Horizontal Circulation Research Articles

Seasonal Prediction of Boreal Winter Rainfall over the Western Maritime Continent during ENSO

Since the beginning of the Association of Southeast Asian Nations Climate Outlook Forum (ASEANCOF) in 2013, the most difficult challenge has been the rainfall forecast in boreal winter. This is the Maritime Continent monsoon season during which rainfall reaches maximum in the annual cycle. This forecast difficulty arises in spite of the general notion that seasonal predictability of the Maritime Continent rainfall may be higher than most places because of the strong and robust influences of ENSO. The lower predictability is consistent with the lower correlation between ENSO and western Maritime Continent rainfall that reaches minimum during the boreal winter monsoon. Various theories have been proposed to explain this low correlation. In this paper, we review the research on ENSO–Maritime Continent rainfall relationship and show that the main cause of the forecast difficulty is the wind–terrain interaction involving the Sumatran and Malay Peninsula mountains, rather than the effect of sea surface temperature (SST). The wind–terrain interaction due to the low-level regional scale anomalous horizontal circulation offsets the anomalous Walker circulation during both El Nino and La Nina. The net result of these two opposing responses to ENSO is a lower local predictability. We propose to call this low-predictability region the WIMP (Western Indonesia–Malay Peninsula) region both for its geographical location and its special characteristic of causing difficulties for forecasters to make a confident forecast for the boreal winter. Our result suggests that climate models lack skills in forecasting rainfall in this region because their predictability depends strongly on SST.

Ultra-clean and smoky marine boundary layers frequently occur in the same season over the southeast Atlantic

Abstract. We study 41 d with daily median surface accumulation mode aerosol particle concentrations below 50 cm−3 (ultra-clean conditions) observed at Ascension Island (ASI; 7.9∘ S, 14.4∘ W) between June 2016 and October 2017 as part of the Layered Atlantic Smoke Interactions with Clouds (LASIC) campaign. Interestingly, these days occur during a period of great relevance for aerosol–cloud–radiation interactions, the southeast Atlantic (SEATL) biomass-burning season (approximately June–October). That means that these critical months can feature both the highest surface aerosol numbers, from smoke intrusion into the marine boundary layer, as well as the lowest. While carbon monoxide and refractory black carbon concentrations on ultra-clean days do not approach those on days with heavy smoke, they also frequently exceed background concentrations calculated in the non-burning season from December 2016 to April 2017. This is evidence that even what become ultra-clean boundary layers can make contact with and entrain from an overlying SEATL smoke layer before undergoing a process of rapid aerosol removal. Because many ultra-clean and polluted boundary layers observed at Ascension Island during the biomass burning season follow similar isobaric back trajectories, the variability in this entrainment is likely more closely tied to the variability in the overlying smoke rather than large-scale horizontal circulation through the boundary layer. Since exceptionally low accumulation mode aerosol numbers at ASI do not necessarily indicate the relative lack of other trace pollutants, this suggests the importance of regional variations in what constitutes an “ultra-clean” marine boundary layer. Finally, surface drizzle rates, frequencies and accumulation – as well as retrievals of liquid water path – all consistently tend toward higher values on ultra-clean days. This implicates enhanced coalescence scavenging in low clouds as the key driver of ultra-clean events in the southeast Atlantic marine boundary layer. These enhancements occur against and are likely mediated by the backdrop of a seasonal increase in daily mean cloud fraction and daily median liquid water path over ASI, peaking in September and October in both LASIC years. Therefore the seasonality in ultra-clean day occurrence seems directly linked to the seasonality in SEATL cloud properties. These results highlight the importance of two-way aerosol–cloud interactions in the region.

The Life Cycle of Annual Waves in the Indian Ocean as Identified by Seamless Diagnosis of the Energy Flux

AbstractIn previous studies, the role of large‐scale waves in tropical‐extratropical interactions has been little investigated in terms of wave energy transfer owing to the lack of appropriate diagnostic techniques. Using a new seamless scheme, the present study identifies a series of well‐defined horizontal circulation routes of wave energy in the Indian Ocean on an annual basis. One of these features represents a localized cyclonic circulation close to the western boundary in each hemisphere while the other manifests as a basin‐scale cyclonic circulation in the eastern Indian Ocean. For the second baroclinic mode, eastward energy fluxes associated with equatorial Kelvin waves appear when zonal velocity anomaly exhibits eastward and westward peaks (four times per year) in response to the monsoon‐wind cycle. Identification of these key pathways of wave energy circulation enables us to better understand how waves in the tropical and subtropical regions interconnect at the zonal boundaries of the Indian Ocean.

