRF-ARW). A mesoscale convective system and a tropical storm (Cindy) that occurred on 16 June 2017 in a strong shear environment and on 21 June 2017 in a weak shear environment, respectively, are selected as case studies. The DAWN wind profiles are assimilated with the NCEP Gridpoint Statistical Interpolation analysis system using a three-dimensional variational (3DVar) and a hybrid three-dimensional ensemble-variational (3DEnVar) data assimilation systems to provide the initial conditions for a short-range forecast. Results show that the assimilation of DAWN wind profiles has significant positive impacts on convective simulations with the two assimilation approaches. The assimilation of DAWN wind profiles creates notable adjustments in the analysis of the divergence field for WRF simulations with a good agreement of wind forecasts with radiosonde observations. The quantitative precipitation forecasting is also improved. In general, the 3DEnVar data assimilation method is deemed more promising for DAWN data assimilation. There are cases with Tropical Storm Cindy in which DAWN data have slight to neutral impact on rainfall forecasts with 3DVAR, implying complicated interactions between errors of retrieved wind data and background error covariance in the lower and upper troposphere.

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How does the relationship between ambient deep-tropospheric vertical wind shear and tropical cyclone tornadoes change between coastal and inland environments?

Weather and Forecasting ◽

10.1175/waf-d-20-0127.1 ◽

2021 ◽

Author(s):

Benjamin A. Schenkel ◽

Michael Coniglio ◽

Roger Edwards

Keyword(s):

Tropical Cyclone ◽

Wind Shear ◽

Vertical Wind Shear ◽

Vertical Wind ◽

Radiosonde Data ◽

Synoptic Scale ◽

Near Surface ◽

Tangential Wind ◽

Convective Scale ◽

The Relationship

AbstractThis work investigates how the relationship between tropical cyclone (TC) tornadoes and ambient (i.e., synoptic-scale) deep-tropospheric (i.e., 850–200-hPa) vertical wind shear (VWS) varies between coastal and inland environments. Observed U.S. TC tornado track data are used to study tornado frequency and location, while dropsonde and radiosonde data are used to analyze convective-scale environments. To study the variability in the TC tornado-VWS relationship, these data are categorized by both: 1) their distance from the coast and 2) reanalysis-derived VWS magnitude. The analysis shows that TCs produce coastal tornadoes regardless of VWS magnitude primarily in their downshear sector, with tornadoes most frequently occurring in strongly sheared cases. Inland tornadoes, including the most damaging cases, primarily occur in strongly sheared TCs within the outer radii of the downshear right quadrant. Consistent with these patterns, drop-sondes and coastal radiosondes show that the downshear right quadrant of strongly sheared TCs has the most favorable combination of enhanced lower-tropospheric near-surface speed shear and veering, and reduced lower-tropospheric thermodynamic stability for tornadic supercells. Despite the weaker intensity further inland, these kinematic conditions are even more favorable in inland environments within the downshear right quadrant of strongly sheared TCs, due to the strengthened veering of the ambient winds and the lack of changes in the TC outer tangential wind strength. The constructive superposition of the ambient and TC winds may be particularly important to inland tornado occurrence. Together, these results will allow forecasters to anticipate how the frequency and location of tornadoes and, more broadly, convection may change as TCs move inland.

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A Physical Basis for the Probabilistic Prediction of the Accumulated Tropical Cyclone Kinetic Energy in the Western North Pacific

Journal of Climate ◽

10.1175/jcli-d-12-00679.1 ◽

2013 ◽

Vol 26 (20) ◽

pp. 7981-7991 ◽

Cited By ~ 14

Author(s):

Hye-Mi Kim ◽

Myong-In Lee ◽

Peter J. Webster ◽

Dongmin Kim ◽

Jin Ho Yoo

Keyword(s):

Tropical Cyclone ◽

Kinetic Energy ◽

El Niño ◽

North Pacific ◽

Wind Shear ◽

Western North Pacific ◽

El Nino ◽

Vertical Wind Shear ◽

Tropical Storm ◽

Probabilistic Prediction

Abstract The relationship between El Niño–Southern Oscillation (ENSO) and tropical storm (TS) activity over the western North Pacific Ocean is examined for the period from 1981 to 2010. In El Niño years, TS genesis locations are generally shifted to the southeast relative to normal years and the passages of TSs tend to recurve to the northeast. TSs of greater duration and more intensity during an El Niño summer induce an increase of the accumulated tropical cyclone kinetic energy (ACE). Based on the strong relationship between the TS properties and ENSO, a probabilistic prediction for seasonal ACE is investigated using a hybrid dynamical–statistical model. A statistical relationship is developed between the observed ACE and large-scale variables taken from the ECMWF seasonal forecast system 4 hindcasts. The ACE correlates positively with the SST anomaly over the central to eastern Pacific and negatively with the vertical wind shear near the date line. The vertical wind shear anomalies over the central and western Pacific are selected as predictors based on sensitivity tests of ACE predictive skill. The hybrid model performs quite well in forecasting seasonal ACE with a correlation coefficient between the observed and predicted ACE at 0.80 over the 30-yr period. A relative operating characteristic analysis also indicates that the ensembles have significant probabilistic skill for both the above-normal and below-normal categories. By comparing the ACE prediction over the period from 2003 to 2011, the hybrid model appears more skillful than the forecast from the Tropical Storm Risk consortium.

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Idealized Tropical Cyclone Responses to the Height and Depth of Environmental Vertical Wind Shear

Monthly Weather Review ◽

10.1175/mwr-d-15-0320.1 ◽

2016 ◽

Vol 144 (6) ◽

pp. 2155-2175 ◽

Cited By ~ 39

Author(s):

Peter M. Finocchio ◽

Sharanya J. Majumdar ◽

David S. Nolan ◽

Mohamed Iskandarani

Keyword(s):

Tropical Cyclone ◽

Wind Shear ◽

Large Scale ◽

Deep Layer ◽

Vertical Wind Shear ◽

Vertical Wind ◽

Polynomial Expansions ◽

The Impact ◽

Tilt Response ◽

Left Quadrant

Abstract Three sets of idealized, cloud-resolving simulations are performed to investigate the sensitivity of tropical cyclone (TC) structure and intensity to the height and depth of environmental vertical wind shear. In the first two sets of simulations, shear height and depth are varied independently; in the third set, orthogonal polynomial expansions are used to facilitate a joint sensitivity analysis. Despite all simulations having the same westerly deep-layer (200–850 hPa) shear of 10 m s−1, different intensity and structural evolutions are observed, suggesting the deep-layer shear alone may not be sufficient for understanding or predicting the impact of vertical wind shear on TCs. In general, vertical wind shear that is shallower and lower in the troposphere is more destructive to model TCs because it tilts the TC vortex farther into the downshear-left quadrant. The vortices that tilt the most are unable to precess upshear and realign, resulting in their failure to intensify. Shear height appears to modulate this tilt response by modifying the thermodynamic environment above the developing vortex early in the simulations, while shear depth modulates the tilt response by controlling the vertical extent of the convective vortex. It is also found that TC intensity predictability is reduced in a narrow range of shear heights and depths. This result underscores the importance of accurately observing the large-scale environmental flow for improving TC intensity forecasts, and for anticipating when such forecasts are likely to have large errors.

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