Chasing rainfall: estimating event precipitation along tracks of tropical cyclones via reanalysis data and in-situ gauges

Tropical cyclones (TCs) are an important water source in many regions around the world, replenishing local dams, waterways and groundwater systems. Three diverse precipitation datasets were tested for dissimilarities in their rainfall characteristics via a new, freely available rainfall tracking toolbox for MATLAB and GNU Octave users: 1) the ERA5 global reanalysis, 2) the Global Historical Climatology Network (GHCN)-Daily station dataset and 3) the regional SILO (Scientific Information for Land Owners) database. Although SILO only covers Australia, its relatively high resolution (0.05°) provides advantages for studies in that region. To test the differences in precipitation datasets, six episodes (eight individual TC events) in all major basins affected by TCs have been selected. These include two instances in which consecutive TCs severely impacted the same region (TCs Idai and Kenneth in south-eastern Africa during March/April 2019 – and hurricanes Eta and Iota in Central America in November 2020). Precipitation for TC episodes was explored through event totals and the proportional contribution to water years within each dataset. Each precipitation dataset demonstrated its inherent advantages and drawbacks, highlighting the benefits of using more than one source to thoroughly evaluate an individual event. These attributes – coupled with the associated impacts of cyclonic events – reinforce the importance of developing tools that can aid in managing TC-related rainfall and flooding potential

Characterizing Australia's east coast cyclones (1950–2019)

East coast cyclones (ECCs) provide an essential reprieve from dry periods across eastern Australia. They also deliver flood‐producing rains with significant economic, social and environmental impacts. Assessing and comparing the influence of different types of cyclones is hindered by an incomplete understanding of ECC typology, given their widely variable spatial and temporal characteristics. This study employs a track‐clustering method (probabilistic curve‐aligned regression model) to identify key cyclonic pathways for ECCs from 1950 to 2019. Six spatially independent clusters were successfully distinguished and further sub‐classified (coastal, continental and tropical) based on their genesis location. The seasonality and long‐term variability, intensity (maximum Laplacian value ± two days) and event‐based rainfall were then evaluated for each cluster to quantify the impact of these storms on Australia. The highest quantity of land‐based rainfall per event is associated with the tropical cluster (Cluster 6), whereas widespread rainfall was also found to occur in the two continental lows (Cluster 4 and 5). Cyclone tracks orientated close to the coast (clusters 1, 2 and 3) were determined to be the least impactful in terms of rainfall and intensity, despite being the most common cyclone type. In terms of interannual variability, sea surface temperature anomalies suggest an increased cyclone frequency for clusters 1 (austral winter) and 4 (austral spring) during a central Pacific El Niño. Further, cyclone incidence during IOD‐negative conditions was more pronounced in winter for clusters 1, 2, 3 – and clusters 4 and 5 in spring. All cyclones also predominantly occurred in SAM‐positive conditions. However, winter ECCs for clusters 1 and 3 had a higher frequency in SAM‐negative. This new typology of ECCs via spatial clustering provides crucial insights into the systems that produce extreme rainfall across eastern Australia and should be used to inform future hazard management of cyclone events. This article is protected by copyright. All rights reserved

The oceanographic and geochemical effects of mixed layer depth variability and increasing anthropogenic CO₂ on the inorganic carbon system of the Coral Sea