About the Steady Horizontal Circulation of Airship

In this paper, the questions of the existence and calculation of the steady circulating motion of the airship in the horizontal plane are considered.

The Intrinsic Temperature and Radiative–Convective Boundary Depth in the Atmospheres of Hot Jupiters

Abstract In giant planet atmosphere modeling, the intrinsic temperature T int and radiative–convective boundary (RCB) are important lower boundary conditions. Often in one-dimensional radiative–convective models and in three-dimensional general circulation models it is assumed that T int is similar to that of Jupiter itself, around 100 K, which yields an RCB around 1 kbar for hot Jupiters. In this work, we show that the inflated radii, and hence high specific entropy interiors (8–11 k b /baryon), of hot Jupiters suggest much higher T int. Assuming the effect is primarily due to current heating (rather than delayed cooling), we derive an equilibrium relation between T eq and T int, showing that the latter can take values as high as 700 K. In response, the RCB moves upward in the atmosphere. Using one-dimensional radiative–convective atmosphere models, we find RCBs of only a few bars, rather than the kilobar typically supposed. This much shallower RCB has important implications for the atmospheric structure, vertical and horizontal circulation, interpretation of atmospheric spectra, and the effect of deep cold traps on cloud formation.

Observed Upper Ocean Seasonal and Intraseasonal Variability in the Andaman Sea

AbstractThe observed seasonal and intraseasonal evolution of near‐surface meteorological and oceanographic variables in the Andaman Sea for the period March 2014 to December 2017 are examined using moored buoy observations at 10.5°N, 94°E. The amplitude of temperature inversions is very weak (0.2 to 0.4 °C), and they appeared primarily during winter (November–January) and latter part of summer (May–August). The net surface heat flux plays a primary role, and vertical processes term contributes secondarily to determine the seasonal mixed layer (ML) heat storage variability. Consistent with the seasonal variations of formation and strength of temperature inversion, vertical processes term shows a positive tendency during winter. The sea surface salinity shows large amplitude intraseasonal variability during fall and winter, and it is attributed to the variability of horizontal circulation in the presence of large lateral sea surface salinity gradients at the mooring location. The sea surface temperature shows the presence of strong intraseasonal variability between 20 and 80 days, though its amplitude of oscillation is distinctly higher during May–October than November–April. Band‐pass filtered (20–80 days) time series of different components of the ML heat budget shows that the net surface heat flux primarily determines the intraseasonal ML heat storage variability. Our analysis further shows that during May–October, both net shortwave radiation and latent heat flux together determine the modulation of the intraseasonal net surface heat flux. In contrast, latent heat flux acts as the sole factor to determine the modulation of the intraseasonal net surface heat flux during November–April.

Reframing the carbon cycle of the subpolar Southern Ocean.

Global climate is critically sensitive to physical and biogeochemical dynamics in the subpolar Southern Ocean, since it is here that deep, carbon-rich layers of the world ocean outcrop and exchange carbon with the atmosphere. Here, we present evidence that the conventional framework for the subpolar Southern Ocean carbon cycle, which attributes a dominant role to the vertical overturning circulation and shelf-sea processes, fundamentally misrepresents the drivers of regional carbon uptake. Observations in the Weddell Gyre-a key representative region of the subpolar Southern Ocean-show that the rate of carbon uptake is set by an interplay between the Gyre's horizontal circulation and the remineralization at mid-depths of organic carbon sourced from biological production in the central gyre. These results demonstrate that reframing the carbon cycle of the subpolar Southern Ocean is an essential step to better define its role in past and future climate change.

Evaluating the Bias of South China Sea Summer Monsoon Precipitation Associated with Fast Physical Processes Using a Climate Model Hindcast Approach

AbstractThe present study aims to identify the precipitation bias associated with the interactions among fast physical processes in the Community Atmospheric Model, version 5 (CAM5), during the abrupt onset of the South China Sea (SCS) summer monsoon, a key precursor of the overall East Asia summer monsoon (EASM). The multiyear hindcast approach is utilized to obtain the well-constrained synoptic-scale horizontal circulation each year during the onset period from the years 1998 to 2012. In the pre-onset period, the ocean precipitation over the SCS is insufficiently suppressed in CAM5 hindcasts and thus weaker land–ocean precipitation contrasts. This is associated with the weaker and shallower convection simulated over the surrounding land, producing weaker local circulation within the SCS basin. In the post-onset period, rainfall of the organized convection over the Philippine coastal ocean is underestimated in the hindcasts, with overestimated upper-level heating. These biases are further elaborated as the underrepresentation of the convection diurnal cycle and coastal convection systems, as well as the issue of precipitation sensitivity to environmental moisture during the SCS onset period. The biases identified in hindcasts are consistent with the general bias of the EASM in the climate simulation of CAM5. The current results highlight that the appropriate representation of land–ocean–convection interactions over coastal areas can potentially improve the simulation of seasonal transition over the monsoon regions.

