2018 Vol. 24, No. 3
2018, 24(3): 263-279.
doi: 10.16555/j.1006-8775.2018.03.001
Abstract:
This paper investigates the effect of horizontal resolution on the precipitation of the super typhoon Rammasun (1409). The experiment uses WRF (V3.4) model with resolutions of 15 km, 9 km and 3 km. The results suggest that the simulated Rammasun rain band shapes and distributions at different horizontal resolutions are nearly the same. When the resolution is increased from 15 km to 9 km and then to 3 km, heavy precipitation is observed to spread in all directions from a concentrated distribution, especially when the resolution is increased from 9 km to 3 km. The 6h and 1h heavy precipitations also show a more significant comma-shape distribution. Moreover, the water vapor distribution shows the same characteristics as the heavy precipitation with a notably enhanced ascending movement and a decreased height of the strongest ascending movement. Of the three resolutions, the precipitation distribution simulated at 3 km resolution is the closest to the observed distribution; however, there is still a noticeable difference between the simulated precipitation and the actual observation. With the absence of the convection parameterization in the model, the precipitation distributions simulated at 9 km and 3 km resolutions demonstrate the same features as when the KF convection parameterization is applied. However, the simulated precipitations at these two resolutions are smaller than those obtained with the KF scheme. Meanwhile the difference between the simulated precipitations at these two resolutions is also smaller than that in the latter case. In general, when KF scheme is applied to the model, the simulation effect of Rammasun precipitation is better than that obtained without the convection parameterization scheme.
This paper investigates the effect of horizontal resolution on the precipitation of the super typhoon Rammasun (1409). The experiment uses WRF (V3.4) model with resolutions of 15 km, 9 km and 3 km. The results suggest that the simulated Rammasun rain band shapes and distributions at different horizontal resolutions are nearly the same. When the resolution is increased from 15 km to 9 km and then to 3 km, heavy precipitation is observed to spread in all directions from a concentrated distribution, especially when the resolution is increased from 9 km to 3 km. The 6h and 1h heavy precipitations also show a more significant comma-shape distribution. Moreover, the water vapor distribution shows the same characteristics as the heavy precipitation with a notably enhanced ascending movement and a decreased height of the strongest ascending movement. Of the three resolutions, the precipitation distribution simulated at 3 km resolution is the closest to the observed distribution; however, there is still a noticeable difference between the simulated precipitation and the actual observation. With the absence of the convection parameterization in the model, the precipitation distributions simulated at 9 km and 3 km resolutions demonstrate the same features as when the KF convection parameterization is applied. However, the simulated precipitations at these two resolutions are smaller than those obtained with the KF scheme. Meanwhile the difference between the simulated precipitations at these two resolutions is also smaller than that in the latter case. In general, when KF scheme is applied to the model, the simulation effect of Rammasun precipitation is better than that obtained without the convection parameterization scheme.
2018, 24(3): 280-287.
doi: 10.16555/j.1006-8775.2018.03.002
Abstract:
The daily FY2E Sea Surface Temperature (SST) data from China National Satellite Meteorological Center (NSMC) was evaluated and compared with the Optimum Interpolation Sea Surface Temperature (OISST) data from US National Oceanic and Atmospheric Administration (NOAA) over Northwest Pacific Ocean (NPO) in this study. The results show that the distribution of FY2E SST is close to OISST in tropical region over NPO, especially in typhoon active season, but the value of FY2E SST is a little lower than that of OISST in tropical ocean, with the absolute deviation 1°C lower and the relative deviation about 6% lower. The correlation coefficient between monthly FY2E SST and monthly OISST is as high as 0.7, which passes the t-test at a significance level of 0.01. Based on the evaluation result, the merged SSTFY over NPO is calculated using a weighting function. Besides, Tropical Cyclone Heat Potential (TCHPFY) is calculated and combined with the simulated sea temperature profile. From three years operational tests in NSMC, the merged SSTFY and TCHPFY are shown to be good indexes in monitoring and predicting the intensity of tropical cyclones (TCs) over NPO.
