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2016 Vol. 33, No. 1

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Variation in Summer Surface Air Temperature over Northeast Asia and Its Associated Circulation Anomalies
Wei CHEN, Xiaowei HONG, Riyu LU, Aifen JIN, Shizhu JIN, Jae-Cheol NAM, Jin-Ho SHIN, Tae-Young GOO, Baek-Jo KIM
2016, 33(1): 1-9. doi: 10.1007/s00376-015-5056-0
This study investigates the interannual variation of summer surface air temperature over Northeast Asia (NEA) and its associated circulation anomalies. Two leading modes for the temperature variability over NEA are obtained by EOF analysis. The first EOF mode is characterized by a homogeneous temperature anomaly over NEA and therefore is called the NEA mode. This anomaly extends from southeast of Lake Baikal to Japan, with a central area in Northeast China. The second EOF mode is characterized by a seesaw pattern, showing a contrasting distribution between East Asia (specifically including the Changbai Mountains in Northeast China, Korea, and Japan) and north of this region. This mode is named the East Asia (EA) mode. Both modes contribute equivalently to the temperature variability in EA. The two leading modes are associated with different circulation anomalies. A warm NEA mode is associated with a positive geopotential height anomaly over NEA and thus a weakened upper-tropospheric westerly jet. On the other hand, a warm EA mode is related to a positive height anomaly over EA and a northward displaced jet. In addition, the NEA mode tends to be related to the Eurasian teleconnection pattern, while the EA mode is associated with the East Asia-Pacific/Pacific-Japan pattern.
Ensemble Transform Sensitivity Method for Adaptive Observations
Yu ZHANG, Yuanfu XIE, Hongli WANG, Dehui CHEN, Zoltan TOTH
2016, 33(1): 10-20. doi: 10.1007/s00376-015-5031-9
The Ensemble Transform (ET) method has been shown to be useful in providing guidance for adaptive observation deployment. It predicts forecast error variance reduction for each possible deployment using its corresponding transformation matrix in an ensemble subspace. In this paper, a new ET-based sensitivity (ETS) method, which calculates the gradient of forecast error variance reduction in terms of analysis error variance reduction, is proposed to specify regions for possible adaptive observations. ETS is a first order approximation of the ET; it requires just one calculation of a transformation matrix, increasing computational efficiency (60%-80% reduction in computational cost). An explicit mathematical formulation of the ETS gradient is derived and described. Both the ET and ETS methods are applied to the Hurricane Irene (2011) case and a heavy rainfall case for comparison. The numerical results imply that the sensitive areas estimated by the ETS and ET are similar. However, ETS is much more efficient, particularly when the resolution is higher and the number of ensemble members is larger.
Dynamic and Thermodynamic Features of Low and Middle Clouds Derived from Atmospheric Radiation Measurement Program Mobile Facility Radiosonde Data at Shouxian, China
Jinqiang ZHANG, Hongbin CHEN, Xiang'ao XIA, Wei-Chyung WANG
2016, 33(1): 21-33. doi: 10.1007/s00376-015-5032-8
By using the radiosonde measurements collected at Shouxian, China, we examined the dynamics and thermodynamics of single- and two-layer clouds formed at low and middle levels. The analyses indicated that the horizontal wind speed above the cloud layers was higher than those within and below cloud layers. The maximum balloon ascent speed (5.3 m s-1) was located in the vicinity of the layer with the maximum cloud occurrence frequency (24.4%), indicating an upward motion (0.1-0.16 m s-1). The average thickness, magnitude and gradient of the temperature inversion layer above single-layer clouds were 117 ± 94 m, 1.3 ± 1.3°C and 1.4 ± 1.5°C (100 m)-1, respectively. The average temperature inversion magnitude was the same (1.3°C) for single-low and single-middle clouds; however, a larger gradient [1.7±1.8°C (100 m)-1] and smaller thickness (94 ±67 m) were detected above single-low clouds relative to those above single-middle clouds [0.9 ±0.7°C (100 m)-1 and 157 ± 120 m]. For the two-layer cloud, the temperature inversion parameters were 106 ± 59 m, 1.0 ± 0.9°C and 1.0 ± 1.0°C (100 m)-1 above the upper-layer cloud and 82 ±60 m, 0.6 ± 0.9°C and 0.7± 0.6°C (100 m)-1 above the low-layer cloud. Absolute differences between the cloud-base height (cloud-top height) and the lifting condensation level (equilibrium level) were less than 0.5 km for 66.4% (36.8%) of the cases analyzed in summer.
