Phillip A. Arkin

Advanced Concepts on Remote Sensing of Precipitation at Multiple Scales

ADVANCED CONCEPTS ON REMOTE SENSING OF PRECIPITATION AT MULTIPLE SCALES by S oroosh S orooshian , A mir A gha K ouchak , P hillip A rkin , J ohn E ylander , E fi F oufoula -G eorgiou , R ussell H armon , J an M. H. H endrickx , B isher I mam , R obert K uligowski , B rian S kahill , and G ail S kofronick -J ackson Overview of Recommendations (i) Uncertainty of merged products and multisensor observations warrants a great deal of research. Quantification of uncertainties and their propa- gation into combined products is vital for future development. (ii) Future improvements in satellite-based precipi- tation retrieval algorithms will rely on more in- depth research on error properties in different climate regions, storm regimes, surface condi- tions, seasons, and altitudes. Given such infor- mation, precipitation algorithms for retrieval, AFFILIATIONS : S orooshian , A gha K ouchak , I mam —University of California, Irvine, Irvine, California; A rkin —University of Maryland, College Park, Maryland; E ylander —U.S. Army Engineer Research and Development Center, Hanover, New Hampshire; F oufoula -G eorgiou —University of Minnesota, Minneapolis, Minnesota; H armon —Army Research Laboratory, Durham, North Carolina; H endrickx —New Mexico Tech, Socorro, New Mexico; K uligowski —NOAA/NESDIS/ STAR, Camp Springs, Maryland; S kahill —U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi; S kofronick -J ackson —NASA GSFC, Greenbelt, Maryland CORRESPONDING AUTHOR : Soroosh Sorooshian, Department of Civil & Environmental Engineering, University of California, Irvine, Irvine, CA 92697 E-mail: soroosh@uci.edu DOI:10.1175/2011BAMS3158.1 In final form 18 April 2011

Comparison of ground-based radar and geosynchronous satellite climatologies of warm-season precipitation over the United States

Abstract Studies in the past several years have documented the climatology of warm-season precipitation-episode statistics (propagation speed, span, and duration) over the United States using a national composited radar dataset. These climatological studies have recently been extended to other continents, including Asia, Africa, and Australia. However, continental regions outside the United States have insufficient radar coverage, and the newer studies have had to rely on geostationary satellite data at infrared (IR) frequencies as a proxy for rainfall. It is well known that the use of IR brightness temperatures to infer rainfall is subject to large errors. In this study, the statistics of warm-season precipitation episodes derived from radar and satellite IR measurements over the United States are compared and biases introduced by the satellite data are evaluated. It is found that the satellite span and duration statistics are highly dependent upon the brightness temperature threshold used but with the a...

The observed sensitivity of the global hydrological cycle to changes in surface temperature

Climate models project large changes in global surface temperature in coming decades that are expected to be accompanied by significant changes in the global hydrological cycle. Validation of model simulations is essential to support their use in decision making, but observing the elements of the hydrological cycle is challenging, and model-independent global data sets exist only for precipitation. We compute the sensitivity of the global hydrological cycle to changes in surface temperature using available global precipitation data sets and compare the results against the sensitivities derived from model simulations of 20th century climate. The implications of the results for the global climate observing system are discussed.

Advancing the remote sensing of precipitation

Author(s): Sorooshian, S; Aghakouchak, A; Arkin, P; Eylander, J; Foufoula-Georgiou, E; Harmon, R; Hendrickx, JMH; Imam, B; Kuligowski, R; Skahill, B; Skofronick-Jackson, G | Abstract: Satellite-based global precipitation data has addressed the limitations of rain gauges and weather radar systems in forecasting applications and for weather and climate studies. Inspite of this ability, a number of issues that require the development of advanced concepts to address key challenges in satellite-based observations of precipitation were identified during the Advanced Concepts Workshop on Remote Sensing of Precipitation at Multiple Scales at the University of California. These include quantification of uncertainties of individual sensors and their propagation into multisensor products warrants a great deal of research. The development of metrics for validation and uncertainty analysis are of great importance. Bias removal, particularly probability distribution function (PDF)-based adjustment, deserves more in-depth research. Development of a near-real-time probabilistic uncertainty model for satellitebased precipitation estimates is highly desirable.

