- Director's Message
- Table of Contents
- Strategic Goals: Science, Facilities & Technology
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Strategic Goal #1, Strategic Priority #1:
Exploring atmospheric, Earth System, and solar processes, variability, and change -
Strategic Goal #1, Strategic Priority #2:
Investigating the interaction of the atmosphere, the broader Earth system, and human society -
Strategic Goal #1, Strategic Priority #3:
Improving prediction of weather, climate, and other atmospheric phenomena -
Strategic Goal #1, Strategic Priority #4:
Developing community models -
Strategic Goal #5, Strategic Priority #1:
Enabling innovative field experiments and measurement campaigns -
Strategic Goal #5, Strategic Priority #2:
Developing new instrumentation
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Strategic Goal #1, Strategic Priority #1:
- Research Catalog
Dave Parsons
Senior Scientist
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Project Summary:
Diurnal cycle of Tropical Convection:
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U.S. Tropical Ocean Study ( TOCS) collage from the 1997 cruise. Researchers have been actively seeking explanations for the observed diurnal cycle of convection and rainfall over the tropical oceans since the late 1800s and early. The observed diurnal cycle well away from the effects of land masses is predawn rainfall maximum with a secondary maximum in the late afternoon and early evening with very light winds. While a consensus is emerging that the secondary maximum in light winds is due to the effects on the atmosphere of a diurnal cycle in the sea surface temperatures due to solar heating, active debate is still ongoing for the explanation for the pre-dawn maxima. The debated mechanisms include direct cloud-radiative interactions, the far field effects of continents, the convergence associated with the semi-diurnal atmospheric tides, and the time required for upscale development of organized convective systems. One difficulty in assessing these mechanisms is the lack of a framework for how the static stability over the tropical oceans varies in the absence of convection. In contrast, over land masses we know that the static stability of the atmosphere over land masses typically decreases during the day as solar insolation heats the earth’s surface and modifies the atmosphere through fluxes of sensible and latent heat. 
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The diurnal variation of CAPE and CIN displayed in CAPE and CIN space with the time of the measurement denoted along the curve. Note the relatively large stability variations in the undisturbed tropical environment and that favorable conditions occur in the pre-dawn and late afternoon hours. The measurements were over the tropical Pacific warm pool during light winds. David Parsons, in collaboration with Francoise Guichard of Meteo France and Kunio Yoneyama of the Japanese Marine Science and Technology Center (JAMSTEC) initiated an effort to collect and composite radiosonde data from JAMSTEC research vessels over the western and central Pacific with a temporal resolution of 3-hr. The goal was to document the variations in static stability over these open ocean regions in the absence of organized tropical convection in an effort to understand the mechanisms driving the diurnal cycles of tropical convection. Special considerations were given to the accuracy of these radiosonde measurements, including correcting the bias of the water vapor measurements through “baselining” the sondes at the temperature and humidity of the tropical boundary layer. In addition, special efforts were made to eliminate the errors introduced by aging of the sondes by using newly purchased radiosondes. The findings of this study are that surprisingly large diurnal variations in static stability were measured in the absence of convection during two JAMSTEC cruises. The framework for the analysis was plotting up the data in CAPE-CIN space, where CAPE is the Convective Available Potential Energy and CIN is the Convective Inhibition. These variations in CAPE and CIN matched the modes of the diurnal cycle of precipitation found in the light and higher wind regime. A simple scaling argument suggested that the variations were large enough to drive the observed diurnal cycle(s) of tropical convection. Thus, one does not need to resort to processes such as cloud-radiative interaction to explain the diurnal cycle as the inherent stability variations are sufficient. Research is ongoing to explain these stability variations but the preliminary finding is that the behavior of boundary layer coupled with the diurnal variations in the clear air radiation budget and the compensating vertical motion can explain these variations. The later two processes essentially comprise the diurnal atmospheric tides, which has been downplayed in most studies that have attempted to explain the diurnal cycle of tropical convection.
