Publications

Export 12 results:
Sort by: Author Title Type [ Year  (Desc)]
2017
Baranowski, DB, Flatau MK, Flatau PJ, Schmidt JM.  2017.  Multiple and spin off initiation of atmospheric convectively coupled Kelvin waves. Climate Dynamics. 49:2991-3009.   10.1007/s00382-016-3487-7   AbstractWebsite

A novel atmospheric convectively coupled Kelvin wave trajectories database, derived from Tropical Rainfall Measuring Mission precipitation data, is used to investigate initiation of sequential Kelvin wave events. Based on the analysis of beginnings of trajectories from years 1998-2012 it is shown that sequential event initiations can be divided into two distinct categories: multiple initiations and spin off initiations, both of which involve interactions with ocean surface and upper ocean temperature variability. The results of composite analysis of the 83 multiple Kelvin wave initiations show that the local thermodynamic forcing related to the diurnal sea surface temperature variability is responsible for sequential Kelvin wave development. The composite analysis of 91 spin off Kelvin wave initiations shows that the dynamic forcing is a dominant effect and the local thermodynamic forcing is secondary. Detail case studies of both multiple and spin off initiations confirm statistical analysis. A multiple initiation occurs in the presence of the high upper ocean diurnal cycle and a spin off initiation results from both dynamic and local thermodynamic processes. The dynamic forcing is related to increased wind speed and latent heat flux likely associated with an off equatorial circulation. In addition a theoretical study of the sequential Kelvin waves is performed using a shallow water model. Finally, conceptual models of these two types of initiations are proposed.

2016
Baranowski, DB, Flatau MK, Flatau PJ, Matthews AJ.  2016.  Phase locking between atmospheric convectively coupled equatorial Kelvin waves and the diurnal cycle of precipitation over the Maritime Continent. Geophysical Research Letters. 43:8269-8276.   10.1002/2016gl069602   AbstractWebsite

Convectively coupled Kelvin waves (CCKWs) are a major component of the tropical atmospheric circulation, propagating eastward around the equatorial belt. Here we show that there are scale interactions between CCKWs and the diurnal cycle over the Maritime Continent. In particular, CCKW packets that pass a base point in the eastern Indian Ocean at 90 degrees E between 0600 and 0900UTC subsequently arrive over Sumatra in phase with the diurnal cycle of convection. As the distance between Sumatra and Borneo is equal to the distance traveled by a CCKW in 1day, these waves are then also in phase with the diurnal cycle over Borneo. Consequently, this subset of CCKWs has a precipitation signal up to a factor of 3 larger than CCKWs that arrive at other times of the day and a 40% greater chance of successfully traversing the Maritime Continent.

Baranowski, DB, Flatau MK, Flatau PJ, Matthews AJ.  2016.  Impact of atmospheric convectively coupled equatorial Kelvin waves on upper ocean variability. Journal of Geophysical Research: Atmospheres. 121:2045-2059.   10.1002/2015JD024150   Abstract

Convectively coupled Kelvin waves (CCKWs) are atmospheric weather systems that propagate eastward along the equatorial wave guide with phase speeds between 11 and 14 m s−1. They are an important constituent of the convective envelope of the Madden-Julian oscillation (MJO), for which ocean-atmosphere interactions play a vital role. Hence, ocean-atmosphere interactions within CCKWs may be important for MJO development and prediction and for tropical climate, in general. Although the atmospheric structure of CCKWs has been well studied, their impact on the underlying ocean is unknown. In this paper, the ocean-atmosphere interactions in CCKWs are investigated by a case study from November 2011 during the CINDY/DYNAMO field experiment, using in situ oceanographic measurements from an ocean glider. The analysis is then extended to a 15 year period using precipitation data from the Tropical Rainfall Measuring Mission and surface fluxes from the TropFlux analysis. A methodology is developed to calculate trajectories of CCKWs. CCKW events are strongly controlled by the MJO, with twice as many CCKWs observed during the convectively active phase of the MJO compared to the suppressed phase. Coherent ocean-atmosphere interaction is observed during the passage of a CCKW, which lasts approximately 4 days at any given longitude. Surface wind speed and latent heat flux are enhanced, leading to a transient suppression of the diurnal cycle of sea surface temperature (SST) and a sustained decrease in bulk SST of 0.1°C. Given that a typical composite mean MJO SST anomaly is of the order of 0.3°C, and more than one CCKW can occur during the active phase of a single MJO event, the oceanographic impact of CCKWs is of major importance to the MJO cycle.

