A Comparison of Adaptive Observing Guidance for Atlantic Tropical Cyclones

Abstract Airborne adaptive observations have been collected for more than two decades in the neighborhood of tropical cyclones, to attempt to improve short-range forecasts of cyclone track. However, only simple subjective strategies for adaptive observations have been used, and the utility of objective strategies to improve tropical cyclone forecasts remains unexplored. Two objective techniques that have been used extensively for midlatitude adaptive observing programs, and the current strategy based on the ensemble deep-layer mean (DLM) wind variance, are compared quantitatively using two metrics. The ensemble transform Kalman filter (ETKF) uses ensembles from NCEP and the ECMWF. Total-energy singular vectors (TESVs) are computed by the ECMWF and the Naval Research Laboratory, using their respective global models. Comparisons of 78 guidance products for 2-day forecasts during the 2004 Atlantic hurricane season are made, on both continental and localized scales relevant to synoptic surveillance missions. The ECMWF and NRL TESV guidance identifies similar large-scale target regions in 90% of the cases, but are less similar to each other in the local tropical cyclone environment (56% of the cases) with a more stringent criterion for similarity. For major hurricanes, all techniques usually indicate targets close to the storm center. For weaker tropical cyclones, the TESV guidance selects similar targets to those from the ETKF (DLM wind variance) in only 30% (20%) of the cases. ETKF guidance using the ECMWF ensemble is more like that provided by the NCEP ensemble (and DLM wind variance) for major hurricanes than for weaker tropical cyclones. Minor differences in these results occur when a different metric based on the ranking of fixed storm-relative regions is used.

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Observational Analysis of Tropical Cyclone Formation Associated with Monsoon Gyres

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-12-0117.1 ◽

2013 ◽

Vol 70 (4) ◽

pp. 1023-1034 ◽

Cited By ~ 38

Author(s):

Liguang Wu ◽

Huijun Zong ◽

Jia Liang

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

Western North Pacific ◽

Large Scale ◽

Vertical Wind Shear ◽

Relative Vorticity ◽

Monsoon Trough ◽

Cyclonic Circulation ◽

Tropical Cyclone Formation ◽

Monsoon Gyre

Abstract Large-scale monsoon gyres and the involved tropical cyclone formation over the western North Pacific have been documented in previous studies. The aim of this study is to understand how monsoon gyres affect tropical cyclone formation. An observational study is conducted on monsoon gyres during the period 2000–10, with a focus on their structures and the associated tropical cyclone formation. A total of 37 monsoon gyres are identified in May–October during 2000–10, among which 31 monsoon gyres are accompanied with the formation of 42 tropical cyclones, accounting for 19.8% of the total tropical cyclone formation. Monsoon gyres are generally located on the poleward side of the composited monsoon trough with a peak occurrence in August–October. Extending about 1000 km outward from the center at lower levels, the cyclonic circulation of the composited monsoon gyre shrinks with height and is replaced with negative relative vorticity above 200 hPa. The maximum winds of the composited monsoon gyre appear 500–800 km away from the gyre center with a magnitude of 6–10 m s−1 at 850 hPa. In agreement with previous studies, the composited monsoon gyre shows enhanced southwesterly flow and convection on the south-southeastern side. Most of the tropical cyclones associated with monsoon gyres are found to form near the centers of monsoon gyres and the northeastern end of the enhanced southwesterly flows, accompanying relatively weak vertical wind shear.

