Weihong Qian

Climate change in China from 1880 to 1998 and its impact on the environmental condition

The global mean surface air temperature (SAT) or the Northern Hemisphere mean SAT has increased since the late nineteenth century, but the mean precipitation around the world has not formed a definite tendency to increase. A lot of studies showed that different climate and environmental changes during the past 100 years over various regions in the world were experienced. The climate change in China over the past 100 years and its impact on Chinas environmental conditions needs to be investigated in more detail.Data sets of surface air temperature and atmospheric precipitation over China since 1880 up to the present are now available. In this paper, a drought index has been formulated corresponding to both the temperature and precipitation. Based on three series of temperature, precipitation, and drought index, interdecadal changes in all 7 regions of China and temperature differences among individual regions are analyzed. Some interesting facts are revealed using the wavelet transform method. In Northeast China, the aridification trend has become more serious since 1970s. Drought index in North China has also reached a high value during 1990s, which seems similar to that period 1920s–1940s. In NorthwestChina, the highest temperature appeared over the period 1930s–1940s. Along the Yangtze River valley in central eastern China and Southwest China, interdecadal high temperature occurred from 1920s to 1940s and in 1990s, but the drought climate mainly appeared from 1920s to early 1940s. In South China, temperature remained at a high value over the period 1910s–1940s,but the smaller-scale variation of drought index was remarkable from 1880 to 1998. Consequently, the quasi-20-year oscillation (smaller-scale variation) and the quasi-70-year oscillation (secular variation) obviously exist in temperature and precipitation series in different regions over China.Climate change and intensified human activity in China have induced certain environmental evolutions, such as the frequency change of dust-storm event in northern China, no-flow in the lower reaches of the Yellow River and the runoff variation in Northwest China. On the other hand, frequent floods along the Yangtze River and high frequency of drought disaster have resulted in tremendous economic losses in the last decade in China. The primary reason for these happenings may be attributed to the evolution of the monsoon system in East Asian.

Seasonal march of Asian summer monsoon

This paper investigates the seasonal march of the summer monsoon through several different sub-divisions of the Asian monsoon region. Five data sets, the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP), the upper-tropospheric water vapour band Brightness Temperature (BT), the Outgoing Longwave Radiation (OLR), the lower tropospheric wind and Korean daily rainfall for 1980–1995, are used. Analysis shows that the largest area of deep convection in the global atmosphere is located over the tropical Indian Ocean–equatorial western Pacific; its centre being positioned 110°E along the equator in boreal winter and then moves northwestward to 80°E at 5°N in late July. In late April, the area of deep convection first extends northward into the Indo-China Peninsula (ICP). In mid-May it abruptly covers over the central South China Sea (SCS) region. After the onset of SCS monsoon, deep convection starts to develop northward along the eastern coast of China, East Tibet Plateau (ETP) and Indian sub-continent, simultaneously. Based on the analysis of BT and lower-tropospheric circulation, Asian summer monsoon can be divided into six inter-linked sub-regional monsoons. They are Indo-China Peninsula monsoon, SCS monsoon, South Asian (Indian) monsoon, ETP monsoon, East Asian (south China, lower Yangtze River and Japan) monsoon and Northeast Asian (north China and Korea) monsoon. In seasonal course, their onset periods take place in late April–mid-May, mid-May, mid-May–late July, mid-May–early June, mid-May–late June and late June–mid-July, respectively. Copyright

A Comparison between a Generalized Beta–Advection Model and a Classical Beta–Advection Model in Predicting and Understanding Unusual Typhoon Tracks in Eastern China Seas

AbstractA total of 163 tropical cyclones (TCs) occurred in the eastern China seas during 1979–2011 with four types of tracks: left turning, right turning, straight moving, and irregular. The left-turning type is unusual and hard to predict. In this paper, 133 TCs from the first three types have been investigated. A generalized beta–advection model (GBAM) is derived by decomposing a meteorological field into climatic and anomalous components. The ability of the GBAM to predict tracks 1–2 days in advance is compared with three classical beta–advection models (BAMs). For both normal and unusual tracks, the GBAM apparently outperformed the BAMs. The GBAM’s ability to predict unusual TC tracks is particularly encouraging, while the BAMs have no ability to predict the left-turning and right-turning TC tracks. The GBAM was also used to understand unusual TC tracks because it can be separated into two forms: a climatic-flow BAM (CBAM) and an anomalous-flow BAM (ABAM). In the CBAM a TC vortex is steered by the lar...

