Yubin Li

Effects of super typhoons on cyclonic ocean eddies in the western North Pacific: A satellite data‐based evaluation between 2000 and 2008

A composite time series of the merged satellite altimeters sea surface height anomaly (SSHA) data and satellite-observed sea surface temperature (SST) data were used to identify eddies in the Western North Pacific Ocean (WNPO), where there were numbers of intense typhoons. This study systematically investigated 15 super typhoons during the period of 2000-2008 in the WNPO to study their impacts on the pre-typhoon ocean features, e.g., the cyclonic ocean eddy (COE) feature (closed contours of SSHA < −6 cm) and neutral condition (SSHA between −6 and 6 cm). Two new COEs are generated by two super typhoons, and 18 pre-existing COEs are intensified by 13 super typhoons. 5 of the 13 super typhoons each influenced two pre-exisiting COEs. Although the typhoon-induced maximum cooling centers had a right bias along the tracks due to wind conditions, pre-existing COEs also play a significant role in determining the strength and location of large SST cooling. Three possible factors (maximum wind speed, typhoon translation speed and the typhoon forcing time, Tf) are employed to explain the interactions. Above all, the changes of the COE geometric and physical parameters (e.g., effective radius, area, SST, SSHA, and eddy kinetic energy) were mostly related to the typhoon forcing time, Tf. This is because Tf is a parameter that is a combination of the typhoons translation speed, intensity and size. Although the typhoons may significantly impact COEs, such samples were not commonly observed. Thus, the impact of typhoon on the strength of COEs is generally inefficient.

Impacts of the binary typhoons on upper ocean environments in November 2007

Abstract. Using multiple satellite observations, Argo floats profiles, and one-dimensional (1-D) ocean mixed layer model, this study systematically investigated the impacts of the binary typhoons Hagibis and Mitag [which coexisted respectively in the South China Sea (SCS) and western North Pacific (WNP) during November, 22 to 26, 2007] on upper ocean environments. It was observed that intense Ekman pumping and two mesoscale cold, cyclonic eddies, which, induced by long forcing time of strong wind stress curls, appeared respectively in two certain areas instead of after the binary typhoons’ trails. Both cyclonic eddies retained for ∼ 39 days, accompanied with maximum sea surface height anomaly (SSHA) reduction of ∼ 25     cm induced by Hagibis and of ∼ 44     cm induced by Mitag, respectively. The largest sea surface temperature (SST) drop of 7°C and 2°C, the maximum chlorophyll a (Chl- a ) enhancement respectively was > 20 times and ∼ 3 times in these two eddies’ regions induced by Typhoon Hagibis and Mitag, respectively. The results of the 1-D ocean mixed layer model showed that, given its 84 h forcing time, the simulated MLT cooling and mixed layer deepening induced by Hagibis were ∼ - 2.8 ° C and 45 m, respectively, ∼ - 0.5 ° C and 25 m for Mitag at its 66 h forcing time. This work provides convincing evidences that typhoons, which appear frequently in the SCS and the WNP, play a notable role in the activities of mesoscale eddies in these areas.

An Empirical Model for Estimating Soil Thermal Conductivity from Soil Water Content and Porosity

AbstractSoil thermal conductivity λ is a vital parameter for soil temperature and soil heat flux forecasting in hydrological models. In this study, an empirical model is developed to relate λ only to soil volumetric water content θ and soil porosity θs. Measured λ values for eight soils are used to establish the empirical model, and data from four other soils are used to evaluate the model. The new model is also evaluated by its performance in the Simple Biosphere Model 2 (SiB2). Results show that the root-mean-square errors (RMSEs; ranging from 0.097 to 0.266 W m−1 K−1) of the new model estimates of λ are lower than those (ranging from 0.416 to 1.006 W m−1 K−1) for an empirical model of similar complexity reported in the literature earlier. Further, with simple inputs and equations, the new model almost has the accuracy of other more complex models (RMSE of λ ranging from 0.040 to 0.354 W m−1 K−1) that require additional detailed soil information. The new model can be readily incorporated in large-scale ...

Assessment of urban surface thermal environment using MODIS with a population-weighted method: a case study

Abstract In this paper, taking the Hefei City in China as an example, a population-weighted urban surface thermal environment index (IPWUSTE) is constructed with the MODIS-based land surface temperature (LST) and the spatial population retrieved from night-time light satellite observations. The results show that the spatial distribution of IPWUSTE corresponds well with the actual distribution of the urban land covers with their surface thermal environments (STEs). Firstly, IPWUSTE can consider and reliably reflect the anthropogenic effects on the urban surface, because spatial IPWUSTE matches well with spatial population and city size. Secondly, IPWUSTE is also useful to understand and reveal the population exposure to high temperature. Thirdly, comparing with the 1-km grid MODIS-based LST, IPWUSTE has a higher resolution of 0.5-km and improves the spatial description of STEs. Over all, IPWUSTE can be effectively applied to reveal the heat exposure of a population and to alleviate heatwave impacts in urban areas in the summer.

Determination of Desert Soil Apparent Thermal Diffusivity Using a Conduction‐Convection Algorithm

Surface soil temperatures impact land-atmosphere interactions in desert environments. Soil apparent thermal diffusivity (k) is a crucial physical parameter affecting soil temperature. Previous studies using the conduction-convection algorithm reported k values of desert soils for only a few days. The main objective of this study is to determine the daily and monthly variations of desert k for a range of water contents over a ten-month period. The k values were estimated with a conduction-convection algorithm using soil temperature measured at the 0.00 m and 0.20 m depths from January 1 to October 11, 2011 at the Tazhong station in the Taklimakan Desert of China. Generally, the daily values of k ranged from 1.46 × 10-7m2  s-1 to 5.88 × 10-7m2  s-1, and the ten month average k value was 2.5(±0.8) × 10-7m2  s-1 for the 0.00 m to 0.20 m soil layer. The k values varied significantly with soil water content. The apparent convection parameter (W), which is the sum of the vertical gradient of k and apparent water flux density, was also determined. Comparison of the magnitudes of W and k gradients indicated that little water movement occurred during the dry months, some water infiltrated downward during the wet months, and some water moved upwards in response to evaporation following the wet months. These findings confirmed that the conduction-convection algorithm described the general pattern of soil water movement. The presented daily and monthly values of k can be used as soil parameters when modeling land-atmosphere interactions in the Taklimakan desert.

On the surface fluxes characteristics and roughness lengths at Zhongshan station, Antarctica

ABSTRACT Over Antarctica, surface fluxes play an important role in the local atmospheric dynamical processes. To reveal the surface fluxes characteristics and aerodynamic and thermal roughness lengths over Zhongshan station, Antarctica, this paper analyzes the data observed at the station during 3 March 2008 through 15 February 2009. It is found that easterlies dominated this site throughout the whole year, with a maximum (average) speed of 25 (5.6) m s−1 at 3.9 m height, and the annual maximum (minimum) surface temperature reached 291.05 (230.05) K, while the annual maximum (minimum) air-specific humidity was 4.1 (0.05) g/kg at 3.9 m height. The maximum (minimum) values of seasonal mean temperature, humidity, each radiation components, sensible and latent heat flux occurred in summer (winter), while for the seasonal averaged wind speed and τ the minimums (maximums) appeared in summer (autumn). After comparing with a partially linear regression method for aerodynamic roughness length and four previous equations that derive thermal roughness length from surface Reynolds number, constant values of aerodynamic roughness length as 3.6 × 10−3 m and thermal roughness length as 1.2 × 10−4 m at this site were validated by using the other three level observations and suggested for future studies.