April 2010
Newly awarded Precipitation projects/connection to NEWS Drought & Flood Extremes working
group
Daniel Cecil/University of Alabama in Huntsville
Precipitation Processes and Retrieval Challenges in Intense Mesoscale Convective
Systems
Intense mesoscale convective systems (MCS) pose challenges for precipitation estimation
and contribute a substantial portion of the normal precipitation in certain regions,
particularly mid-latitude continental locations. These systems have well-developed
mixed phase regions with abundant large graupel and often hail, much of which melts
while falling to the surface as rain. The hypothesis of this proposal is that precipitation
retrieval algorithms that are well suited for more common rainfall situations may have
larger errors due to the radar and radiometric characteristics of these intense MCS. This
proposed study will examine the structure and precipitation properties of intense MCS,
with an emphasis on how they are treated by precipitation retrieval algorithms. It will
also examine the spatial / temporal variability of intense MCS occurrence, and
implications for error characteristics of precipitation climatologies.
A large sample of intense MCS observed by the TRMM satellite (TMI, PR, LIS, and
VIRS measurements, retrievals from the TRMM algorithms, and retrievals from future
algorithms as they become available through the science team) will be used to evaluate
the variability and relative error characteristics among precipitation retrieval algorithms,
and to characterize the types of systems and environments that pose particular challenges
for retrievals. The full 1997-present TRMM dataset will also be used to quantify the
contribution to regional / seasonal rainfall from these intense MCS in the regions where
they occur. Passive microwave measurements from AMSR-E and SSM/I will be used for
extending the study through middle and high latitudes.
Field campaign measurements (e.g., Mid-latitude Continental Convective Clouds
Experiments (MC3E) in the North American plains; campaigns led by South American
GPM investigators) will be used for more detailed study of individual intense MCS.
These field campaigns and additional ground-based validation measurements (e.g., rain
gauge networks in the U.S., Argentina, and Brazil) will contribute to quantifying the error
characteristics of retrieval algorithms for intense MCS.
This proposal addresses multiple topics in the NASA Precipitation Science program. It is
submitted under research category 2.1 (algorithm development and validation), topics
1.1.2, 1.1.3, and 1.3 (testing and validation of radar and radiometer retrieval algorithms,
and error characterization of satellite rainfall retrievals and/or ground-based
measurements...). It will examine the performance and error characteristics of current
satellite rainfall products in intense MCS, and future products as they become available
from GPM team members. Although not contributing development of a new algorithm, it
will contribute to testing / validation of radar and radiometer retrieval algorithms
(primarily over land, where the intense storms most often occur). Results will be
routinely conveyed to algorithm developers, so that test versions of algorithms can be
improved before they are finalized. The proposal also applies to research category 2,
topics 2.1 (use of satellite and field campaign data to study precipitation and
microphysical processes, particularly for mixed phase and frozen precipitation...) and 2.3
(analysis of TRMM and other current satellite-based precipitation information for studies
of climate and weather...).
Robert Houze/University of Washington
Structures of Precipitating Cloud Systems Over Oceans, Continents and Mountains
TRMM Precipitation Radar (PR) data and other observations will be analyzed to improve
understanding of precipitation mechanisms and aid the development of algorithms for
remote sensing of precipitation systems important to the global general circulation and
water cycle. In particular, we focus on precipitation systems that are responsible for 1)
large amounts of rain accumulation, 2) extreme forms of convection, and 3) mountain
snowpack. To make the study tractable, it is divided into oceanic, continental, and coastal
components.
The research will use methodology developed at the UW to optimize the vertical
structure information in the PR data. We reprocess the PR data by geo-locating them and
interpolating them to a Cartesian grid. The reprocessed data are ingested into customized
visualization software allowing for highly flexible joint analysis of diverse data and
model output. Using the visualization capability facilitates identification of echo features
that can be defined and analyzed objectively, e.g. extreme deep convective echo cores,
wide convective cores, and broad stratiform regions. The objectively identified elements
can be mapped to create climatologies of particular types of convective system structure,
and/or analyzed via contoured frequency by altitude diagrams (CFADs) and other
statistical tools.
