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Lisan Yu
and
Robert A. Weller

A 25-yr (1981–2005) time series of daily latent and sensible heat fluxes over the global ice-free oceans has been produced by synthesizing surface meteorology obtained from satellite remote sensing and atmospheric model reanalyses outputs. The project, named Objectively Analyzed Air–Sea Fluxes (OAFlux), was developed from an initial study of the Atlantic Ocean that demonstrated that such data synthesis improves daily flux estimates over the basin scale. This paper introduces the 25-yr heat flux analysis and documents variability of the global ocean heat flux fields on seasonal, interannual, decadal, and longer time scales suggested by the new dataset.

The study showed that, among all the climate signals investigated, the most striking is a long-term increase in latent heat flux that dominates the data record. The globally averaged latent heat flux increased by roughly 9 W m−2 between the low in 1981 and the peak in 2002, which amounted to about a 10% increase in the mean value over the 25-yr period. Positive linear trends appeared on a global scale, and were most significant over the tropical Indian and western Pacific warm pool and the boundary current regions. The increase in latent heat flux was in concert with the rise of sea surface temperature, suggesting a response of the atmosphere to oceanic forcing.

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THE PIRATA PROGRAM

History, Accomplishments, and Future Directions *

Bernard Bourlès
,
Rick Lumpkin
,
Michael J. McPhaden
,
Fabrice Hernandez
,
Paulo Nobre
,
Edmo Campos
,
Lisan Yu
,
Serge Planton
,
Antonio Busalacchi
,
Antonio D. Moura
,
Jacques Servain
, and
Janice Trotte

The Pilot Research Moored Array in the tropical Atlantic (PIRATA) was developed as a multinational observation network to improve our knowledge and understanding of ocean-atmosphere variability in the tropical Atlantic. PIRATA was motivated by fundamental scientific issues and by societal needs for improved prediction of climate variability and its impact on the economies of West Africa, northeastern Brazil, the West Indies, and the United States. In this paper the implementation of this network is described, noteworthy accomplishments are highlighted, and the future of PIRATA in the framework of a sustainable tropical Atlantic observing system is discussed. We demonstrate that PIRATA has advanced beyond a “Pilot” program and, as such, we have redefined the PIRATA acronym to be “Prediction and Research Moored Array in the Tropical Atlantic.”

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C. L. Gentemann
,
Joel P. Scott
,
Piero L. F. Mazzini
,
Cassia Pianca
,
Santha Akella
,
Peter J. Minnett
,
Peter Cornillon
,
Baylor Fox-Kemper
,
Ivona Cetinić
,
T. Mike Chin
,
Jose Gomez-Valdes
,
Jorge Vazquez-Cuervo
,
Vardis Tsontos
,
Lisan Yu
,
Richard Jenkins
,
Sebastien de Halleux
,
Dave Peacock
, and
Nora Cohen
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C. L. Gentemann
,
Joel P. Scott
,
Piero L. F. Mazzini
,
Cassia Pianca
,
Santha Akella
,
Peter J. Minnett
,
Peter Cornillon
,
Baylor Fox-Kemper
,
Ivona Cetinić
,
T. Mike Chin
,
Jose Gomez-Valdes
,
Jorge Vazquez-Cuervo
,
Vardis Tsontos
,
Lisan Yu
,
Richard Jenkins
,
Sebastien De Halleux
,
Dave Peacock
, and
Nora Cohen

Abstract

From 11 April to 11 June 2018 a new type of ocean observing platform, the Saildrone surface vehicle, collected data on a round-trip, 60-day cruise from San Francisco Bay, down the U.S. and Mexican coast to Guadalupe Island. The cruise track was selected to optimize the science team’s validation and science objectives. The validation objectives include establishing the accuracy of these new measurements. The scientific objectives include validation of satellite-derived fluxes, sea surface temperatures, and wind vectors and studies of upwelling dynamics, river plumes, air–sea interactions including frontal regions, and diurnal warming regions. On this deployment, the Saildrone carried 16 atmospheric and oceanographic sensors. Future planned cruises (with open data policies) are focused on improving our understanding of air–sea fluxes in the Arctic Ocean and around North Brazil Current rings.

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Wouter Dorigo
,
Stephan Dietrich
,
Filipe Aires
,
Luca Brocca
,
Sarah Carter
,
Jean-François Cretaux
,
David Dunkerley
,
Hiroyuki Enomoto
,
René Forsberg
,
Andreas Güntner
,
Michaela I. Hegglin
,
Rainer Hollmann
,
Dale F. Hurst
,
Johnny A. Johannessen
,
Christian Kummerow
,
Tong Lee
,
Kari Luojus
,
Ulrich Looser
,
Diego G. Miralles
,
Victor Pellet
,
Thomas Recknagel
,
Claudia Ruz Vargas
,
Udo Schneider
,
Philippe Schoeneich
,
Marc Schröder
,
Nigel Tapper
,
Valery Vuglinsky
,
Wolfgang Wagner
,
Lisan Yu
,
Luca Zappa
,
Michael Zemp
, and
Valentin Aich

ABSTRACT

Life on Earth vitally depends on the availability of water. Human pressure on freshwater resources is increasing, as is human exposure to weather-related extremes (droughts, storms, floods) caused by climate change. Understanding these changes is pivotal for developing mitigation and adaptation strategies. The Global Climate Observing System (GCOS) defines a suite of essential climate variables (ECVs), many related to the water cycle, required to systematically monitor Earth’s climate system. Since long-term observations of these ECVs are derived from different observation techniques, platforms, instruments, and retrieval algorithms, they often lack the accuracy, completeness, and resolution, to consistently characterize water cycle variability at multiple spatial and temporal scales. Here, we review the capability of ground-based and remotely sensed observations of water cycle ECVs to consistently observe the hydrological cycle. We evaluate the relevant land, atmosphere, and ocean water storages and the fluxes between them, including anthropogenic water use. Particularly, we assess how well they close on multiple temporal and spatial scales. On this basis, we discuss gaps in observation systems and formulate guidelines for future water cycle observation strategies. We conclude that, while long-term water cycle monitoring has greatly advanced in the past, many observational gaps still need to be overcome to close the water budget and enable a comprehensive and consistent assessment across scales. Trends in water cycle components can only be observed with great uncertainty, mainly due to insufficient length and homogeneity. An advanced closure of the water cycle requires improved model–data synthesis capabilities, particularly at regional to local scales.

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