THORPEX:
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THORPEX seeks to reduce and mitigate the effects of natural disasters on society by transforming timely and accurate weather forecasts into specific and definite information in support of decisions that produce the desired benefits. One aspect of the TIIMES mission is to be the administrative home of programs that cut across the divisional and laboratory structure of NCAR. One such effort is The Observing-System Research and Predictability Experiment (THORPEX & WMO:THORPEX), which is a long-term effort within the World Meteorological Organization’s (WMO) World Weather Research Program. The overarching goals of THORPEX are to accelerate both the forecast skill of high impact weather events on the 1 to 14-day time scale and utilization of forecast information. THORPEX research is meant to benefit society, the economy and the environment with one focus to mitigation of disasters in the developing world. While THORPEX was designed to concentrate on the 1 to 14-day time-scale, THORPEX is also developing collaborations with the World Climate Research Program for time-scales that fall between the time-scales of numerical weather prediction and climate projections. These time-scales include seasonal prediction and longer subseasonal time-scales, such as the Madden Julian Oscillations. The THORPEX and the WCRP collaboration includes research on topics of mutual interest (e.g., improving the characterization in numerical models of a variety of processes that include tropical convection, polar precipitation events and the triggering and enhancements of Rossby wave trains). 
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Distribution in the monsoon trough over the western North Pactic/p> TIIMES hosts both the US THORPEX Project and the co-chair of the North American THORPEX Regional Committee. Both efforts are led by David Parsons. The THORPEX research effort in the US already has significant participation within the university community and the effort has the potential to involve weather and climate researchers within ESSL at NCAR and the activities of CISL, RAL and SERE. One aspect of THORPEX is to move the user and research community from relying on deterministic forecasts to ensemble forecast systems that better represent the uncertainty in simulations of the non-linear, partly chaotic nature of the atmosphere. During the past year, NCAR CISL initiated an archive of the ensemble members of the ensemble global forecasts of the major operational forecast centers, which when fully operational will include ~256 ensemble members produced daily for forecast periods from 1 to 14-days. The archive includes the basic model derived parameters as well as derived parameters that are of interest to researchers. This ensemble archive is called the THORPEX Interactive Grand Global Ensemble (TIGGE). TIGGE is well utilized by the research community as, for example, within months of opening the beta test phase of archive there were over 50 registered users. 
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A CNES stratospheric balloon from the launch site to be used for
CONCORDIASI. Parsons research activities during the past year include continuing research on a driftsonde observing system test for THORPEX during the African Monsoon Multidisciplinary Analyses campaign (AMMA). The driftsonde system consists of a stratospheric carrier balloon that allows the deployment of dropsondes on demand. Parsons research is looking at the preconditioning of the tropical cyclone genesis environment that occurs from Africa Easterly Waves over the Atlantic showing that the waves produce favorable environment for genesis with deep moisture that extends to ~3 to 5 km. Parsons is also collaborating with Anna Agusti-Panareda at the ECMWF to determine how well these moist layers are replicated in the model initial conditions and forecast fields to assess model initial condition and forecast errors.
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The THORPEX Pacific Asian Regional Campaign (T-PARC) is a multi-national field campaign planned by the Asian and North American Regional Committees and their associated national science committees that address the shorter-range dynamics and forecast skill of one region (Eastern Asian and the western North Pacific) and its impact on the medium-range dynamics and forecast skill of downstream regions (eastern North Pacific, North America and perhaps stretching to Europe). Parsons research activities also include significant time spent being the led Principal Investigator for two major international field experiments with accompanying numerical modeling efforts called THORPEX Pacific Asian Regional Campaign (T-PARC & EOL:T-PARC) and CONCORDIASI. The goals of T-PARC are to advance understanding and improve prediction of i) high impact weather over the western Pacific and east Asia with a focus tropical cyclones from genesis to extratropical transition (ET) or decay; ii) downstream high impact weather events over North America, the Arctic and Europe whose dynamical roots and forecast errors are over the western Pacific and east Asia. The tropical cyclone and ET phases of T-PARC will take place from August to early October 2008 with a winter phase planned for January to March 2009. The CONCORDIASI project will also take place from August to early October 2008. This program has multi-disciplinary goals, such as i) more accurate representation of the atmosphere over Antarctica through advancing satellite data assimilation for weather prediction and the climate record, ii) advancing prediction of precipitation events near Antarctica and the impact of these events on lower latitude circulations; iii) more accurate prediction of ozone concentrations through Lagrangian measurements of ozone depletion and the microphysics of stratospheric NAT clouds. |
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Community Service:
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Presentations:
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TIIMES External Collaborators:Chris Bretherton, University of Washington |
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Publications:Pinto, J. O., D. B. Parsons, W. O. J. Brown, S. Cohn, N. Chamberlain, B. Morley, 2006: Coevolution of down-valley flow and the nocturnal boundary layer in complex terrain, J. Applied Meterorolgy & Climatology, 45(10), 1429-1449. |
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