Atmospheric Sciences (A)

A11D
 Poster Hall (Moscone South)
 Monday
 0800

Multiscale Organization of Tropical Convection: Year of Tropical Convection (YOTC) I Posters


Presiding:  M W Moncrieff, MMM, NCAR, Boulder; D E Waliser, Jet Propulsion Laboratory/Caltech, Pasadena

A11D-0066 Poster

Determining the Factors for the Simulation of the Madden-Julian Oscillation: Use of NCEP CFS RAS Model

*Seo, K   (khseo@pusan.ac.kr), Department of Atmospheric Sciences, Pusan National University, Busan, Republic of Korea
Choi, J   (jhchoi34@pusan.ac.kr), Department of Atmospheric Sciences, Pusan National University, Busan, Republic of Korea
Wang, W   (wanqiu.wang@noaa.gov), Climate Prediction Center, NCEP/NOAA, Camp Springs, MD, USA

This study investigates the capability for simulating the Madden-Julian oscillation (MJO) in a series of atmosphere-ocean coupled and uncoupled simulations using NCEP operational general circulation models. The effect of air-sea coupling on the MJO is examined by comparing long-term simulations from the coupled Climate Forecast System (CFS T62) and the atmospheric Global Forecast System (GFS T62) models. Another coupled simulation with a higher horizontal resolution model (CFS T126) is performed to investigate the impact of model horizontal resolution. Furthermore, to examine the impact on a deep convection scheme, an additional coupled T126 run (CFS T126RAS) is conducted with the relaxed Arakawa-Schubert (RAS) scheme. The most important factors for the proper simulation of the MJO are investigated from these runs. The empirical orthogonal function, lagged regression and spectral analyses indicated that the interactive air-sea coupling greatly improved the coherence between convection, circulation and other surface fields on the intraseasonal time scale. In contrast to the model simulations using the simplified Arakawa-Schubert (SAS) cumulus scheme, CFS T126RAS produced statistically significant spectral peaks in the MJO frequency band, and greatly improved the strength of the MJO convection and circulation. Most importantly, the ability of MJO convection signal to penetrate into the Maritime Continent and western Pacific was demonstrated. In this simulation, an early-stage shallow heating and moistening preconditioned the atmosphere for subsequent intense MJO convection and a top-heavy vertical heating profile was formed by stratiform heating in the upper and middle troposphere, working to increase temperature anomalies and hence eddy available potential energy that sustains the MJO. The stratiform heating arose from convective detrainment of moisture to the environment and stratiform anvil clouds. Therefore, the following factors were analyzed to be most important for the proper simulation of the MJO rather than the correct simulations of basic-state precipitation, sea surface temperature, intertropical convergence zone, vertical zonal wind shear and lower-level zonal winds: (1) an elevated vertical heating structure (by stratiform heating), (2) a moisture-stratiform instability process (a positive feedback process between moisture and convective/stratiform clouds), (3) the low-level moisture convergence to the east of MJO convection (through the appropriate moisture-convective/stratiform cloud processes-circulation interactions). In addition, a series of sensitivity tests will be performed to investigate the roles of shallow convection, evaporation from convective and grid-scale precipitation, and tropical topography in the MJO simulation.

A11D-0067 Poster

Evaluation of the Diurnal Evolution of the Size of Tropical Convective Systems in Large Domain, High Resolution Simulations using Observations of Outgoing Longwave Radiation

*Pearson, K   (k.j.pearson@rdg.ac.uk), Environmental Systems Science Centre, University of Reading, Reading, United Kingdom
Hogan, R   (r.j.hogan@reading.ac.uk), Department of Meteorology, University of Reading, Reading, United Kingdom
Allan, R   (rpa@mail.nerc-essc.ac.uk), Department of Meteorology, University of Reading, Reading, United Kingdom
Holloway, C E  (chollow@ucla.edu), Department of Meteorology, University of Reading, Reading, United Kingdom
Lister, G   (g.m.s.lister@rdg.ac.uk), Department of Meteorology, University of Reading, Reading, United Kingdom

A long-standing problem in climate models is the failure to capture either the correct diurnal cycle in convective clouds or the growth of individual cells into larger scale complexes. Cascade is a multi-institution project to study the formation and development of tropical convective systems using high-resolution numerical modeling (down to 1.5~km) run over large domains ($\sim2000\times2000\mbox{~km}$) and observations. As one element of this, we have developed a technique for visualizing and testing the diurnal cycle in the size of convective cloud systems using observations of outgoing longwave radiation. This has been applied to a 2006 test case over Africa using GERB observations and models run with differing configurations and resolutions. We are now applying this to a large domain simulation of the Maritime continent covering several weeks during April 2009 comparing with TRMM observations. The image shows a comparison of the Met Office Unified Model run at 4~km and 12~km resolution, with and without convective parametrization respectively, for the West Africa test case. The grayscale represents the anomaly in the number of systems falling into each lengthscale bin against time. The middle panel is derived from observations by the Geostationary Earth Radiation Budget (GERB) instrument. It shows a broad upward stripe reflecting growth from smaller to larger systems beginning in the late afternoon. The 12~km model shows the effect of the parametrization scheme with systems of all sizes peaking at similar times much earlier than the observations. The 4~km model bears much closer comparison to the observations with growth in the middle to large size range occurring at a similar time to the observations. The small scale behavior, however, is affected by an unrealistic "shattering" of the large systems into many fragments in the early morning rather than a gradual decay.

