The University of Arizona Department of Atmospheric Sciences

ATMO Seminar Series Archive (2013)

Spatiotemporal scale limits and roles of biogeochemical cycles in climate prediction (PhD Oral Defense)

Koichi Sakaguchi, University of Arizona

Wednesday, January 16 2013, 2:00pm



There is high confidence in global temperature change and its attribution to human activities, but climate prediction remains a serious challenge and bears large uncertainty, particularly so as the scale of interest becomes small. On the other hand, the recent coordinated efforts of intercomparisons of coupled climate models (Coupled Model Intercomparison Project, CMIP) have made it possible to assess such uncertainty in a manner that was not possible a decade ago, namely using a collection of more than twenty global climate models that have attained unprecedented complexity to represent the climate system and its feedbacks to external forcings.

With the increasing interests in regional impact studies for decision-making, one of the urgent tasks is a systematic and quantitative evaluation of the expected skill of these models over a range of spatiotemporal scales. The first part of this dissertation is devoted to this task, focusing on the predictive skill in the linear trend of surface air temperature. By evaluating the hindcasts for the last 120 year period in the form of deterministic and probabilistic predictions, it is found that the hindcasts show reliable skill over a few thousand km (30 deg x 30 deg) or larger spatial scales and 30 years or longer temporal scales. Their skill is still limited for smaller scales where we see no significant differences from climatology or random guesses.

Over longer temporal scales, the feedbacks from the carbon cycle to the increasing atmospheric CO2 concentration become important. However, the carbon cycle is still a new component in global climate models, and previous studies have suggested a large uncertainty in its feedback processes, particularly in the terrestrial biosphere. Therefore the rest of the dissertation attempts to find key model components that could be contributing to this uncertainty using one of the leading land-climate models, the National Center for Atmospheric Research (NCAR) Community Land Model (CLM). Detailed model-observation comparison pinpointed several key deficiencies in these models, including the positive bias in plant productivity, improper formulations for drought-related stress and mortality, and simplified representation of the whole forest by one average tree. The last two aspects can lead to a catastrophic forest die-off over unrealistically short temporal scales.

Continued from the second part, the impact of nitrogen cycle and dynamic vegetation on the carbon cycle feedback at global scale is analyzed by CLM version 4. It is found that the nitrogen limitation on the CO2 fertilization works similarly with or without dynamic vegetation. However, dynamic vegetation significantly altered the sensitivity to surface air temperature, most likely through the different partitioning of terrestrial carbon between vegetation and soil pools, which leads to more stringent nitrogen limitation in the case of higher carbon distributed to vegetation. It suggests that the impact of the nitrogen cycle depends on the state of the terrestrial carbon system, which in turn varies and is possibly biased by the particular dynamic vegetation models used. A modeling study of such feedbacks with specified and constant vegetation cover may not fully sample its uncertainty in future climate projections.

The Surface Climate Response to 11-Yr Solar Forcing During Northern Winter

Lon Hood, Lunar and Planetary Lab, University of Arizona

Thursday, January 17 2013, 3:30pm

PAS 220, Refreshments in PAS546 from 3:00-3:30p

*Note: Dr. Hood's website


The surface climate response in sea level pressure (SLP) and sea surface temperature (SST) to 11-Yr solar forcing during boreal winter (DJF) is investigated using a combination of observational analyses and comparisons with GCM simulations. First, a multiple linear regression (MLR) statistical model is applied to DJF averages of Hadley Centre SLP and SST data over the 1880-2009 period. In addition to a significant positive SLP response in the North Pacific found in previous studies, a positive SST response is obtained across the midlatitude North Pacific. Negative but insignificant SLP responses are obtained in the Arctic. The derived SLP response at zero lag therefore resembles a positive phase of the Arctic Oscillation. For comparison, a similar MLR analysis is applied to model SLP and SST data from a series of simulations using an atmosphere-ocean general circulation model (EGMAM). The simulations, which were performed by a German group (U. Cubasch and colleagues), differed only in the assumed solar cycle variation of stratospheric ozone. It is found that the simulation that assumed an ozone variation estimated from satellite data, tapering to zero at the poles, produces solar SLP and SST responses that are most consistent with observational results, especially during a selected centennial period. This indicates that top-down forcing (via the stratosphere) is probably important for producing the observed surface response.


