Tropical Rainfall Measuring Mission Datasets Research Articles

Comparison of the global TRMM and WFD precipitation datasets in driving a large-scale hydrological model in southern Africa

This paper provides a comparison of two widely used global precipitation datasets in southern Africa: Tropical Rainfall Measuring Mission (TRMM) and Water and Global Change (WATCH) Forcing Data (WFD). We also evaluate the performance of the water and snow balance modelling system (WASMOD-D) in a water balance simulation of 22 gauged basins over the southern Africa region. Water balance for southern Africa was simulated using the two global datasets as input with regionalized model parameter values. The results reveal that the special variation patterns of mean annual precipitation from TRMM and WFD datasets and temporal changing trend are similar in southern Africa. However, they are quite different in terms of probability distributions. Simulation of WASMOD-D based on two datasets in southern Africa results in model performances of above 0.5 for Nash–Sutcliffe (NS) values, below 10% for volume error (VE) values and a good reproduction of the observed flow duration curves for the majority of the basins. Finally, WFD data which have been bias corrected were observed to outperform TRMM data in southern Africa. The approaches and results described in this study contribute to the limited literature on regional hydrological modelling in the data-scarce region of southern Africa.

Convective activity in Mato Grosso state (Brazil) from microwave satellite observations: Comparisons between AMSU and TRMM data sets

We present a characterization of convective activity at sub‐regional scale from two sets of satellite‐based microwave observations: the Advanced Microwave Sounding Unit (AMSU) and the combined Tropical Rainfall Measuring Mission (TRMM) microwave imager and precipitation radar data, for the period 2001 to 2011. We focus on the state of Mato Grosso, Brazil, located at the southern edge of the so‐called “Legal Amazon” which has undergone intense land cover transformation in the last 4 decades. The annual cycle of mean convective activity described by AMSU and TRMM are in good agreement, with a correlation close to 0.80. The mean amplitude of convective activity is maximal early in the rainy season, except for AMSU deep convective area, which presents a maximum in January. The diurnal cycle of convection was examined for the period 2003 to 2007, and it was found that convection is maximal near 1500 local time (LT) and minimal around 0700 LT. Unlike the amplitude, the phase shows little intraseasonal and interannual variability. A slight decrease in convective activity in the studied period was found, possibly indicating an extension of the dry season. Comparisons of convective activity between deforested and forested areas showed no significant differences in the phase of the diurnal cycle, but our analysis shows a tendency for increase (decrease) in convection in deforested (forested) areas for the period considered. A longer time series is however necessary in order to strengthen the robustness of our results.

Precipitation Characteristics of the South American Monsoon System Derived from Multiple Datasets

Abstract The South American monsoon system (SAMS) is the most important climatic feature in South America and is characterized by pronounced seasonality in precipitation during the austral summer. This study compares several statistical properties of daily gridded precipitation from different data (1998–2008): 1) Physical Sciences Division (PSD), Earth System Research Laboratory [1.0° and 2.5° latitude (lat)/longitude (lon)]; 2) Global Precipitation Climatology Project (GPCP; 1° lat/lon); 3) Climate Prediction Center (CPC) unified gauge (CPC-uni) (0.5° lat/lon); 4) NCEP Climate Forecast System Reanalysis (CFSR) (0.5° lat/lon); 5) NASA Modern-Era Retrospective Analysis for Research and Applications (MERRA) reanalysis (0.5° lat/0.3° lon); and 6) Tropical Rainfall Measuring Mission (TRMM) 3B42 V6 data (0.25° lat/lon). The same statistical analyses are applied to data in 1) a common 2.5° lat/lon grid and 2) in the original resolutions of the datasets. All datasets consistently represent the large-scale patterns of the SAMS. The onset, demise, and duration of SAMS are consistent among PSD, GPCP, CPC-uni, and TRMM datasets, whereas CFSR and MERRA seem to have problems in capturing the correct timing of SAMS. Spectral analyses show that intraseasonal variance is somewhat similar in the six datasets. Moreover, differences in spatial patterns of mean precipitation are small among PSD, GPCP, CPC-uni, and TRMM data, while some discrepancies are found in CFSR and MERRA relative to the other datasets. Fitting of gamma frequency distributions to daily precipitation shows differences in the parameters that characterize the shape, scale, and tails of the frequency distributions. This suggests that significant uncertainties exist in the characterization of extreme precipitation, an issue that is highly important in the context of climate variability and change in South America.