2014
Matthews, AJ, Baranowski DB, Heywood KJ, Flatau PJ, Schmidtko S.  2014.  The surface diurnal warm layer in the Indian Ocean during CINDY/DYNAMO. Journal of Climate. 27:9101-9122.   10.1175/jcli-d-14-00222.1   AbstractWebsite

A surface diurnal warm layer is diagnosed from Seaglider observations and develops on half of the days in the Cooperative Indian Ocean Experiment on Intraseasonal Variability/Dynamics of the Madden-Julian Oscillation (CINDY/DYNAMO) Indian Ocean experiment. The diurnal warm layer occurs on days of high solar radiation flux (>80 W m(-2)) and low wind speed (<6 ms(-1)) and preferentially in the inactive stage of the Madden-Julian oscillation. Its diurnal harmonic has an exponential vertical structure with a depth scale of 4-5m (dependent on chlorophyll concentration), consistent with forcing by absorption of solar radiation. The effective sea surface temperature (SST) anomaly due to the diurnal warm layer often reaches 0.8 degrees C in the afternoon, with a daily mean of 0.2 degrees C, rectifying the diurnal cycle onto longer time scales. This SST anomaly drives an anomalous flux of 4Wm(-2) that cools the ocean. Alternatively, in a climate model where this process is unresolved, this represents an erroneous flux that warms the ocean. A simple model predicts a diurnal warm layer to occur on 30%-50% of days across the tropical warm pool. On the remaining days, with low solar radiation and high wind speeds, a residual diurnal cycle is observed by the Seaglider, with a diurnal harmonic of temperature that decreases linearly with depth. As wind speed increases, this already weak temperature gradient decreases further, tending toward isothermal conditions.

Baranowski, DB, Flatau PJ, Chen S, Black PG.  2014.  Upper ocean response to the passage of two sequential typhoons. Ocean Science. 10:559-570.   10.5194/os-10-559-2014   AbstractWebsite

The atmospheric wind stress forcing and the oceanic response are examined for the period between 15 September 2008 and 6 October 2008, during which two typhoons - Hagupit and Jangmi - passed through the same region of the western Pacific at Saffir-Simpson intensity categories one and three, respectively. A three-dimensional oceanic mixed layer model is compared against the remote sensing observations as well as high-repetition Argo float data. Numerical model simulations suggested that magnitude of the cooling caused by the second typhoon, Jangmi, would have been significantly larger if the ocean had not already been influenced by the first typhoon, Hagupit. It is estimated that the temperature anomaly behind Jangmi would have been about 0.4 degrees C larger in both cold wake and left side of the track. The numerical simulations suggest that the magnitude and position of Jangmi's cold wake depends on the precursor state of the ocean as well as lag between typhoons. Based on sensitivity experiments we show that temperature anomaly difference between "single typhoon" and "two typhoons" as well as magnitude of the cooling strongly depends on the distance between them. The amount of kinetic energy and coupling with inertial oscillations are important factors for determining magnitude of the temperature anomaly behind moving typhoons. This paper indicates that studies of ocean-atmosphere tropical cyclone interaction will benefit from denser, high-repetition Argo float measurements.

2012
Schmidt, JM, Flatau PJ, Harasti PR, Yates RD, Littleton R, Pritchard MS, Fischer JM, Fischer EJ, Kohri WJ, Vetter JR, Richman S, Baranowski DB, Anderson MJ, Fletcher E, Lando DW.  2012.  Radar observations of individual rain drops in the free atmosphere. Proceedings of the National Academy of Sciences of the United States of America. 109:9293-9298.   10.1073/pnas.1117776109   AbstractWebsite

Atmospheric remote sensing has played a pivotal role in the increasingly sophisticated representation of clouds in the numerical models used to assess global and regional climate change. This has been accomplished because the underlying bulk cloud properties can be derived from a statistical analysis of the returned microwave signals scattered by a diverse ensemble comprised of numerous cloud hydrometeors. A new Doppler radar, previously used to track small debris particles shed from the NASA space shuttle during launch, is shown to also have the capacity to detect individual cloud hydrometeors in the free atmosphere. Similar to the traces left behind on film by subatomic particles, larger cloud particles were observed to leave a well-defined radar signature (or streak), which could be analyzed to infer the underlying particle properties. We examine the unique radar and environmental conditions leading to the formation of the radar streaks and develop a theoretical framework which reveals the regulating role of the background radar reflectivity on their observed characteristics. This main expectation from theory is examined through an analysis of the drop properties inferred from radar and in situ aircraft measurements obtained in two contrasting regions of an observed multicellular storm system. The observations are placed in context of the parent storm circulation through the use of the radar's unique high-resolution waveforms, which allow the bulk and individual hydrometeor properties to be inferred at the same time.

