Review of Global Ocean Intermediate Water Masses: 1.Part A, the Neutral Density Surface (the ‘McDougall Surface’) as a Study Frame for Water-Mass Analysis

This review article commences with a comprehensive historical review of the evolution and application of various density surfaces in atmospheric and oceanic studies. The background provides a basis for the birth of the neutral density idea. Attention is paid to the development of the neutral density surface concept from the nonlinearity of the equation of state of seawater. The definition and properties of neutral density surface are described in detail as developed from the equations of state of seawater and the buoyancy frequency when the squared buoyancy frequency N2 is zero, a neutral state of stability. In order to apply the neutral density surface to intermediate water-mass analysis, this review also describes in detail its practical oceanographic application. The mapping technique is focused for the first time on applying regularly gridded data in this review. It is reviewed how a backbone and ribs framework was designed to flesh out from a reference cast and first mapped the global neutral surfaces in the world’s oceans. Several mapped neutral density surfaces are presented as examples for each world ocean. The water-mass property is analyzed in each ocean at mid-depth. The characteristics of neutral density surfaces are compared with those of potential density surfaces.

Mapping of an Approximate Neutral Density Surface with Ungridded Data

A neutral density surface is a logical study frame for water-mass mixing since water parcels spread along such a surface without doing work against buoyancy restoring force. Mesoscale eddies are believed to stir and subsequently mix predominantly along such surfaces. Because of the nonlinear nature of the equation of state of seawater, the process of accurately mapping a neutral density surface necessarily involves lateral computation from one conductivity, temperature and depth (CTD) cast to the next in a logical sequence. By contrast, the depth of a potential density surface on any CTD cast is found solely from the data on this cast. The lateral calculation procedure causes a significant inconvenience. In a previous paper by present author published in this journal (You, 2006), the mapping of neutral density surfaces with regularly gridded data such as Levitus data has been introduced. In this note, I present a new method to find the depth of a neutral density surface from a cast without having to specify an integration path in space. An appropriate reference point is required that is on the neutral density surface and thereafter the neutral density surface can be de- termined by using the CTD casts in any order. This method is only approximate and the likely errors can be estimated by plotting a scatter diagram of all the pressures and potential temperatures on the neutral density surfaces. The method assumes that the variations of potential temperature and pressure (with respect to the values at the reference point) on the neutral density surface are proportional. It is important to select the most appropriate reference point in order to approximately satisfy this assumption, and in practice this is found by inspecting the θ-p plot of data on the surface. This may require that the algorithm be used twice. When the straight lines on the θ-p plot, drawn from the reference point to other points on the neutral density surface, enclose an area that is external to the clus- ter of θ-p points of the neutral density surface, errors will occur, and these errors can be quantified from this diagram. Examples showing the use of the method are presented for each of the world’s main oceans.

Recent advancements in aircraft and in situ observations of tropical cyclones

Observations of tropical cyclones(TC)from aircraft and in situ platforms provide critical and unique information for analyzing and forecasting TC intensity,structure,track,and their associated hazards.This report,prepared for the tenth International Workshop on Tropical Cyclones(IWTC-10),discusses the data collected around the world in TCs over the past four years since the IWTC-9,improvements to observing techniques,new instruments designed to achieve sustained and targeted atmospheric and oceanic observations,and select research results related to these observations.In the Atlantic and Eastern and Central Pacific basins,changes to operational aircraft reconnaissance are discussed along with several of the research field campaigns that have taken place recently.The changes in the use and impact of these aircraft observations in numerical weather prediction models are also provided along with updates on some of the experimental aircraft instrumentation.Highlights from three field campaigns in the Western Pacific basin are also discussed.Examples of in-situ data collected within recent TCs such as Hurricane Ian(2022),also demonstrate that new,emerging technologies and observation strategies reviewed in this report,definitely have the potential to further improve ocean-atmosphere coupled intensity forecasts.

Reproductive biology of largehead hairtail(Trichiurus lepturus)in south-eastern Australia

Knowledge of reproductive biology and life-history traits of populations exploited by fisheries is important for their sustainable management.We investigated the life-history traits of Trichiurus lepturus(largehead hairtail)in south-eastern Australia;a region of low exploitation for this otherwise heavily exploited circumglobal species,to investigate whether there were differences in the reproductive biology and life-history traits in the south-east Australian population compared with those in other regions.We also used histological sections to examine male and female gonads at a microscopic level.Trichiurus lepturus in south-eastern Australia had a greater maximum length(193 cm total length(TL)),matured at a larger length(108 cm TL at 50%mature)and had a spawning period(March to September,Austral winter)that was inconsistent with other regions.The overall sex ratio of 1:0.4 females:males was consistent with a female dominant sex ratio observed in other regions,particularly in larger length classes.However,females in the current study dominated samples from both estuarine and coastal habitats,as well as during the spawning and non-spawning periods,which is not consistent with the patterns found in other regions.Differences in south-eastern Australia may relate to limited fishing pressure,genetic variation,or differences in environmental factors that influence reproductive development,including temperature,trophic resources and habitat.