This research identifies dominant modes of annual variability of the marine stratocumulus (MSc) cloud in the eastern tropical Pacific and Atlantic obtained from the International Satellite Cloud Climatology Project (ISCCP) dataset from January 1984 throughout December 2004, and describes the evolution of the macroscopic and radiative properties related with these physical modes. These modes are extracted from observational data using the cyclostationary empirical orthogonal function (CSEOF) technique, which retrieves the evolution of each mode together with its amplitude time series. This, in combination with comprehensive analysis of the many key physical variables (e.g., SST, surface wind, stability, horizontal temperatures advection) associated with the mode enhances us to depict the understanding the dynamic and thermodynamic processes for the formation and dissipation of these low level clouds. Finally, the development of diagnostic and prognostic models for the low cloud amount (CA) is an additional feature of this research, and helps to improve low cloud parameterization by SST in global climate models in the long term. The main scientific objective of this study is to investigate the timing, location, strength, and moving direction of the SST and the cloud throughout the year and gain some insights for parameterization of cloud properties using the evolution of SST and the interaction relationship between SST and cloud over these eastern tropical oceans. The most pronounced features of the evolution of the SST and cloud property anomalies are equatorward expansion along the coastal regions of the eastern tropical Pacific and Atlantic, and westward propagation along the equator. A positive (negative) CA and the accompanying cold (warm) SST anomalies stretch equatorward along the coastal regions during Summer and early Fall (Winter and early Spring) seasons. With the negative correlation between SST and CA anomalies, CA leads SST about one month at latitude 15°-5°S of the coastal regions of the eastern tropical Pacific. In the view of large-scale environment at the surface, the "trough-like" discontinuity of distorted SLP anomaly due to the land-sea distribution causes the persistently strong southerly surface wind anomaly blowing outward from the contour of SLP anomaly. This southerly surface wind anomaly pumps up the coastal upwelling that drags the cold water from the lower depths of the ocean. This describes schematically the surface wind-SST process occurring over the coastal region of the eastern tropical Pacific (equatorward of 20°S). Considering the cloud effect in this region, the southerly wind off the coasts of the coastal region pumps up cold water from the ocean subsurface. The onset of cooling in the region is conducive to more clouds and less surface insolation, which further promotes southerly wind anomalies. This southerly induces locally stronger, more extensive dynamical and evaporative cooling. This cooling expands to northwest via southerly wind. This is a schematic description of the wind-SST-MSc relationship. The lag/lead pattern between variables supports this relationship. The meridional wind component (V) leads SST about one month in the region. The increasing (decreasing) shielding effect of shortwave radiation at the cloud top drives the cold (warm) SST anomaly. CA also leads SST about one month. After equatorward expansions of the SST and CA anomalies reach maximum, westward propagation of the positive (negative) CA and the cold (warm) SST anomalies starts to occur simultaneously along the equator. These propagations advance further east to the dateline in November (May) along the equator, where the SST gradient is maximum. Easterly surface wind plays an important role of westward propagation of cold SST anomaly and zonal gradient SST anomaly. Easterly surface wind starts to blow where zonal gradient of SST anomaly is negative along the western edge of the nearcoastal zone in the eastern tropical Pacific. At this point, it leads the negative zonal gradient of SST anomaly. As the easterly wind strengthens due to redistribution of SLP pattern by the zonal gradient of SST anomaly, it generates the equatorial upwelling, enhancing cold phase of SST anomaly. The cooling in the region generates more cloudiness and more reflection, which further enhances the gradient of SST anomaly and in turns, the resulting easterly wind anomaly becomes strong. This easterly causes locally stronger, more extensive dynamical and evaporative cooling as well. The schematic wind-SST-MSc relationship is described by the interesting lead/lag relationship between physical variables provides. The easterly wind in tropical equatorial Pacific leads the cold SST anomaly about one month due to equatorial upwelling from the ocean subsurface. However, there is no lag/lead relationship between SST (or stability) and CA, that is, their interaction happens simultaneously in this region. This lead/lag relationship is important in understanding any interactions between them (e.g., cloud-SST feedback, wind-SST feedback). Results of this analysis may lead to improvement of diagnostic model/parameterization for the MSc cloud properties in GCMs. Stability is defined as the difference of potential temperature between 700 hPa and the surface. It is reflected in the atmosphere and ocean field. Therefore, it can be better key physical variable to express the MSc CA variability than SST. Two major atmospheric factors to control stability over the eastern tropical Pacific and Atlantic: the vertical structure of the horizontal temperature advection at the surface and lower level, and subsidence at lower and upper levels. They play significant roles during the positive (negative) phase of CA anomaly. The horizontal temperature advection from warm air aloft (brought on by warm advection) coupled with cold air at the surface (caused by nighttime radiative cooling, cold advection, or a cold surface). Subsidence in the subtropics occurs over the MSc clouds and generates the temperature inversion at low troposphere because dry air aloft is compressed and warmed. Mixing between upper and lower level affects instability. Mixing increases warming below and cooling higher up in the atmosphere. This inversion plays to prevent mixing with drier air above the top of the marine atmospheric boundary layer (MABL) and maintain the moisture in the MABL. In this study, we also evaluate a new parameterization that generates the mean LWP, based on the Gaussian distribution of cloud depths, and assumption that internal homogeneity is due to variation of cloud depths. Based on our comparison of the parameterized results to observations, we discuss the possibility of applying the predicted distribution of mean LWP to a GCM. / A Dissertation Submitted to the Department of Meteorology in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy. / Spring Semester, 2007. / November 30, 2006. / annual cycle, SST, Stratocumulus, feedback / Includes bibliographical references. / Ming Cai, Professor Directing Dissertation; Kaisheng Song, Outside Committee Member; Paul H. Ruscher, Committee Member; Sharon E. Nicholson, Committee Member; Guosheng Liu, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_176238 |
| Contributors | Shin, Jinho, 1970- (authoraut), Cai, Ming (professor directing dissertation), Song, Kaisheng (outside committee member), Ruscher, Paul H. (committee member), Nicholson, Sharon E. (committee member), Liu, Guosheng (committee member), Department of Earth, Ocean and Atmospheric Sciences (degree granting department), Florida State University (degree granting institution) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource, computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
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