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An objective analysis of monthly ocean subsurface temperatures from 1950 to 1998 is carried out. The analysis scheme and the results with estimated analysis errors are presented. The analysis domain is global with a horizontal grid of 1° × 1° and 14 vertical levels in the upper 500 m. Subsurface temperature observations used in the objective analysis are archived by the National Ocean Data Center of the National Oceanic and Atmospheric Administration, together with those collected through the global telecommunication system and domestic communication lines in Japan. All the observations are preprocessed by quality control and data selection procedures developed in this study. Together with these observations, threedimensional fields of the upper-ocean temperature are optimally estimated using a variational technique. To ensure smooth and continuous vertical temperature profiles, a constraint term is introduced to the cost function that is minimized in the analysis. In addition, the analysis scheme is formulated to constrain mixed layer temperatures to become close to sea surface temperatures produced by the Met Office. The three-dimensional structure of thermal anomalies is represented by the objective analysis. Interannual variations of temperature anomalies in the northern and tropical Pacific are presented and examined with the estimated errors. For the purpose of verification against independent observations of the objective analysis, dynamical heights estimated from the analyzed temperatures and climatological salinity are compared with tide gauge and sea surface height observations. An investigation of analysis errors and signal-to-noise (S-N) ratio reveals that the reliability increases in the tropical Pacific since the 1970s and the S-N ratio for seasonally averaged temperatures in a 3° latitude × 6° longitude box at 100-m depth is 2.5 in the 1990s. This is not only due to the increase in data sampling but also to an increase... [ABSTRACT FROM AUTHOR]

This study compares three TMI rainfall datasets generated by two versions of NASA's Goddard Profiling algorithm (GPROF2010 and GPROF2017) and JAXA's Global Satellite Mapping of Precipitation algorithm (GSMaP) over land, coast, and ocean. We use TRMM precipitation radar observations as the reference, and also include CloudSat cloud profiling radar (CPR) observations as the reference over ocean. First, the dynamic thresholds for rainfall detection used by GSMaP and GPROF2017 have better detection capability, indicating by larger Heidke skill score (HSS) values, compared with GPROF2010 over both land and coast. Over ocean, all three datasets have very similar HSS regardless of including CPR observations. Next, intensity analysis shows that no single dataset performs the best according to all three statistical metrics (correlation, root-mean-square error, and relative bias), except that GSMaP performs the best for stratiform precipitation over coast, and GPROF2017 performs the best for convective precipitation over ocean, based on all three metrics. Finally, an error decomposition analysis shows that the total error and its three components have very different characteristics over several regions among these three datasets. For example, the positive total error in GPROF2010 and GSMaP is primarily caused by the positive hit bias over central Africa, while the false bias in GPROF2017 is largely responsible for this positive total error. For future algorithm development, results from this study imply that a convective–stratiform separation technique may be necessary to reduce the large underestimation for convective rain intensity. [ABSTRACT FROM AUTHOR]

The authors improve the high-resolution Global Satellite Mapping of Precipitation (GSMaP) product for Typhoon Morakot (2009) over Taiwan by using an orographic/nonorographic rainfall classification scheme. For the estimation of the orographically forced upward motion used in the orographic/nonorographic rainfall classification scheme, the optimal horizontal length scale for averaging the elevation data is examined and found to be about 50 km. It is inferred that as the air ascends en masse on the horizontal scale, it becomes unstable and convection develops. The orographic/nonorographic rainfall classification scheme is extended to the GSMaP algorithm for all passive microwave radiometers in orbit, including not just microwave imagers but also microwave sounders. The retrieved rainfall rates, together with infrared images, are used for the high-resolution rainfall products, which leads to much better agreement with rain gauge observations. [ABSTRACT FROM AUTHOR]