Hood, L., and B. Soukharev (2012) The lower stratospheric response to 11-yr solar forcing: Coupling to the troposphere-ocean response, J. Atmos. Sci., v. 69, 1841-1864.

Bal, S., S. Schimanke, T. Spangehl, and U. Cubasch (2011) On the robustness of the solar cycle signal in the Pacific region, GRL, v. 38, doi:10.1029/2011GL047964.

Hood, L., S. Schimanke, T. Spangehl, S. Bal, and U. Cubasch (2013) The surface climate response to 11-yr solar forcing: Observational analyses and comparisons with GCM simulations, J. Climate, submitted.

On the Incidence and Behavior of Cloud-to-ground Lightning in Complex Terrain: Grand Canyon, Rocky Mountains, and the Ozarks

Ken Cummins, University of Arizona

Thursday, January 31 2013, 3:30pm

PAS220, Refreshments in PAS546 from 3:00-3:30p

*Note: Dr. Cummins's website


The climatological incidence of cloud-to-ground (CG) lightning is known to have large regional differences associated synoptic-scale variations in weather that impact the development and propagation of deep convection. At smaller spatial scales, terrain variations are also known to play a significant role in the development of deep convection leading to thunderstorms. At even smaller scales, there are flash-scale interactions between downward propagating leaders and terrain variations that can alter the nature and location of attachment to ground. This talk will focus on terrain-related variations in the incidence (area density) of CG lightning and some of the physical parameters of lightning flashes. Estimates of these parameters are derived from measurements obtained from the U.S. National Lightning Detection Network (NLDN), and presented at kilometer-scale spatial resolution.

As a special case of terrain effects, the incidence of NLDN-derived CG lightning strike observations near the Grand Canyon show strong variations near the canyon rim/walls, with roughly 8-times more strokes/km2/yr than within the canyon. There is also a clear increased incidence of lightning attachment near the top edge of the canyon rim. The possible contributing factors will be presented, along with the evidence-to-date obtained during a preliminary field campaign in July 2009 (high-speed video, radar animations, and remote electric field recordings).

A recently-developed method for classifying a CG stroke as creating a new ground contact or occurring in a pre-existing channel will also be presented. The method employs information that can be provided by modern Lightning Locating Systems. Detailed analyses of ground contact behavior will be presented for two regions -- the front range of the Rocky Mountains and the Ozark/Washita mountains in Oklahoma and Arkansas.

Message in a Bottle: Development of a Laboratory Chamber for Studies of Aerosol and Cloud Processes in the Atmosphere

Raymond Shaw, Michigan Tech University

Thursday, February 7 2013, 3:30pm

PAS220, Refreshments in PAS546 from 3:00-3:30p

*Note: Dr. Shaw's website


Clouds come in bewildering varieties, complete with their own Latin-derived lexicon, and exist under the full range of temperatures and pressures encountered in the earth's atmosphere. While their main constituent is water, the water itself can exist as liquid, ice, or even metastable, supercooled liquid, always dispersed over a broad range of particle sizes and concentrations. Furthermore, many trace species in the atmosphere, in both gas and condensed (aerosol) phases depend on chemical cycles that are tightly coupled to aqueous or surface-catalyzed reactions in clouds. The clear picture that has emerged in recent years is that clouds, in all of their multi-faceted complexity, represent one of the primary uncertainties in our understanding of weather and climate. At Michigan Tech we are developing a laboratory chamber that will allow cloud processes to be investigated under controlled, repeatable conditions, and with a level of detail that is currently impossible to achieve in the field. The chamber, currently under construction, is capable of simulating tropospheric conditions, including the ability to generate realistic turbulent convection and mixing processes. The scientists involved with this project will be exploring processes from ice nucleation to organic aerosol formation, and optical properties to turbulent mixing.