The daily FY2E Sea Surface Temperature (SST) data from China National Satellite Meteorological Center (NSMC) was evaluated and compared with the Optimum Interpolation Sea Surface Temperature (OISST) data from US National Oceanic and Atmospheric Administration (NOAA) over Northwest Pacific Ocean (NPO) in this study. The results show that the distribution of FY2E SST is close to OISST in tropical region over NPO, especially in typhoon active season, but the value of FY2E SST is a little lower than that of OISST in tropical ocean, with the absolute deviation 1°C lower and the relative deviation about 6% lower. The correlation coefficient between monthly FY2E SST and monthly OISST is as high as 0.7, which passes the t-test at a significance level of 0.01. Based on the evaluation result, the merged SSTFY over NPO is calculated using a weighting function. Besides, Tropical Cyclone Heat Potential (TCHPFY) is calculated and combined with the simulated sea temperature profile. From three years operational tests in NSMC, the merged SSTFY and TCHPFY are shown to be good indexes in monitoring and predicting the intensity of tropical cyclones (TCs) over NPO.
2018, 24(3): 288-299.
doi: 10.16555/j.1006-8775.2018.03.003
Abstract:
The formation and development of typhoons are closely related to the disturbed low vortexes at the planetary boundary layer (PBL). The effects of five PBL parameterization schemes (PBL schemes hereinafter) on the trajectory, intensity, and distribution of physical quantities are studied using the mesoscale WRF model on Super Typhoon Sanba (2012) during its initial stage. Results show that the five PBL schemes exhibit significant different effects on the simulated intensity and path. The results simulated by QNSE and ACM2 without the Bogus method are close to the best track data in the numerical experiments. When the Bogus method is adopted, the simulated trajectories improve significantly because the initial field is close to the true data. Among the five PBL schemes, QNSE and ACM2 with the Bogus method present improved simulated path and intensity compared with the three other schemes. This finding indicates that the two schemes deal with the initial PBL process satisfactorily, especially in the formation and development of disturbed low vortexes. The differences in the treatment methods of the five PBL schemes affect the surface layer physical quantities and the middle and upper atmospheres during the middle to late periods of the typhoon. Although QNSE and ACM2 present better simulation results than other schemes, they exhibit a few differences in the internal structure of the typhoon. The results simulated by MYJ are worse, and this method may be unsuitable for studying the formation and development of typhoons.
The formation and development of typhoons are closely related to the disturbed low vortexes at the planetary boundary layer (PBL). The effects of five PBL parameterization schemes (PBL schemes hereinafter) on the trajectory, intensity, and distribution of physical quantities are studied using the mesoscale WRF model on Super Typhoon Sanba (2012) during its initial stage. Results show that the five PBL schemes exhibit significant different effects on the simulated intensity and path. The results simulated by QNSE and ACM2 without the Bogus method are close to the best track data in the numerical experiments. When the Bogus method is adopted, the simulated trajectories improve significantly because the initial field is close to the true data. Among the five PBL schemes, QNSE and ACM2 with the Bogus method present improved simulated path and intensity compared with the three other schemes. This finding indicates that the two schemes deal with the initial PBL process satisfactorily, especially in the formation and development of disturbed low vortexes. The differences in the treatment methods of the five PBL schemes affect the surface layer physical quantities and the middle and upper atmospheres during the middle to late periods of the typhoon. Although QNSE and ACM2 present better simulation results than other schemes, they exhibit a few differences in the internal structure of the typhoon. The results simulated by MYJ are worse, and this method may be unsuitable for studying the formation and development of typhoons.
2018, 24(3): 300-313.
doi: 10.16555/j.1006-8775.2018.03.004
Abstract:
Based on a successful simulation of Typhoon Haikui (2012) using WRF (Weather Research & Forecasting) model with the WSM6 microphysics scheme, a high-resolution model output is presented and analyzed in this study. To understand the cause of the average gridded rainfall stability and increases after Haikui’s landfall, this research examines the fields of the physical terms as well as the vapor and condensate distributions and budgets, including their respective changes during the landing process. The environmental vapor supply following the typhoon landfall has no significant difference from that before the landfall. Although Haikui’s secondary circulation weakens, this circulation is not conducive to typhoon rainfall stability or increases, although the amounts of the six kinds of water substances (vapor, cloud water, cloud ice, snow, rain, and graupel) increase in the outer region of the typhoon. This reallocation of water substances is essential to the maintenance of rainfall. The six kinds of water substances are classified as vapor, clouds (cloud water and ice) and precipitation (snow, rain, and graupel) to diagnose their budgets. This sorting reveals that the changes in the budgets of different kinds of water substances, caused by the reduced mixing ratios of snow and ice, the water consumption of clouds, and the transformation of graupel, induce increased concentrations of precipitation fallout, which occur closer to the ground after typhoon landfall. In addition, this pattern is an efficient way for Haikui’s rainfall to remain stable after its landfall. Thus, the allocation and budget analyses of water substances are meaningful when forecasting the typhoon rainfall stability and increases after landfall.