CMORPH: A “Morphing” Approach for High Resolution Precipitation Product Generation

The CMORPH technique was developed to synergize the most desirable aspects of passive microwave (high quality) and infrared (spatial and temporal resolution) data. CMORPH is a global (in longitude; 60°N–60°S) high-resolution (∼0.10° latitude/longitude, 1/2-hourly) precipitation analysis technique that uses motion vectors derived from half-hourly geostationary satellite IR imagery to propagate precipitation estimates derived from passive microwave data. Multi-hour precipitation totals derived via the CMORPH methodology are an improvement over both simple averaging of all available microwave-derived precipitation estimates and over other merging techniques that blend microwave and infrared information but which derive estimates of precipitation directly from infrared data when passive microwave data are not available.

CPC MORPHING Technique (CMORPH)

IR data are available globally nearly everywhere nearly all the time. However, IR channels measure cloud top temperatures and those temperatures do not always correlate well with rainfall. In many instances the cold cloud shield in a precipitating complex may be several times larger than the areal coverage of the actual precipitating region, sometimes with no rainfall directly under the coldest section. In contrast to the IR, relatively low frequency passive microwave (PMW) signals sense the thermal emission of raindrops while higher frequencies sense the scattering of upwelling radiation from the earth to space due to ice particles in the rain layer and tops of convective systems. Although rainfall estimates from PMW instruments are more accurate than those that are derived from IR data, PMW sensors are restricted to low orbit platforms and thus the temporal sampling from them is substantially less compared to geostationary IR data. Given this situation, the natural next step is to combine the data from these disparate sensors to take advantage of the strengths that each has to offer. A number of techniques have been developed in which the IR data are manipulated in a statistical fashion to mimic the behavior of PMW derived precipitation estimates. In these techniques, precipitation estimates are calculated directly from IR data through an empirical relationship between the rain rate and cloud top temperature and are used when PMW data are unavailable. An alternative method of combining these disparate data is proposed, one that uses precipitation estimates derived from low orbiter satellite PMW retrievals exclusively, and whose features are transported via spatial propagation information obtained from geostationary satellite IR data during periods when instantaneous PMW data are not available at a location.

An empirical parameterization for the salinity of subsurface water entrained into the ocean mixed layer (Se) in the tropical Pacific

n n An empirical parameterization for S-e is proposed and tested in an intermediate ocean model (IOM) of the Tropical Pacific Ocean. An inverse modeling approach is first adopted to estimate S-e from a sea surface salinity (SSS) anomaly (SSSA) model using observed in-situ SSS measurements, simulated upper ocean currents, and freshwater flux (evaporation minus precipitation, E-P) data. A relationship between S-e and sea level (SL) anomalies is then obtained by utilizing an empirical orthogonal function (EOF) technique. This empirical scheme is able to estimate S-e anomalies reasonably well in the equatorial Pacific Ocean and can be used to parameterize S-e fields in terms of SL anomalies for use in SSSA calculations. An optimized S-e parameterization naturally leads to a balanced depiction of the subsurface effect on SSS variability in association with entrainment and vertical mixing. As a result, SSSA simulations can be potentially improved in the Tropical Pacific.

Twentieth century ENSO-related precipitation mean states in twentieth century reanalysis, reconstructed precipitation and CMIP5 models