A11D-0068 Poster

Boreal Summer ISO hindcast experiment: preliminary results from SNU

*Heo, S   (srheo@climate.snu.ac.kr), School of Earth and Environmental Science, Seoul National University, Seoul, Republic of Korea
Kang, I   (kang@climate.snu.ac.kr), School of Earth and Environmental Science, Seoul National University, Seoul, Republic of Korea
Kim, D   (dkim@ldeo.columbia.edu), Lamont-Doherty Earth Observatory of Columbia University, New York, NY, USA
Ham, Y   (ygham@climate.snu.ac.kr), GSFC Global Modeling and Assimilation Office, Greenbelt, and Goddard Earth Sciences and Technology Center, University of Maryland, Baltimore, MD, USA

As a part of internationally coordinated research program, hindcast experiments with focus on boreal summer intraseasonal oscillation (ISO) have been done in Seoul National University (SNU). This study aims to show preliminary results from SNU’s efforts. The ISO prediction system used in the hindcast experiment consists of SNU coupled model and SNU initialization method. The SNU coupled model is an ocean-atmosphere coupled model which couples the SNU Atmospheric GCM (SNU AGCM) to the Modular Ocean Model ver.2.2 (MOM2.2) Ocean GCM developed at Geophysical Fluid Dynamics Laboratory (GFDL). In the SNU initialization method, both atmospheric and oceanic states are nudged toward reanalysis data (ERAinterim and GODAS) before prediction starting date. For the results here, 2 ensemble members are generated by using different nudging period, 8 and 9 days, respectively. The initial dates of 45-day predictions are the 1st, 11th, 21st of months during boreal summer season (May to October). Prediction skills and its dependency on the initial amplitude, the initial phase, and the number of ensemble members are investigated using the Real-time Multivariate MJO (RMM) index suggested by Wheeler and Hendon (2004). It is shown in our hindcast experiment that, after 13 forecast lead days (the forecast skill is about 0.7), the prediction skill does not depend on the strength of the initial state. Also, we found that the prediction skill has a phase dependency. The prediction skill is particularly low when the convective center related to the MJO is over the Indian Ocean (phase 2). The ensemble prediction has more improved correlation skill than each member. To better understand the phase dependency, we compared the observed and predicted behavior of the MJO that propagates from different starting phases. The phase speed of the prediction is slower than the observation. The MJO in the hindcast experiment propagates with weaker amplitudes than observed except for initial phase 3. Also investigated is the climatology and anomalies of precipitable water to understand the difference of the propagation. The difference between observed and predicted climatology shows strong dry bias over the eastern Indian Ocean, in where convective anomalies are not properly developed in hindcast data, especially those from initial phase 2. Our results suggest possible impacts of mean bias on prediction skills of the MJO.

A11D-0069 Poster

Electrically-Active Convection and Tropical Cyclogenesis in the Atlantic and East Pacific

*Leppert, K   (leppert@nsstc.uah.edu), Atmospheric Science, University of Alabama in Huntsville, Huntsville, AL, USA
Petersen, W A  (walt.petersen@nasa.gov), Earth Sciences Office, NASA-MSFC, Huntsville, AL, USA

It has been hypothesized that deep, intense convective-scale “hot” towers may aid the process of tropical cyclogenesis and intensification through dynamic and thermodynamic feedbacks on the larger meso-to-synoptic scale circulation. In this study, we make use of NCEP Reanalysis data and Tropical Rainfall Measurement Mission (TRMM) lightning imaging sensor (LIS), precipitation radar (PR), and microwave imager (TMI) data to investigate the role that widespread and/or intense lightning-producing convection (i.e., “electrically-hot towers”) present in African easterly waves (AEWs) may play in tropical cyclogenesis over the Atlantic, Caribbean, and East Pacific regions. NCEP Reanalysis 700 hPa meridional winds for the months of June to November for the years 2001-2009 were analyzed for the domain of 5°N-20°N and 130°W-20°E in order to partition individual AEWs into northerly, southerly, trough, and ridge phases. Subsequently, information from National Hurricane Center (NHC) storm reports was used to divide the waves into developing and non-developing waves and to further divide the developing waves into those waves that spawned storms that only developed to tropical storm strength and those that spawned storms that reached hurricane strength. The developing waves were also divided by the region in which they developed. To help determine the gross nature of the smaller convective scale, composites were created of all developing and non-developing waves as a function of AEW wave phase over the full analysis domain and over various smaller longitude bands by compositing TRMM PR, TMI, LIS, and IR brightness temperature data extracted from the NASA global-merged IR brightness temperature dataset. Finally, similar composites were created using various NCEP variables to assess the nature of the larger scale environment and circulation. Results suggest a clear distinction between developing and non-developing waves as developing waves near their region of development in terms of the intensity of convection (indicated by lightning flash rate), coverage of cold cloudiness (indicated by the percentage of a 2.5° by 2.5° box covered by IR brightness temperatures less than 210 K), and large-scale variables, such as midlevel moisture and upper-level upward motion. For example, waves that developed in the East Pacific longitude band (i.e., 130°W-95°W) were observed in that band to have a flash rate of 56.4 flashes day-1, a coverage by brightness temperatures less than 210 K equal to 2.2%, a 700-hPa specific humidity anomaly of 0.4 g kg-1, and a 300-hPa omega value of -0.04 Pascals s-1 in the trough phase compared to the non-developing wave trough values of 22.1 flashes day-1, a coverage by brightness temperatures less than 210 K equal to 0.9%, a 700-hPa specific humidity anomaly of -0.3 g kg-1, and a 300-hPa omega value of -0.01 Pascals s-1. Further analysis is being conducted to determine if the aforementioned behavior is observed for developing waves farther from their region of development and to determine any significant differences between waves that spawned storms that reached tropical storm strength and those that spawned storms that reached hurricane strength.

