Seasonal Forecasts of Tropical Cyclone Activity in a High-Atmospheric-Resolution Coupled Prediction System*

Abstract Seasonal forecast skill of the basinwide and regional tropical cyclone (TC) activity in an experimental coupled prediction system based on the ECMWF System 4 is assessed. As part of a collaboration between the Center for Ocean–Land–Atmosphere Studies (COLA) and the ECMWF called Project Minerva, the system is integrated at the atmospheric horizontal spectral resolutions of T319, T639, and T1279. Seven-month hindcasts starting from 1 May for the years 1980–2011 are produced at all three resolutions with at least 15 ensemble members. The Minerva system demonstrates statistically significant skill for retrospective forecasts of TC frequency and accumulated cyclone energy (ACE) in the North Atlantic (NA), eastern North Pacific (EP), and western North Pacific. While the highest scores overall are achieved in the North Pacific, the skill in the NA appears to be limited by an overly strong influence of the tropical Pacific variability. Higher model resolution improves skill scores for the ACE and, to a lesser extent, the TC frequency, even though the influence of large-scale climate variations on these TC activity measures is largely independent of resolution changes. The biggest gain occurs in transition from T319 to T639. Significant skill in regional TC forecasts is achieved over broad areas of the Northern Hemisphere. The highest-resolution hindcasts exhibit additional locations with skill in the NA and EP, including land-adjacent areas. The feasibility of regional intensity forecasts is assessed. In the presence of the coupled model biases, the benefits of high resolution for seasonal TC forecasting may be underestimated.

Download Full-text

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.

Download Full-text

Developing versus Nondeveloping Disturbances for Tropical Cyclone Formation. Part II: Western North Pacific

Monthly Weather Review ◽

10.1175/2011mwr3618.1 ◽

2012 ◽

Vol 140 (4) ◽

pp. 1067-1080 ◽

Cited By ~ 63

Author(s):

Bing Fu ◽

Melinda S. Peng ◽

Tim Li ◽

Duane E. Stevens

Keyword(s):

Tropical Cyclone ◽

North Pacific ◽

Western North Pacific ◽

Large Scale ◽

Relative Vorticity ◽

Tropical Cyclone Genesis ◽

Horizontal Shear ◽

The North ◽

Thermodynamic Variables ◽

Cyclone Genesis

Global daily reanalysis fields from the Navy Operational Global Atmospheric Prediction System (NOGAPS) are used to analyze Northern Hemisphere summertime (June–September) developing and nondeveloping disturbances for tropical cyclone (TC) formation from 2003 to 2008. This is Part II of the study focusing on the western North Pacific (WNP), following Part I for the North Atlantic (NATL) basin. Tropical cyclone genesis in the WNP shows different characteristics from that in the NATL in both large-scale environmental conditions and prestorm disturbances. A box difference index (BDI) is used to identify parameters in differentiating between the developing and nondeveloping disturbances. In order of importance, they are 1) 800-hPa maximum relative vorticity, 2) rain rate, 3) vertically averaged horizontal shear, 4) vertically averaged divergence, 5) 925–400-hPa water vapor content, 6) SST, and 7) translational speed. The study indicates that dynamic variables are more important in TC genesis in the WNP, while in Part I of the study the thermodynamic variables are identified as more important in the NATL. The characteristic differences between the WNP and the NATL are compared.

Download Full-text

Changes in the Past and Projected Western North Pacific Tropical Cyclone Activity in a Warmed Climate

10.5194/egusphere-egu2020-7521 ◽

2020 ◽

Author(s):

Liang Wu

Keyword(s):

Tropical Cyclone ◽

North Pacific ◽

Western North Pacific ◽

Large Scale ◽

Climate Models ◽

Rapid Development ◽

Current Trend ◽

Coupled Model ◽

Rcp 8.5 ◽

Projected Changes

Two high-resolution climate models (the HiRAM and MRI-AGCM3.2) are used to simulate present-day western North Pacific (WNP) tropical cyclone (TC) activity and investigate the projected changes for the late 21st century. Compared toobservations, the models are able to realistically simulate many basic features of the WNP TC activity climatology. Future projections with the coupled model inter-comparison project phase 5 (CMIP5) under Representative Concentration Pathway (RCP) 8.5 scenario show a tendency for decreases in the number of WNP TCs, and of increases in the more intense TCs. It is unknown to what cause this inverse variation with number and intensity should be generally linked to similar large-scale environmental conditions. To examine the WNP TC genesis and intensity with environmental variables, we show that most of the current trend of decreasing genesis of TCs can be attributed to weakened dynamic environments and the current trend of increasing intensity of TCs might be linked to increased thermodynamic environments. Thus, the future climate warms under RCP 8.5 will likely lead to strong reductions in TC genesis frequency over the WNP, with project decreases of 36-63% by the end of the twenty-first century, but lead to greater TC intensities with rapid development of thermodynamic environments.