The impacts of terrestrial hydrological processes on climate predictions

Guo-Yue Niu, University of Arizona

Thursday, February 28 2013, 3:30pm

PAS220, Refreshments in PAS546 from 3:00-3:30p

*Note: Dr. Niu's website


Land surface can 'memorize' climate dynamics by recording and filtering the signals of weather events through heat and water storages and feed back to the atmosphere through surface energy and water fluxes. Arid-to-wet transition regions over land are identified as 'hot spots', where changes in surface water fluxes associated with soil moisture have greater impacts on precipitation. This talk will present how groundwater and vegetation dynamics affect warm-season climate predictions in the central US.

Through a community effort, we first improved the realism of the community Noah land surface model (LSM) with multiple options of physics (NoahMP). NoahMP enhanced its hydrological scheme with a TOPMODEL-based runoff scheme and a simple groundwater model. It is demonstrated that NoahMP greatly improves the simulation of surface energy and water fluxes, runoff, groundwater, and vegetation dynamics. Coupled with the Weather Research and Forecast (WRF) model, groundwater dynamics interacting with vegetation dynamics prolongs the land surface 'memory' and enhances the persistence of intraseasonal precipitation.

The talk will also show challenges in representing some specific hydrological processes that may affect climate predictions and how controlled experiments in the tropical forest and the Landscape Evolution Observatory (LEO) in Biosphere 2 may facilitate understanding and parameterizing these processes.

Creating a unified perspective of the North American monsoon: from the paleoclimate record to climate change projections

Christopher Castro, University of Arizona

Thursday, March 7 2013, 3:30pm

PAS220, Refreshments in PAS546 from 3:00-3:30p

*Note: Dr. Castro's website


In the Southwest United States, the North American monsoon is the main driver of severe weather and accounts for nearly half the annual precipitation. How the monsoon has behaved in the past and how it will change in the future is a question of major importance for natural resource management and infrastructural planning. In this presentation, I will summarize the results of several projects that have investigated the North American monsoon from the perspective of the paleoclimate (tree-ring) record, long-term instrumental record of the late 20th century, high resolution numerical weather prediction of organized convection during a field experiment, and dynamically downscaled climate change projections. Some particular points of discussion include 1) consideration of natural climate variability in the past and future, 2) necessary requirements for regional atmospheric models to reasonably represent the monsoon, and 3) how the monsoon will change in the future, with an emphasis on how climate variability is synergistically interacting with natural variability to intensify climate extremes. Finally, I will discuss the importance of establishing the commonalities between observational and modeling perspectives of the monsoon, necessary to facilite the use of climate change projection information for decision making.

Aviation Weather: Operations and Testbed at the Aviation Weather Center


Thursday, April 4 2013, 3:30pm

PAS220, Refreshments in PAS546 from 3:00-3:30p


Fire-climate feedbacks: Understanding mechanisms and implications for sustainably managing fires during the 21st century

James Randerson, University of California, Irvine

Thursday, April 18 2013, 3:30pm

PAS220, Refreshments in PAS546 from 3:00-3:30p

*Note: Link to Dr. Randerson's website.

Students and postdocs interested on this topic are invited for a group discussion with Dr. Randerson on Friday, April 19 8:30-10am at PAS 218


Contemporary fire emissions contribute to the buildup of carbon dioxide and other greenhouse gases in the Earth's atmosphere. They also influence the climate in other ways, including by modifying aerosol composition and load, and the distribution of vegetation types present in different biomes. In my talk, I describe recent work to quantify trends in global burned area and fire emissions using remote sensing and atmospheric observations. I also will summarize results from several recent studies that have investigated fire effects on regional and global climate using an Earth system model. For the Amazon basin, I will discuss how sea surface temperatures and terrestrial water storage measurements may be used to forecast year to year changes in drought and fire season severity with 3-6 month lead times, enabling new opportunities for forest conservation. In the final part of my talk, I describe a series of recommendations that have emerged from recent empirical and modeling work related to managing fires more effectively for climate change mitigation and planetary stewardship.