Based on a successful simulation of Typhoon Haikui (2012) using WRF (Weather Research & Forecasting) model with the WSM6 microphysics scheme, a high-resolution model output is presented and analyzed in this study. To understand the cause of the average gridded rainfall stability and increases after Haikui’s landfall, this research examines the fields of the physical terms as well as the vapor and condensate distributions and budgets, including their respective changes during the landing process. The environmental vapor supply following the typhoon landfall has no significant difference from that before the landfall. Although Haikui’s secondary circulation weakens, this circulation is not conducive to typhoon rainfall stability or increases, although the amounts of the six kinds of water substances (vapor, cloud water, cloud ice, snow, rain, and graupel) increase in the outer region of the typhoon. This reallocation of water substances is essential to the maintenance of rainfall. The six kinds of water substances are classified as vapor, clouds (cloud water and ice) and precipitation (snow, rain, and graupel) to diagnose their budgets. This sorting reveals that the changes in the budgets of different kinds of water substances, caused by the reduced mixing ratios of snow and ice, the water consumption of clouds, and the transformation of graupel, induce increased concentrations of precipitation fallout, which occur closer to the ground after typhoon landfall. In addition, this pattern is an efficient way for Haikui’s rainfall to remain stable after its landfall. Thus, the allocation and budget analyses of water substances are meaningful when forecasting the typhoon rainfall stability and increases after landfall.
2018, 24(3): 314-322.
doi: 10.16555/j.1006-8775.2018.03.005
Abstract:
This study investigates the influences of tropical Indian Ocean (TIO) warming on tropical cyclone (TC) genesis in different regions of the western North Pacific (WNP) from July to October (JASO) during the decaying El Niño. The results show significant negative TC frequency anomalies localized in the southeastern WNP. Correlation analysis indicates that a warm sea surface temperature anomaly (SSTA) in the TIO strongly suppresses TC genesis south of 21°N and east of 140°E in JASO. Reduced TC genesis over the southeastern WNP results from a weak monsoon trough and divergence and subsidence anomalies associated with an equatorial baroclinic Kelvin wave. Moreover, suppressed convection in response to a cold local SSTA, induced by the increased northeasterly connected by the wind-evaporation-SST positive feedback mechanism, is found unfavorable for TC genesis. Positive TC genesis anomalies are observed over higher latitudinal regions (at around 21°N, 140°E) and the western WNP because of enhanced convection along the northern flank of the WNP anomalous anticyclone and low-level convergence, respectively. Although local modulation (e.g., local SST) could have greater dominance over TC activity at higher latitudes in certain anomalous years (e.g., 1988), a warm TIO SSTA can still suppress TC genesis in lower latitudinal regions of the WNP. A better understanding of the contributions of TIO warming could help improve seasonal TC predictions over different regions of the WNP in years of decaying El Niño.
This study investigates the influences of tropical Indian Ocean (TIO) warming on tropical cyclone (TC) genesis in different regions of the western North Pacific (WNP) from July to October (JASO) during the decaying El Niño. The results show significant negative TC frequency anomalies localized in the southeastern WNP. Correlation analysis indicates that a warm sea surface temperature anomaly (SSTA) in the TIO strongly suppresses TC genesis south of 21°N and east of 140°E in JASO. Reduced TC genesis over the southeastern WNP results from a weak monsoon trough and divergence and subsidence anomalies associated with an equatorial baroclinic Kelvin wave. Moreover, suppressed convection in response to a cold local SSTA, induced by the increased northeasterly connected by the wind-evaporation-SST positive feedback mechanism, is found unfavorable for TC genesis. Positive TC genesis anomalies are observed over higher latitudinal regions (at around 21°N, 140°E) and the western WNP because of enhanced convection along the northern flank of the WNP anomalous anticyclone and low-level convergence, respectively. Although local modulation (e.g., local SST) could have greater dominance over TC activity at higher latitudes in certain anomalous years (e.g., 1988), a warm TIO SSTA can still suppress TC genesis in lower latitudinal regions of the WNP. A better understanding of the contributions of TIO warming could help improve seasonal TC predictions over different regions of the WNP in years of decaying El Niño.