Download Full-text

Projection of North Pacific Tropical Upper-Tropospheric Trough in CMIP5 Models: Implications for Changes in Tropical Cyclone Formation Locations

Journal of Climate ◽

10.1175/jcli-d-17-0292.1 ◽

2018 ◽

Vol 31 (2) ◽

pp. 761-774 ◽

Cited By ~ 9

Author(s):

Chao Wang ◽

Liguang Wu

Keyword(s):

Tropical Cyclone ◽

North Pacific ◽

Climate Models ◽

Coupled Model ◽

Atmospheric Composition ◽

Cmip5 Models ◽

The North ◽

The Mean ◽

The Impact ◽

The North Pacific

The strong westerly shear to the south flank of the tropical upper-tropospheric trough (TUTT) limits the eastward extension of tropical cyclone (TC) formation over the western North Pacific (WNP) and thus the zonal shift of the TUTT in warming scenarios has an important implication for the mean formation location of TCs. The impact of global warming on the zonal shift of the TUTT is investigated by using output from phase 5 of the Coupled Model Intercomparison Project (CMIP5) of 36 climate models in this study. It is found that considerable spread exists in the zonal position, orientation, and intensity of the simulated-climatologic TUTT in the historical runs, which is forced by observed conditions such as changes in atmospheric composition, solar forcing, and aerosols. The large spread is closely related to the diversity in the simulated SST biases over the North Pacific. Based on the 15 models with relatively high skill in their historical runs, the near-term (2016–35) projection shows no significant change of the TUTT longitude, while the TUTT experiences an eastward shift of 1.9° and 3.2° longitude in the representative concentration pathway (RCP) 4.5 and 8.5 scenarios in the long-term (2081–2100) projection with considerable intermodel variability. Further examination indicates that the projected changes in the zonal location of the TUTT are also associated with the projected relative SST anomalies over the North Pacific. A stronger (weaker) relative SST warming over the North Pacific favors an eastward (westward) shift of the TUTT, suggesting that the spatial pattern of the future SST change is an important factor for the zonal shift of the mean formation location of TCs.

Download Full-text

Evaluating Tropical Cyclone Forecasts from the NCEP Global Ensemble Forecasting System (GEFS) Reforecast Version 2

Weather and Forecasting ◽

10.1175/waf-d-15-0176.1 ◽

2016 ◽

Vol 31 (3) ◽

pp. 895-916 ◽

Cited By ~ 8

Author(s):

Weiwei Li ◽

Zhuo Wang ◽

Melinda S. Peng

Keyword(s):

Tropical Cyclone ◽

North Pacific ◽

Large Scale ◽

Southern Oscillation ◽

Regional Scale ◽

Ensemble Forecasting ◽

Tropical Cyclogenesis ◽

Easterly Waves ◽

The North ◽

Forecasting System

Abstract Tropical cyclone (TC) forecasts from the NCEP Global Ensemble Forecasting System (GEFS) Reforecast version 2 (1985–2012) were evaluated from the climate perspective, with a focus on tropical cyclogenesis. Although the GEFS captures the climatological seasonality of tropical cyclogenesis over different ocean basins reasonably well, large errors exist on the regional scale. As different genesis pathways are dominant over different ocean basins, genesis biases are related to biases in different aspects of the large-scale or synoptic-scale circulations over different basins. The negative genesis biases over the western North Pacific are associated with a weaker-than-observed monsoon trough in the GEFS, the erroneous genesis pattern over the eastern North Pacific is related to a southward displacement of the ITCZ, and the positive genesis biases near the Cape Verde islands and negative biases farther downstream over the Atlantic can be attributed to the hyperactive Africa easterly waves in the GEFS. The interannual and subseasonal variability of TC activity in the reforecasts was also examined to evaluate the potential skill of the GEFS in providing subseasonal and seasonal predictions. The GEFS skillfully captures the interannual variability of TC activity over the North Pacific and the North Atlantic, which can be attributed to the modulation of TCs by the El Niño–Southern Oscillation (ENSO) and the Atlantic meridional mode (AMM). The GEFS shows promising skill in predicting the active and inactive periods of TC activity over the Atlantic. The skill, however, has large fluctuations from year to year. The analysis presented herein suggests possible impacts of ENSO, the Madden–Julian oscillation (MJO), and the AMM on the TC subseasonal predictability.