Natural convection in differentially heated enclosures subjected to variable temperature boundaries

PurposeNatural convection in differentially heated enclosures has been extensively investigated due to its importance in many industrial applications and has been used as a benchmark solution for testing numerical schemes. However, most of the published works considered uniform heating and cooling of the vertical boundaries. This paper aims to examine non-uniform heating and cooling of the mentioned boundaries. The mentioned case is very common in many electronic cooling devices, thermal storage systems, energy managements in buildings, material processing, etc.Design/methodology/approachFour cases are considered, the left-hand wall’s temperature linearly decreases along the wall, while the right-hand wall’s temperature is kept at a constant, cold temperature. In the second case, the left-hand wall’s temperature linearly increases along the wall, while the right-hand wall’s temperature is kept a constant, cold temperature. The third case, the left-hand wall’s temperature linearly decreases along the wall, while the right-hand wall’s temperature linearly increases along the wall. In the fourth case, the left-hand and the right-hand walls’ temperatures decrease along the wall, symmetry condition. Hence, four scenarios of natural convection in enclosures were covered.FindingsIt has been found that the average Nusselt number of the mentioned cases is less than the average Nusselt number of the uniformly heated and cooled enclosure, which reflects the physics of the problem. The work quantifies the deficiency in the rate of the heat transfer. Interestingly one of the mentioned cases showed two counter-rotating horizontal circulations. Such a flow structure can be considered for passively, highly controlled mechanism for species mixing processes application.Originality/valuePrevious works assumed that the vertical boundary is subjected to a constant temperature or to a sinusoidal varying temperature. The subject of the work is to examine the effect of non-uniformly heating and/or cooling vertical boundaries on the rate of heat transfer and flow structure for natural convection in a square enclosure. The temperature either linearly increases or decreases along the vertical coordinate at the boundary. Four scenarios are explored.

Horizontal circulation and volume transports in the Weddell Gyre derived from Argo float data

Argo floats provide both hydrographic and trajectory data, affording the opportunity to investigate surface to mid-depth ocean dynamics. Here, Argo float data are used to determine the absolute geostrophic velocity field of the upper 50–2000 m of the Weddell Gyre, from which the overall circulation pattern is investigated. The Weddell Gyre plays a pivotal role in the modification of climate by advecting heat towards the Antarctic ice shelves and by modifying the water masses that feed into the lowest limb of the global ocean overturning circulation. Warm Deep Water, the source water mass that delivers heat to the Weddell Gyre, is conveniently located within the upper 2000 m domain covered by the floats; we investigate its volume transport as it circulates the gyre. Full depth volume transports are estimated by applying a quadratic function to extrapolate the relative dynamic height field component to the full ocean depth, using CTD profiles from ship-based surveys to determine an extrapolation error. Major new insights are provided by this study. There is an established double-gyre structure to the circulation, with a strong eastern cell and a weaker western cell. Regional variation of the baroclinic component of the flow field is revealed, indicating a northeast-to-southwest reduction in the baroclinic flow, along with a strong meridional gradient of baroclinic flow along the northern limb of the gyre, especially east of ∼25°W. The zonal mean gyre strength away from the shelf edge is 32 ± 5 Sv (1 Sv = 1 × 106 m3 s−1), of which 13 ± 3 Sv are associated with the advection of Warm Deep Water. There is a considerable amount of recirculation within the gyre interior, where water does not traverse the full zonal extent of the gyre. The recirculation is stronger in the eastern cell of the observed double-gyre structure. The interior circulation cells partly explain the large variations in previous gyre strength estimates. We provide an extensive review of previous estimates in context of the new results obtained.