2018, 24(3): 323-333.
doi: 10.16555/j.1006-8775.2018.03.006
Abstract:
The intraseasonal oscillation (ISO) of the atmosphere is closely related to weather and climate systems and is also an important aspect of extended numerical weather forecast research. This phenomenon is significant in tropical regions and is one of the key indices for assessing the simulation capability of a climate model. To better evaluate numerical model simulations of the tropical ISO using the 10-year historic data calculated by the POEM2 climate system model developed by the University of Hawaii in the U.S., we utilized the methods of variance and power spectral analysis to compare and assess the simulation ability of this model for the ISO in tropical regions. Our results showed that the simulated variance results for the 850 hPa zonal wind and outgoing long-wave radiation (OLR) by POEM2 are overall consistent with the observed distribution pattern, and the simulated variance is relatively larger than the observed in the North Indian Ocean and West Pacific regions. With respect to the summer model, the winter model can better simulate the eastward propagation motion of the Madden–CJulian oscillation (MJO) and the 850 hPa zonal wind. In comparison, the summer model can better simulate the northward propagation motion of MJO and atmospheric precipitation than the winter model. The eastward propagation speed of the simulated MJO signal is faster in the model than in the observation, and the high frequency region for the power spectra of meteorological element anomalies are concentrated in wavenumber 2-3 in the simulation and in wavenumber 1-2 in the observation. The multivariate combined empirical orthogonal function (EOF) results showed that this model can simulate the relationship between high-low level wind distributions and precipitation over the East Indian Ocean and the West Pacific, but the simulated signal is weaker than the observed. The lagging correlation of time coefficients between the first two EOFs from observation and simulation shows a similar cycle. Thus, these results indicate that in the future, the POEM2 climate system model needs to optimize the involved physical processes and parameterization scheme, strengthen the dynamic description of the mixed Rossby gravity wave, and improve the simulated ability of wavenumber 1.
The intraseasonal oscillation (ISO) of the atmosphere is closely related to weather and climate systems and is also an important aspect of extended numerical weather forecast research. This phenomenon is significant in tropical regions and is one of the key indices for assessing the simulation capability of a climate model. To better evaluate numerical model simulations of the tropical ISO using the 10-year historic data calculated by the POEM2 climate system model developed by the University of Hawaii in the U.S., we utilized the methods of variance and power spectral analysis to compare and assess the simulation ability of this model for the ISO in tropical regions. Our results showed that the simulated variance results for the 850 hPa zonal wind and outgoing long-wave radiation (OLR) by POEM2 are overall consistent with the observed distribution pattern, and the simulated variance is relatively larger than the observed in the North Indian Ocean and West Pacific regions. With respect to the summer model, the winter model can better simulate the eastward propagation motion of the Madden–CJulian oscillation (MJO) and the 850 hPa zonal wind. In comparison, the summer model can better simulate the northward propagation motion of MJO and atmospheric precipitation than the winter model. The eastward propagation speed of the simulated MJO signal is faster in the model than in the observation, and the high frequency region for the power spectra of meteorological element anomalies are concentrated in wavenumber 2-3 in the simulation and in wavenumber 1-2 in the observation. The multivariate combined empirical orthogonal function (EOF) results showed that this model can simulate the relationship between high-low level wind distributions and precipitation over the East Indian Ocean and the West Pacific, but the simulated signal is weaker than the observed. The lagging correlation of time coefficients between the first two EOFs from observation and simulation shows a similar cycle. Thus, these results indicate that in the future, the POEM2 climate system model needs to optimize the involved physical processes and parameterization scheme, strengthen the dynamic description of the mixed Rossby gravity wave, and improve the simulated ability of wavenumber 1.