Download Full-text

A Climatology of Multiple Tropical Cyclone Events

Journal of Climate ◽

10.1175/jcli-d-15-0048.1 ◽

2016 ◽

Vol 29 (13) ◽

pp. 4861-4883 ◽

Cited By ~ 8

Author(s):

Benjamin A. Schenkel

Keyword(s):

Tropical Cyclone ◽

North Pacific ◽

Large Scale ◽

Wave Radiation ◽

Annual Number ◽

Substantial Fraction ◽

Temporal Separation ◽

The North ◽

Development Region ◽

Group Velocities

Abstract The present study provides a climatology of multiple tropical cyclone (TC) events (MTCEs) and the potential environmental factors responsible for triggering MTCEs in the North Atlantic (NATL), eastern North Pacific (EPAC), and western North Pacific (WPAC). While single TC events (STCEs) occur more frequently than MTCEs in each basin, a substantial fraction (34%–57%) of all TCs within each basin occur during MTCEs. Comparison of the total monthly number of MTCEs and STCEs reveals significant correlations (0.79 ≤ R ≤ 0.90), while nonsignificant correlations exist between the annual number of MTCEs and STCEs. New TCs that form during MTCEs occur in the eastern main development region east of the STCE formation location in the NATL and EPAC, while new TC formation locations are spread evenly throughout the WPAC during both MTCEs and STCEs. The spatiotemporal separation between TCs during MTCEs is consistent among basins with median zonal distances between TCs of ~(1640–2010) km and median temporal separation between TC formation of 3.00–3.25 days. Composites of EPAC MTCEs suggest the existence of significantly stronger large-scale intraseasonal anomalies compared to STCEs, which may favor EPAC MTCE occurrence. Eastward zonal group velocities and the agreement of the zonal wavelength of TC-induced Rossby waves with the observed zonal distance between TCs suggests that Rossby wave radiation may contribute to a substantial fraction of MTCEs in all basins. These results suggest remarkable similarity in MTCE characteristics among basins, while potentially indicating that the large-scale environment is preconditioned for EPAC MTCE occurrence.

Download Full-text

Evaluation of Simulation Capability for Multiple Tropical Cyclone Events in the Western North Pacific of the UH_HCM Model

Frontiers in Earth Science ◽

10.3389/feart.2020.598473 ◽

2021 ◽

Vol 8 ◽

Author(s):

Tianhang Li ◽

Hong-Li Ren ◽

Yujie Wu ◽

Jianyun Gao

Keyword(s):

Tropical Cyclone ◽

North Pacific ◽

Western North Pacific ◽

Large Scale ◽

Intraseasonal Variability ◽

Coupled Model ◽

Active Phase ◽

Monsoon Trough ◽

Factors Affecting ◽

Potential Index

The intraseasonal variability of multiple tropical cyclone (MTC) events in the western North Pacific (WNP) during 1979–2015 is analyzed using the best-track dataset archived at the Joint Typhoon Warning Center. MTC events are divided into three phases according to the time intervals of the tropical cyclone (TC) genesis, that is, active, normal, and inactive phases. Composite analysis results indicate that MTC events tend to occur in the active phase when the monsoon trough is stronger and located farther north than at other times. Initialized by the data from a 10-year stable running result, a 12-year control experiment is carried out using the hybrid atmosphere–ocean coupled model developed at the University of Hawaii (UH_HCM model) to evaluate its simulation capability. Compared with the climate observations, the model shows good skill in simulating the large-scale environmental conditions in the WNP, especially the subtropical high and the monsoon trough. In addition, the model can well simulate the climate characteristics of TCs in the WNP, as well as the differences in each MTC phase. However, the simulated frequency of TCs is less and their locations are more northeast, compared with the observations. The vorticity and moisture in the model appear to be the two main factors affecting MTC activity based on analyses of the genesis potential index.

Download Full-text

The Impact of Anthropogenic Climate Change on North Atlantic Tropical Cyclone Tracks*

Journal of Climate ◽

10.1175/jcli-d-12-00342.1 ◽

2013 ◽

Vol 26 (12) ◽

pp. 4088-4095 ◽

Cited By ~ 36

Author(s):

Angela J. Colbert ◽

Brian J. Soden ◽

Gabriel A. Vecchi ◽

Ben P. Kirtman

Keyword(s):

