Courtney Schumacher

Stratiform Rain in the Tropics as Seen by the TRMM Precipitation Radar

Abstract Across the Tropics (20°N–20°S), the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) indicates that for reflectivities ≥17 dBZ, stratiform precipitation accounts for 73% of the area covered by rain and 40% of the total rain amount over a 3-yr period (1998–2000). The ratio of the convective rain rate to the stratiform rain rate is 4.1 on average at the horizontal resolution of the PR data. Convective rain rates remain constant or decrease as the stratiform contribution to total rain increases, implying that stratiform rain production is not very dependent on the strength of convection. This relationship is especially evident over the ocean, where there are weaker convective rain rates than over land but relatively larger stratiform rain amounts. The ocean environment appears more efficient in the production of stratiform precipitation through either the sustainability of convection by a warm, moist boundary layer with only a weak diurnal variation and/or by the near–moist adiaba...

The Tropical Dynamical Response to Latent Heating Estimates Derived from the TRMM Precipitation Radar

A 3-yr (1998‐2000) climatology of near-surface rainfall and stratiform rain fraction observed by the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) was used to calculate the four-dimensional distribution of tropical latent heating on seasonal-to-annual time scales. The TRMM-derived latent heating was then used to force an idealized primitive equation model using an initial value approach in order to obtain the quasi-steady-state, nonlinear, zonally asymmetric atmospheric response to precipitating tropical cloud systems. In agreement with previous studies, an increase in stratiform rain fraction elevates circulation centers and strengthens the upper-level response. Furthermore, horizontal variations in the vertical heating profile implied by the PR stratiform rain fraction pattern lead to circulation anomalies of varying height and vertical extent that

Comparison of Radar Data from the TRMM Satellite and Kwajalein Oceanic Validation Site

Data from the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) and Kwajalein S-band validation radar (KR) agree well for reflectivity exceeding the sensitivity of the PR threshold ( ;17 dBZ). For echoes above this intensity threshold, the products derived from reflectivity, particularly maps of rainfall rate and convective/stratiform classification, compare well, even though slightly different convective‐stratiform separation techniques and different reflectivity‐rainfall rate ( Z‐R) relations are used for the PR and KR. The KR observations indicate the PR misses only 2.3% of near-surface rainfall but 46% of near-surface rain area (

The TRMM Precipitation Radar's View of Shallow, Isolated Rain

0 dBZ) because of its 17-dBZ threshold. The PR senses less than 15% of the echo area observed by the KR above 5-km altitude (i.e., above the 08C level). Thus, the PR highly undersamples weaker echoes associated with stratiform rain near the surface and ice particles aloft but still manages to capture most of the near-surface precipitation accumulation. The temporal sampling of the TRMM PR accurately captures the KR’s overall frequency distribution of reflectivity and its subdivision into convective and stratiform components. However, diurnal and latitudinal variations of precipitation in the vicinity of Kwajalein are not well sampled.

Uncertainties in Oceanic Radar Rain Maps at Kwajalein and Implications for Satellite Validation

Abstract The Tropical Rainfall Measuring Mission (TRMM) 2A23 convective–stratiform separation algorithm applied to the TRMM satellites precipitation radar identifies shallow, isolated precipitation over much of the tropical oceans. The shallow, isolated rain elements dominate the outer fringes of the tropical rain area but give way to deeper, more organized convective systems and associated stratiform areas toward heavy-rain regions. The majority of the shallow, isolated radar echoes are classified as stratiform by version 5 of the 2A23 algorithm. Because the shallow, isolated echoes probably represent warm rain processes, they should be classified as convective. This reclassification leads to a more reasonable pattern of stratiform rain contribution across the Tropics.

Heating Structures of the TRMM Field Campaigns

The Kwajalein, Marshall Islands, Tropical Rainfall Measuring Mission (TRMM) ground validation radar has provided a multiyear three-dimensional radar dataset at an oceanic site. Extensive rain gauge networks are not feasible over the ocean and, hence, are not available to aid in calibrating the radar or determining a conversion from reflectivity to rain rate. This paper describes methods used to ensure the calibration and allow the computation of quantitative rain maps from the radar data without the aid of rain gauges. Calibration adjustments are made by comparison with the TRMM satelliteborne precipitation radar. The additional steps required to convert the calibrated reflectivity to rain maps are the following: correction for the vertical profile of reflectivity below the lowest elevation angle using climatological convective and stratiform reflectivity profiles; conversion of reflectivity ( Z) to rain rate (R) with a relationship based on disdrometer data collected at Kwajalein, and a gap-filling estimate. The time series of rain maps computed by these procedures include low, best, and high estimates to frame the estimated overall uncertainty in the radar rain estimation. The greatest uncertainty of the rain maps lies in the calibration of the radar (630%). The estimation of the low-altitude vertical profile of reflectivity is also a major uncertainty ( 615%). The Z‐R and data-gap uncertainties are relatively minor (65% or less). These uncertainties help to prioritize the issues that need to be addressed to improve quantitative rainfall mapping over the ocean and provide useful bounds when comparing radar-derived rain estimates with other remotely sensed measures of oceanic rain (such as from satellite passive microwave sensors).