Observational Facts Regarding the Joint Activities of the Southwest Vortex and Plateau Vortex after Its Departure from the Tibetan Plateau
Shuhua YU, Wenliang GAO, Dixiang XIAO, Jun PENG
2016, 33(1): 34-46. doi: 10.1007/s00376-015-5039-1
Using atmospheric observational data from 1998 to 2013, station rainfall data, TRMM (Tropical Rainfall Measuring Mission) data, as well as annual statistics for the plateau vortex and shear line, the joint activity features of sustained departure plateau vortexes (SDPVs) and southwest vortexes (SWVs) are analyzed. Some new and useful observational facts and understanding are obtained about the joint activities of the two types of vortex. The results show that: (1) The joint active period of the two vortexes is from May to August, and mostly in June and July. (2) The SDPVs of the partnership mainly originate near Zaduo, while the SWVs come from Jiulong. (3) Most of the two vortexes move in almost the same direction, moving eastward together with the low trough. The SDPVs mainly act in the area to the north of the Yangtze River, while the SWVs are situated across the Yangtze River valley. (4) The joint activity of the two vortexes often produces sustained regional heavy rainfall to the south of the Yellow River, influencing wide areas of China, and even as far as the Korean Peninsula, Japan and Vietnam. (5) Most of the two vortexes are baroclinic or cold vortexes, and they both become strengthened in terms of their joint activity. (6) When the two vortexes move over the sea, their central pressure descends and their rainfall increases, especially for SWVs. (7) The two vortexes might spin over the same area simultaneously when there are tropical cyclones in the eastern and southern seas of China, or move southward together if a tropical cyclone appears near Hainan Island.
Teleconnected Influence of the Boreal Winter Antarctic Oscillation on the Somali Jet: Bridging Role of Sea Surface Temperature in Southern High and Middle Latitudes
Wenjing SHI, Ziniu XIAO, Jianjun XUE
2016, 33(1): 47-57. doi: 10.1007/s00376-015-5094-7
The teleconnection impact of the boreal winter Antarctic Oscillation (AAO) on the Somali Jet (SMJ) intensity in the following spring and summer is examined in this paper. The variability of the boreal winter AAO is positively related to the SMJ intensity in both spring and summer. The analyses show that the SST in southern high and middle latitudes seems to serve as a bridge linking these two systems. When the AAO is in strong positive phase, SST over the Southern Ocean cools in the high latitudes and warms in the middle latitudes, which persists into summer; however, the variability of SST in southern high and middle latitudes is also closely correlated to SMJ intensity. A possible mechanism that links SST variability with the AAO-SMJ relationship is also discussed. The AAO in boreal winter produces an SST anomaly pattern in southern high and middle latitudes through the air-sea coupling. This AAO-related SST anomaly pattern modulates the local Ferrel cell anomaly in summer, followed by the regional Hadley cell anomaly in tropics. The anomalous vertical motion in tropics then changes the land-sea thermal contrast between the tropical Indian Ocean and the Asian continent through the variability of low cloud cover and downward surface longwave radiation flux. Finally, the land-sea thermal contrast anomaly between the tropical Indian Ocean and the Asian continent changes the SMJ intensity. The results from Community Atmosphere Model experiments forced by the SST anomaly in southern high and middle latitudes also confirm this diagnostic physical process to some extent.