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Naval Research Laboratory Multiscale Targeting Guidance for T-PARC and TCS-08

Weather and Forecasting ◽

10.1175/2009waf2222292.1 ◽

2010 ◽

Vol 25 (2) ◽

pp. 526-544 ◽

Cited By ~ 15

Author(s):

Carolyn A. Reynolds ◽

James D. Doyle ◽

Richard M. Hodur ◽

Hao Jin

Keyword(s):

Tropical Cyclone ◽

Research Laboratory ◽

Large Scale ◽

Adjoint System ◽

Horizontal Resolution ◽

Naval Research Laboratory ◽

Naval Research ◽

Prediction System ◽

Initial State ◽

The North

Abstract As part of The Observing System Research and Predictability Experiment (THORPEX) Pacific Asian Regional Campaign (T-PARC) and the Office of Naval Research’s (ONR’s) Tropical Cyclone Structure-08 (TCS-08) experiments, a variety of real-time products were produced at the Naval Research Laboratory during the field campaign that took place from August through early October 2008. In support of the targeted observing objective, large-scale targeting guidance was produced twice daily using singular vectors (SVs) from the Navy Operational Global Atmospheric Prediction System (NOGAPS). These SVs were optimized for fixed regions centered over Guam, Taiwan, Japan, and two regions over the North Pacific east of Japan. During high-interest periods, flow-dependent SVs were also produced. In addition, global ensemble forecasts were produced and were useful for examining the potential downstream impacts of extratropical transitions. For mesoscale models, TC forecasts were produced using a new version of the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) developed specifically for tropical cyclone prediction (COAMPS-TC). In addition to the COAMPS-TC forecasts, mesoscale targeted observing products were produced using the COAMPS forecast and adjoint system twice daily, centered on storms of interest, at a 40-km horizontal resolution. These products were produced with 24-, 36-, and 48-h lead times. The nonhydrostatic adjoint system used during T-PARC/TCS-08 contains an exact adjoint to the explicit microphysics. An adaptive response function region was used to target favorable areas for tropical cyclone formation and development. Results indicate that forecasts of tropical cyclones in the western Pacific are very sensitive to the initial state.

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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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Physical Mechanisms Underlying Selected Adaptive Sampling Techniques for Tropical Cyclones

Monthly Weather Review ◽

10.1175/mwr-d-12-00269.1 ◽

2013 ◽

Vol 141 (11) ◽

pp. 4008-4027 ◽

Cited By ~ 1

Author(s):

Brett T. Hoover ◽

Chris S. Velden ◽

Sharanya J. Majumdar

Keyword(s):

Tropical Cyclone ◽

Adaptive Sampling ◽

Field Experiments ◽

Guidance System ◽

Naval Research ◽

Initial Condition ◽

Downstream Targets ◽

Physical Mechanisms ◽

Indirect Measures ◽

Adaptive Observations

Abstract To efficiently and effectively prioritize resources, adaptive observations can be targeted by using some objective criteria to estimate the potential impact an initial condition perturbation (or analysis increment) in a specific region would have on the future forecast. Several objective targeting guidance techniques have been developed, including total-energy singular vectors (TESV), adjoint-derived sensitivity steering vectors (ADSSV), and the ensemble transform Kalman filter (ETKF), all of which were tested during the 2008 The Observing System Research and Predictability Experiment (THORPEX) Pacific Asian Regional Campaign (T-PARC) and the Office of Naval Research Tropical Cyclone Structure-2008 (TCS-08) field experiments. An intercomparison between these techniques is performed in order to find underlying physical mechanisms in the respective guidance products, based on four tropical cyclone (TC) cases from the T-PARC/TCS-08 field campaigns. It is found that the TESV energy norm and the ADSSV response function are largely indirect measures of the TC track divergence that can be produced by an initial condition perturbation, explaining the strong correlation between these products. The downstream targets routinely chosen by the ETKF guidance system are often not found in the TESV and ADSSV guidance products, and it is found that downstream perturbations can affect the steering of a TC through the development of a Rossby wave in the subtropics that modulates the strength of the nearby subtropical ridge. It is hypothesized that the ubiquitousness of these downstream targets in the ETKF is largely due to the existence of large uncertainties downstream of the TC that are not taken into consideration by either the TESV or ADSSV techniques.

