Interest in mapping the global distribution of malaria is motivated by a need to define populations at risk for appropriate resource allocation and to provide a robust framework for evaluating its global economic impact. Comparison of older and more recent malaria maps shows how the disease has been geographically restricted, but it remains entrenched in poor areas of the world with climates suitable for transmission. Here we provide an empirical approach to estimating the number of clinical events caused by Plasmodium falciparum worldwide, by using a combination of epidemiological, geographical and demographic data. We estimate that there were 515 (range 300-660) million episodes of clinical P. falciparum malaria in 2002. These global estimates are up to 50% higher than those reported by the World Health Organization (WHO) and 200% higher for areas outside Africa, reflecting the WHO's reliance upon passive national reporting for these countries. Without an informed understanding of the cartography of malaria risk, the global extent of clinical disease caused by P. falciparum will continue to be underestimated.

/pdf/the-global-distribution-of-clinical-episodes-of-plasmodium-20zeeiovaa.pdf

The global distribution of clinical episodes of Plasmodium falciparum malaria

We assembled a dataset of 14C-based productivity measurements to understand the critical variables required for accurate assessment of daily depth-integrated phytoplankton carbon fixation (PP(PPeu)u) from measurements of sea surface pigment concentrations (Csat)(Csat). From this dataset, we developed a light-dependent, depth-resolved model for carbon fixation (VGPM) that partitions environmental factors affecting primary production into those that influence the relative vertical distribution of primary production (Pz)z) and those that control the optimal assimilation efficiency of the productivity profile (P(PBopt). The VGPM accounted for 79% of the observed variability in Pz and 86% of the variability in PPeu by using measured values of PBopt. Our results indicate that the accuracy of productivity algorithms in estimating PPeu is dependent primarily upon the ability to accurately represent variability in Pbopt. We developed a temperature-dependent Pbopt model that was used in conjunction with monthly climatological images of Csat sea surface temperature, and cloud-corrected estimates of surface irradiance to calculate a global annual phytoplankton carbon fixation (PPannu) rate of 43.5 Pg C yr‒1. The geographical distribution of PPannu was distinctly different than results from previous models. Our results illustrate the importance of focusing Pbopt model development on temporal and spatial, rather than the vertical, variability.

https://aslopubs.onlinelibrary.wiley.com/doi/epdf/10.4319/lo.1997.42.1.0001

Photosynthetic rates derived from satellite‐based chlorophyll concentration

[1] A new 2° resolution global climatology of the mixed layer depth (MLD) based on individual profiles is constructed. Previous global climatologies have been based on temperature or density-gridded climatologies. The criterion selected is a threshold value of temperature or density from a near-surface value at 10 m depth (ΔT = 0.2°C or Δσθ = 0.03 kg m−3). A validation of the temperature criterion on moored time series data shows that the method is successful at following the base of the mixed layer. In particular, the first spring restratification is better captured than with a more commonly used larger criteria. In addition, we show that for a given 0.2°C criterion, the MLD estimated from averaged profiles results in a shallow bias of 25% compared to the MLD estimated from individual profiles. A new global seasonal estimation of barrier layer thickness is also provided. An interesting result is the prevalence in mid- and high-latitude winter hemispheres of vertically density-compensated layers, creating an isopycnal but not mixed layer. Consequently, we propose an optimal estimate of MLD based on both temperature and density data. An independent validation of the maximum annual MLD with oxygen data shows that this oxygen estimate may be biased in regions of Ekman pumping or strong biological activity. Significant differences are shown compared to previous climatologies. The timing of the seasonal cycle of the mixed layer is shifted earlier in the year, and the maximum MLD captures finer structures and is shallower. These results are discussed in light of the different approaches and the choice of criterion.