Effects of Surface Flux Parameterization on the Numerically Simulated Intensity and Structure of Typhoon Morakot (2009)
2016, 33(1): 58-72. doi: 10.1007/s00376-015-4202-z
The effects of surface flux parameterizations on tropical cyclone (TC) intensity and structure are investigated using the Advanced Research Weather Research and Forecasting (WRF-ARW) modeling system with high-resolution simulations of Typhoon Morakot (2009). Numerical experiments are designed to simulate Typhoon Morakot (2009) with different formulations of surface exchange coefficients for enthalpy (C K) and momentum (C D) transfers, including those from recent observational studies based on in situ aircraft data collected in Atlantic hurricanes. The results show that the simulated intensity and structure are sensitive to C K and C D, but the simulated track is not. Consistent with previous studies, the simulated storm intensity is found to be more sensitive to the ratio of C K/C D than to C K or C D alone. The pressure-wind relationship is also found to be influenced by the exchange coefficients, consistent with recent numerical studies. This paper emphasizes the importance of C D and C K on TC structure simulations. The results suggest that C D and C K have a large impact on surface wind and flux distributions, boundary layer heights, the warm core, and precipitation. Compared to available observations, the experiment with observed C D and C K generally simulated better intensity and structure than the other experiments, especially over the ocean. The reasons for the structural differences among the experiments with different C D and C K setups are discussed in the context of TC dynamics and thermodynamics.
Verification and Correction of Cloud Base and Top Height Retrievals from Ka-band Cloud Radar in Boseong, Korea
Su-Bin OH, Yeon-Hee KIM, Ki-Hoon KIM, Chun-Ho CHO, Eunha LIM
2016, 33(1): 73-84. doi: 10.1007/s00376-015-5058-y
In this study, cloud base height (CBH) and cloud top height (CTH) observed by the Ka-band (33.44 GHz) cloud radar at the Boseong National Center for Intensive Observation of Severe Weather during fall 2013 (September-November) were verified and corrected. For comparative verification, CBH and CTH were obtained using a ceilometer (CL51) and the Communication, Ocean and Meteorological Satellite (COMS). During rainfall, the CBH and CTH observed by the cloud radar were lower than observed by the ceilometer and COMS because of signal attenuation due to raindrops, and this difference increased with rainfall intensity. During dry periods, however, the CBH and CTH observed by the cloud radar, ceilometer, and COMS were similar. Thin and low-density clouds were observed more effectively by the cloud radar compared with the ceilometer and COMS. In cases of rainfall or missing cloud radar data, the ceilometer and COMS data were proven effective in correcting or compensating the cloud radar data. These corrected cloud data were used to classify cloud types, which revealed that low clouds occurred most frequently.
Simulation of Quasi-Linear Mesoscale Convective Systems in Northern China: Lightning Activities and Storm Structure
Wanli LI, Xiushu QIE, Shenming FU, Debin SU, Yonghai SHEN
2016, 33(1): 85-100. doi: 10.1007/s00376-015-4170-3
Two intense quasi-linear mesoscale convective systems (QLMCSs) in northern China were simulated using the WRF (Weather Research and Forecasting) model and the 3D-Var (three-dimensional variational) analysis system of the ARPS (Advanced Regional Prediction System) model. A new method in which the lightning density is calculated using both the precipitation and non-precipitation ice mass was developed to reveal the relationship between the lightning activities and QLMCS structures. Results indicate that, compared with calculating the results using two previous methods, the lightning density calculated using the new method presented in this study is in better accordance with observations. Based on the calculated lightning densities using the new method, it was found that most lightning activity was initiated on the right side and at the front of the QLMCSs, where the surface wind field converged intensely. The CAPE was much stronger ahead of the southeastward progressing QLMCS than to the back it, and their lightning events mainly occurred in regions with a large gradient of CAPE. Comparisons between lightning and non-lightning regions indicated that lightning regions featured more intense ascending motion than non-lightning regions; the vertical ranges of maximum reflectivity between lightning and non-lightning regions were very different; and the ice mixing ratio featured no significant differences between the lightning and non-lightning regions.