2018, 24(3): 334-345.
doi: 10.16555/j.1006-8775.2018.03.007
Abstract:
To reduce the spatial correlation of representation error in observations and computational complexity, we propose a thinning scheme that can extract typical observations within a certain range. This scheme is applied to the Global/Regional Assimilation and Prediction System (GRAPES) with three-dimensional variation (3DVAR) to study the effect of the thinning radius on the assimilation results. The assimilation experiments indicate that when the ratio of the model resolution to the observational resolution is 1:3, the simulated results for precipitation are relatively good and have a relatively high equitable threat score (ETS). Moreover, the analysis errors in the temperature and the specific humidity are the smallest, the dependence of the norm gradient vector of the objective function on the number of iterations is slow, gentle, and close to 0, and the minimization results in improved conditions.
To reduce the spatial correlation of representation error in observations and computational complexity, we propose a thinning scheme that can extract typical observations within a certain range. This scheme is applied to the Global/Regional Assimilation and Prediction System (GRAPES) with three-dimensional variation (3DVAR) to study the effect of the thinning radius on the assimilation results. The assimilation experiments indicate that when the ratio of the model resolution to the observational resolution is 1:3, the simulated results for precipitation are relatively good and have a relatively high equitable threat score (ETS). Moreover, the analysis errors in the temperature and the specific humidity are the smallest, the dependence of the norm gradient vector of the objective function on the number of iterations is slow, gentle, and close to 0, and the minimization results in improved conditions.
2018, 24(3): 346-355.
doi: 10.16555/j.1006-8775.2018.03.008
Abstract:
Cloud radiative and microphysical effects on the relation between spatial mean rain rate, rain intensity and fractional rainfall coverage are investigated in this study by conducting and analyzing a series of two-dimensional cloud resolving model sensitivity experiments of pre-summer torrential rainfall in June 2008. The analysis of time-mean data shows that the exclusion of radiative effects of liquid clouds reduces domain mean rain rate by decreasing convective rain rate mainly through the reduced convective-rainfall area associated with the strengthened hydrometeor gain in the presence of radiative effects of ice clouds, whereas it increases domain mean rain rate by enhancing convective rain rate mainly via the intensified convective rain intensity associated with the enhanced net condensation in the absence of radiative effects of ice clouds. The removal of radiative effects of ice clouds decreases domain mean rain rate by reducing stratiform rain rate through the suppressed stratiform rain intensity related to the suppressed net condensation in the presence of radiative effects of liquid clouds, whereas it increases domain mean rain rate by strengthening convective rain rate mainly via the enhanced convective rain intensity in response to the enhanced net condensation in the absence of radiative effects of liquid clouds. The elimination of microphysical effects of ice clouds suppresses domain mean rain rate by reducing stratiform rain rate through the reduced stratiform-rainfall area associated with severely reduced hydrometeor loss.
Cloud radiative and microphysical effects on the relation between spatial mean rain rate, rain intensity and fractional rainfall coverage are investigated in this study by conducting and analyzing a series of two-dimensional cloud resolving model sensitivity experiments of pre-summer torrential rainfall in June 2008. The analysis of time-mean data shows that the exclusion of radiative effects of liquid clouds reduces domain mean rain rate by decreasing convective rain rate mainly through the reduced convective-rainfall area associated with the strengthened hydrometeor gain in the presence of radiative effects of ice clouds, whereas it increases domain mean rain rate by enhancing convective rain rate mainly via the intensified convective rain intensity associated with the enhanced net condensation in the absence of radiative effects of ice clouds. The removal of radiative effects of ice clouds decreases domain mean rain rate by reducing stratiform rain rate through the suppressed stratiform rain intensity related to the suppressed net condensation in the presence of radiative effects of liquid clouds, whereas it increases domain mean rain rate by strengthening convective rain rate mainly via the enhanced convective rain intensity in response to the enhanced net condensation in the absence of radiative effects of liquid clouds. The elimination of microphysical effects of ice clouds suppresses domain mean rain rate by reducing stratiform rain rate through the reduced stratiform-rainfall area associated with severely reduced hydrometeor loss.