2008
Markowicz, KM, Flatau PJ, Remiszewska J, Witek M, Reid EA, Reid JS, Bucholtz A, Holben B.  2008.  Observations and modeling of the surface aerosol radiative forcing during UAE(2). Journal of the Atmospheric Sciences. 65:2877-2891.   10.1175/2007jas2555.1   AbstractWebsite

Aerosol radiative forcing in the Persian Gulf region is derived from data collected during the United Arab Emirates (UAE) Unified Aerosol Experiment (UAE(2)). This campaign took place in August and September of 2004. The land -sea-breeze circulation modulates the diurnal variability of the aerosol properties and aerosol radiative forcing at the surface. Larger aerosol radiative forcing is observed during the land breeze in comparison to the sea breeze. The aerosol optical properties change as the onshore wind brings slightly cleaner air. The mean diurnal value of the surface aerosol forcing during the UAE2 campaign is about -20 W m(-2), which corresponds to large aerosol optical thickness (0.45 at 500 nm). The aerosol forcing efficiency [i. e., broadband shortwave forcing per unit optical depth at 550 nm, W m(-2) (tau(500))(-1)] is -53 W m(-2) (tau(500))(-1) and the average single scattering albedo is 0.93 at 550 nm.

2003
Markowicz, KM, Flatau PJ, Quinn PK, Carrico CM, Flatau MK, Vogelmann AM, Bates D, Liu M, Rood MJ.  2003.  Influence of relative humidity on aerosol radiative forcing: An ACE-Asia experiment perspective. Journal of Geophysical Research-Atmospheres. 108   10.1029/2002jd003066   AbstractWebsite

We present direct radiometric observations of aerosol radiative forcing during the ACE-Asia experiment (March and April of 2001). The observational analysis is based on radiometer data obtained from the NOAA ship Ronald H. Brown, and shipboard measurements of the aerosol chemical and scattering properties are used to construct a model of the aerosol optical properties for use in radiative transfer calculations. The model is validated against the radiometric observations and is used to diagnose the aerosol and environmental factors that contribute to the observed forcings. The mean value of aerosol optical thickness observed during the ACE-Asia cruise over the Sea of Japan was 0.43 (+/-0.25) at 500 nm, while the single-scattering albedo was 0.95 (+/-0.03) at ambient relative humidity. We find a large correlation (r(2) = 0.69) between single-scattering albedo and relative humidity. Aerosols caused a mean decrease in the diurnally averaged solar radiation of 26.1 W m(-2) at the surface, while increasing the atmospheric solar absorption and top of atmosphere reflected solar radiation by 13.4 W m(-2) and 12.7 W m(-2), respectively. The mean surface aerosol forcing efficiency (forcing per unit optical depth) over the Sea of Japan was -60 W m(-2) and is influenced by high values of relative humidity. We show that decreasing the relative humidity to 55% enhances the aerosol forcing efficiency by as much as 6-10 W m(-2). This dependency on relative humidity has implications for comparisons of aerosol forcing efficiencies between different geographical locations.

2002
Lelieveld, J, Berresheim H, Borrmann S, Crutzen PJ, Dentener FJ, Fischer H, Feichter J, Flatau PJ, Heland J, Holzinger R, Korrmann R, Lawrence MG, Levin Z, Markowicz KM, Mihalopoulos N, Minikin A, Ramanathan V, de Reus M, Roelofs GJ, Scheeren HA, Sciare J, Schlager H, Schultz M, Siegmund P, Steil B, Stephanou EG, Stier P, Traub M, Warneke C, Williams J, Ziereis H.  2002.  Global air pollution crossroads over the Mediterranean. Science. 298:794-799.   10.1126/science.1075457   AbstractWebsite

The Mediterranean Intensive Oxidant Study, performed in the summer of 2001, uncovered air pollution layers from the surface to an altitude of 15 kilometers. In the boundary layer, air pollution standards are exceeded throughout the region, caused by West and East European pollution from the north. Aerosol particles also reduce solar radiation penetration to the surface, which can suppress precipitation. In the middle troposphere, Asian and to a lesser extent North American pollution is transported from the west. Additional Asian pollution from the east, transported from the monsoon in the upper troposphere, crosses the Mediterranean tropopause, which pollutes the lower stratosphere at middle latitudes.

