The need to characterize the increase and distribution of greenhouse gases is a first order scientific goal of the atmospheric composition and climate communities. The HIAPER Pole-to-Pole Observations (HIPPO) program will provide global, meridional coverage, via vertical profiles throughout the depth of the troposphere enabling closure and inversion of global budgets of critical greenhouse gases (e.g. carbon dioxide, CO2; carbon monoxide, CO; and methane, CH4), and related long-lived tracers and ratios (e.g. the oxygen/nitrogen ratio, O2/N2). This suite of chemical measurements, made from 80 N to 70 S, and repeated over approximately six monthly intervals, will provide a unique and definitive data set, to be used in inversion and other global modeling analyses of carbon cycle gases.
Observed gradients in the hemispheric concentrations of greenhouse gases are critical to our ability to predict the fate of anthropogenic emissions of carbon gases. Previous chemical transport modeling studies used to infer CO2 surface fluxes, sources and sinks have been generally constrained to using boundary layer CO2 concentrations. The field experiments will thus take advantage of transformative capabilities newly available to the atmospheric science community provided by the use of the HIAPER G-V aircraft platform.
This work is supported under the NSF Carbon and Water in the Earth System solicitation, an interdisciplinary funding opportunity from the Directorate of Geosciences.
Climate change carries with it social and economic ramifications. Mitigating and preparing for these ramifications requires a level of predictability of that change. Data generated by the HIPPO campaign represents a big step forward in constraining and improving our understanding of the atmosphere as a whole. In particular, the models used to predict climate change, including the chemical composition of the atmosphere, are to a large degree constrained in the troposphere by a network of surface measurements. Satellite measurements often lack the spatial resolution and/or precision to address the vertical structure and processes occurring in the troposphere. The high degree of spatial resolution and precision, coupled with the seasonal coverage of the HIPPO data set, put a much tighter constraint on these models, ultimately improving the accuracy of their representation of the current atmosphere, lleading to an improvement in their predictability of climate change. With the public release of the HIPPO data, through the Carbon Dioxide Information Analysis Center (CDIAC) managed archive at http://hippo.ornl.gov/dataaccess, there came a vibrant request for, and use of, the data set by this modeling community. This has resulted in a large number of publications in peer-reviewed journals and presentations at international conferences, many with support and co-authorship from the NOAA/GMD airborne group supported by this grant. So far this work has quantified temporal and spatial structure in emissions of important greenhouse and ozone-depleting gases, improved estimates of the tropospheric OH field that controls much of atmospheric chemistry, and has led to improved estimates of transport time scales. Over 50 species of data were collected as shown in the appended figures. All data collected are both temporally and spatially correlated within the data set, and represent a common distribution of paths (back trajectories) and chemical history leading to the discrete point of each correlated measurement. Spatial and temporal resolutions of past measurements often only give a statistical picture, and lacked the coherence needed to address the processes occurring in the troposphere. HIPPO has generated a "curtain" of this highly correlated data with near full latitudinal and altitude coverage over the open Pacific in the troposphere. With two curtains of data on each of the five deployments, this gives good seasonal coverage. For most of the species measured, there remains a distributed and uncertain boundary condition that is coupled, via highly variable transport and chemistry, into the troposphere. For these species, the data set is ideally suited to comparisons with model simulations where the agreement and disagreement has shed new light on sources, sinks, and modeled transport. Because the data were collected over the open Pacific, many of the local hot spots of sources and sinks over land have had some time to mix. In this sense they may be thought of as a good approximation to the longitudinal (zonal) average for many studies. In addition to validating and improving models, the HIPPO data set has and will continue to be used to reduce uncertainties in inventories and lifetimes of many important greenhouse and ozone depleting gases. The data are also beneficial in process-oriented studies such as inter-hemispheric exchange, vertical transport in the tropics and extra-tropics, and the competition between bulk transport and mixing to name a few. An excellent website maintained by UCAR can be found at www.eol.ucar.edu/projects/hippo/. Information about the GV aircraft, the HIPPO flight tracks, the instrumentation, the HIPPO participants, and the large HIPPO outreach program can be found there.