2018, 24(3): 356-368.
doi: 10.16555/j.1006-8775.2018.03.009
Abstract:
Using the measurements from the Halogen Occultation Experiment (HALOE) and the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim reanalysis data for the period 1994–C2005, we analyzed the relationship between tropical tropopause temperature anomalies and stratospheric water vapor anomalies. It is found that tropical tropopause temperature is correlated with stratospheric water vapor, i.e., an anomalously high (low) tropical tropopause temperature corresponds to anomalously high (low) stratospheric water vapor during the period 1994–C2005, except for 1996. The occurrence frequency and strength of deep convective activity during the ‘mismatched’ months is less and weaker than that during the ‘matched’ months in 1996. However, the instantaneous intensity of four short periods of deep convective activity, caused by strong surface cyclones and high sea surface temperatures, are greater during the ‘mismatched’ months than during the ‘matched’ months. Water vapor is transported from the lower troposphere to the lower stratosphere through a strong tropical upwelling, leading to an increase in stratospheric water vapor. On the other hand, deep convective activity can lift the tropopause and cool its temperature. In short, the key factor responsible for the poor correlation between tropical tropopause temperature and stratospheric water vapor in 1996 is the instantaneous strong deep convective activity. In addition, an anomalously strong Brewer–CDobson circulation brings more water vapor into the stratosphere during the ‘mismatched’ months in 1996, and this exacerbates the poor correlation between tropical tropopause temperature and stratospheric water vapor.
Using the measurements from the Halogen Occultation Experiment (HALOE) and the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim reanalysis data for the period 1994–C2005, we analyzed the relationship between tropical tropopause temperature anomalies and stratospheric water vapor anomalies. It is found that tropical tropopause temperature is correlated with stratospheric water vapor, i.e., an anomalously high (low) tropical tropopause temperature corresponds to anomalously high (low) stratospheric water vapor during the period 1994–C2005, except for 1996. The occurrence frequency and strength of deep convective activity during the ‘mismatched’ months is less and weaker than that during the ‘matched’ months in 1996. However, the instantaneous intensity of four short periods of deep convective activity, caused by strong surface cyclones and high sea surface temperatures, are greater during the ‘mismatched’ months than during the ‘matched’ months. Water vapor is transported from the lower troposphere to the lower stratosphere through a strong tropical upwelling, leading to an increase in stratospheric water vapor. On the other hand, deep convective activity can lift the tropopause and cool its temperature. In short, the key factor responsible for the poor correlation between tropical tropopause temperature and stratospheric water vapor in 1996 is the instantaneous strong deep convective activity. In addition, an anomalously strong Brewer–CDobson circulation brings more water vapor into the stratosphere during the ‘mismatched’ months in 1996, and this exacerbates the poor correlation between tropical tropopause temperature and stratospheric water vapor.
2018, 24(3): 369-384.
doi: 10.16555/j.1006-8775.2018.03.010
Abstract:
In this paper, a sudden heavy rainfall event is analyzed, which occurred over the Yellow River midstream during 5–C6 August 2014. We used observational, NCEP/NCAR reanalysis, high-resolution satellite, and numerical simulation data. The main results are as follows. Under an unfavorable environmental circulation, inadequate water vapor and unfavorable dynamic conditions but sufficient energy, a local sudden heavy rainfall was caused by the release of strong unstable energy that was triggered by cold air transport into middle and lower layers and the propagation of gravity waves. The distributions of rain area, rain clusters, and 10-minute rainfall showed typical mesoscale and microscale fluctuation characteristics. In the mesoscale rain area or upstream, there was a quasi-stationary wave of mesoscale gravity waves with their propagation downstream. In the course of propagation from southwest to northeast, the wavelength became longer and the amplitude attenuated. In the various phases of gravity wave development, there were evident differences in the direction of the wave front. Wave energy was mainly in the lower layers. Unstable vertical wind shear at heights of 1–C6 km provided fluctuation energy for the gravity waves. The mechanisms of heavy rainfall formation were different at Linyou and Hancheng stations. Diabatic heating was the main source of disturbed effective potential energy at Linyou. The explosive short-period strong precipitation was caused by the release of strong effective potential energy triggered by the gravity waves, and its development and propagation after that energy maximized. In contrast, the latent heat release of upstream precipitation was the main source of disturbed effective potential energy at Hancheng. This formed a positive feedback mechanism that produced continuous precipitation. In the studied event, the development of westerly belt systems had disturbed the wind field. The contribution of kinetic energy generated by this disturbance could not be ignored. The Froude number, mountain shape parameter, and ratio between mountain height and temperature inversion layer thickness had various effects of atmosphere and terrain on mesoscale and microscale mountain waves. In upper and lower layers, there were five airflows that were strengthened by the terrain. All these had important influences on local heavy rainfall at Linyou and Hancheng stations.