2000
Collins, WD, Bucholtz A, Flatau P, Lubin D, Valero FPJ, Weaver CP, Pilewski P.  2000.  Determination of surface heating by convective cloud systems in the central equatorial Pacific from surface and satellite measurements. Journal of Geophysical Research-Atmospheres. 105:14807-14821.   10.1029/2000jd900109   AbstractWebsite

The heating of the ocean surface by longwave radiation from convective clouds has been estimated using measurements from the Central Equatorial Pacific Experiment (CEPEX). The ratio of the surface longwave cloud forcing to the cloud radiative forcing on the total atmospheric column is parameterized by the f factor. The f factor is a measure of the partitioning of the cloud radiative effect between the surface and the troposphere. Estimates of the f factor have been obtained by combining simultaneous observations from ship, aircraft, and satellite instruments. The cloud forcing near the ocean surface is determined from radiometers on board the National Oceanic and Atmospheric Administration P-3 aircraft and the R/V John Vickers. The longwave cloud forcing at the top of the atmosphere has been estimated from data obtained from the Japanese Geostationary Meteorological Satellite GMS 4. A new method for estimating longwave fluxes from satellite narrowband radiances is described. The method is based upon calibrating the satellite radiances against narrowband and broadband infrared measurements from the high-altitude NASA ER-2 aircraft. The average value of f derived from the surface and satellite observations of convective clouds is 0.15 +/- 0.02. The area-mean top-of-atmosphere longwave forcing by convective clouds in the region 10 degrees S-10 degrees N, 160 degrees E-160 degrees W is 40 W/m(2) during CEPEX. Those results indicate that the surface longwave forcing by convective clouds was approximately 5 W/m(2) in the central equatorial Pacific and that this forcing is the smallest radiative component of the surface energy budget.

1997
Valero, FPJ, Collins WD, Pilewskie P, Bucholtz A, Flatau PJ.  1997.  Direct radiometric observations of the water vapor greenhouse effect over the equatorial Pacific ocean. Science. 275:1773-1776.   10.1126/science.275.5307.1773   AbstractWebsite

Airborne radiometric measurements were used to determine tropospheric profiles of the clear sky greenhouse effect. At sea surface temperatures (SSTs) larger than 300 kelvin, the clear sky water vapor greenhouse effect was found to increase with SST at a rate of 13 to 15 watts per square meter per kelvin. Satellite measurements of infrared radiances and SSTs indicate that almost 52 percent of the tropical oceans between 20 degrees N and 20 degrees S are affected during all seasons. Current general circulation models suggest that the increase in the clear sky water vapor greenhouse effect with SST may have climatic effects an a planetary scale.

Valero, FPJ, Bucholtz A, Bush BC, Pope SK, Collins WD, Flatau P, Strawa A, Gore WJY.  1997.  Atmospheric Radiation Measurements Enhanced Shortwave Experiment (ARESE): Experimental and data details. Journal of Geophysical Research-Atmospheres. 102:29929-29937.   10.1029/97jd02434   AbstractWebsite

Atmospheric Radiation Measurements Enhanced Shortwave Experiment (ARESE) was conducted to study the magnitude and spectral characteristics of the absorption Of solar radiation by the clear and cloudy atmosphere. Three aircraft platforms, a Grob Egrett, a NASA ER-2, and a Twin Otter, were used during ARESE in conjunction with the Atmospheric Radiation Measurements (ARM) central and extended facilities in north central Oklahoma. The aircraft were coordinated to simultaneously measure solar irradiances in the total spectral broadband (0.224-3.91 mu m), near infrared broadband (0.678-3.3 mu m), and in seven narrow band-pass (similar to 10 nm width) channels centered at 0.500, 0.862, 1.064, 1.249, 1.501, 1.651, and 1.750 mu m. Instrumental calibration issues are discussed in some detail, in particular radiometric power, angular, and spectral responses. The data discussed in this paper are available at the ARM ARESE data archive via anonymous FTP to ftp.arm.gov.