Over tropical oceans, echo objects will be identified and mapped into composite
frameworks to determine how precipitation processes vary with respect to the large-scale
equatorial wave structure dominating the MJO and between the eastern vs. western
regions of the tropical Pacific basin. For tropical cyclones, the PR echoes will be
composited with respect to a normalized radius from storm center, and processes within
the eyewall, rainband, and distant environment will be determined.
Over tropical and subtropical continents, convection will be investigated by focusing on
South Asia and South America, where extreme convection is favored by mountains and
other surface conditions. The frequency of occurrence of systems containing extreme
convective and stratiform echo structures will be analyzed climatologically, with CFADs,
and in limited case studies. Hypotheses will be tested regarding the mesoscale
organization, the vertical structure and associated latent heating profiles of convective
systems, the effect of mesoscale life cycles on convective climatologies, and the role of
the low-level jet and foothill terrain in triggering extreme systems. The studies of
continental, oceanic, and coastal convective systems will be evaluated to determine if
their highly varied structures are accurately represented in the nascent TRMM latent
heating algorithm.
Coastal regimes will be studied upstream and over the Burma mountains, which is the
best natural laboratory for studying coastal enhancement within the TRMM orbit.
Enhancement precipitation at mountainous coastlines is very important in the overall
pattern of global rainfall. In this regime, echo objects identified upstream of and over the
coastal terrain will be mapped, and CFAD analysis will be organized by distance from
the barrier to investigate several hypotheses for triggering of convective cells and
enhancement of stratiform precipitation upstream of and over the coastal terrain. Results
of this analysis will be evaluated to determine if the TRMM convective/stratiform
separation algorithm overestimates the stratiform precipitation and hence incorrectly
distributes latent heating in regions of coastal rainfall enhancement.
Storms producing snowpack over mountain ranges will be addressed by CFAD analysis
of echo layers intersecting mountain tops above the melting level. For low-latitude
mountains, TRMM PR data will be used over the Andes and Himalayas. For higher
latitudes, the CloudSat radar will be used as a proxy for GPM. These studies will provide
a statistical database useful for GPM algorithm design and validation of GPM after
launch.
Witold Krajewski/University of Iowa
Studies of Error Structure of GPM Rainfall Estimates and Scale Aspects of Floods
The overarching goal of the proposed research is evaluation of the accuracy of spacebased estimates of rainfall and their suitability for hydrologic applications. The
evaluation will be based on the data and resources provided by the Ground Validation
Program of the Global Precipitation Measurement mission. The central objectives of the
work include (1) uncertainty characterization of space-based precipitation products; (2)
characterization of the utility of GPM precipitation products for flood monitoring and
analysis, based on hydrologic studies that focus on extreme flooding; and (3) support of
Ground Validation field experiments.
Uncertainty characterization will be based on satellite rainfall products, carefully selected
ground-based radar and in-situ instrument data from rain gauge networks and
disdrometers. The methodologies will include statistical and probabilistic modeling of
satellite rainfall error structure. The developed models will be applied to a number of
precipitation products so that algorithms could be validated and their scale-dependent
error characteristics better understood.
Hydrologic studies will be carried out with the objective of assessing not only the
accuracy of GPM rainfall estimates, but also the impact on hydrologic forecasting. The
focus of hydrologic studies will be extreme flooding and related validation activities will
target GPM rainfall estimates for extreme flood episodes. Flood studies will be carried
out for the eastern US, with a focus on the potential Hydromet Test-bed site in the Tar-
Neusse river system of North Carolina and in the central US with a focus on Oklahoma
and Iowa. Analyses will provide guidance on use of the dense network of USGS stream
gauging stations in the US for GMP ground validation activities. Research in the eastern
US will include analyses of extreme rainfall in mountainous terrain, with a special focus
on landfalling tropical cyclones. We will assemble composite Hydro-NEXRAD rainfall
fields for storm events that have produced major flooding in the eastern US (since the full
deployment of the WSR-88D network), as well as rain gage data sets for analysis of error
structure of radar rainfall estimates from storms that produce heavy rainfall and flooding.