Vertical Diabatic Heating Structure of the MJO: Intercomparison between Recent Reanalyses and TRMM Estimates

Abstract Capitalizing on recently released reanalysis datasets and diabatic heating estimates based on Tropical Rainfall Measuring Mission (TRMM), the authors have conducted a composite analysis of vertical anomalous heating structures associated with the Madden–Julian oscillation (MJO). Because diabatic heating lies at the heart of prevailing MJO theories, the intention of this effort is to provide new insights into the fundamental physics of the MJO. However, some discrepancies in the composite vertical MJO heating profiles are noted among the datasets, particularly between three reanalyses and three TRMM estimates. A westward tilting with altitude in the vertical heating structure of the MJO is clearly evident during its eastward propagation based on three reanalysis datasets, which is particularly pronounced when the MJO migrates from the equatorial eastern Indian Ocean (EEIO) to the western Pacific (WP). In contrast, this vertical tilt in heating structure is not readily seen in the three TRMM products. Moreover, a transition from a shallow to deep heating structure associated with the MJO is clearly evident in a pressure–time plot over both the EEIO and WP in three reanalysis datasets. Although this vertical heating structure transition is detectable over the WP in two TRMM products, it is weakly defined in another dataset over the WP and in all three TRMM datasets over the EEIO. The vertical structures of radiative heating QR associated with the MJO are also analyzed based on TRMM and two reanalysis datasets. A westward vertical tilt in QR is apparent in all these datasets: that is, the low-level QR is largely in phase of convection, whereas QR in the upper troposphere lags the maximum convection. The results also suggest a potentially important role of radiative heating for the MJO, particularly over the Indian Ocean. Caveats in heating estimates based on both the reanalysis datasets and TRMM are briefly discussed.

Object-Based Analysis and Verification of WRF Model Precipitation in the Low- and Midlatitude Pacific Ocean

Abstract An extended version of the Method for Object-based Diagnostic Evaluation (MODE) was used to perform a verification of precipitation provided by the Weather Research and Forecasting (WRF) model Tropical Channel Simulation (performed by NCAR). Model 3-hourly precipitation accumulations were compared to the Tropical Rainfall Measuring Mission (TRMM) 3B42 satellite-derived precipitation in the low- and midlatitude Pacific Ocean during 1998–2000. Overall, the spatial distribution of annual mean precipitation (i.e., the clear shape of the ITCZ with two maxima—one located in the east and one in the west) was reproduced well by the WRF model; however, there was considerably more precipitation in the WRF simulation than in the TRMM dataset. Object-based analysis identified more precipitation objects with life spans less than 30 h and fewer objects with life spans longer than 60 h in the TRMM dataset compared to the WRF simulation. Objects with the longest life span (>90 h) tended to occur in similar regions in both the modeled and satellite-derived datasets. Two of these regions were in the western part of the domain and one was in the eastern portion of the ITCZ, although these regions did not necessarily coincide with the regions of maximum precipitation accumulations. Both datasets had mostly eastward movement in the midlatitudes. The datasets, however, diverged around the central part of the ITCZ where the TRMM dataset displayed both eastward and westward movement, while westward movement was dominant in the WRF simulation. The analysis also showed that precipitation object trajectories were smoother in the model than in the TRMM dataset.

MJO Signals in Latent Heating: Results from TRMM Retrievals

Abstract Four Tropical Rainfall Measuring Mission (TRMM) datasets of latent heating were diagnosed for signals in the Madden–Julian oscillation (MJO). In all four datasets, vertical structures of latent heating are dominated by two components—one deep with its peak above the melting level and one shallow with its peak below. Profiles of the two components are nearly ubiquitous in longitude, allowing a separation of the vertical and zonal/temporal variations when the latitudinal dependence is not considered. All four datasets exhibit robust MJO spectral signals in the deep component as eastward propagating spectral peaks centered at a period of 50 days and zonal wavenumber 1, well distinguished from lower- and higher-frequency power and much stronger than the corresponding westward power. The shallow component shows similar but slightly less robust MJO spectral peaks. MJO signals were further extracted from a combination of bandpass (30–90 day) filtered deep and shallow components. Largest amplitudes of both deep and shallow components of the MJO are confined to the Indian and western Pacific Oceans. There is a local minimum in the deep components over the Maritime Continent. The shallow components of the MJO differ substantially among the four TRMM datasets in their detailed zonal distributions in the Eastern Hemisphere. In composites of the heating evolution through the life cycle of the MJO, the shallow components lead the deep ones in some datasets and at certain longitudes. In many respects, the four TRMM datasets agree well in their deep components, but not in their shallow components and in the phase relations between the deep and shallow components. These results indicate that caution must be exercised in applications of these latent heating data.