The Impact of Overturning and Horizontal Circulation in Pine Island Trough on Ice Shelf Melt in the Eastern Amundsen Sea

AbstractThe ice shelves around the Amundsen Sea are rapidly melting as a result of the circulation of relatively warm ocean water into their cavities. However, little is known about the processes that determine the variability of this circulation. Here we use an ocean circulation model to diagnose the relative importance of horizontal and vertical (overturning) circulation within Pine Island Trough, leading to Pine Island and Thwaites ice shelves. We show that melt rates and southward Circumpolar Deep Water (CDW) transports covary over large parts of the continental shelf at interannual to decadal time scales. The dominant external forcing mechanism for this variability is Ekman pumping and suction on the continental shelf and at the shelf break, in agreement with previous studies. At the continental shelf break, the southward transport of CDW and heat is predominantly barotropic. Farther south within Pine Island Trough, northward and southward barotropic heat transports largely cancel, and the majority of the net southward temperature transport is facilitated by baroclinic and overturning circulations. The overturning circulation is related to water mass transformation and buoyancy gain on the shelf that is primarily facilitated by freshwater input from basal melting.

Structure and Forcing of Observed Exchanges across the Greenland–Scotland Ridge

The Atlantic meridional overturning circulation and associated poleward heat transport are balanced by northern heat loss to the atmosphere and corresponding water-mass transformation. The circulation of northward-flowing Atlantic Water at the surface and returning overflow water at depth is particularly manifested—and observed—at the Greenland–Scotland Ridge where the water masses are guided through narrow straits. There is, however, a rich variability in the exchange of water masses across the ridge on all time scales. Focusing on seasonal and interannual time scales, and particularly the gateways of the Denmark Strait and between the Faroe Islands and Shetland, we specifically assess to what extent the exchanges of water masses across the Greenland–Scotland Ridge relate to wind forcing. On seasonal time scales, the variance explained of the observed exchanges can largely be related to large-scale wind patterns, and a conceptual model shows how this wind forcing can manifest via a barotropic, cyclonic circulation. On interannual time scales, the wind stress impact is less direct as baroclinic mechanisms gain importance and observations indicate a shift in the overflows from being more barotropically to more baroclinically forced during the observation period. Overall, the observed Greenland–Scotland Ridge exchanges reflect a horizontal (cyclonic) circulation on seasonal time scales, while the interannual variability more represents an overturning circulation.

A coupled model of hydrodynamics circulation and water quality applied to the Rio Verde reservoir, Brazil

This work applied the coupled horizontal two-dimensional hydrodynamic circulation model (2DH) and the vertically integrated water quality model for non-conservative and passive scalars to the Rio Verde reservoir in the state of Paraná, Brazil, to simulate flow, temperature and water quality parameters. The water quality model uses the same spatial grid applied for the hydrodynamics model. Flow velocities and turbulence coefficients previously defined in the hydrodynamics model can be used directly in the water quality model. Modeling results were compared to field data for a period of 308 days, from February 27th 2010 and December 31th 2010. Field data included water and air temperature, wind, relative humidity, radiation, discharges and concentration values of some substances in the tributaries of the reservoir. The results indicated that hydrodynamic circulation and, consequently, horizontal transport, are strongly dependent on the wind. Inflows/outflows generated a localized circulation. The results for the temperature and dissolved oxygen concentration were compared with field measures and a satisfactory consistency was achieved. Despite the errors associated with boundary conditions, the models demonstrated their potential to adequately simulate the data set collected from the reservoir.

First Direct Estimates of Volume and Water Mass Transports Across the Reykjanes Ridge

AbstractThe Reykjanes Ridge is a major topographic feature located south of Iceland in the North Atlantic Ocean that strongly influences the subpolar gyre circulation. Based on velocity and hydrographic measurements carried out along the crest of the Reykjanes Ridge from the Icelandic continental shelf to 50°N during the RREX cruise in June–July 2015, we derived the first direct estimates of volume and water mass transports over the Reykjanes Ridge. North of 53.15°N, circulation was mainly westward; south of this latitude it was mainly eastward. The westward transport was estimated at 21.9 ± 2.5 Sv (Sv = 106 m3 s−1) and represents the subpolar gyre intensity. The westward flows followed two main pathways at 57°N near the Bight Fracture Zone and at 59–62°N. We argue that those pathways were connected to the northern branch of the North Atlantic Current and to the Sub‐Arctic Front, respectively, which were both intersected by the southern part of the section. In addition to this horizontal circulation, mixing and bathymetry shaped the water mass distribution. Water mass transformations in the Iceland Basin lead to the formation of weakly stratified Subpolar Mode Water. We explain why Subpolar Mode Water, the main water mass contributing to the westward flow, was denser at 57°N than at 59–62°N. At higher densities, both Intermediate Water and Icelandic Slope Water contributed more to the westward transport across the Reykjanes Ridge than the sum of Labrador Sea Water and Iceland‐Scotland Overflow Water.