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Rapid Weakening of Tropical Cyclones in Monsoon Gyres over the Tropical Western North Pacific

Journal of Climate ◽

10.1175/jcli-d-16-0784.1 ◽

2018 ◽

Vol 31 (3) ◽

pp. 1015-1028 ◽

Cited By ~ 9

Author(s):

Jia Liang ◽

Liguang Wu ◽

Guojun Gu

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

North Pacific ◽

Western North Pacific ◽

Large Scale ◽

Vertical Wind Shear ◽

Tropical Cyclone Intensity ◽

Cyclone Intensity ◽

Operational Forecasts ◽

Tropical Western North Pacific

Abstract As one major source of forecasting errors in tropical cyclone intensity, rapid weakening of tropical cyclones [an intensity reduction of 20 kt (1 kt = 0.51 m s−1) or more over a 24-h period] over the tropical open ocean can result from the interaction between tropical cyclones and monsoon gyres. This study aims to examine rapid weakening events occurring in monsoon gyres in the tropical western North Pacific (WNP) basin during May–October 2000–14. Although less than one-third of rapid weakening events happened in the tropical WNP basin south of 25°N, more than 40% of them were associated with monsoon gyres. About 85% of rapid weakening events in monsoon gyres occurred in September and October. The rapid weakening events associated with monsoon gyres are usually observed near the center of monsoon gyres when tropical cyclone tracks make a sudden northward turn. The gyres can enlarge the outer size of tropical cyclones and tend to induce prolonged rapid weakening events with an average duration of 33.2 h. Large-scale environmental factors, including sea surface temperature changes, vertical wind shear, and midlevel environmental humidity, are not primary contributors to them, suggesting the possible effect of monsoon gyres on these rapid weakening events by modulating the tropical cyclone structure. This conclusion is conducive to improving operational forecasts of tropical cyclone intensity.

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The Interannual Variability of Tropical Cyclones

Monthly Weather Review ◽

10.1175/mwr3435.1 ◽

2007 ◽

Vol 135 (10) ◽

pp. 3587-3598 ◽

Cited By ~ 76

Author(s):

William M. Frank ◽

George S. Young

Keyword(s):

Tropical Cyclone ◽

Interannual Variability ◽

Tropical Cyclones ◽

Large Scale ◽

Storm Activity ◽

Modes Of Variability ◽

The North ◽

Temporal And Spatial ◽

Using Data ◽

The North Atlantic Oscillation

Abstract This paper examines the interannual variability of tropical cyclones in each of the earth’s cyclone basins using data from 1985 to 2003. The data are first analyzed using a Monte Carlo technique to investigate the long-standing myth that the global number of tropical cyclones is less variable than would be expected from examination of the variability in each basin. This belief is found to be false. Variations in the global number of all tropical cyclones are indistinguishable from those that would be expected if each basin was examined independently of the others. Furthermore, the global number of the most intense storms (Saffir–Simpson categories 4–5) is actually more variable than would be expected because of an observed tendency for storm activity to be correlated between basins, and this raises important questions as to how and why these correlations arise. Interbasin correlations and factor analysis of patterns of tropical cyclone activity reveal that there are several significant modes of variability. The largest three factors together explain about 70% of the variance, and each of these factors shows significant correlation with ENSO, the North Atlantic Oscillation (NAO), or both, with ENSO producing the largest effects. The results suggest that patterns of tropical cyclone variability are strongly affected by large-scale modes of interannual variability. The temporal and spatial variations in storm activity are quite different for weaker tropical cyclones (tropical storm through category 2 strength) than for stronger storms (categories 3–5). The stronger storms tend to show stronger interbasin correlations and stronger relationships to ENSO and the NAO than do the weaker storms. This suggests that the factors that control tropical cyclone formation differ in important ways from those that ultimately determine storm intensity.