GNSS/GPS Meteorology in the Tropics: A New Look at Deep Convective Processes

David K. Adams , Universidad Nacional Autonoma de Mexico

Friday, May 31 2013, 11:00am

PAS224, Refreshments in PAS546 from 10:30-11:00a

*Note: Link to Dr. Adams's website.


We report on results from the first studies ever of deep convection in the equatorial tropics using GNSS/GPS.Data from the two Amazon Dense GNSS Meteorological Networks (Manaus, Central Amazon and Belem, coastal Amazon) are used to characterize the diurnal cycle of convection, propagation of convective events, as well as their intensity. Furthermore, utilizing the conservation of total water equation, a water vapor convergence metric is developed. GNSS observations employing this metric offer estimates of important physical time scales inherent in deep tropical convection; in particular the shallow-to-deep convective transition, a transition that has proved troublesome for numerical models to replicate.

We also briefly report on the North American Monsoon GPS Transect Experiment 2013, a collaborative effort between the Centro de Ciencias de la Atmosfera, UNAM and the UA Departments of Atmospheric Sciences and Geosciences.

ATMO Faculty Showcase

ATMO Faculty,

Thursday, September 5 2013, 3:30pm

PAS224, Refreshments in PAS546 from 3:00-3:30p


Members of the ATMO faculty will present a brief summary of their teaching and research activities. This will be a good opportunity to know the faculty and their areas of expertise. Each faculty member will present for 5 minutes.

What Self Driving Cars can teach us about the Future of Operational Weather Forecasting

John Brost,

Thursday, September 19 2013, 3:30pm

PAS224, Refreshments in PAS546 from 3:00-3:30p


The world of operational weather forecasting is rapidly evolving; much like the world of transportation. Major car manufacturers and technology firms are joining together to develop the car of the future. This future vehicle will be completely automated and may be hitting the streets sooner than one might think. This level of automation is inspiring to some, but frightening to others. Along the same lines, atmospheric models are more advanced and accurate than any time in history. New advancements in atmospheric modeling combined with ever increasing computing power suggest the future of the human manipulated weather forecast is in serious jeopardy. Much like self driving cars, this future is wonderfully inspiring to some, and terrifying to others. This future is also much closer than many believe. What will the role of the human weather forecaster be in the next few years? How will humans participate in the weather forecast process? What skills are necessary to be a weather forecaster in the future? What do the social sciences teach us about future weather information dissemination? JJ Brost, Science and Operations Officer with the National Weather Service in Tucson, will try to answer these questions (and more) on September 19th, at 3:30 pm in the Physics and Atmospheric Science Building, room 224.

