REGENERATION STRATEGIES OF PALMS (ARECACEAE) IN RESPONSE TO CYCLONIC DISTURBANCES

LATIFAH, D., CONGDON, R. A. & HOLTUM, J. A. 2016. Regeneration strategies of palms (Arecaceae) in response to cyclonic disturbances. Reinwardtia 15 (1): 43 ? 59. — Tropical cyclones may act as important ecological drivers in northern Australia including north Queensland, as several cyclones impact this region each year between November and May. Extensive research has been conducted to investigate how regeneration of rainforest plant communities respond to frequent cyclonic disturbances. However, there have been few such studies on palms although they are important components of many rainforests. This research aimed to investigate the effects of canopy gaps following cyclonic disturbance (case study: Cyclone Larry) on regeneration of Arenga australasica (H. Wendl. & Drude) S. T. Blake ex H. E. Moore, Calamus australis Mart., C. moti F. M. Bailey, Hydriastele wendlandiana (F. Muell.) H. Wendl. & Drude and Licuala ramsayi var. ramsayi (F. Muell.) H. Wendl. & Drude. The field research was carried out at five sites in three areas located in northern Queensland: Tam O’Shanter/Djiru National Park, Clump Mountain National Park and Kurrimine Beach Conservation Park. Observations were made of recruitment, growth rate, leaf turnover and life history. We found that responses of palm regeneration following cyclonic disturbance varied among study sites; however, the recruitment of several species was favoured in gaps created by cyclones. The results also provide information on the various stages in the life cycle of the study palms.

Influence of Equatorial Waves on the Genesis of Super Typhoon Haiyan (2013)

The influence of equatorial wave disturbances on the genesis of Super Typhoon Haiyan (2013) is investigated through spectral, composite, and ensemble sensitivity analysis of various observational datasets in combination with predictions from an operational ensemble. Under the favorable large-scale environmental conditions of the Asian monsoon combined with the Madden–Julian oscillation (MJO), the incipient Haiyan develops from a cyclonic disturbance that originates from a train of westward-propagating mixed Rossby–gravity (MRG) waves. Haiyan eventually develops in the monsoon trough region at the leading edge of the moist MJO phase that has strong low-level convergence, high moisture content, and weak shear, along with high sea surface temperature. These favorable environmental conditions promote the intensification of deep moist convection that facilitates the development of the cyclonic disturbance from an MRG wave into a tropical depression, which later intensifies rapidly into Super Typhoon Haiyan, one of the world’s strongest and most destructive tropical storms ever recorded. Results from ensemble sensitivity analyses are consistent with this finding and further show that the uncertainties in tropical waves and their interactions can impact the large-scale environment surrounding Haiyan’s precursor and therefore limit the predictability of tropical cyclone formation and intensity. The better-performing members tend to have a stronger initial MRG wave disturbance, which provides a stronger initial seed for the later development of the storm, as well as a stronger moist MJO wave in the tropical region, which not only promotes deep convection near the precursor location, but also reduces the environmental vertical wind shear by strengthening the tropical westerlies.

Local Wintertime Tropospheric Response to Oceanic Heat Anomalies in the Nordic Seas Area

A regression analysis between observed summertime Atlantic water temperature anomalies at the entrance to the Barents Sea and atmospheric fields in the following winter from the NCEP–NCAR reanalysis in the period 1982–2006 is carried out. It shows that the ocean plays a key role in shaping wintertime tropospheric variability in the Nordic seas (Greenland–Iceland–Norwegian and Barents Seas) region. The oceanically driven atmospheric circulation anomaly around the Nordic seas marginal ice zone is intensified at the surface as a result of a thermally direct baroclinic adjustment. Frictional convergence in the cyclonic disturbance corresponding to warm ocean temperature anomalies forces ascending motion at the top of the planetary boundary layer and a compensating divergence aloft, which over the Barents Sea is extreme at the tropopause. A quasi-meridional overturning circulation anomaly is closed by descending motion south of the cyclonic disturbance. In addition, an equivalent barotropic flow anomaly appears in the upper troposphere. It is partly driven by eddy–mean flow interactions, as revealed by anomalies in the vorticity budget. The atmospheric response to oceanic forcing in the Nordic seas area is unique because of the prominent role of surface friction and because of specific profiles of diabatic heating and eddy heat flux convergence over the Barents Sea. As revealed by anomalies in the heat budget, the combined effect of diabatic heating and thermal eddy forcing acts, when the diabatic heating is positive, as a heat sink at the surface and a heat source aloft. The strongest anomalous heating occurs in the upper troposphere/lower stratosphere where it counteracts the dynamic cooling owing to anomalous ascending motion.

Topographically generated cyclonic disturbance and lee waves in a stratified rotating fluid

The flow about an obstacle in horizontal motion relative to a stratified Boussinesq fluid in a deep, rapidly rotating container is studied. Numerical and asymptotic analyses of the linearized boundary-value problems for a shallow topography are made to delineate the influence of stratification and ground topography on wave and flow structure, and to ascertain the presence of a solitary anticyclonic, or cyclonic, disturbance in the far field at high as well as low stratification. Although the analyses are restricted to the rapidly rotating case corresponding to a vanishingly small Rossby number, it is pointed out that the cyclonic feature remains a valid inviscid description in the far field except for an infinite Rossby number corresponding to no rotation.