Impacts from SSTs, ENSO, stratospheric QBO and global warming on Hurricanes over the North Atlantic

Processes affecting hurricane development over the North Atlantic like the El Niño Southern Oscillation (ENSO), the stratospheric Quasi-Biennial Oscillation (QBO) and Sea Surface Temperatures (SSTs) are discussed. Global coupled climate model simulations cannot answer directly the question on enhancement of hurricane activities (or its absence) under increased greenhouse gas concentrations because of their too coarse resolution. Therefore large-scale quantities that affect hurricane formation are investigated in a future warmer climate. More frequent or more intense hurricanes are expected from an increase in the local SST, from more latent heat flux from the ocean to the atmosphere, from more westerly winds in the tropical stratosphere that reduces the occurrence of strong easterly phases of the QBO and from a more moist-unstable stratification of the atmosphere. However, a stronger vertical wind shear similar to the difference between El Niño and La Niña events suggests fewer hurricanes in the northern Atlantic. Also a more dry-stable atmosphere would lead to fewer hurricanes. Of the various forcing factors, the impact of wind shear appears to be more decisive, i.e. with a strong wind shear over the tropical Atlantic like during El Niño events strong hurricanes hardly happen while impacts from SSTs over the tropical Atlantic are less significant. As there are some factors favouring an increase of hurricane activity in a future climate and others favouring a decrease, it remains so far difficult to estimate their joint effect and to suggest any decisive trend. The area of hurricane development is limited among others by an increase of vertical wind shear towards the north and south from a minimum at 5-10˚N. This wind shear pattern does not change in a future climate and has the potential of superseding impacts from ocean warming. A need for very long time series for obtaining robust results becomes obvious. Here at least 50 years of data were used

Wind and Wave Extremes over the World Oceans from Very Large Ensembles

Global return values of marine wind speed and significant wave height are estimated from very large aggregates of archived ensemble forecasts at +240-h lead time. Long lead time ensures that the forecasts represent independent draws from the model climate. Compared with ERA-Interim, a reanalysis, the ensemble yields higher return estimates for both wind speed and significant wave height. Confidence intervals are much tighter due to the large size of the dataset. The period (9 yrs) is short enough to be considered stationary even with climate change. Furthermore, the ensemble is large enough for non-parametric 100-yr return estimates to be made from order statistics. These direct return estimates compare well with extreme value estimates outside areas with tropical cyclones. Like any method employing modeled fields, it is sensitive to tail biases in the numerical model, but we find that the biases are moderate outside areas with tropical cyclones.Comment: 28 pages, 16 figure

The role of the equivalent blackbody temperature in the study of Atlantic Ocean tropical cyclones

Satellite measured equivalent blackbody temperatures of Atlantic Ocean tropical cyclones are used to investigate their role in describing the convection and cloud patterns of the storms and in predicting wind intensity. The high temporal resolution of the equivalent blackbody temperature measurements afforded with the geosynchronous satellite provided sequential quantitative measurements of the tropical cyclone which reveal a diurnal pattern of convection at the inner core during the early developmental stage; a diurnal pattern of cloudiness in the storm's outer circulation throughout the life cycle; a semidiurnal pattern of cloudiness in the environmental atmosphere surrounding the storms during the weak storm stage; an outward modulating atmospheric wave originating at the inner core; and long term convective bursts at the inner core prior to wind intensification

Tropical cyclone rainbands can trigger meteotsunamis

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Shi, L., Olabarrieta, M., Nolan, D. S., & Warner, J. C. Tropical cyclone rainbands can trigger meteotsunamis. Nature Communications, 11(1), (2020): 678, doi:10.1038/s41467-020-14423-9.Tropical cyclones are one of the most destructive natural hazards and much of the damage and casualties they cause are flood-related. Accurate characterization and prediction of total water levels during extreme storms is necessary to minimize coastal impacts. While meteotsunamis are known to influence water levels and to produce severe consequences, their impacts during tropical cyclones are underappreciated. This study demonstrates that meteotsunami waves commonly occur during tropical cyclones, and that they can contribute significantly to total water levels. We use an idealized coupled ocean–atmosphere–wave numerical model to analyze tropical cyclone-induced meteotsunami generation and propagation mechanisms. We show that the most extreme meteotsunami events are triggered by inherent features of the structure of tropical cyclones: inner and outer spiral rainbands. While outer distant spiral rainbands produce single-peak meteotsunami waves, inner spiral rainbands trigger longer lasting wave trains on the front side of the tropical cyclones.We thank all the developers of COAWST, ROMS, WRF, and SWAN models. D.N. was supported by NSF grant AGS-1654831. We would like to thank Dr. K. Bagamian for her editorial and writing suggestions. We would like to thank Dr. A. Aretxabaleta for the internal US Geological Survey internal revision and suggestions

Northwestern Pacific typhoon intensity controlled by changes in ocean temperatures.

Dominant climatic factors controlling the lifetime peak intensity of typhoons are determined from six decades of Pacific typhoon data. We find that upper ocean temperatures in the low-latitude northwestern Pacific (LLNWP) and sea surface temperatures in the central equatorial Pacific control the seasonal average lifetime peak intensity by setting the rate and duration of typhoon intensification, respectively. An anomalously strong LLNWP upper ocean warming has favored increased intensification rates and led to unprecedentedly high average typhoon intensity during the recent global warming hiatus period, despite a reduction in intensification duration tied to the central equatorial Pacific surface cooling. Continued LLNWP upper ocean warming as predicted under a moderate [that is, Representative Concentration Pathway (RCP) 4.5] climate change scenario is expected to further increase the average typhoon intensity by an additional 14% by 2100

Climate change vulnerability and adaptation assessment for Fiji

All nations, including Fiji, that are signatories to the United Nations Framework Convention on Climate Change(UNFCCC) are obliged to provide National Communications to the Conference of Parties (COP) of the UNFCCC. The COP4 stressed the need for parties to the Convention to take into account the need for establishing implementation strategies for adaptation to climate and sea-level changes. As such, Fiji is required to submit a National Communication document that shall include information on climate change vulnerability and adaptation implementation policies and strategies. The methodology used in this assessment is based on the Intergovernmental Panel on Climate Change (IPCC) technical guidelines (Carter et al, 1994) for assessing climate change impacts and adaptation. Firstly, the present conditions are examined and key sectors identified. Then, future climatic and non-climatic scenarios are used to examine the possible effects of climate and sea-level changes on the various sectors identified. These then form the basis for identifying possible adaptation response measures for endorsement, adoption and implementation by the Fiji government. Because of the many gaps in present knowledge, and the fact that this study is focussed only on Viti Levu, the recommendations in this report should be seen as starting point for an on-going process of vulnerability and adaptation assessment in Fij

Coriolis force in Geophysics: an elementary introduction and examples

We show how Geophysics may illustrate and thus improve classical Mechanics lectures concerning the study of Coriolis force effects. We are then interested in atmospheric as well as oceanic phenomena we are familiar with, and are for that reason of pedagogical and practical interest. Our aim is to model them in a very simple way to bring out the physical phenomena that are involved.Comment: Accepted for publication in European Journal of Physic