A11D-0070 Poster

Changes in the tropical hydrologic cycle in a warming environment: influence on organized deep convection

*Posselt, D J  (dposselt@umich.edu), Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI, USA
van den Heever, S C  (sue@atmos.colostate.edu), Atmospheric Science, Colorado State University, Fort Collins, CO, USA
Stephens, G L  (stephens@atmos.colostate.edu), Atmospheric Science, Colorado State University, Fort Collins, CO, USA

In this study, changes in the interaction between organized deep convection and the tropical environment at radiative-convective equilibrium, and under conditions of surface warming, are examined using three-dimensional cloud system resolving simulations on a large horizontal domain. Three separate simulations are driven with fixed sea surface temperatures of 298 K, 300 K, and 302 K, and all exhibit deep convection that organizes into coherent regions of large-scale ascent separated by areas with relatively clear air and troposphere-deep ascent. Aspects of our simulations correspond to previously observed features of the tropical climate system, including the transition to strong precipitation above a critical value of total column water vapor and an increase in convective intensity with SST amidst weakening of the large-scale overturning circulation. Results of our experiments indicate a positive feedback between deep convective intensity and surface warming, but also one that operates as a nonmonotonic function of SST, and with complex interaction between deep convection and the environmental relative humidity and static stability profile.

A11D-0071 Poster

Scale interaction of the Diurnal Cycle of Rainfall: Influence of Large-scale Circulations

*Rauniyar, S P  (spr.unimelb@gmail.com), School of Earth Sciences, The University of Melbourne, Parkville 3010, VIC, Australia
Walsh, K J  (kevin.walsh@unimelb.edu.au), School of Earth Sciences, The University of Melbourne, Parkville 3010, VIC, Australia

The influence of the large-scale circulations on the phase and amplitude of the diurnal cycle of rainfall during Australian Summer (‘December- February’; DJF) over the Maritime Continent (MC) and northern Australia was investigated using the TRMM 3B42 and 3G68 dataset. The gridded rainfalls were partitioned into MJO categories (active, suppressed and weak) and ENSO phases (La Nina, El Nino and neutral). The Real-time Multivariate MJO (RMM) Index of Wheeler and Hendon (2004) is used to stratify the rainfall into the three MJO phases. The diurnal cycles were composited and Empirical Orthogonal Analysis (EOF) was applied to extract the spatial and temporal variability. Distinct variations in the rainfall distribution pattern amongst categories of the MJO over land and ocean are seen. The result of the composite mean rainfall distribution shows that the average daily rainfall rate over islands is higher during suppressed MJO days, while for surrounding oceans and northern regions of Australia, more rainfall occurs during MJO active days. The normalized relative amplitude (NRA) of the diurnal cycle of rainfall shows that morning rainfall near coastal areas during active days of the MJO is one and a half times greater than the climatological mean rainfall, but is less than or equal to the climatological mean during other phases of the MJO. Similarly, during the suppressed phase of the MJO evening rainfall is greater over the islands than in other MJO phases. The first two modes of the EOF alone explain more than 88 (65) % of the variance for the 3B42 (3G68) rainfall and the corresponding principal component time series show a marked diurnal cycle. The results show that both the amplitude and phase of the diurnal cycle of rainfall are modulated by the categories of the MJO. In general, the peak in the diurnal cycle for active (suppressed/weak) days of the MJO lags (leads) the peak in the diurnal cycle for total rainfall by two hours. Over Darwin and its adjacent regions, the active phase of the MJO is responsible for the occurrence of maximum rainfall after midnight, which is unusual in this region. The influence of ENSO phases is currently being assessed.

A11D-0072 Poster

Moist thermodynamics of Madden Julian Oscillation in a high resolution regional model

*Hagos, S M  (samson.hagos@pnl.gov), Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, USA
Leung, L   (ruby.leung@pnl.gov), Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, USA

The moist thermodynamic processes that sustain the Madden Julian Oscillation and provide it with its characteristic timescale are investigated using moisture and eddy available potential energy budget analyses on a cloud resolving WRF simulation. The model realistically simulates the two MJO episodes observed during the winter of 2007-2008. The various moistening and drying processes involved in determining the timescale of the low-frequency variability in the model are evaluated. The roles of various types of clouds in creating instability and damping during the lifecycle of the MJO are identified. The implications of these results for improving the representation of the interactions between convective systems and their environment in low-resolution models are discussed.

A11D-0073 Poster

Vertical Structure of Diabatic Heating of Convectively-Coupled Kelvin Waves from TRMM Satellite Products

Slawski, B L  (bslawski01@gmail.com), California Institute of Technology, Pasadena, CA, USA
*Li, K   (kfl@gps.caltech.edu), California Institute of Technology, Pasadena, CA, USA
Jiang, X   (xianan.jiang@gmail.com), Jet Propulsion Laboratory, Pasadena, CA, USA
Waliser, D E  (duane.waliser@jpl.nasa.gov), Jet Propulsion Laboratory, Pasadena, CA, USA
Yung, Y L  (yly@gps.caltech.edu), California Institute of Technology, Pasadena, CA, USA

A set of Kelvin wave indices has been developed to > characterize convectively-coupled Kelvin waves in the tropics. These indices are derived from the outgoing longwave radiation data during 1998-2008, which are filtered according to the shallow-water wave theory using the two-dimensional Fourier analysis. The Kelvin wave indices are then applied to the heating-rate data estimated from TRMM measurements. We examined the vertical heating-rate structures of Kelvin waves as they progress along the equator. We perform a detailed analysis and compare the resultant vertical structures with those discussed in Kiladis et al. [Rev. Geophys., 27, RG2003, 2009].