/pdf/mixed-layer-depth-over-the-global-ocean-an-examination-of-3xkoso12fd.pdf

Mixed layer depth over the global ocean: An examination of profile data and a profile-based climatology

[1] The Madden-Julian Oscillation (MJO) is the dominant component of the intraseasonal (30–90 days) variability in the tropical atmosphere. It consists of large-scale coupled patterns in atmospheric circulation and deep convection, with coherent signals in many other variables, all propagating eastward slowly (∼5 m s−1) through the portion of the Indian and Pacific oceans where the sea surface is warm. It constantly interacts with the underlying ocean and influences many weather and climate systems. The past decade has witnessed an expeditious progress in the study of the MJO: Its large-scale and multiscale structures are better described, its scale interaction is recognized, its broad influences on tropical and extratropical weather and climate are increasingly appreciated, and its mechanisms for disturbing the ocean are further comprehended. Yet we are facing great difficulties in accurately simulating and predicting the MJO using sophisticated global weather forecast and climate models, and we are unable to explain such difficulties based on existing theories of the MJO. It is fair to say that the MJO remains an unmet challenge to our understanding of the tropical atmosphere and to our ability to simulate and predict its variability. This review, motivated by both the acceleration and gaps in our knowledge of the MJO, intends to synthesize what we currently know and what we do not know on selected topics: its observed basic characteristics, mechanisms, numerical modeling, air-sea interaction, and influences on the El Nino and Southern Oscillation.

/pdf/madden-julian-oscillation-2f6izjkiaw.pdf

Madden‐Julian Oscillation

During El Nino-Southern Oscillation (ENSO) events, the atmospheric response to sea surface temperature (SST) anomalies in the equatorial Pacific influences ocean conditions over the remainder of the globe. This connection between ocean basins via the ''atmospheric bridge'' is reviewed through an examination of previous work augmented by analyses of 50 years of data from the National Centers for Environmental Prediction- National Center for Atmospheric Research (NCEP-NCAR) reanalysis project and coupled atmospheric general circulation (AGCM)-mixed layer ocean model experiments. Observational and modeling studies have now established a clear link between SST anomalies in the equatorial Pacific with those in the North Pacific, north tropical Atlantic, and Indian Oceans in boreal winter and spring. ENSO-related SST anomalies also appear to be robust in the western North Pacific during summer and in the Indian Ocean during fall. While surface heat fluxes are the key component of the atmospheric bridge driving SST anomalies, Ekman transport also creates SST anomalies in the central North Pacific although the full extent of its impact requires further study. The atmospheric bridge not only influences SSTs on interannual timescales but also affects mixed layer depth (MLD), salinity, the seasonal evolution of upper-ocean temperatures, and North Pacific SST variability at lower fre- quencies. The model results indicate that a significant fraction of the dominant pattern of low-frequency (.10 yr) SST variability in the North Pacific is associated with tropical forcing. AGCM experiments suggest that the oceanic feedback on the extratropical response to ENSO is complex, but of modest amplitude. Atmosphere- ocean coupling outside of the tropical Pacific slightly modifies the atmospheric circulation anomalies in the Pacific-North America (PNA) region but these modifications appear to depend on the seasonal cycle and air- sea interactions both within and beyond the North Pacific Ocean.

The Atmospheric Bridge: The Influence of ENSO Teleconnections on Air-Sea Interaction over the Global Oceans

THE physical structure of the Pacific and Indian oceans is substantially affected by the inter-ocean transport of excess fresh water from the North Pacific Ocean through the Indonesian seas1,2. The efficiency of this transport is an important regulator of the meridional overturning of these oceans1,2, and hence perhaps of the global thermohaline circulation3; in addition, the seepage of warm water out of the Pacific affects the volume of the western Pacific warm pool, and thus may influence EI Nino events24. But the sources, pathways and physical properties of the Indonesian throughflow are not well enough characterized to allow its influence on ocean circulation and the climate system to be quantified. Here we report salinity, temperature and chemical-tracer data from the Indonesian seas which show that the throughflow is dominated by two components: one of low-salinity, well ventilated North Pacific water through the upper thermocline of the Makassar Strait, and the other of more saline South Pacific water through the lower thermocline of the eastern Indonesian seas. Seasonal (monosonal) variations in the ratio of these components, perhaps modulated by EI Nino conditions, imply the existence of potentially important variable feedbacks to the ocean circulation and climate system.

