{"id":29,"date":"2016-02-20T15:29:36","date_gmt":"2016-02-20T20:29:36","guid":{"rendered":"https:\/\/sites.bu.edu\/efm\/?page_id=29"},"modified":"2018-10-12T13:51:02","modified_gmt":"2018-10-12T17:51:02","slug":"atmospheric-turbulence","status":"publish","type":"page","link":"https:\/\/sites.bu.edu\/efm\/atmospheric-turbulence\/","title":{"rendered":"Atmospheric turbulence"},"content":{"rendered":"

The atmospheric boundary layer, which spans\u00a0from the Earth’s surface to about 1-2 kms above the ground, is highly\u00a0turbulent (i.e., full of random and swirling motions). Understanding turbulent transport of momentum and scalars such as water vapor and CO2\u00a0in the atmospheric boundary layer plays an important role in many disciplines such as meteorology, hydrology, agriculture and air quality control. One\u00a0particularly\u00a0interesting\u00a0feature of atmospheric turbulence is that it is not only generated by shear force but also affected by buoyancy force (sometimes also called stability) resulting from surface heating and cooling in a typical diurnal cycle. <\/span><\/p>\n

As a\u00a0result of buoyancy, many turbulent theories need to be adjusted and many assumptions applicable to neutral conditions (i.e., there is no buoyancy) break down.\u00a0For example, it is often assumed that turbulence\u00a0transports\u00a0momentum and scalars similarly, which is usually referred to as the Reynolds analogy. This has been\u00a0demonstrated\u00a0to be\u00a0incorrect under unstable conditions in our work using experimental data and phenomenological models such as Figure 1(Li and Bou-Zeid, 2011<\/a>; Li et al. 2012<\/a>). <\/span><\/p>\n

\"Fig2\"<\/a>Figure 1:\u00a0Turbulent momentum and sensible heat fluxes due to the turnover of an isotropic eddy of radius s acting on a mean velocity and temperature profile.<\/p>\n

In addition, it is also often assumed that turbulence transports all scalars similarly. This assumption has been implicitly used in numerous applications including most\u00a0numerical weather and climate models. The dissimilarity between active scalars (i.e., scalars that affect the flow dynamics such as sensible heat) and passive scalars (i.e., scalars that hardly\u00a0affect the flow dynamics such as water vapor and CO2) is another important topic studied in our group\u00a0(Li et al. 2012<\/a>; Zhao et al. 2013<\/a>;\u00a0Wang et al. 2014<\/a>;\u00a0Sun et al. 2015<\/a>). For example, we used the dissimilarity measure between water vapor and temperature to parameterize the Priestley-Taylor coefficient over water surfaces (Assouline et al. 2016<\/a>).<\/p>\n

Monin-Obukhov similarity theory, proposed more than 60 years ago, remains the basic framework for us to understand the impact of buoyancy on turbulent characteristics in the atmospheric surface layer. How we can tackle\u00a0Monin-Obukhov similarity functions from a theoretical perspective remains elusive. In a series of work inspired by recently-proposed linkages between turbulent spectra and mean velocity profile in pipe flows, we theoretically derived\u00a0mean velocity\/temperature profiles based on idealized\u00a0turbulent spectra of velocity velocity and air temperature as shown in Figure 2 (Katul et al. 2013<\/a>; Li et al. 2015a<\/a> ; Li et al. 2015b<\/a>). The model is also applied to understand the turbulent longitudinal velocity variance (Banerjee et al. 2015<\/span><\/a>) and the ‘-1’ scaling in the temperature spectrum (Li et al. 2016<\/a>).<\/p>\n

\"idealspectra\"<\/p>\n

Figure 2: The idealized spectra of vertical velocity (a), air temperature (b), eddy turnover scale for momentum flux (c) and heat flux (d).<\/p>\n

In summary,\u00a0turbulent transport is one of the most important processes in the atmospheric boundary layer and has important implications. Our\u00a0aim is to better understand turbulent transport under idealized and non-idealized conditions, which forms the basis to design better parameterizations that can be utilized in numerical models.<\/p>\n","protected":false},"excerpt":{"rendered":"

The atmospheric boundary layer, which spans\u00a0from the Earth’s surface to about 1-2 kms above the ground, is highly\u00a0turbulent (i.e., full of random and swirling motions). Understanding turbulent transport of momentum and scalars such as water vapor and CO2\u00a0in the atmospheric boundary layer plays an important role in many disciplines such as meteorology, hydrology, agriculture and […]<\/p>\n","protected":false},"author":11624,"featured_media":0,"parent":0,"menu_order":6,"comment_status":"closed","ping_status":"closed","template":"","meta":[],"_links":{"self":[{"href":"https:\/\/sites.bu.edu\/efm\/wp-json\/wp\/v2\/pages\/29"}],"collection":[{"href":"https:\/\/sites.bu.edu\/efm\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sites.bu.edu\/efm\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sites.bu.edu\/efm\/wp-json\/wp\/v2\/users\/11624"}],"replies":[{"embeddable":true,"href":"https:\/\/sites.bu.edu\/efm\/wp-json\/wp\/v2\/comments?post=29"}],"version-history":[{"count":21,"href":"https:\/\/sites.bu.edu\/efm\/wp-json\/wp\/v2\/pages\/29\/revisions"}],"predecessor-version":[{"id":496,"href":"https:\/\/sites.bu.edu\/efm\/wp-json\/wp\/v2\/pages\/29\/revisions\/496"}],"wp:attachment":[{"href":"https:\/\/sites.bu.edu\/efm\/wp-json\/wp\/v2\/media?parent=29"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}