The Skill of ECMWF Medium-Range Forecasts during the Year of Tropical Convection 2008

Abstract This study uses the European Centre for Medium-Range Weather Forecasts (ECMWF) model-generated high-resolution 10-day-long predictions for the Year of Tropical Convection (YOTC) 2008. Precipitation forecast skills of the model over the tropics are evaluated against the Tropical Rainfall Measuring Mission (TRMM) estimates. It has been shown that the model was able to capture the monthly to seasonal mean features of tropical convection reasonably. Northward propagation of convective bands over the Bay of Bengal was also forecasted realistically up to 5 days in advance, including the onset phase of the monsoon during the first half of June 2008. However, large errors exist in the daily datasets especially for longer lead times over smaller domains. For shorter lead times (less than 4–5 days), forecast errors are much smaller over the oceans than over land. Moreover, the rate of increase of errors with lead time is rapid over the oceans and is confined to the regions where observed precipitation shows large day-to-day variability. It has been shown that this rapid growth of errors over the oceans is related to the spatial pattern of near-surface air temperature. This is probably due to the one-way air–sea interaction in the atmosphere-only model used for forecasting. While the prescribed surface temperature over the oceans remain realistic at shorter lead times, the pattern and hence the gradient of the surface temperature is not altered with change in atmospheric parameters at longer lead times. It has also been shown that the ECMWF model had considerable difficulties in forecasting very low and very heavy intensity of precipitation over South Asia. The model has too few grids with “zero” precipitation and heavy (>40 mm day−1) precipitation. On the other hand, drizzle-like precipitation is too frequent in the model compared to that in the TRMM datasets. Further analysis shows that a major source of error in the ECMWF precipitation forecasts is the diurnal cycle over the South Asian monsoon region. The peak intensity of precipitation in the model forecasts over land (ocean) appear about 6 (9) h earlier than that in the observations. Moreover, the amplitude of the diurnal cycle is much higher in the model forecasts compared to that in the TRMM estimates. It has been seen that the phase error of the diurnal cycle increases with forecast lead time. The error in monthly mean 3-hourly precipitation forecasts is about 2–4 times of the error in the daily mean datasets. Thus, effort should be given to improve the phase and amplitude forecast of the diurnal cycle of precipitation from the model.

Spatial and Temporal Distribution of Latent Heating in the South Asian Monsoon Region

Abstract Information from the Tropical Rainfall Measuring Mission (TRMM) level 3 monthly 0.5° × 0.5° Convective and Stratiform Heating (CSH) product and TRMM Microwave Imager (TMI) 2A12 datasets is used to examine the four-dimensional latent heating (LH) structure over the Asian monsoon region between 1998 and 2006. High sea surface temperatures, ocean–land contrasts, and complex terrain produce large precipitation and atmospheric heating rates whose spatial and temporal characteristics are relatively undocumented. Analyses show interannual and intraseasonal LH variations with a large fraction of the interannual variability induced by internal intraseasonal variability. Also, the analyses identify a spatial dipole of LH anomalies between the equatorial Indian Ocean and the Bay of Bengal regions occurring during the summer active and suppressed phases of the monsoon intraseasonal oscillation. Comparisons made between the TRMM CSH and TMI 2A12 datasets indicate differences in the shape of the vertical profile of LH. A comparison of TRMM LH retrievals with sounding budget observations made during the South China Sea Monsoon Experiment shows a high correspondence in the timing of positive LH episodes during the rainy periods. Negative values of atmospheric heating, associated with radiative cooling and with upper-tropospheric cooling from nonsurface-precipitating clouds, are not captured by either of the TRMM datasets. In summary, LH algorithms based on satellite information are capable of representing the spatial and temporal characteristics of the vertically integrated heating in the Asian monsoon region. However, the vertical distribution of atmospheric heating is not captured accurately throughout different convective phases. It is suggested that satellite-derived radiative heating/cooling products are needed to supplement the LH products in order to give a better overall depiction of atmospheric heating.