A11D-0074 Poster

Inter-comparison of deep convection over the Tibetan Plateau-Asian Monsoon Region and subtropical North America in boreal summer using CloudSat/CALIPSO data

*Luo, Y   (yali@cams.cma.gov.cn), State Key Lab of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China
Zhang, R   (renhe@cams.cma.gov.cn), State Key Lab of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China
Qian, W   (qianweimiao@163.com), State Key Lab of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China
Luo, Z   (luo@sci.ccny.cuny.edu), Department of Earth & Atmospheric Sciences and NOAA CREST Center, City College of New York, New York, NY, USA

Deep convection at the Tibetan Plateau-Southern Asian Monsoon Region (TP-SAMR) is analyzed using CloudSat and CALIPSO data for the boreal summer season (June-August) from 2006 to 2009. Three sub-regions - the Tibetan Plateau (TP), southern slope of the Plateau (PSS), and southern Asian monsoon region (SAMR) - are defined and deep convection properties are compared among these sub-regions. To cast them in a broader context, we also bring in four additional regions that bear some similarity to the TP-SAMR: East Asia (EA), tropical northwestern Pacific (NWP), west and east North America (WNA, ENA). The principal findings are as follows: 1) Compared to the other two sub-regions of the TP-SAMR, deep convection at the TP is shallower, less frequent, and embedded in smaller-size convection systems, but the cloud tops are more densely packed. These characteristics of deep convection at the TP are closely related to the significantly lower level of neutral buoyancy (LNB) and much drier atmosphere. 2) In a broader context where all seven regions are brought together, deep convection at the two tropical regions (NWP and SAMR; mostly over ocean) is similar in many regards. Similar conclusion can be drawn among the four subtropical continental regions (TP, EA, WNA, and ENA). However, tropical oceanic and subtropical land regions present some significant contrasts: deep convection in the latter region occurs less frequently, has lower cloud tops but comparable or slightly higher tops of large radar echo, and is embedded in smaller systems. The cloud tops of the subtropical land regions are generally more densely packed. Hence, the difference between TP and SAMR is more of a general contrast between subtropical land regions and tropical oceanic regions during the boreal summer. 3) Deep convection at the PSS possesses some uniqueness of its own because of the distinctive terrain (slopes) and moist low-level monsoon flow. 4) Results from comparison between the daytime and the nighttime overpasses are largely consistent with our general understanding of the diurnal variation of tropical and subtropical deep convection.

A11D-0075 Poster

Tropical overshooting convection from CloudSat and ISCCP

*Takahashi, H   (htakahashi@gc.cuny.edu), Earth and Atmospheric Science, City College of New York, New York, NY, USA
Luo, Z   (luo@sci.ccny.cuny.edu), Earth and Atmospheric Science, City College of New York, New York, NY, USA

Twelve months (Sep 2006 - Aug 2007) of CloudSat data are analyzed, in conjunction with ISCCP convection tracking (CT) database, to characterize tropical overshooting convection and the cloud systems in which they are embedded. Overshooting convection is defined as deep convective profiles from the CloudSat radar reflectivity that extend beyond the corresponding level of neutral buoyancy (LNB). The primary findings are as follows: 1) CTH and LNB show good correlation suggesting that the vertical development of deep convection tends to scale with LNB. 2) We identify two independent proxies to describe convective strength: echo top height (ETH) of large radar reflectivity (e.g., 10 dBZ) and overshooting distance, defined as cloud-top height (CTH) minus LNB. Although measuring different aspects of deep convection, they show good correlation. 3) Most of the overshooting convection penetrates into the tropical tropopause layer (TTL) so they have the potential to significantly affect the heat and water vapor budget of the tropical upper troposphere and lower stratosphere. Finally, we analyze the cloud systems in which these overshooting convective motions are embedded. Most of them are mesoscale convective systems (MCS). Overshooting convection tends to occur in certain type of MCSs at some preferred life stage.

A11D-0076 Poster

Investigating the atmospheric energy spectra using ECMWF analysis: Regional dependence

*Mukherjee, P   (parama.mukherjee83@gmail.com), SOMAS, Stony Brook University, Stony Brook, NY, USA
Zhang, M   (mzhang@notes.cc.sunysb.edu), SOMAS, Stony Brook University, Stony Brook, NY, USA

The atmospheric turbulence energy spectrum has been a subject of active research for a long time. Beginning with Kolmogorov’s theory of three-dimensional turbulence, to Kraichnan’s two-dimensional turbulence and its extension to the quasi-geostrophic case by Charney, various theoretical models and hypothesis have tried to explain the energy spectrum slope. However, the success or failure of a theory can only be gauged by comparing its output with actual observational data. Nastrom and Gage were able to do just that by analyzing thousands of flight observation data and plotting the wave number spectra of wind and temperature in 1980’s. But, the flight data was confined only to the upper atmosphere and mostly mid-latitudes of northern hemisphere. We use the high-resolution ECMWF analysis data, as a part of Year of Tropical Convection (YOTC) to study the atmospheric energy spectra over a wide range of conditions. We compared and interpreted the differences of the atmospheric energy spectra in the tropics and mid-latitudes, in the winter (DJF) and summer (JJA), at the surface and in the upper troposphere. Our results conform to the previously observed -3 power law for mid-latitude data in the upper troposphere, but the slope of the energy spectrum from the surface wind data and for the tropics exhibited quite different shapes. The causes of these differences are discussed.

A11D-0077 Poster

Spatial-Temporal Evolution of Kelvin Waves and the Vertical Structure of Associated Heating-Rates

*Yung, Y L  (yly@gps.caltech.edu), Caltech, Pasadena, CA, USA
Slawski, B L  (bslawski@caltech.edu), Caltech, Pasadena, CA, USA
Li, K   (kfl@gps.caltech.edu), Caltech, Pasadena, CA, USA
Jiang, X   (xianan.jiang@gmail.com), Caltech, Pasadena, CA, USA
Waliser, D E  (duane.waliser@jpl.nasa.gov), JPL, Pasadena, CA, USA

A set of Kelvin wave indices has been developed to characterize the strength of the Kelvin waves in six equatorial regions. These indices are derived from the outgoing long-wave radiation (OLR) data during 1998-2008. The data are filtered according to the shallow-water wave theory using two-dimensional Fourier transform. The Kelvin wave indices are then applied to study the heating rates estimated from the Tropical Rainfall Measuring Mission (TRMM) measurements. The results on the vertical structure of the heating rates are compared with those discussed in Kiladis et al. [Rev. Geophys., 27, RG2003, 2009].

