Showing papers by "I-I Lin published in 2016"

Tropical cyclone-ocean interaction in Typhoon Megi (2010)—A synergy study based on ITOP observations and atmosphere-ocean coupled model simulations

Abstract: A mesoscale model coupling the Weather Research and Forecasting model and the three-dimensional Price-Weller-Pinkel ocean model is used to investigate the dynamical ocean response to Megi (2010). It is found that Megi induces sea surface temperature (SST) cooling very differently in the Philippine Sea (PS) and the South China Sea (SCS). The results are compared to the in situ measurements from the Impact of Typhoons on the Ocean in the Pacific (ITOP) 2010 field experiment, satellite observations, and ocean analysis field from Eastern Asian Seas Ocean Nowcast/Forecast System of the U.S. Naval Research Laboratory. The uncoupled and coupled experiments simulate relatively accurately the track and intensity of Megi over PS; however, the simulated intensity of Megi over SCS varies significantly among the experiments. Only the experiment coupled with three-dimensional ocean processes, which generates rational SST cooling, reasonably simulates the storm intensity in SCS. Our results suggest that storm translation speed and upper ocean thermal structure are two main factors responsible for Megi's distinct different impact over PS and over SCS. In addition, it is shown that coupling with one-dimensional ocean process (i.e., only vertical mixing process) is not enough to provide sufficient ocean response, especially under slow translation speed (~2–3 m s−1), during which vertical advection (or upwelling) is significant. Therefore, coupling with three-dimensional ocean processes is necessary and crucial for tropical cyclone forecasting. Finally, the simulation results show that the stable boundary layer forms on top of the Megi-induced cold SST area and increases the inflow angle of the surface wind.

Improvements in Typhoon Intensity Change Classification by Incorporating an Ocean Coupling Potential Intensity Index into Decision Trees

Abstract: Tropical cyclone (TC) intensity prediction, especially in the warning time frame of 24–48 h and for the prediction of rapid intensification (RI), remains a major operational challenge. Sea surface temperature (SST) based empirical or theoretical maximum potential intensity (MPI) is the most important predictor in statistical intensity prediction schemes and rules derived by data mining techniques. Since the underlying SSTs during TCs usually cannot be observed well by satellites because of rain contamination and cannot be produced on a timely basis for operational statistical prediction, an ocean coupling potential intensity index (OC_PI), which is calculated based on pre-TC averaged ocean temperatures from the surface down to 100 m, is demonstrated to be important in building the decision tree for the classification of 24-h TC intensity change ΔV24, that is, RI (ΔV24 ≥ 25 kt, where 1 kt = 0.51 m s−1) and non-RI (ΔV24 < 25 kt). Cross validations using 2000–10 data and independent verification usin...

Influence of Oceanic Intraseasonal Kelvin Waves on Eastern Pacific Hurricane Activity

Abstract: Recent studies have highlighted the role of subsurface ocean dynamics in modulating eastern Pacific (EPac) hurricane activity on interannual time scales. In particular, the well-known El Nino–Southern Oscillation (ENSO) recharge–discharge mechanism has been suggested to provide a good understanding of the year-to-year variability of hurricane activity in this region. This paper investigates the influence of equatorial subsurface subannual and intraseasonal oceanic variability on tropical cyclone (TC) activity in the EPac. That is to say, it examines previously unexplored time scales, shorter than interannual, in an attempt to explain the variability not related to ENSO. Using ocean reanalysis products and TC best-track archive, the role of subannual and intraseasonal equatorial Kelvin waves (EKW) in modulating hurricane intensity in the EPac is examined. It is shown first that these planetary waves have a clear control on the subannual and intraseasonal variability of thermocline depth in the EPac...

Impacts of Tides and Typhoon Fanapi (2010) on Seas Around Taiwan

Abstract: We used satellite data, typhoon-resolving atmospheric forcing and a data assimilating ocean model, the East Asian Seas Nowcast/Forecast System (EASNFS), to investigate circulation and three upwelling regions perturbed by tides and Typhoon Fanapi (2010) in the seas around Taiwan. The three upwelling areas located off northeast Taiwan, off southeast China and over the Penghu Channel off southwest Taiwan are normally limited in expanse before Fanapi. The tidal currents enhance all three. To cope with typhoon strength atmospheric forcing, we applied typhoon-resolving Weather Research and Forecasting (WRF) model wind fields that significantly enhanced Fanapi-induced upwelling. Approaching Taiwan, Fanapi induces a cold wake spreading preferably on the right side of the essentially westward running track in the western Pacific. The three upwelling areas in the East China Sea and Taiwan Strait subsequently become expansive as Fanapi approaches and enters the Taiwan Strait. The mechanisms leading to normal or Fanapi-perturbed upwelling and circulation in seas around Taiwan, especially the latter two mentioned above, are suggested. In essence, Fanapi disrupts circulation in the Taiwan Strait, and also the Taiwan Strait outflow entering the East China Sea, leading to expanded upwelling areas. We also suggest that high-resolution wind and tides application is essential for the upwelling modeling study and also the general circulation in the region with and without typhoons.

Modes of hurricane activity variability in the Eastern Pacific: implications for the 2016 season

Abstract: A gridded product of Accumulated Cyclone Energy (ACE) in the Eastern Pacific is constructed to assess the dominant mode of Tropical Cyclone (TC) activity variability Results of an EOF decomposition and regression analysis of environmental variables indicate that the two dominant modes of ACE variability (40% of the total variance) are related to different flavors of the El Nino Southern Oscillation (ENSO) The first mode, more active during the later part of the hurricane season (September-November), is linked to the Eastern Pacific El Nino through the delayed oceanic control associated with the recharge-discharge mechanism The second mode, dominant in the early months of the hurricane season, is related to the Central Pacific El Nino mode and the associated changes in atmospheric variability A multi-linear regression forecast model of the dominant principal components of ACE variability is then constructed The wintertime subsurface state of the eastern equatorial Pacific (characterizing ENSO heat discharge), the east-west tilt of the thermocline (describing ENSO phase transition), the anomalous ocean surface conditions in the TC region in spring (portraying atmospheric changes induced by persistence of local surface anomalies) and the intraseasonal atmospheric variability in the Western Pacific are found to be good predictors of TC activity Results complement NOAA's official forecast, by providing additional spatial and temporal information They indicate a more active 2016 season (~2 times the ACE mean) with a spatial expansion into the Central Pacific associated with the heat discharge from the 2015/16 El Nino