Pathways of water between the Pacific and Indian oceans in the Indonesian seas

The Western Equatorial Pacific Ocean Circulation Study (WEPOCS) III expedition was conducted from June 18 through July 31, 1988, in the far western equatorial Pacific Ocean to observe the low-latitude western boundary circulation there, with emphasis on the Mindanao Current. This survey provides the first quasi-synoptic set of current measurements which resolve all of the important upper-ocean currents in the western tropical Pacific. Observations were made of the temperature, salinity, dissolved oxygen, and current profiles with depth; of water mass properties including transient tracers; and of evolving surface flows with a dense array of Lagrangian drifters. This paper provides a summary of the measurements and a preliminary description of the results. The Mindanao Current was found to be a narrow, southward-flowing current along the eastward side of the southern Philippine Islands, extending from 14°N to the south end of Mindanao near 6°N, where it then separates from the coast and penetrates into the Celebes Sea. The current strengthens to the south and is narrowest at 10°N. Direct current measurements reveal transports in the upper 300 m increasing from 13 Sv to 33 Sv (1 Sverdrup = 1 × 106 m3 s−1) between 10°N and 5.5°N. A portion of the Mindanao Current appears to recurve cyclonically in the Celebes Sea to feed the North Equatorial Countercurrent, merging with waters from the South Equatorial Current and the New Guinea Coastal Undercurrent. Another portion of the Mindanao Current appears to flow directly into the NECC without entering the Celebes Sea. The turning of the currents into the NECC is associated with the Mindanao and Halmahera eddies.

Observations of the Mindanao Current during the western equatorial Pacific Ocean circulation study

The isothermal compressibility of water from 0 to 100 °C and 0 to 1000 bar has been determined from Wilson's sound velocity measurements which have been normalized to Kell's 1 atm values. The isothermal compressibilities determined from the sound velocities have been fit, with a maximum deviation in compressibility of ± 0.016 × 10−6 bar−1, to an extended bulk modulus equation V 0 P/(V 0‐V P ) = B + A 1 P + A 2 P 2, where V 0 and V P are the specific volume at an applied pressure of zero and P; and B, A 1, and A 2 are temperature dependent constants. Our specific volume results are in reasonable agreement with the work of Kell and Whalley at low pressures; however, our results at high pressures (1000 bar) disagree by as much as 169 ppm (the average deviation is approximately 115 ppm). A comparison of the compressibilities indicates a parabolic shift in Kell and Whalley's work with a maximum of approximately 0.205 × 10−6 bar−1 at 400 bar and 5 °C. Since the velocity of sound data is extremely reliable (± 0.2 m/sec) and the maximum error in the compressibilities derived from the sound data is within ± 0.016 × 10−6 bar−1, our PVT results based upon the sound data are more accurate than any direct measurements made to date.

Compressibility of water as a function of temperature and pressure

The western equatorial Pacific is a crossroads for thermocline and intermediate waters formed at higher latitudes. The role of the equatorward flowing, low-latitude western boundary currents (LLWBCs) in advecting well-ventilated (with respect to atmospheric gases), higher-latitude waters varies with density. At densities <26.5 r 0 the Mindanao Current (MC) (Wyrtki, 1961; Masuzawa, 1969) advects recently ventilated water observed as tracer maxima predominantly from the North Pacific subtropical gyre (tropical water is <3 years old and the remnant subtropical mode water is <5 years); it branches into the southern Celebes Sea feeding the Indonesian throughflow and toward the east north of the equator. Between 26.5 and 26.8 r 0 the MC advects predominantly North Pacific Intermediate Water (having a component that is <20 years old) mainly into the southern Celebes Sea; there is also some indication of a tracer maximum extending eastward north of the equator. However, below 26.8 r 0, South Pacific water masses appear to be stronger, so that they are the major ventilation source for the western equatorial region, including the Celebes Sea. At 27.2 r 0 the New Guinea Coastal Undercurrent advects Antarctic Intermediate Water (having a component that is <25 years) into a background of older water. The presence of subtropical mode water in the western tropical North Pacific and Celebes Sea is attributed to an equatorward LLWBC in the North Pacific (and suggests a reason for the absence of 18 o water in the tropical North Atlantic). The absence of a LLWBC in the North Atlantic highlights a basic difference between the circulation of the two oceans, which may be due to the different ways they import and export water. At the western boundary in the North Atlantic, warm water is imported and cold water is exported as part of the global thermohaline circulation, whereas at the western boundary in the North Pacific, warm water (above 26.8 r 0) is mainly exported to the Indian Ocean via the Indonesian throughflow and cold water is imported.

Rana A. Fine

Papers

Pathways of water between the Pacific and Indian oceans in the Indonesian seas

Observations of the Mindanao Current during the western equatorial Pacific Ocean circulation study

Compressibility of water as a function of temperature and pressure

The western equatorial Pacific: A water mass crossroads

Source waters of the Pacific Equatorial Undercurrent