A11D-0078 Poster

Interannual Variations of Clouds Observed by A-Train Satellites

*Bhawar, R   (rohinibhawar@gmail.com), Jet Propulsion Laboratory, Pasadena, CA, USA
Jiang, J H  (jonathan.h.jiang@jpl.nasa.gov), Jet Propulsion Laboratory, Pasadena, CA, USA
Su, H   (hui.su@jpl.nasa.gov), Jet Propulsion Laboratory, Pasadena, CA, USA

The three NASA A-train satellites, CALIPSO, Aura MLS and CloudSat fly in formation and provide unprecedented 3-dimensional measurements of cloud profiles nearly simultaneously. CALIPSO is sensitive to thin cirrus and provides information on multiple cloud layers as long as they are not too thick. The newly released CALIPSO (V3.01) Ice Water Content (IWC) profile data in conjunction with Aura MLS and CloudSat is used to describe interannual variations of tropical clouds from 2006 to 2010. During this period both El Nino and La Nina were observed and the phase shift in Indian Ocean Dipole events of 2006, 2007 and 2008 is studied. We also examine clouds by large-scale parameters ω500, OLR, temperature, SST, etc. from this datasets. The impacts of clouds on radiation will also be estimated.

A11D-0079 Poster

Systematic Relation between Intraseasonal Variability and Mean State Bias in AGCM Simulations

*Kim, D   (dkim@ldeo.columbia.edu), Lamont-Doherty Earth Observatory of Columbia University, Palisade, NY, USA
Sobel, A H  (ahs129@columbia.edu), Columbia University, New York, NY, USA
Maloney, E D  (emaloney@atmos.colostate.edu), Colorado State University, Fort Collins, CO, USA
Frierson, D M  (dargan@atmos.washington.edu), University of Washington, Seattle, WA, USA
Kang, I   (kang@climate.snu.ac.kr), Seoul National University, Seoul, Republic of Korea

Previous studies have shown that the strength of intraseasonal variability (ISV) simulated by global climate model (GCM) can be controlled through modifications in convection scheme. When convection is more sensitive to environmental moisture, ISV becomes stronger. The method is often used to improve model’s fidelity to represent the Madden-Julian oscillation, a dominant mode of ISV over the tropics. Recent intercomparison study, however, demonstrated that most of GCMs involved in 4th assessment report (AR4) of Intergovernmental Panel for Climate Change (IPCC) have poor MJO (Lin et al. 2006). The current study suggests possible reason for this discrepancy between our knowledge and capability of models used in official programs. Authors found systematic relation between ISV and mean state bias in a number of GCM simulations. When GCMs are grouped into strong-ISV and weak-ISV models, it is shown that seasonal mean precipitation pattern is similar among models in same group, but significantly different from that of other group. In particular, strong-ISV models simulate excessive rainfall over the south Asian summer monsoon and the northwest Pacific monsoon regions during boreal summer season. When sea surface temperature is prescribed into atmospheric GCM (AGCM), positive moisture-convection feedback over the warm pool produces excessive rainfall there. This is in part because of lack of negative feedback mechanism (e.g. reduced shortwave radiation cools down surface temperature) in AGCM.

A11D-0080 Poster

Variability in Rainfall Drop-Size Distributions observed at the Darwin ARM site

*Jensen, M P  (mjensen@bnl.gov), Brookhaven National Laboratory, Centerport, NY, USA
Giangrande, S   (sgrande@bnl.gov), Brookhaven National Laboratory, Centerport, NY, USA
Bartholomew, M J  (bartholomew@bnl.gov), Brookhaven National Laboratory, Centerport, NY, USA

The variability of rainfall drop-size distributions as a function of large-scale atmospheric conditions and cloud/storm characteristics is investigated using observations from the Atmospheric Radiation Measurement (ARM) program's research facility at Darwin, Australia. Drop-size distribution observations are obtained from an impact disdrometer over four years (2006-2010) including the YOTC. The suite of complementary long-term observations from the ARM suite of instruments, including a millimeter cloud radar, micropulse lidar, ceilometers, microwave radiometer, radiosondes, solar and infrared radiometers, etc.provide a means to describe the cloud and storm characteristics and the local atmospheric state and partition the statistics of drop-size distribution observations. Larger-scale precipitation radar and satellite observations will also provide a context for partitioning the drop-size distribution variability at different scales.