Rainfall estimation for hydrology using volumetric weather radar

Pieter Hazenberg,

Thursday, October 3 2013, 3:30pm

PAS224, Refreshments in PAS546 from 3:00-3:30p


Radars are known for their ability to obtain a wealth of information about the spatial and temporal characteristics of rainfall fields. Unfortunately, precipitation estimates obtained by weather radar are affected by multiple sources of error, which have to be corrected for in order to provide realistic rainfall estimates. In general, weather radar measurement errors can be split into two main groups: 1) errors related to reflectivity measurements of the radar (e.g. radar calibration, blockage, clutter, signal attenuation and vertical profile of reflectivity (VPR)), and 2) errors related to the conversion of the measured reflectivity values into a rainfall intensity (variable Z-R relationship due to raindrop size variability). This presentation present some of the work which was obtained a part of my PhD program at Wageningen University, The Netherlands, and focuses specifically on weather radar rainfall measurements in cold-season precipitation. In North-Western Europe this type of precipitation is most dominant in winter and leads to the largest hydrological response of catchments. For this type of precipitation the quality of uncorrected radar rainfall estimates decreases at close range from the radar due to vertical variations in the precipitation field. Over the last decades a number of methods have been developed to improve the quality of the radar precipitation measurements. However, traditional Eulerian based correction approaches, have a limited impact to improve the corrected weather radar precipitation measurements. As such, the quality of weather radar measurements still is heavily dependent on applying some kind of final bias correction method using in situ rain gauge observations. In order overcome this and become less dependent on rain gauge observations, we propose to start using a Lagrangian procedure to correct weather radar reflectivity measurements for its dominant sources of error, since precipitation fields are continuously changing in space and time. By implementing a flexible cluster algorithm (RoCaSCA) it is possible to detect and temporally track precipitation regions, discriminate between between precipitation type (convective, stratiform and undefined), estimate a piecewise-linear VPR using a newly developed approach, and obtain rainfall rates using a precipitation type dependent Z-R relationship. For the winter half-year of study, results show that the newly proposed procedure leads to a large improvement in the quality of weather radar rainfall estimates up to distances of 150 km giving rise to similar quality in precipitation estimates as obtained from in situ rain gauge measurements, without performing any final bias correction using rain gauge observations. It is recognized that after correcting for errors considerable differences between the measurements of both devices remain, though. In order to account for these differences, a novel method was developed to estimate the uncertainty originating from spatial and temporal variability of the VPR. For the region of study, this type of uncertainty is expected to be dominant. Results confirm this hypothesis and show that once either type of uncertainty is taken into account, a large part of the difference between weather radar and rain gauge measurements can be accounted for. As a last aspect of this presentation, the impact of the error-corrected weather radar rainfall measurements on hydrological response simulations will be assessed. Using the corrected weather radar data in a lumped hydrological model, discharge simulations have a similar quality as those based on in situ rain gauge data. However, in the current study using weather radar leads to serious improvements in the flood peak

Ultrafine particle concentrations and new particle formation in an urban environment

Anna Wonaschuetz,

Thursday, October 10 2013, 3:30pm

PAS224, Refreshments in PAS546 from 3:00-3:30p


While current air quality regulations on particulate matter are mass-based, number concentrations of ultrafine particles have been considered critical for human health. This study explores the sources of ultrafine particles in an urban environment, in particular their secondary formation in nucleation events, which show a high dependence on season and meteorological conditions.

Challenges Associated with Sustainable Urban Development

Matei Georgescu,

Thursday, October 17 2013, 3:30pm

PAS224, Refreshments in PAS546 from 3:00-3:30p


Undeniably sustainable development paths require incorporating solutions focused on both greenhouse gas emissions and the direct effects associated with landscape change (e.g., the conversion of natural or agricultural lands to the built environment). Modification of natural landscapes to cities is a global phenomenon that is responsible for what is commonly known as the urban heat island (UHI) effect. We will discuss physical mechanisms driving the UHI effect today and also frame the discussion in a forward-looking context to examine potential hydroclimatic impacts associated with future urbanization both within our state of Arizona and nationally, across the United States. Lastly, implications of large-scale urbanization for energy and health, both locally and domestically, will be considered.