Climatological characteristics of the synoptic changes accompanying South China Sea summer monsoon withdrawal

This manuscript analyses the climatological characteristics (especially the synoptic phenomena and changes) of the South China Sea (SCS) summer monsoon withdrawal (SCSSMW) based on monsoon retreat dates from the National Climate Center of China Meteorological Administration. The SCSSMW is mainly defined as the westerly to easterly shift in the zonal winds due to the westwards intrusion of the western North Pacific (WNP) subtropical high in the northern SCS region. At the low level (850 hPa), the weakening and retreat of the intertropical convergence zone (ITCZ) and rain belt in the SCS–WNP are pertinent, and the southwesterly winds over the north Indian Ocean and the SCS also weaken and retreat. The anomalous anticyclone centred over the northern SCS resembles a Rossby wave response to the reduced precipitation over the SCS and the Philippine Sea. Changes in the upper‐level (200 hPa) circulations include the deceleration of the tropical easterly stream (from the Indo‐China Peninsula to the Arabian Sea) and northerly cross‐equatorial flow (around the equatorial eastern Indian Ocean and Maritime Continent). At the mid‐level (500 hPa), the ascending centre moves equatorwards, shifting from the northern to the southern SCS. There appears an anomalous vertical circulation cell (descending/ascending in the northern/southern SCS), which links the anomalous horizontal circulation through the Sverdrup balance. In addition, the upper‐level divergent centre is shifted southeastwards, as is the generating centre of tropical cyclones. Moreover, an anomalous convergent centre over Taiwan Island is prominent in the upper level. The time series of several atmospheric variables (e.g., zonal wind, precipitation, convection) also exhibited abrupt changes during the SCSSMW. The reasons for not simultaneous retreat of monsoonal westerlies and rainy season in the SCS are also explored.

Pattern of vertical velocity in the Lofoten vortex (the Norwegian Sea)

Mean radial distributions of various dynamic characteristics of the permanently existing anticyclonic Lofoten vortex (LV) in the Norwegian Sea are obtained from an eddy-permitting regional hydrodynamic MIT general circulation model. It is shown that the model adequately reproduces the observed 3D thermohaline and dynamic structure of the vortex. The obtained radial distribution of the mean vertical velocity is found to form a complex structure: with the upward fluxes along the axis in and above the anticyclonically rotating LV core, compensated by the downward fluxes in the vortex skirt. These vertical motions maintain the vortex potential energy anomaly against dissipation. This secondary circulation is generated by the centrifugal force and, to a lesser extent, by the horizontal dispersion of the vortex energy, both intensified towards the sea surface. Below the vortex core, the maximum downward vertical velocity converges towards the vortex axis with depth. At these depth levels, the secondary circulation is forced by Ekman divergence in the bottom mixed layer. The theory of columnar vortices with helical structure, applied to the LV, relate the radial profiles of the vertical velocity with those of the horizontal circulation. The theoretically predicted the radial patterns of the mean vertical velocity in the LV were close to those, obtained from the primitive equation ocean model, when approximating the radial patterns of the azimuthal velocity with the Rayleigh profile.

Horizontal Circulation Patterns in a Large Shallow Lake: Taihu Lake, China

Wind induced hydrodynamic circulations play significant roles in the transport and mixing process of pollutants and nutrients in large shallow lakes, but they have been usually overlooked, while environmental, biological, and ecological aspects of eutrophication problems get the most focus. Herein we use a three-dimensional model, driven by steady/unsteady wind, river discharge, rainfall, evaporation to investigate the spatially heterogeneous, large-scale hydrodynamic circulations and their role in transporting and mixing mechanisms in Taihu Lake. Wind direction and velocity determines the overall hydrodynamic circulation structure, i.e. direction, intensity, and position. A relative stable hydrodynamic circulation pattern has been formed shortly with steady wind (~2 days). Vertical profiles of horizontal velocities are linearly correlated to the relative shallowness of water depth. Volume exchange between subbasins, influenced by wind speed and initial water level, differs due to the complex topography and irregular shape. With unsteady wind, these findings are still valid to a high degree. Vertical variations in hydrodynamic circulation are important in explaining the surface accumulation of algae scums in Meiliang Bay in summers. Vorticity of velocity field, a key indicator of hydrodynamic circulation, is determined by wind direction, bathymetry gradient, and water depth. The maximum change of velocity vorticity happens when wind direction is perpendicular to bathymetry gradient. Furthermore, Lagrangian-based tracer transport is used to estimate emergency pollution leakage impacts, and also to evaluate operational management measurements, such as, the large-scale water transfer. The conclusion is that the large-scale water transfer does not affect the hydrodynamic circulation and volume exchanges between subbasins significantly, but succeeds to transport and then mix the fresh, clean Yangtze River water to a majority area of Taihu Lake.