A11D-0081 Poster [WITHDRAWN]

Two Types of El Niño Events Simulated in the SNU Coupled GCM

*Lim, M   (mjlim@climate.snu.ac.kr), School of Earth and Environmental Sciences, Seoul National University, Seoul, Republic of Korea
Kang, I   (kang@climate.snu.ac.kr), School of Earth and Environmental Sciences, Seoul National University, Seoul, Republic of Korea
KUG, J   (jskug@kordi.re.kr), Korea Ocean Research and Development Institute, Ansan, Republic of Korea
Ham, Y   (ygham@climate.snu.ac.kr), GSFC Global Modeling and Assimilation Office, Greenbelt, and Goddard Earth Sciences and Technology Center, University of Maryland, Baltimore, MD, USA

Recent studies have reported that there exist more than one type of El Niño. One is the cold tongue (CT) El Niño, which shows stronger sea surface temperature anomalies (SSTA) in the eastern Pacific, and the other is the warm pool (WP) El Niño, which features SSTA in the central Pacific. The WP El Niño is different from the CT El Niño, not only the action center but also developing and transition mechanisms. In addition, WP El Niño occurs more frequently in recent decades. Furthermore, Yeh et al. (2009) suggests that WP El Niño occurrence will increase in future climate under global warming . Given the importance of correct simulations and predictions of the two types of El Niño events, it is required to better understand mechanisms which control them in numerical models. The present study investigates the CT and WP El Niño events simulated by two different versions of the SNU coupled GCM (SNUCGCM). The SNUCGCM is an ocean-atmosphere coupled model which couples the SNU Atmospheric GCM (SNUAGCM) to the Modular Ocean Model ver. 2.2 (MOM 2.2) Ocean GCM developed at Geophysical Fluid Dynamics Laboratory (GFDL). Two versions are control version (CNTL), second version (CTOK) includes the cumulus momentum transport parameterization and minimum entrainment rate. All two versions of the SNUCGCM used in this study reasonably simulate ENSO variability, with center of positive SSTA shifted slightly to the west compared to the observation. It is worthwhile to note that models simulate the major observed features of the WP El Niño distinguished from the CT El Niño. Furthermore, all versions of model simulate the occurrence of the CT El Niño more frequently than that of the WP El Niño as the observation. The CNTL shows interannual variability of SSTA over the tropical Pacific weaker than that in the CTOK, while the intensity of the WP El Niño event in the CNTL is stronger than that of the CTOK. In addition, the WP El Niño frequently occurs in the CNTL compared to the CTOK. We suggest that above different characteristics mainly come from different basic state simulated in the models with different physics. The frequency of the WP El Niño is associated with the mean thermocline depth. The mean thermocline depth in the CNTL is shallower than that in the CTOK. Therefore, our results are consistent with Yeh et al. (2010). In addition, the mean precipitation in the CNTL is shifted westward compared to that in the CTOK.

A11D-0082 Poster

Variations in Convectively Coupled Wave Activity and their Relationship with the Background Environment

*Leroux, S   (stephanie.leroux@noaa.gov), Physical Sciences Division, ESRL/NOAA, Boulder, CO, USA
Kiladis, G N  (george.kiladis@noaa.gov), Physical Sciences Division, ESRL/NOAA, Boulder, CO, USA

Different types of convectively coupled equatorial waves are isolated through space-time filtering techniques applied to the NCAR/NCEP Outgoing Long-wave Radiation (OLR) global daily dataset. For each type of wave, a wavelet analysis is applied on the filtered OLR time-series at each grid-point in the Tropics, and the wavelet power is averaged over the range of scale corresponding to the wave type. The resulting daily quantity can be used as an index of the evolution of wave activity with time. The variations of these envelopes of wave activity, and the main time-scales involved, are studied in the context of the waves’ background environment through Empirical Orthogonal Function (EOF) and lag-regression analyses. The evolution of the waves’ envelope of activity onto an index of the Madden Julian Oscillation for the winter and summer seasons suggest that part of the Kelvin wave and Equatorial Rossby (ER) wave activity signals are modulated by MJO phases. Interestingly, the first spatial EOF mode of the Kelvin wave activity envelope does not correspond directly to an MJO signal. This suggests that other modulating factors are likely to be involved. The potential influence of the background flow and of the extra-tropical transient activity in the mid-latitude storm-tracks are also explored. It is found that Pacific Kelvin wave activity is favored during periods of westerly shear with height on the equator in that basin. Strong co-dependence of Kelvin wave activity on the extratropical storm track activity is seen, suggesting that at least some periods of Kelvin activity is excited by extratropical forcing.

A11D-0083 Poster

An improved 20-km AGCM for global warming experiments

*Ose, T   (tomoaose@mri-jma.go.jp), Meteorological Research Institute, Tsukuba, Japan
Mizuta, R   (rmizuta@mri-jma.go.jp), Meteorological Research Institute, Tsukuba, Japan
Yoshimura, H   (hyoshimu@mri-jma.go.jp), Meteorological Research Institute, Tsukuba, Japan
Murakami, H   (himuraka@mri-jma.go.jp), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan
Endo, H   (hendo@mri-jma.go.jp), Meteorological Research Institute, Tsukuba, Japan
Matsueda, M   (mimatsue@mri-jma.go.jp), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan
Kitoh, A   (kitoh@mri-jma.go.jp), Meteorological Research Institute, Tsukuba, Japan

There are increasing demands for simulations by high-resolution climate models, which can provide ore detail and localized information about the climate change by global warming. In the high-resolution climate models, not only individual phenomena are simulated in fine scale, but their climatological states and variances also have to be simulated well. We have focused on this issue and developed MRI/JMA 20-km AGCM (Mizuta et al., 2006). Here, we have introduced a new cumulus parameterization scheme for improvements of the model, and made time-slice experiments for present-day and the end of 21th century climates. The new model improves in simulating heavy monthly-mean precipitation around tropical Western Pacific, tropical precipitation variability, global distribution of tropical cyclones and their strength, seasonal march of East Asian summer monsoon, inter-annual variability of tropical precipitation, blocking in the Pacific. The improvements of climatology are confirmed numerically with Taylor Diagram. A preliminary result on the future experiment indicates that the fraction of strong tropical cyclones is increasing in the end of 21C experiment. The output of the experiments will be open as one of CMIP5 experiments.