From Hot Towers to TRMM: Joanne Simpson and Advances in Tropical Convection Research

Joanne Simpson began contributing to advances in tropical convection about half a century ago. The hot tower hypothesis jointly put forth by Joanne Simpson and Herbert Riehl postulated that deep convective clouds populating the “equatorial trough zone” were responsible for transporting heat from the boundary layer to the upper troposphere. This hypothesis was the beginning of a 50-year quest to describe and understand near-equatorial deep convection. Tropical field experiments in the 1970s [Global Atmospheric Research Program Atlantic Tropical Experiment (GATE) and the Monsoon Experiment (MONEX)] in which Joanne participated documented the mesoscale structure of the convective systems, in particular the deep, stratiform, dynamically active mesoscale clouds that are connected with the hot towers. In the 1980s these new data led to better understanding of how tropical mesoscale convective systems vertically transport heat and momentum. The role of the mesoscale stratiform circulation in this transport was quantified. Tropical field work in the 1990s [especially the Coupled Ocean-Atmosphere Response Experiment (COARE), in which Joanne again participated] showed the importance of a still larger scale of convective organization, the “supercluster.” This larger scale of organization has a middle-level inflow circulation that appears to be an important transporter of momentum. The mesoscale and supercluster scale of organization in tropical convective systems are associated with the stratiform components of the cloud systems. Joint analysis of satellite and radar data from COARE show a complex, possibly chaotic relationship between cloud-top temperature and the size of a stratiform precipitation area. The Tropical Rainfall Measuring Mission (TRMM) satellite, for which Joanne served as project scientist for nearly a decade, is now providing a global census of mesoscale and supercluster-scale organization of tropical convection. The TRMM dataset should therefore provide some closure to the question of the nature of deep convection in the equatorial trough zone.

Early radiometric validation results of the CERES Flight Model 1 and 2 instruments onboard NASA's Terra Spacecraft

The CERES Flight Model 1 and 2 instruments were launched aboard NASA's Earth Observing System (EOS) Terra Spacecraft on December 18, 1999 into a 705 Km sun-synchronous orbit with a 10:30 a.m. equatorial crossing time. These instruments supplement measurements made by the CERES Proto Flight Model (PFM) instrument launched aboard NASA's Tropical Rainfall Measuring Mission (TRMM) spacecraft on November 27, 1997 into a 350 Km, 38-degree mid-inclined orbit. An important aspect of the EOS program is the rapid archival and dissemination of datasets measured by EOS instruments to the scientific community. On September 22, 2000 the CERES Science Team voted to archive the Edition 1 CERES/Terra Level 1b and Level 2 and 3 ERBE-Like data products. These products consist of instantaneous filtered and unfiltered radiances through temporally and spatially averaged TOA fluxes. CERES filtered radiance measurements cover three spectral bands including shortwave (0.3 to 5 μm), total (0.3 to <100 μm) and an atmospheric window channel (8 to 12 μm). The current work summarizes both the philosophy and results of validation efforts undertaken to quantify the quality of the Terra data products as well as the level of agreement between the Terra and TRMM datasets.

TRMM Observations of Intraseasonal Variability in Convective Regimes over the Amazon

This study utilizes the Tropical Rainfall Measuring Mission (TRMM) satellite precipitation radar (PR), lightning imaging sensor (LIS), and passive microwave imager (TMI) data together with ground-based lightning data to investigate the vertical structure, lightning, and rainfall characteristics of Amazonian and subtropical South American convection for three separate wet seasons. These characteristics are partitioned as a function of 850mb zonal wind direction, motivated by observations collected during the 6-week TRMM‐Large-scale Biosphere‐ Atmosphere Experiment in Amazonia (LBA) field campaign. The TRMM‐LBA field campaign observations suggest that systematic variations in Amazonian convective vertical structure, lightning, and rainfall are all linked to bimodal variations in the low-level zonal wind (e.g., easterly and westerly regimes). The more spatially and temporally comprehensive TRMM dataset used in this study extends the TRMM‐LBA observations by examining regime variability in Amazonian and South American convective structure over a continental-scale domain. On a continental scale, patterns of east and west regime 850‐700-mb winds combined with LIS lightning flash densities suggest the presence of synoptic-scale controls [e.g., intrusion of extratropical frontal systems and interaction with the South Atlantic Convergence Zone (SACZ)] on regional-scale variability in convective vertical structure. TRMM PR, TMI, and ground-based lightning data suggest that regional variability in wetseason convective structure is most evident over the southern Amazon, Mato Grosso, Altiplano, southern Brazil, and eastern coastal regions of central and southern South America. Convective vertical structure, convective rainfall rates, and lightning activity are all more pronounced during easterly (westerly) regimes over the southern Amazon and Mato Grosso (Altiplano, and southern Brazil). Importantly, when considered with case study results from TRMM‐LBA, the systematic differences in convective structure that occur as a function of regime suggest that associated regime differences may exist in the vertical distribution of diabatic heating. Hence the discrimination of convective vertical structure ‘‘regimes’’ over parts of the Amazon and vicinity based on a resolved variable such as the 850‐700-mb zonal wind direction, while far from being perfect, may have important applications to the problems of cumulus parameterization, rainfall estimation, and retrievals of latent heating over the Amazon.