Precipitation and Latent Heating Characteristics of the Major Tropical Western Pacific Cloud Regimes

Abstract Heating profiles calculated from sounding networks and other observations during three Tropical Rainfall Measuring Mission (TRMM) field campaigns [the Kwajalein Experiment (KWAJEX), TRMM Large-Scale Biosphere–Atmosphere Experiment in Amazonia (LBA), and South China Sea Monsoon Experiment (SCSMEX)] show distinct geographical differences between oceanic, continental, and monsoon regimes. Differing cloud types (both precipitating and nonprecipitating) play an important role in determining the total diabatic heating profile. Variations in the vertical structure of the apparent heat source, Q1, can be related to the diurnal cycle, large-scale forcings such as atmospheric waves, and rain thresholds at each location. For example, TRMM-LBA, which occurred in the Brazilian Amazon, had mostly deep convection during the day while KWAJEX, which occurred in the western portion of the Pacific intertropical convergence zone, had more shallow and moderately deep daytime convection. Therefore, the afternoon heigh...

Heating in the tropical atmosphere: what level of detail is critical for accurate MJO simulations in GCMs?

Abstract An objective tropical cloud regime classification based on daytime averaged cloud-top pressure and optical thickness information from the International Satellite Cloud Climatology Project (ISCCP) is combined with precipitation and latent heating characteristics derived using the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR). TRMM precipitation information is stratified into the ISCCP regimes in the tropical western Pacific (TWP), revealing the following three major precipitation regimes: a heavy (12 mm day−1) precipitation regime dominated by stratiform precipitation and top-heavy latent heating; a regime with moderate (5 mm day−1) precipitation amounts, mostly convective in nature with more midlevel latent heating; and a low (2 mm day−1) precipitation regime with a relatively large rain contribution from shallow convection, compared to the other regimes. Although three of the ISCCP cloud regimes are linked to the more convective, moderate precipitation regime, only one of t...

Anvil Characteristics as Seen by C-POL during the Tropical Warm Pool International Cloud Experiment (TWP-ICE)

Dozens of studies have been done in recent years documenting factors in large-scale models that affect the simulation of the Madden–Julian oscillation (MJO). All of these studies discuss processes that affect heating in some facet. In this study, we examine various heating adjustments in Community Atmospheric Model version 4 (CAM4) to determine what the vertical and horizontal heating distributions need to look like in order to simulate a realistic MJO. Heating is added to CAM4 using two different methods. In the first method, we add top-, bottom-, or middle-heavy heating blobs at various locations for each phase of the MJO. We describe a new technique for adding these heating perturbations in CAM4. In the second method, we add observed latent heating profiles from the tropical rainfall measuring mission Precipitation Radar to CAM4 in order to more accurately depict both the horizontal and vertical distribution of heating throughout the Tropics. We find that a realistic vertical and horizontal distribution of heating is critical for accurate representation of the MJO in CAM4. Observed heating distributions are top-heavy, but merely putting idealized top-heavy heating blobs into CAM4 does not produce an MJO as realistic as inputting the observed spatial distributions. Improvements in the simulation of the MJO are also seen with an interactive ocean, but the improvements are not as large as those seen using realistic heating distributions and prescribed SSTs.

Top‐of‐atmosphere radiation budget of convective core/stratiform rain and anvil clouds from deep convective systems

Abstract The Tropical Pacific Warm Pool International Cloud Experiment (TWP-ICE) took place in Darwin, Australia, in early 2006. C-band radar data were used to characterize tropical anvil (i.e., thick, nonprecipitating cloud associated with deep convection) areal coverage, height, and thickness during the monthlong field campaign. The morphology, evolution, and longevity of the anvil were analyzed, as was the relationship of the anvil to the rest of the precipitating system. The anvil was separated into mixed (i.e., echo base below 6 km) and ice-only categories. The average areal coverage for each anvil type was between 4% and 5% of the radar grid. Ice anvil thickness averaged 2.8 km and mixed anvil thickness averaged 6.7 km. Areal peaks show that mixed anvil typically formed out of the stratiform rain region. Peak production in ice anvil usually followed the mixed anvil peak by 1–3 h. Anvil typically lasted 4–10 h after the initial convective rain area peak. TWP-ICE experienced three distinct regimes: an...