A11D-0084 Poster

Modes of Intraseasonal Variability within the Inter-Americas Sea and the Modulation of Easterly Waves During 2008 and 2009

*Serra, Y L  (serra@atmo.arizona.edu), Atmospheric Sciences, University of Arizona, Tucson, AZ, USA

Tropical storm frequency and easterly wave activity was anti-correlated between the Northeast Pacific and Atlantic during both 2008 and 2009. This anti-correlation in storm frequency between the two basins is not uncommon over the full record of the NHC Best Track data set (-0.36 correlation at the 89% confidence level). While there is significant interannual variability in tropical storm and easterly wave activity within the Inter-Americas Sea (IAS), studies also show the importance of intraseasonal variability, such as the Madden-Julian Oscillation (MJO), in modulating synoptic-scale activity in the IAS. The results of this study further suggest that the Caribbean Low-Level Jet (CLLJ) is modulated by 10-day and 20-day modes of variability in the subtropical high over the West Atlantic. The CLLJ has been shown to significantly modulate both storm frequency and easterly wave activity in the region. This study aims to understand the relative importance of both the MJO and these additional modes of intraseaonal variability to tropical storm and easterly wave activity in the Inter-Americas Sea during the 2008 and 2009 seasons.

A11D-0085 Poster

Relating large scale dynamic patterns and cloud properties at Darwin, Australia

*Evans, S M  (sevans@atmos.washington.edu), Atmospheric Sciences, University of Washington, Seattle, WA, USA
Marchand, R   (rojmarch@u.washington.edu), JISAO, University of Washington, Seattle, WA, USA
Ackerman, T P  (ackerman@atmos.washington.edu), Atmospheric Sciences, University of Washington, Seattle, WA, USA

Improving cloud parameterizations in large scale models hinges on understanding the statistical connection between large scale dynamics and the cloud fields they produce. We use an atmospheric classification technique developed and applied by Marchand and coauthors (2009, J. Climate) to investigate the relationship between synoptic scale dynamic patterns and cloud properties. Our technique uses a neural net classifier acting on reanalysis data to identify atmospheric states and then uses independent cloud radar observations of vertical cloud occurrence to test the statistical significance of each state. Here we apply our method to four years of ECMWF reanalysis data and associated vertically pointing millimeter wavelength cloud radar observations from the Atmospheric Systems Research program site in Darwin, Australia. From this data we produce a set of atmospheric states for the region, each with its own distinct meteorology. Given simultaneous time series of our state classification and other observables, we can determine the distribution of observables associated with each dynamical state. Observables include ground-based quantities such as cloud occurrence, precipitation, liquid water path, cloud optical depth and surface fluxes, and satellite quantities such as fractional cloud cover, top-of-atmosphere fluxes and cloud effect, and retrieved cloud properties. The multi-year record allows us to investigate the seasonal variability of the dynamic patterns and the influence of the MJO. In addition, we can examine the diurnal cycle of the states, the duration of particular patterns (since we classify the atmospheric pattern every 3 hours) and the transition probability from any state to any other state. Our analysis approach is, to the best or our knowledge, unique in the way it statistically links large-scale dynamics to cloud occurrence and, subsequently, other physical observables. It provides new opportunities for analysis of the behavior of the atmosphere. Our near term goal is to apply this technique to climate model output to determine to what extent climate models can duplicate the observed linkage between dynamical states and associated hydrological and radiative properties.

A11D-0086 Poster

NASA Giovanni Tool for Visualization and Analysis Support for the YOTC Program

*Ostrenga, D   (dana.m.ostrenga@nasa.gov), Adnet Systems, Inc, Greenbelt, MD, USA
Leptoukh, G G  (gregory.leptoukh@nasa.gov), Adnet Systems, Inc, Greenbelt, MD, USA
Waliser, D E  (duane.waliser@jpl.nasa.gov), JPL NASA/ California Institute of Technology, La Canada, CA, USA
Liu, Z   (Zhong.Liu@nasa.gov), George Mason University, Fairfax, VA, USA
Savtchenko, A K  (Andrey.Savtchenko@nasa.gov), Wyle Information Systems, Greenbelt, MD, USA

Giovanni is NASA’s Interactive Online Visualization and analysis tool for exploring and working with very large, global datasets. The current Giovanni analytical and statistical tools have been expanded to support the Year of Tropical Convection (YOTC) Dataset. YOTC provides a unique and comprehensive multi-sensor satellite and model data set that is designed to facilitate the study and model improvement of “tropical convection” and its multi-scale organization. The data target period, May 01, 2008-April 30, 2010, is long enough to encompass a number of scientifically challenging cases of tropical convection with significant human impact. This includes mesoscale and synoptic variability, easterly waves and hurricanes, convectively coupled waves, the MJO and the culmination of these in terms of the monsoon, their interactions with the extra-tropics, and mean characteristics such as tropical-to-subtropical transitions. To facilitate research utilizing data from the YOTC program period a YOTC-Giovanni tool was developed to allow users to plot vertical profiles or lat-lon maps from level 3 and level 2 data and get the corresponding data. Included features for some products includes generating the same spatial resolution for inter-comparison. Some case studies will be presented to show functionalities and capabilities of the application and possible future developments.