In this paper, a sudden heavy rainfall event is analyzed, which occurred over the Yellow River midstream during 5–C6 August 2014. We used observational, NCEP/NCAR reanalysis, high-resolution satellite, and numerical simulation data. The main results are as follows. Under an unfavorable environmental circulation, inadequate water vapor and unfavorable dynamic conditions but sufficient energy, a local sudden heavy rainfall was caused by the release of strong unstable energy that was triggered by cold air transport into middle and lower layers and the propagation of gravity waves. The distributions of rain area, rain clusters, and 10-minute rainfall showed typical mesoscale and microscale fluctuation characteristics. In the mesoscale rain area or upstream, there was a quasi-stationary wave of mesoscale gravity waves with their propagation downstream. In the course of propagation from southwest to northeast, the wavelength became longer and the amplitude attenuated. In the various phases of gravity wave development, there were evident differences in the direction of the wave front. Wave energy was mainly in the lower layers. Unstable vertical wind shear at heights of 1–C6 km provided fluctuation energy for the gravity waves. The mechanisms of heavy rainfall formation were different at Linyou and Hancheng stations. Diabatic heating was the main source of disturbed effective potential energy at Linyou. The explosive short-period strong precipitation was caused by the release of strong effective potential energy triggered by the gravity waves, and its development and propagation after that energy maximized. In contrast, the latent heat release of upstream precipitation was the main source of disturbed effective potential energy at Hancheng. This formed a positive feedback mechanism that produced continuous precipitation. In the studied event, the development of westerly belt systems had disturbed the wind field. The contribution of kinetic energy generated by this disturbance could not be ignored. The Froude number, mountain shape parameter, and ratio between mountain height and temperature inversion layer thickness had various effects of atmosphere and terrain on mesoscale and microscale mountain waves. In upper and lower layers, there were five airflows that were strengthened by the terrain. All these had important influences on local heavy rainfall at Linyou and Hancheng stations.
2018, 24(3): 385-394.
doi: 10.16555/j.1006-8775.2018.03.011
Abstract:
The planetary boundary layer height (PBLH) was calculated using the radiosonde sounding data, including 120 L-band operational sites and 8 GPS sites in China. The diurnal and seasonal variations of PBLH were analyzed using radiosonde sounding (OBS-PBLH) and ERA data (ERA-PBLH). Based on comparison and error analyses, we discussed the main error sources in these data. The frequency distributions of PBLH variations under different regimes (the convective boundary layer, the neutral residual layer, and the stable boundary layer) can be well fitted by a Gamma distribution and the shape parameter k and scale parameter s values were obtained for different regions of China. The variation characteristics of PBLH were found in summer under these three regimes for different regions. The relationships between PBLH and PM2.5 concentration generally follow a power law under very low or no precipitation conditions in the region of Beijing, Tianjin and Hebei in summer. The results usually deviated from this power distribution only under strong precipitation or high relative humidity conditions because of the effects of hygroscopic growth of aerosols or wet deposition. The OBS-PBLH provided a reasonable spatial distribution relative to ERA-PBLH. This indicates that OBS-PBLH has the potential for identifying the variation of PM2.5 concentration.
The planetary boundary layer height (PBLH) was calculated using the radiosonde sounding data, including 120 L-band operational sites and 8 GPS sites in China. The diurnal and seasonal variations of PBLH were analyzed using radiosonde sounding (OBS-PBLH) and ERA data (ERA-PBLH). Based on comparison and error analyses, we discussed the main error sources in these data. The frequency distributions of PBLH variations under different regimes (the convective boundary layer, the neutral residual layer, and the stable boundary layer) can be well fitted by a Gamma distribution and the shape parameter k and scale parameter s values were obtained for different regions of China. The variation characteristics of PBLH were found in summer under these three regimes for different regions. The relationships between PBLH and PM2.5 concentration generally follow a power law under very low or no precipitation conditions in the region of Beijing, Tianjin and Hebei in summer. The results usually deviated from this power distribution only under strong precipitation or high relative humidity conditions because of the effects of hygroscopic growth of aerosols or wet deposition. The OBS-PBLH provided a reasonable spatial distribution relative to ERA-PBLH. This indicates that OBS-PBLH has the potential for identifying the variation of PM2.5 concentration.
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