We will also assemble radar rainfall fields for heavy rain/flood events in the central US
and eastern US for regions with high-quality rain gage networks. These analyses will
provide the principal resources for assessing error structure of radar rainfall estimates for
extreme flood-producing storm systems. They will also be used for flood studies to
assess the scale-dependent monitoring capabilities from GPM-like rainfall products.
A mobile network of four X-band polarimetric radars will be made available to support
Ground Validation Program activities. In particular, the network will be used at the
Hydromet Test-bed site at the Tar-Neusse river system of North Carolina to study
precipitation in complex terrain and the associated flooding. The network can be
controlled over the Internet and will provide data in real time. The observations will
support hydrologic modeling for flood forecasting as well as space-based algorithm
development by providing information on the vertical structure of precipitation in
complex terrain.
The proposed research will result in a probabilistic description of uncertainties of spacebased precipitation products and their error characteristics across scales. The emphasis
will be on heavy rainfall and the resulting flooding. Hydrologic studies will establish
scale-dependent detection capabilities of flooding from satellite precipitation products
and the requirements for their space-time resolution and accuracy that would permit
useful flood forecasting around the world.
**William Lau/NASA Goddard Space Flight Center
Characteristics of extreme precipitation events and modulation by climate
variations
High-impact weather events in the tropics are primarily fueled by condensation heating
from extreme precipitation events (EPE) . Using TRMM rainfall data in conjunction with
numerical experiments with the Goddard Multi-Model Framework (MMF), the Goddard
Cumulus Ensemble Model (GCE), we propose to study the characteristics of EPE
rainfall, clouds, and latent heating structures, associated weather systems, and their
modulations by tropical climate processes such as the Madden and Julian Oscillation
(MJO) and the El Nino Southern Oscillation (ENSO), and possibility climate change.
The following research tasks are proposed:
1. Identifying extreme rainfall events: We will identify the regional and seasonal
distribution of EPEs in the tropics using TRMM 3-hourly and daily and pentad data, with
different space and time resolution to establish a unified definition of EPEs, their
frequency of occurrence and intensity can be compared. The linkages of these EPEs to
prevailing weather regimes such as tropical cyclones, mesoscale convective complexes,
monsoon circulation and other weather phenomena will be established.
2. We will us TRMM rainfall, radar echo top heights, meso-scale precipitation
features , and lightning data to determine the rainfall and cloud characteristics, and
examine the developmental stages of these systems, leading up to the extreme rainfall
events, over tropical lands and oceans respectively. The roles of warm-, mixed-phase,
and cold rain, and convective vs. stratiform rain will be elucidated.
3. Modulation of extreme rainfall events: We will examine the modulation of
extreme rainfall events and associated characteristics PDFs, by the seasonal cycle, MJO
and ENSO. Rainfall PDFs for the seasons, and different phases of MJO and ENSO will
be compared and contrasted, with focus on the temporal and regional clustering of
extreme rain events, and their relationship with the large-scale dynamical and SST
forcing. We will also investigate possible trends in the TRMM data, with respect to light,
moderate, heavy, and very heavy rainrates, defined by percentile ranked rain rates, and
their relationships to SST and other long-term climate forcing. . Assimilated data from
the NASA MERRA will be used to identify phases of MJO, ENSO, SST and other longterm climate forcing .
4. Modeling task: This task will focus on the improved understanding of cloud and
rain microphysics in the development and maintenance of the extreme events using both
global, and cloud scale models. We will conduct a) simulations of select cases of
extreme events relate to specific extreme, high-impact events identified from Task 1,
using the Goddard Cloud Ensemble (GCE) model, and b) decadal scale ensemble
numerical integration using the MMF for the TRMM data period (1998 -present) to
provide a test bed for analysis of climate scale modulation of rainfall extreme events.
Expected Results: The proposed research will provide unified definition and better
understanding of extreme rainfall events associated a wide range of tropical weather and
climate processes. The methodology can be used to address similar issues globally
during the GPM era. The results will also be very useful to provide the scientific bases
for assessment of impacts of fresh water available and re-distribution as a result of
climate change.