Directorate

• Contents
• EXECUTIVE SUMMARY
• 1. SCOPE OF THE PROGRAM
• 2. IMPROVING OUR UNDERSTANDING OF EARTH-SYSTEM PROCESSES
• 2.1 Scale Interactions Associated with Precipitating Convective Systems
• 2.2 Understanding the Dynamics and Predictability of Weather Systems on Time Scales of 0-48 h
• 2.3 Fundamental Research on Precipitation Processes, with an Emphasis on their Improved Representation in Numerical Models
• 2.4 Understanding the Dynamics, Physics and Chemistry of Multi-Scale Atmospheric Chemical Constituent and Particulate Transport, Dispersion and Transformations
• 2.5 Fundamental Research in Boundary Layers and their Interfacial Interactions
• 3. ADVANCING THE SCIENCE OF ATMOSPHERIC PREDICTION
• 3.1 Advancing Short-Range Weather Prediction
• 3.2Advancing Data Assimilation Research
• 3.3 Improving Forecasting of Pollutants and Hazardous Materials
• 4. ADVANCED COMMUNITY RESEARCH TOOLS
• 4.1 WRF Community Model
• 4.2 Community Data Assimilation Techniques
• 4.3 Nested Community Climate Model
• 5. SUMMARY
• Acronym List
• Print Version
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Mesoscale & Microscale Meteorology Division Science Plan:

2.1 Scale Interactions Associated with Precipitating Convective Systems

Goal: To advance basic knowledge of precipitating convective systems, with emphasis on up- and down-scale interactions between convection and other modes of atmospheric motion, for improving weather prediction and climate models.

Quantifying precipitating convective systems and their underlying scale interactions is a multi-faceted problem, one which provides exciting research challenges with a need for integration across a range of disciplines and other programs.

We define the phrase “precipitating convective systems” as referring to the coupled physics of precipitating convection, boundary layer turbulence, surface exchange, cloud-microphysics and cloud-radiative interaction, all of which are interacting with large-scale dynamics. MMM’s traditional strengths are in these physical and dynamical disciplines. Better knowledge of such coupled physics will enable us to better tackle important characteristics of the atmospheric water cycle, the atmospheric convective-radiative-dynamical equilibrium, and the optimal ways of improving 2-way coupling between regional and global weather and climate models.

A unifying concept, to which MMM is well poised to contribute, involves the scale interaction between organized precipitating convection and the large-scale environment. Our planned activities include representing convection explicitly using numerical cloud-system models run at adequately fine resolution over large domains, observational analysis, theory, and other modeling/analysis frameworks. This is well suited for collaboration with other divisions and laboratories. For example, the general theme of convection and scale interactions with an emphasis on tropical convection, and the subsequent downstream generation of high impact weather events through Rossby wave trains and other disturbances, has been proposed as an area of scientific focus for NCAR’s involvement in the THORPEX program. In addition, aspects of this work are well suited for collaborations with NOAA and the university community and with existing efforts with the Water-cycle Across Scales Program in TIMES (The Institute for Multidisciplinary Earth Studies).

Observed and numerically simulated Hovmoller diagrams of tropical superclusters (left), together with the vertical structure in the simulated system and the schematic of the dynamical model from Moncrieff.

Our research in precipitating convective cloud systems and scale interaction will thus focus on four major strategic efforts:

• Multiscale tropical convection;
• Tropical cyclogenesis;
• Warm-season precipitation over mid-latitude and tropical continents; and
• Interaction between tropical convection and high-impact convective weather in mid-latitudes in the 1-2 week range.

Much of this work has been defined as a priority by the GEWEX Cloud Systems Study (GCSS) under the Global Energy and Water cycle Experiment (GEWEX) of the World Meteorological Organization (WMO). MMM scientists maintain leading roles in this major international effort.
Inadequate knowledge of tropical intraseasonal variability is recognized as a major impediment to skillful seasonal prediction. For example the lack of skill in forecasting the Madden Julian Oscillation (MJO) and other sources of persistent convection in the tropics is a major impediment to medium range forecasting over much of the globe. Our large-scale tropical convection research will focus on tropical intraseasonal variability, as an extension to ongoing work on the MJO. Of particular interest is the role of the MJO in monsoon breaks and the related high impact on precipitation in the deep tropics.