Global warming is predicted to result in a significant shallowing of the mixed layer depth (MLD) in many ocean regions and, thus, warmer surface waters (within the MLD), which could have dire consequences for coral reef ecosystems and the ocean’s capability for CO₂ uptake. The seasonal to long-term variability of the MLD within the Coral Sea was examined using conductivity-temperature-depth (CTD) profiles from the World Ocean Database (WOD), and of Argo floats deposited within the Coral Sea or its vicinity since July 2001. A distinct seasonality in the MLD is evident throughout the Coral Sea, but was generally more pronounced in higher latitudes as a result of greater seasonality in sea surface temperature and wind stress. While summer mixed layers are relatively homogeneously shallow throughout the Coral Sea, winter mixed layers in higher latitudes tend to be significantly deeper compared to tropical regions. No long-term trends in mean monthly MLD are evident, possibly due to the relative data scarcity prior to the onset of the Argo project. The Argo program represents a significant advancement for marine studies. In the future, it will enable more detailed studies on long-term variability and trends of the MLD and its associated impact on the photic zone and the Great Barrier Reef. \ud \ud Due to the absence of a similar program for ocean biogeochemistry, seasonal and long-term changes in fugacity of CO₂ (fCO₂) and pH within the Coral Sea were investigated not only using observational data (from WOD and other sources), but also with the sophisticated coupled regional model ROMS-PISCES. Both observational fCO₂ and pH exhibit some seasonality in the Coral Sea. Seawater fCO₂ (fCO₂sea) values tend to increase towards summer, which is linked to the positive relationship between fugacity and sea surface temperature. As a result, the capacity of the Coral Sea to act as a sink of atmospheric CO₂ is reduced during summer, and is more likely to act as a source of CO₂ to the atmosphere. No long-term changes were discernible in the very sporadically observed pH values, whereas fCO₂sea appears to have increased at a rate of 1.41 ± 0.04 μatm/year from 1983 to 2001.\ud \ud As a result of increased atmospheric CO₂ levels, oceanic geochemistry has already significantly changed since 1880. The effects of higher atmospheric fCO₂ will likely be further aggravated by shallower MLDs as a result of reduced upper ocean mixing due to warmer sea surface temperatures. Various IPCC scenarios for predicted atmospheric CO₂ levels were used to determine likely changes in the geochemistry of the Coral Sea during the 21st century. Projected increases of atmospheric CO₂ to 650-1000 ppmv results in a decrease of sea surface pH by 0.14-0.38 units in the numerical model, with the Coral Sea simultaneously changing from a seasonal source of atmospheric CO₂ to a predominant sink. Concurrent with increased ocean acidification and fCO₂, the saturation state of aragonite and calcite will decline significantly, which would have wide-reaching effects on the coral calcification rates and the general health, and structural strength, of calcifying organisms. These biogeochemical effects will be exacerbated by an expected decrease in the MLD throughout the Coral Sea, and concomitant higher temperatures within the mixed layer. To this date, there has been surprisingly little effort to monitor the changes in biogeochemistry within the Coral Sea and, specifically, within the GBR as a result of increased atmospheric fCO₂. Further large-scale studies are required throughout the entire Coral Sea in order to accurately determine the long-term trends in the oceanic carbon cycle

GHCN-Daily: a treasure trove of climate data awaiting discovery

International collaboration to create and maintain international, freely accessible datasets greatly facilitates research in many scientific fields. The Global Historical Climatology Network (GHCN)-Daily database provides access to a diverse range of daily weather station data, including precipitation and temperature variables. These data are supplied as individual, station-specific files and structured in a non-delimited format. Here, the GHCN-Daily data structure, spatio-temporal content and associated caveats are delineated. The regularly updated collection now features data from over 100 000 stations in 218 countries and territories. While rigorous quality tests are routinely applied for GHCN-Daily, the database excludes the original quality flags from the source agencies. The extraction of climate variables from the GHCN-Daily database can be challenging for novice users and may thus dissuade from the uptake of this valuable dataset. Consequently, a user-friendly toolkit for MATLAB and GNU Octave is also provided to aid data retrieval from all relevant weather stations. The toolkit reformats the extracted GHCN-Daily data into a more accessible structure to facilitate data mining and research on a large scale

Geographical position of Argo floats within the Coral Sea.

<p>The colour scheme of the Argo data is denoting ocean heat content (OHC, 10⁶ kJ/250 m), which was integrated to a depth of 250 m. Locations are only displayed for CTD profiles that encompass the entire top 250 m of water.</p

Comparison of MLD_ref with the depths obtained by four different threshold values.

<p>The mean of paired absolute differences (mean_ad) and bias (mean difference) are listed with their associated standard error (standard deviation divided by , <i>N</i> = sample size).</p

Seasonality of sea surface temperature (SST).

<p>Spatial distribution of SST during A) January–March, B) April–June, C) July–September and D) October–December. The SST data has been obtained from Argo floats and represent temperatures in the upper 10 m.</p

Total Argo CTD profile availability.

<p>The distribution of total number of Argo CTD profiles available within the Coral Sea prior to 2009 is displayed.</p