Radiative Effects on Torrential Rainfall during the Landfall of Typhoon Fitow (2013)
Lingyun LOUSchool, of Earth, Zhejiang University, Xiaofan LISchool
2016, 33(1): 101-109. doi: 10.1007/s00376-015-5139-y
Cloud microphysical and rainfall responses to radiative processes are examined through analysis of cloud-resolving model sensitivity experiments of Typhoon Fitow (2013) during landfall. The budget analysis shows that the increase in the mean rainfall caused by the exclusion of radiative effects of water clouds corresponds to the decrease in accretion of raindrops by cloud ice in the presence of radiative effects of ice clouds, but the rainfall is insensitive to radiative effects of water clouds in the absence of radiative effects of ice clouds. The increases in the mean rainfall resulting from the removal of radiative effects of ice clouds correspond to the enhanced net condensation. The increases (decreases) in maximum rainfall caused by the exclusion of radiative effects of water clouds in the presence (absence) of radiative effects of ice clouds, or the removal of radiative effects of ice clouds in the presence (absence) of radiative effects of water clouds, correspond mainly to the enhancements (reductions) in net condensation. The mean rain rate is a product of rain intensity and fractional rainfall coverage. The radiation-induced difference in the mean rain rate is related to the difference in rain intensity. The radiation-induced difference in the maximum rain rate is associated with the difference in the fractional coverage of maximum rainfall.
Evolution of Instability before and during a Torrential Rainstorm in North China
Lu LIU, Lingkun RAN, Shouting GAO
2016, 33(1): 110-120. doi: 10.1007/s00376-015-5080-0
NCEP-NCAR reanalysis data were used to analyze the characteristics and evolution mechanism of convective and symmetric instability before and during a heavy rainfall event that occurred in Beijing on 21 July 2012. Approximately twelve hours before the rainstorm, the atmosphere was mainly dominated by convective instability in the lower level of 900-800 hPa. The strong southwesterly low-level jet conveyed the moist and warm airflow continuously to the area of torrential rain, maintaining and enhancing the unstable energy. When the precipitation occurred, unstable energy was released and the convective instability weakened. Meanwhile, due to the baroclinicity enhancement in the atmosphere, the symmetric instability strengthened, maintaining and promoting the subsequent torrential rain. Deriving the convective instability tendency equation demonstrated that the barotropic component of potential divergence and the advection term played a major role in enhancing the convective instability before the rainstorm. Analysis of the tendency equation of moist potential vorticity showed that the coupled term of vertical vorticity and the baroclinic component of potential divergence was the primary factor influencing the development of symmetric instability during the precipitation. Comparing the effects of these factors on convective instability and symmetric instability showed some correlation.
Revisiting the Second EOF Mode of Interannual Variation in Summer Rainfall over East China
Zhongda LIN, Qin SU, Riyu LU
2016, 33(1): 121-134. doi: 10.1007/s00376-015-5010-1
The second EOF (EOF2) mode of interannual variation in summer rainfall over East China is characterized by inverse rainfall changes between South China (SC) and the Yellow River-Huaihe River valleys (YH). However, understanding of the EOF2 mode is still limited. In this study, the authors identify that the EOF2 mode physically depicts the latitudinal variation of the climatological summer-mean rainy belt along the Yangtze River valley (YRRB), based on a 160-station rainfall dataset in China for the period 1951-2011. The latitudinal variation of the YRRB is mostly attributed to two different rainfall patterns: one reflects the seesaw (SS) rainfall changes between the YH and SC (SS pattern), and the other features rainfall anomalies concentrated in SC only (SC pattern). Corresponding to a southward shift of the YRRB, the SS pattern, with above-normal rainfall in SC and below-normal rainfall in the YH, is related to a cyclonic anomaly centered over the SC-East China Sea region, with a northerly anomaly blowing from the YH to SC; while the SC pattern, with above-normal rainfall in SC, is related to an anticyclonic anomaly over the western North Pacific (WNP), corresponding to an enhanced southwest monsoon over SC. The cyclonic anomaly, related to the SS pattern, is induced by a near-barotropic eastward propagating wave train along the Asian upper-tropospheric westerly jet, originating from the mid-high latitudes of the North Atlantic. The anticyclonic anomaly, for the SC pattern, is related to suppressed rainfall in the WNP.