A11D-0087 Poster

High-frequency Waves in the Asian Monsoon: Results From an Observational and Modeling Study

*DeMott, C A  (demott@atmos.colostate.edu), Atmospheric Science, Colorado State University, Fort Collins, CO, USA
Stan, C   (stan@cola.iges.org), Center for Ocean-Land-Atmosphere Studies, Calverton, MD, USA
Randall, D A  (randall@atmos.colostate.edu), Atmospheric Science, Colorado State University, Fort Collins, CO, USA
Kinter, J L  (kinter@cola.iges.org), Center for Ocean-Land-Atmosphere Studies, Calverton, MD, USA
Khairoutdinov, M   (lookupcool@yahoo.com), School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY, USA

Climate simulations using a multi-scale modeling framework (MMF), or “super-parameterization” may offer new insights into the role of convection, air-sea coupling, and equatorially-trapped waves on the simulation of the Asian monsoon system. In this study, we compare the monsoon simulation in the Community Climate System Model (CCSM, v3.0), which uses a traditional cumulus parameterization, to super-parameterized coupled and uncoupled versions of CCSM, in which the traditionally parameterized effects of cumulus convection are explicitly simulated with multiple realizations of a cloud resolving model. The atmosphere-only super-parameterized model is referred to as SP-CAM, and the fully coupled super-parameterized model is SP-CCSM. CCSM simulates a very weak monsoon. The monsoon in SP-CAM is more robust, with improved simulation of the eastward- and westward-propagating components, but the variability is too high. SP-CCSM offers the best simulation of the monsoon, including the signature NW-SE tilted rainband structure that arises from the combined eastward- and northward-propagating components of the monsoon. We focus on the role of the n=1 equatorial Rossby (ER) and mixed Rossby-gravity (MRG) waves in the northward-propagating component of monsoonal precipitation. In observations, Indian Ocean ER and MRG waves both contribute to northwestward (NW)-propagating monsoon precipitation, with an MRG/ER variance ratio of 0.4~0.8. Similar behavior is observed in SP-CCSM but not in SP-CAM or CCSM, where individual MRG waves propagate southwestward (SW). For observations and SP-CCSM, the train of NW-propagating ER and MRG waves results in a nearly continuous northward-propagating rain front at a given longitude, representing the “onset” phases of the Indian monsoon. In contrast, the combination of NW-propagating ER waves and SW-propagating MRG waves in SP-CAM and CCSM results in discrete or disjointed propagation of the monsoonal rain front. Comparison of each model’s basic state climate and high-frequency wave activity lead us to conclude that successful simulation of the Asian monsoon depends on a model’s ability to simulate a realistic basic state climate, as well as a variety of wave types, especially ER and MRG waves. Explicitly simulating convection is important for increasing variability, but convection only organizes into modes similar to those seen in nature when the resulting waves propagate through a realistic basic state atmosphere. Another conclusion drawn from this work is the benefit of examining low-frequency (intraseasonal) variability in terms of the interactions of higher-frequency waves.

A11D-0088 Poster

Observational study of the 1997/1998 El Nino-Induced Changes in Rainfall Vertical Structure in the East Pacific

*Li, R   (rui_li@asrc.cestm.albany.edu), ASRC, State Univerisity of New York, Albany, NY, USA
Min, Q   (min@asrc.cestm.albany.edu), ASRC, State Univerisity of New York, Albany, NY, USA
Fu, Y   (fyf@ustc.edu.cn), Department of Earth and Space Science, University of Science and Technology of China, Hefei, China

The 1997/1998 El Nino induced changes in rainfall vertical structure in the East Pacific are studied by using Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) and TRMM Microwave Imager (TMI) measurements during January-April of 1998, 1999, and 2000. NOAA OI daily SST and the nearest 6-hour ERA-40 reanalysis datasets are collocated with each PR FOV to provide the best estimation of associated SST and atmospheric states. We segregate PR precipitation profiles into convective, straitform, and warm rain regimes, and study the response of their vertical structures to the sea surface temperature. The precipitation top height (PTH) and precipitation top temperature (PTT) of convective rains change with SST at a rate of 0.51km/oC and -2.17 oC / oC, respectively. For stratiform rains, the associated rates are 0.59 km/ oC and -2.06 oC / oC, respectively. It implies that the storm system expanded vertically at a rate of about 6.4% per oC, which is close to the storm horizontal expansion rate of about 8.4% per oC estimated by Del Genio and Kovari (2002). Furthermore, the shape of rain fall profiles changes with SST. The difference of rainfall growth rate at the upper layer between El Nino (1998) and Non-El Nino (1999 and 2000) is relatively small. The rainfall growth rate at the melting layer (about -5 to +5 oC) under El Nino conditions is clearly faster than under Non-El Nino conditions. The mean rainfall growth rate increases with SST about 10% per oC. For the layer with temperature warmer than +5 oC, the rain growth rate under El Nino conditions is slower than under Non-El Nino conditions. The results are consistent for all rain regimes under various surface rain rates and precipitation tops. These mean that for given surface rain rate or precipitation top more rain drops are formed at higher layers under El Nino conditions than under Non-El Nino conditions. It suggests an upward shift of latent heat under El Nino conditions or to the increase of SST, which will certainly influence the large-scale circulation.



The response of Precipitation Top Height (PTH) and Precipitation Top Temperature (PTT) to the increasing Sea Surface Temperature (SST) for convective rains in the Tropical East Pacific during 1998, 1999 and 2000 JFMA.

A11D-0089 Poster

An Observational Analysis of the Relation Between MJO and ENSO

*Krishnamurthy, V   (krishna@cola.iges.org), Center for Ocean-Land-Atmosphere Studies, Institute of Global Environment and Society, Beltsville, MD, USA
Kirtman, B P  (bkirtman@rsmas.miami.edu), Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, USA

The relation between Madden Julian Oscillation (MJO) and El Niño-Southern Oscillation (ENSO) is examined in order to understand if MJO plays a role in the stochastic forcing of ENSO. Specifically, it is intended to investigate the way in which westerly wind bursts are associated with MJO and thus influence the ENSO. This study examines if certain phases of MJO are conducive for westerly wind bursts to occur. For this purpose, the MJO signal is extracted from daily convection, precipitation and horizontal winds in the Indian and Pacific oceans in a data adaptive manner. The ENSO signal is also extracted in a similar manner on daily time scale. The MJO phase composites of daily sea surface temperature, surface wind stress and latent heat flux are analyzed and their interrelationships are examined.