El Niño–Southern Oscillation (ENSO)-related precipitation during the entire twentieth century is compared among the twentieth century reanalysis (20CR), a statistically reconstructed precipitation dataset (REC) and 30 Coupled Model Intercomparison Project Phase 5 (CMIP5) models. Empirical orthogonal functions, ENSO-related precipitation composites based on sea surface temperature (SST)-constructed ENSO index and singular value decomposition (SVD) are employed to extract ENSO-related precipitation/SST signals in each dataset. With the background trend being removed in all of the data, our results show that the REC and the 20CR resemble both in their precipitation climatology and ENSO-related precipitation results. The biases in the CMIP5 models precipitation climatology such as dry equator over the Pacific Ocean, “double-intertropical convergence zones (ITCZs)” and overly zonal Southern Pacific convergence zone (SPCZ) are major reasons for lowering spatial correlations with the REC and the 20CR precipitation climatology. Two groups of CMIP5 models are built based on severity of these biases in their precipitation background and the spatial correlations of ENSO-related precipitation with the observations. Compared with the group with more severe biases in its precipitation climatology, the group with smaller biases tends to produce more ENSO-like precipitation patterns, simulate more realistic mean magnitude and seasonal variability of ENSO precipitation signals, as well as generating better ENSO-related SST/precipitation correlation patterns produced in its SVD analysis. The ENSO-related precipitation biases in the CMIP5 models over the western Pacific and Indian Ocean, as well as the equatorial Pacific, are strongly related with their precipitation climatology biases over these regions. The ENSO-related precipitation biases over the off-equator eastern Pacific Ocean are associated with both the “double-ITCZs” biases in the precipitation climatology and the ENSO-related SST biases in the models.

Retrieving Layer-Averaged Tropospheric Humidity From Advanced Technology Microwave Sounder Water Vapor Channels

A method is presented to calculate layer-averaged tropospheric humidity (LAH) from the observations of the Advanced Technology Microwave Sounder (ATMS) water vapor channels. The method is based on a linear relation between the satellite brightness temperatures (Tb) and natural logarithm of Jacobian weighted humidity. The empirical coefficients of this linear relation were calculated using different data sets, as well as a fast and a line-by-line radiative transfer (RT) model. It was found that the coefficients do not significantly depend on the data set or the RT model. This Tb to the LAH transformation method can be applied to either original or limb-corrected ATMS Tbs. The method was validated using both simulated and observed ATMS Tbs. The systematic difference between the estimated and calculated LAH values was less than 10% in most cases. We also tested the transformation method using a fixed Jacobian for each channel. The bias generally increases when fixed Jacobians are used, but there is still a satisfactory agreement between estimated and calculated LAH values. In addition, the spatial distribution of the bias was investigated using the European Center for Medium-Range Weather Forecasting (ECMWF) Interim Reanalysis (ERA-interim) and collocated ATMS observations. The bias did not indicate any significant regional dependence when actual Jacobians were used, but in the case of fixed Jacobians, the bias generally increased from middle latitude toward the poles.

The Effectiveness of Science on a Sphere Stories to Improve Climate Literacy Among the General Public

ABSTRACT Engaging the general public on climate topics and deepening their understanding of key discoveries by the Earth science community requires a collaborative approach between scientists, developers, and museum educators to converge on the most effective format. Large Science On a Sphere (SOS) displays of Earth attract attention to global data at museums worldwide, yet just looking at raw data does not generally lead to new insights by the public. Working closely with the Maryland Science Center, the EarthNow project realized the time limitations of the museum staff and audience and began creating short, narrated videos for SOS. The videos introduce recent climate science findings on a variety of topics and can be used as part of live, facilitated programs or played while SOS is in its autorun mode. To measure the effectiveness of the delivery method, we developed a survey and tested several groups that saw a video within a live show compared to groups that saw it in autorun without a live program. We also wondered whether adding a hands-on activity would enhance learning and how hearing the information while doing an activity would compare to watching and hearing the SOS show, so we tested two large groups using the activity with and without seeing Science On a Sphere. Overall survey results demonstrate the groups who saw an SOS show gained certain concepts better than the group that only heard the information while doing the activity. The live shows conferred a slight but not substantial advantage over the autorun shows. Playing short, narrated videos on SOS that include global Earth processes, such as atmospheric and oceanic circulation, seems to enhance understanding of certain concepts more than hearing the information while doing an activity. Ongoing communication with museums and their visitors is critical for ensuring that these stories are as effective as possible and make best use of the strengths of the Science On a Sphere exhibit to enhance the publics climate literacy.