The adequacy of hourly rainfall sampling was examined in terms of the detection of diurnal variations using 8 yr (1998–2005) of data observed by the precipitation radar on the Tropical Rainfall Measuring Mission (TRMM) satellite. It was found that the monthly and hourly rain samples for each 0.2° grid point over the 8-yr period are composed of multiple precipitation systems. In this study, a “3-h-significant diurnal peak” was defined as the time of maximum rainfall with consecutive positive anomalies for more than 3 h. The fraction of the analyzed area with a 3-h-significant diurnal peak increased annually and accounted for 43% of the total global tropics at 0.2° resolution over the 8-yr period. The diurnal signature over Tibet and the Amazon showed a high degree of spatial uniformity (at >10° scale). The degree of similarity and locations of the regional diurnal characteristics are described in terms of seasonal variations and at multiple resolutions based on spatial uniformity. For example, uniform early-afternoon peaks generally appear over the coastal land and areas of high relief, whereas a seasonally invariant early-afternoon peak over the low-lying Amazon basin is recognized as a regional characteristic. In areas of coastal ocean, early-morning peaks appear in certain regions such as the area surrounding the so-called Maritime Continent and the area off the west coast of Mexico. These peaks are distinct from the global characteristics of late-morning rainfall maxima recorded over most coastal oceans and early-morning peaks recorded over open ocean. The results are also compared with those derived from TRMM Microwave Imager (TMI) data. In addition to obtaining a coherent signal, regional differences in the timing of maximum rainfall over the Tibetan Plateau were addressed; this discrepancy is attributed to limitations of the scattering algorithm used for TMI data in terms of detecting shallow convection and screening cold surfaces. [ABSTRACT FROM AUTHOR]

Satellite remote sensing is an indispensable means of measuring and monitoring precipitation on a global scale. The Tropical Rainfall Measuring Mission (TRMM) is continuing to make significant progress in helping the global features of precipitation to be understood, particularly with the help of a pair of spaceborne microwave sensors, the TRMM Microwave Imager (TMI) and precipitation radar (PR). The TRMM version-5 standard products, however, are known to have a systematic inconsistency in mean monthly rainfall. To clarify the origin of this inconsistency, the authors investigate the zonal mean precipitation and the regional trends in the hydrometeor profiles in terms of the precipitation water content (PWC) and the precipitation water path (PWP) derived from the TMI profiling algorithm (2A12) and the PR profile (2A25). An excess of PR over TMI in near-surface PWC is identified in the midlatitudes (especially in winter), whereas PWP exhibits a striking excess of TMI over PR around the tropical rainfall maximum. It is shown that these inconsistencies arise from TMI underestimating the near-surface PWC in midlatitude winter and PR underestimating PWP in the Tropics. This conclusion is supported by the contoured-frequency-by-altitude diagrams as a function of PWC. Correlations between rain rate and PWC/ PWP indicate that the TMI profiling algorithm tends to provide a larger rain rate than the PR profile under a given PWC or PWP, which exaggerates the excess by TMI and cancels the excess by PR through the conversion from precipitation water to rain rate. As a consequence, the disagreement in the rainfall products between TMI and PR is a combined result of the intrinsic bias originating from the different physical principles between TMI and PR measurements and the purely algorithmic bias inherent in the conversion from precipitation water to rain rate. [ABSTRACT FROM AUTHOR]

Decadal climate variations in the Atlantic Ocean found in observational fields and a coupled general circulation model (CGCM) are investigated. In particular, physical processes responsible for the phase reversal are compared. Observed and modeled decadal variations have dominant periodicities around 12.3 and 9.9 yr, respectively. Both variations show similar spatial features: sea surface temperature (SST) anomalies in the western subtropical Atlantic sandwiched by those with opposite sign to the north and south, and a dipole of sea level pressure anomalies, which resemble the North Atlantic Oscillation. Their temporal evolutions are, however, different from each other, suggestive of different dynamics of the oscillation. In the observations, SST and surface-layer (0-- 100 m) temperature anomalies move eastward from the subtropical western Atlantic to the European coast along the Gulf Stream. Northward propagation of SST anomalies are also found along the western boundaries including the Gulf of Mexico. A budget analysis for the temperature equation shows that these features are the manifestation of the advection of SST anomalies by the mean current, which acts to switch one phase of the oscillation to another. Anomalous gyre intensity appears to have little contribution to the phase switching process of the near-surface variability, although the influence of the anomalous gyre is found in the lower subsurface up to 500 m. In contrast, SST anomalies in the CGCM are more strongly tied with subsurface temperature anomalies that propagate westward, consistent with a slow gyre adjustment by the baroclinic Rossby wave propagation. The wave-induced advection acts to change the phase of SST as well as the subsurface temperature anomalies in the model. Subduction of temperature anomalies is found to occur on decadal timescales both in the observation and in the model over the eastern basin where the winter mixed layer is deepened, although the consequence. [ABSTRACT FROM AUTHOR]