Dynamics of an Abyssal Circulation Driven by Bottom-Intensified Mixing on Slopes

AbstractThe large-scale circulation of the abyssal ocean is enabled by small-scale diapycnal mixing, which observations suggest is strongly enhanced toward the ocean bottom, where the breaking of internal tides and lee waves is most vigorous. As discussed recently, bottom-intensified mixing induces a pattern of near-bottom up- and downwelling that is quite different from the traditionally assumed widespread upwelling. Here the consequences of bottom-intensified mixing for the horizontal circulation of the abyssal ocean are explored by considering planetary geostrophic dynamics in an idealized “bathtub geometry.” Up- and downwelling layers develop on bottom slopes as expected, and these layers are well described by boundary layer theory. The basin-scale circulation is driven by flows in and out of these boundary layers at the base of the sloping topography, which creates primarily zonal currents in the interior and a net meridional exchange along western boundaries. The rate of the net overturning is controlled by the up- and downslope transports in boundary layers on slopes and can be predicted with boundary layer theory.

Role of the circulation on the anthropogenic CO2 inventory in the North-East Atlantic: A climatological analysis

Climatology-based storage rate of anthropogenic CO2 (Cant, referred to year 2000) in the North-East Atlantic (53 ± 9 kmol s−1, 0.020 ± 0.003 Pg-C yr−1) is described on annual mean terms. Cant advection (32 ± 14 kmol s−1) occurs mostly in the upper 1800 m and contributes to 60% of the Cant storage rate. The Azores and Portugal Currents act as ‘Cant streams’ importing 389 ± 90 kmol s−1, most of which recirculates southwards with the Canary Current (−214 ± 34 kmol s−1). The Azores Counter Current (−79 ± 36 kmol s−1) and the northward-flowing Mediterranean Water advective branch (−31 ± 12 kmol s−1) comprise secondary Cant export routes. By means of Cant transport decomposition, we find horizontal circulation to represent 11% of the Cant storage rate, while overturning circulation is the main driver (48% of the Cant storage rate). Within the domain of this study, overturning circulation is a key mechanism by which Cant in the upper layer (0–500 dbar) is drawdown (74 ± 14 kmol s−1) to intermediate levels (500–2000 dbar), and entrained (37 ± 7 kmol s−1) into the Mediterranean Outflow Water to form Mediterranean Water. This newly formed water mass partly exports Cant to the North Atlantic at a rate of −39 ± 9 kmol s−1 and partly contributes to the Cant storage in the North-East Atlantic (with up to 0.015 ± 0.006 Pg-C yr−1). Closing the Cant budget, 40% of the Cant storage in the North-East Atlantic is attributable to anthropogenic CO2 uptake from the atmosphere (21 ± 10 kmol s−1).

Optimizing Multi-Level Shopping Mall Design Using Agent Simulation Based on Visual Perception— Taking Taskin Square in Changsha as an Example

In the case of Changsha Taskin Square, according to the theory of space syntax, the multi-level shopping mall is translated into a two-dimensional model by connecting each floor with models of vertical path in DEPTHMAP. Then a visibility analysis is made with the model. According to the theory of ecological approach to visual perception, an agent model is built to simulate the pedestrian distribution in the multi-level shopping mall, by using the result of the visibility analysis. By simulating the pedestrian distribution of initial plan and optimized plan of Taskin Square, and comparing the simulation results, several principles and measures for optimizing the multi-level shopping mall design are verified: (1) the form of horizontal circulation space should be concise and symmetry as possible; (2) a core space should be set to connect each floor in the vertical direction; (3) elevators and escalators should be set in the central area with high visual accessibility; (4) the atrium and vertical path, like escalators and elevators, should be set near the entrance of the building, and an aisle should be set to connect them to the entrance directly.