Coupling of Diurnal Climate to Clouds, Land-use and Snow

Alan Betts,

Thursday, October 31 2013, 3:30pm

PAS224, Refreshments in PAS546 from 3:00-3:30p


We use hourly observations from 1953-2011 of temperature, RH, opaque cloud cover and snow depth from 14 climate stations across the Canadian Prairies, together with ecodistrict crop data, to analyze the coupling of the diurnal climate to clouds, land-use and snow. 1) The cloud forcing of the diurnal climate has distinct warm and cold season behavior. From April to October, when incoming shortwave radiation dominates over longwave cooling, maximum temperature and the diurnal ranges of temperature and relative humidity increase with decreasing opaque cloud cover, while minimum temperature is almost independent of cloud. During the winter period, both maximum and minimum temperature fall with decreasing cloud, as longwave cooling dominates over the net shortwave flux. The diurnal range of temperature, relative humidity and all the net radiative fluxes have a quasi-linear dependence on the effective cloud albedo. 2) The agricultural land-use conversion from summerfallow to annual cropping on 5 MHa (15-20% of the land area in Saskatchewan) in recent decades has cooled and moistened the summer climate due to increased transpiration. 3) The fall-winter and winter-spring transitions in November and March between warm and cold seasons occur within days of snowfall and snowmelt. With lying snow, 2-m temperature drops 10oC, and the daily range of humidity falls 20%. So 10% fewer days with snow cover gives a winter climate warming of 1oC. References Betts, A.K., R. Desjardins and D. Worth (2013a), Cloud Radiative Forcing of the Diurnal Cycle Climate of the Canadian Prairies. J. Geophys. Res. 118, 1Ė19, doi:10.1002/jgrd.50593. ycle-climate-of-the-canadian-prairies/#abstract Betts, A.K., R. Desjardins, D. Worth and D. Cerkowniak (2013b), Impact of Land-use Change on the Diurnal Cycle Climate of the Canadian Prairies. Submitted to J. Geophys. Res. 2013JD020717 -cycle-climate-of-the-canadian-prairies-preprint/#abstract Betts, A.K., R. Desjardins, and D. Worth (2013), Coupling of winter climate transitions to snow and clouds over the Prairies (in preparation).

Interactions between Dry Air and Hurricane Nadine

Deanna Hence,

Thursday, November 7 2013, 3:30pm

PAS224, Refreshments in PAS546 from 3:00-3:30p


High-altitude airborne observations from the Hurricane and Severe Storm Sentinel Experiment (HS3), in conjunction with satellite observations, document the ability of sources of dry air such as the Saharan Air Layer (SAL) and upper-level subsidence to enter and impact the development of Hurricane Nadine (2012). Preliminary results indicate that during the first four days of being a tropical cyclone, Hurricane Nadine interacted with a distinctly SAL air mass, with this dry dusty air wrapping around the stormís eastern and northern sides. This study combines data from dropsondes and the Scanning High-resolution Interferometer Sounder (S-HIS) aboard the NASA Global Hawk with satellite observations from MODIS and AIRS instruments aboard the Aqua and Terra platforms to characterize this and other air masses surrounding Hurricane Nadine, and how these air masses are modified as they enter the inner core of the storm. This study thus aims to determine if, when, and how much these air masses penetrate the storm, and evaluate the stormís corresponding changes in intensity and structure.

The Establishment of the U.S. Global Change Research Program

Michael Hall,

Thursday, November 14 2013, 3:30pm

PAS224, Refreshments in PAS546 from 3:00-3:30p


The USGCRP was established in 1989/1990 as a result of several distinct threads being woven into an action agenda for a new program of climate related research. From its inception it was intended to introduce strong interdisciplinary qualities into what had previously been largely reductionist approaches to the problem.This presentation will explore the interplay of previous global scale research programs, several governmental and private institutions, the scientific community at large, and the roles played by a small group of motivated individuals. During the last days of the Global Atmospheric Research Program (GARP) most meteorologists thought that climate system behavior may well be an intractable research problem. How, exactly did we get from there to where we are today? Implications for further research will be discussed.

no seminar


Thursday, November 21 2013, 3:30pm


Experiences of 40+ years with NASA by an ''ATMO'' graduate

Robert Curran,

Thursday, December 5 2013, 3:30pm

PAS220, Refreshments in PAS546 from 3:00-3:30p


The use of satellites to quantitatively observe the Earth's atmosphere for research and operations has made steady, and in some cases spectacular progress over the last four decades. Several professors and their graduates from the University of Arizona (Physics, Atmospheric Sciences, and Electrical Engineering) have contributed to this evolution. The Atmospheric Sciences Department's (previously Meteorology) internationally recognized leadership position in atmospheric radiation transfer provided NASA with expertise needed to develop techniques and instruments for satellite remote sensing. The speaker will describe personal experiences involved in NASA's evolutionary journey from Nimbus to the Earth Observing System and how graduate study contributed to these experiences. The contributions of several other U of A graduates will also be mentioned. At the end of the talk, time will made available for questions and discussion.