The Effect of Satellite Observing System Changes on MERRA Water and Energy Fluxes

Abstract

Because reanalysis data sets offer state variables and fluxes at regular space / time intervals, atmospheric reanalyses have become a mainstay of the climate community for diagnostic purposes and for driving offline ocean and land models. Although one weakness of these data sets is the susceptibility of the flux products to uncertainties because of shortcomings in parameterized model physics, another issue, perhaps less appreciated, is the fact that continual but discreet changes in the evolving observational system, particularly from satellite sensors, may also introduce artifacts in the time series of quantities.In this paper we examine the ability of the NASA MERRA (Modern Era Retrospective Analysis for Research and Applications) and other recent reanalyses to determine variability in the climate system over the satellite record (~ the last 30 years). In particular we highlight the effect on the reanalysis of discontinuities at the junctures of the onset of passive microwave imaging (Special Sensor Microwave Imager) in late 1987 as well as improved sounding and imaging with the Advanced Microwave Sounding Unit, AMSU-A, in 1998. We first examine MERRA fluxes from the perspective of how physical modes of variability (e.g. ENSO events, Pacific Decadal Variability) are contamined by artificial step-like trends induced by the onset of new moisture data these two satellite observing systems. Secondly, we show how Redundancy Analysis, a statistical regression methodology, is effective in relating these artifact signals in the moisture and temperature analysis increments to their presence in the physical flux terms (e.g. precipitation, radiation). This procedure is shown to be effective greatly reducing the artificial trends in the flux quantities.https://ntrs.nasa.gov/search

Quantifying the global atmospheric power budget

“…In some publications kinetic power is assumed equal to the volume integral of dp/dt (e.g., Robertson et al, 2011, their Eq. 1).…”

Critical mechanisms for the formation of extreme arctic sea-ice extent in the summers of 2007 and 1996

“…To have a reliable application of MERRA cloud and radiation fluxes in the study of the Arctic sea-ice state, it is important to have a reasonable estimate of the errors and accuracies of the reanalyzed cloud and radiative properties. There are a number of such evaluation studies in the recent MERRA special issue Rienecker et al 2011;Robertson et al 2011), some focused on the Arctic regions Vavrus et al 2012). As Rienecker et al (2011) pointed out, one of the strengths of the most recent reanalyses is overall better representations of the inter-annual variability in the atmospheric state on monthly to seasonal time scales, such as 500-hPa height, vertical velocity and large-scale atmospheric transports.…”

“…However, the accuracy of the representation strongly depends on both the specific variables and regions under consideration. Robertson et al (2011) analyzed the effects of the changing observing system on MERRA's energy and water fluxes where the re-analyzed results are still quite sensitive to observing system changes. For example, the MERRA re-analyzed precipitation has a series of jumps and different trends that are mainly associated with the SSM/I and AMSU-A changes (see table 1 of Rienecker et al 2011).…”

Different atmospheric moisture divergence responses to extreme and moderate El Niños

“…Evaporation from reanalysis is not constrained by precipitation and radiation (Hartmann et al 2013), spurious trends and biases can be introduced by changing satellite observations (e.g. Bosilovich et al 2005;Robertson et al 2011), which also contribute considerably to budget errors over land (Pan et al 2012). Similarly, precipitation from reanalysis also depends strongly on the parameterization schemes adopted by a specific model (i.e.…”