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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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Projected Twenty-First-Century Changes in the Length of the Tropical Cyclone Season

Journal of Climate ◽

10.1175/jcli-d-14-00686.1 ◽

2015 ◽

Vol 28 (15) ◽

pp. 6181-6192 ◽

Cited By ~ 15

Author(s):

John G. Dwyer ◽

Suzana J. Camargo ◽

Adam H. Sobel ◽

Michela Biasutti ◽

Kerry A. Emanuel ◽

...

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

General Circulation ◽

Large Scale ◽

General Circulation Models ◽

First Century ◽

Season Length ◽

Length Changes ◽

Twenty First Century ◽

Tropical Cyclone Season

Abstract This study investigates projected changes in the length of the tropical cyclone season due to greenhouse gas increases. Two sets of simulations are analyzed, both of which capture the relevant features of the observed annual cycle of tropical cyclones in the recent historical record. Both sets use output from the general circulation models (GCMs) of either phase 3 or phase 5 of the CMIP suite (CMIP3 and CMIP5, respectively). In one set, downscaling is performed by randomly seeding incipient vortices into the large-scale atmospheric conditions simulated by each GCM and simulating the vortices’ evolution in an axisymmetric dynamical tropical cyclone model; in the other set, the GCMs’ sea surface temperature (SST) is used as the boundary condition for a high-resolution global atmospheric model (HiRAM). The downscaling model projects a longer season (in the late twenty-first century compared to the twentieth century) in most basins when using CMIP5 data but a slightly shorter season using CMIP3. HiRAM with either CMIP3 or CMIP5 SST anomalies projects a shorter tropical cyclone season in most basins. Season length is measured by the number of consecutive days that the mean cyclone count is greater than a fixed threshold, but other metrics give consistent results. The projected season length changes are also consistent with the large-scale changes, as measured by a genesis index of tropical cyclones. The season length changes are mostly explained by an idealized year-round multiplicative change in tropical cyclone frequency, but additional changes in the transition months also contribute.

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Tropical cyclone genesis across palaeoclimates

Climate of the Past Discussions ◽

10.5194/cpd-11-181-2015 ◽

2015 ◽

Vol 11 (1) ◽

pp. 181-220 ◽

Cited By ~ 1

Author(s):

J. H. Koh ◽

C. M. Brierley

Keyword(s):

Carbon Dioxide ◽

Tropical Cyclone ◽

Tropical Cyclones ◽

Large Scale ◽

Climate Models ◽

Tropical Cyclogenesis ◽

Tropical Cyclone Genesis ◽

Inter Tropical Convergence Zone ◽

Potential Index ◽

Cyclone Genesis

Abstract. Tropical cyclone genesis is investigated for the Pliocene, Last Glacial Maximum (LGM) and the mid-Holocene through analysis of five climate models. The genesis potential index is used to estimate this from large scale atmospheric properties. The mid-Pliocene and LGM characterise periods where carbon dioxide levels were higher and lower than pre-industrial respectively, while the mid-Holocene differed primarily in its orbital configuration. The number of tropical cyclones formed each year is found to be fairly consistent across the various palaeoclimates. Although there is some model uncertainty in the change of global annual tropical cyclone frequency, there are coherent changes in the spatial patterns of tropical cyclogenesis. During the Pliocene and LGM, changes in carbon dioxide led to sea surface temperature changes throughout the tropics, yet the potential intensity of tropical cyclones appears relatively insensitive to these variations. Changes in tropical cyclone genesis during the mid-Holocene are observed to be asymmetric about the Equator: genesis is reduced in the Northern Hemisphere, but enhanced in the Southern Hemisphere. This is clearly driven by the altered seasonal insolation. Nonetheless, the enhanced seasonality may have driven localised effects on tropical cyclone genesis, through changes to the strength of monsoons and shifting of the inter-tropical convergence zone. Trends in future tropical cyclone genesis are neither consistent between the five models studied, nor with the palaeoclimate results. It is not clear why this should be the case.

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