Understanding tropical cyclone formation is of importance for both medium and seasonal forecasting and for improved assessment of potential climatic changes to tropical cyclone occurrence. Current work on tropical cyclogenesis indicates a substantial role for interaction across all scales. Of particular interest is the manner in which Rossby waves in the equatorial duct, such as the ubiquitous easterly waves of the North Atlantic, may respond to varying larger-scale atmospheric flow to produce a downscale focus of cyclonic vorticity, which, in turn, supports the organization of moist convection and associated mesoscale interactions that have been observed to lead to cyclogenesis. Other areas of interest include the manner in which impinging mid-latitude systems can enhance or reduce cyclogenesis potential and the role of the dry Saharan air in effecting hurricane genesis, intensity and structure. Our tropical cyclogenesis research will be addressed through high-resolution numerical modeling and field programs. Attention will be given to the genesis of Atlantic hurricanes, which may include a field and research campaign in association with the African Monsoon Multi-disciplinary Analysis (AMMA) program, called ASHE (AMMA Seedling Hurricane Experiment).

Our third strategic effort addresses the need for improved prediction of warm-season precipitation over mid-latitude continents, where models have vexingly poor skill. Although in some aspects mid-latitude convection is similar to tropical convection, differences arise through the degree to which the convection can directly change the balanced flow and the nature of surface forcing. Focal areas of research are to quantify the role of upper-tropospheric disturbances, diurnal phasing and the interaction among convective systems. We will interact with investigators from the outside community and other NCAR divisions and laboratories in this strategic effort, particularly through the Water-cycle Across Scales Program in TIMES.

Our fourth effort on the ways in which tropical convection affects mid-latitude weather through planetary wave teleconnection and wave-mean flow interaction interlinks the first and third efforts above. Research will focus on the genesis and life-cycle of the MJO (winter and summer), the related generation of planetary waves and gravity waves by large-scale tropical convection, and planetary wave teleconnection and shortwave excitation in the context of warm-season convection over North America and eastern Asia. The global modeling and analysis expertise of CGD will be an important contribution to furthering this research area.

Our research into the scale interactions accompanying precipitating convective systems is an integrating factor for other research relevant to this area, including: cloud microphysics, planetary boundary layers, and numerical weather prediction in the 0-48 hr timeframe. The cloud system science we address is relevant to current regional scale models of weather and climate, and especially to the manner in which 2-way scale interactions must be incorporated across the nesting boundaries to adequately represent the full physical processes. In this context, the research will contribute to the development of the WRF and nested climate models in MMM. Our work is also relevant to next-generation global numerical prediction models where the grid resolution will be approaching 10 km over the next five years.

Potential collaborations across NCAR include: improved understanding of vertically propagating gravity waves, which is of considerable importance to the general circulation of the upper stratosphere and mesosphere (HAO); and the explicit approach to scale interactions and convection opening up new avenues for convective parameterization and nested climate modeling (CGD).

Outside of NCAR, our tropical convection research provides opportunity for interaction with universities and other research institutions. For example in this area, MMM leads work undertaken under the Memorandum of Understanding between NCAR and the National Centre for Medium Range Weather Forecasting, New Delhi, India.

The wide dynamic range of scale interactions associated with precipitating convective systems simulation puts new demands on model development and validation. Data sets from field campaigns are necessary to this effort, but not sufficient. We shall need, in particular to call on increased use of satellite data. Because of our limited expertise in satellite analysis and assimilation, we shall seek collaborations with universities and other research institutions that have such expertise.

Next section: Understanding the Dynamics and Predictability of Weather Systems on Time Scales of 0-48 h

 

 

 

 

 

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