Tropical Cyclone ◽

Greenhouse Gases ◽

North Atlantic ◽

Large Scale ◽

Coupled Model ◽

The North ◽

Steering Flow ◽

Southern Gulf Of Mexico ◽

Projected Changes ◽

The Impact

Abstract The authors examine the change in tropical cyclone (TC) tracks that results from projected changes in the large-scale steering flow and genesis location from increasing greenhouse gases. Tracks are first simulated using a Beta and Advection Model (BAM) and NCEP–NCAR reanalysis winds for all TCs that formed in the North Atlantic Ocean’s Main Development Region (MDR) for the period 1950–2010. Changes in genesis location and large-scale steering flow are then estimated from an ensemble mean of 17 models from phase 3 of the Coupled Model Intercomparison Project (CMIP3) for the A1b emissions scenario. The BAM simulations are then repeated with these changes to estimate how the TC tracks would respond to increased greenhouse gases. As the climate warms, the models project a weakening of the subtropical easterlies as well as an eastward shift in genesis location. This results in a statistically significant decrease in straight-moving (westward) storm tracks of ~5.5% and an increase in recurving (open ocean) tracks of ~5.5%. These track changes decrease TC counts over the southern Gulf of Mexico and Caribbean by 1–1.5 decade−1 and increase counts over the central Atlantic by 1–1.5 decade−1. Changes in the large-scale steering flow account for a vast majority of the projected changes in TC trajectories.

Download Full-text

Response of the North Pacific Tropical Cyclone Climatology to Global Warming: Application of Dynamical Downscaling to CMIP5 Models

Journal of Climate ◽

10.1175/jcli-d-16-0496.1 ◽

2017 ◽

Vol 30 (4) ◽

pp. 1233-1243 ◽

Cited By ~ 25

Author(s):

Lei Zhang ◽

Kristopher B. Karnauskas ◽

Jeffrey P. Donnelly ◽

Kerry Emanuel

Keyword(s):

Global Warming ◽

Tropical Cyclone ◽

North Pacific ◽

Large Scale ◽

Dynamical Downscaling ◽

Vertical Wind Shear ◽

Global Climate Models ◽

Cmip5 Models ◽

The North ◽

The North Pacific

Abstract A downscaling approach is applied to future projection simulations from four CMIP5 global climate models to investigate the response of the tropical cyclone (TC) climatology over the North Pacific basin to global warming. Under the influence of the anthropogenic rise in greenhouse gases, TC-track density, power dissipation, and TC genesis exhibit robust increasing trends over the North Pacific, especially over the central subtropical Pacific region. The increase in North Pacific TCs is primarily manifested as increases in the intense and relatively weak TCs. Examination of storm duration also reveals that TCs over the North Pacific have longer lifetimes under global warming. Through a genesis potential index, the mechanistic contributions of various physical climate factors to the simulated change in TC genesis are explored. More frequent TC genesis under global warming is mostly attributable to the smaller vertical wind shear and greater potential intensity (primarily due to higher sea surface temperature). In contrast, the effect of the saturation deficit of the free troposphere tends to suppress TC genesis, and the change in large-scale vorticity plays a negligible role.

Download Full-text

Impact of air–sea coupling on the climate change signal over the Iberian Peninsula

Climate Dynamics ◽

10.1007/s00382-021-05812-x ◽

2021 ◽

Author(s):

Alba de la Vara ◽

William Cabos ◽

Dmitry V. Sein ◽

Claas Teichmann ◽

Daniela Jacob

Keyword(s):

Climate Change ◽

Iberian Peninsula ◽

Mediterranean Sea ◽

Large Scale ◽

Regional Distribution ◽

Coupled Model ◽

Climate Change Signal ◽

The North ◽

The Mediterranean ◽

The Impact

AbstractIn this work we use a regional atmosphere–ocean coupled model (RAOCM) and its stand-alone atmospheric component to gain insight into the impact of atmosphere–ocean coupling on the climate change signal over the Iberian Peninsula (IP). The IP climate is influenced by both the Atlantic Ocean and the Mediterranean sea. Complex interactions with the orography take place there and high-resolution models are required to realistically reproduce its current and future climate. We find that under the RCP8.5 scenario, the generalized 2-m air temperature (T2M) increase by the end of the twenty-first century (2070–2099) in the atmospheric-only simulation is tempered by the coupling. The impact of coupling is specially seen in summer, when the warming is stronger. Precipitation shows regionally-dependent changes in winter, whilst a drier climate is found in summer. The coupling generally reduces the magnitude of the changes. Differences in T2M and precipitation between the coupled and uncoupled simulations are caused by changes in the Atlantic large-scale circulation and in the Mediterranean Sea. Additionally, the differences in projected changes of T2M and precipitation with the RAOCM under the RCP8.5 and RCP4.5 scenarios are tackled. Results show that in winter and summer T2M increases less and precipitation changes are of a smaller magnitude with the RCP4.5. Whilst in summer changes present a similar regional distribution in both runs, in winter there are some differences in the NW of the IP due to differences in the North Atlantic circulation. The differences in the climate change signal from the RAOCM and the driving Global Coupled Model show that regionalization has an effect in terms of higher resolution over the land and ocean.

Download Full-text