An Anomaly-Based Method for Identifying Signals of Spring and Autumn Low-Temperature Events in the Yangtze River Valley, China

AbstractAbnormally low temperature (LT) events in spring and autumn can cause severe damage to spring and autumn rice production in the mid- to lower Yangtze River valley in China. Advanced predictions of such events can help mitigate their damage. However, the current methods have limited success in describing and predicting those weather events. In this study, a new method is proposed to decompose any one of the meteorological variables into its climatic component and an anomaly, and the anomaly is used in identifying signals of the LT events. The method is used in 20 strong spring LT events and 44 autumn events during 1960–2008. The results show the advanced ability of this method to clearly describe the LT events as compared with the vague indications of such events that are produced by conventional methods currently in practice in China. In addition, the composite profile of vertical anomalies shows that a negative center of geopotential height anomalies at around 300 hPa, coexisting with a strong co...

Dry/wet alternation and global monsoon

This paper deals with dry/wet alternation and related globe-scale monsoon. The data sets used are the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP), the National Meteorological Center global wind analysis and the Upper-Tropospheric Water Vapor (UTWV) band Brightness Temperature (BT) observed by NOAA polar orbiting satellites for 1980-1995. The BT and wind at 850hPa level are compared with the CMAP. Results show that the BT can indicate the convective precipitation in both tropical and subtropical regions. The summer monsoon in subtropics is defined as the expansions of three deep convective areas or three wet centers at the equatorial region. The major distributions of dry/wet alternation are determined according to the threshold of BT less than 244K. In the global mid-low latitudes, there are six major seasonal dry/wet alternative regions with the dry/wet period lasting more than one month. The largest one is located over the subtropical North Africa-Asia-northwest Pacific. Other five alternative regions appear in the subtropical South Africa, Indonesia-Australia, southwest Pacific, Mexico-Caribbean Sea and subtropical South America. In Asia, the largest dry/wet alternative region covers all India, Indochina Peninsula, South China and southern Japan. These wet/dry alternative regions are the reflection of the seasonal advance of summer monsoon.

Thermocline oscillation and warming event in the tropical Indian Ocean

Abstract In this paper, an indicator that shows the maximum subsurface temperature anomalies (MSTA) is first defined to represent the thermocline variations through a case analysis of 1997/98. By using the past 46‐year (1955–2000) subsurface temperature data, thermocline oscillation and wave‐signal propagation in the tropical Indian Ocean are revealed. The thermocline oscillation is robust in the tropical Indian Ocean in spite of the coincidence with the strong El Niño/Southern Oscillation (ENSO) cycle as well as the anomalous Walker circulation in the tropical Pacific and the anomalous monsoon circulation in the tropical Indian Ocean. Due to the nature of the propagation of subsurface wave signals, the oscillation may be a potential factor for the predictability of climate and for the dynamical study of the air‐sea interaction in the Indian Ocean region. The warming of sea surface temperature in the tropical Indian Ocean is a basin‐wide phenomenon and results from the reflection of the tropical Rossby waves. By defining an MSTA dipole mode index (M‐DMI), some features of the interannual climate anomalies that correspond to the different phases of M‐DMI obviously exist in the tropical Indian Ocean and tropical central‐western Pacific Ocean. In the positive phase of the M‐DMI, strong 850‐hPa easterly winds appear in the equatorial central‐eastern Indian Ocean while strong 850‐hPa westerly winds occur over the equatorial central western Pacific. Also, for the positive M‐DMI, above‐normal precipitation is located in the tropical central‐western Indian Ocean while below‐normal precipitation is situated over the tropical eastern Indian Ocean and the tropical western Pacific Ocean. The reverse is noted for the negative M‐DMI phase. A scenario for the warming event and the MSTA dipole event in the tropical Indian Ocean is also proposed.

Anomaly-Based Weather Analysis versus Traditional Total-Field-Based Weather Analysis for Depicting Regional Heavy Rain Events

AbstractAlthough the use of anomaly fields in the forecast process has been shown to be useful and has caught forecasters’ attention, current short-range (1–3 days) weather analyses and forecasts are still predominantly total-field based. This paper systematically examines the pros and cons of anomaly- versus total-field-based approaches in weather analysis using a case from 1 July 1991 (showcase) and 41 cases from 1998 (statistics) of heavy rain events that occurred in China. The comparison is done for both basic atmospheric variables (height, temperature, wind, and humidity) and diagnostic parameters (divergence, vorticity, and potential vorticity). Generally, anomaly fields show a more enhanced and concentrated signal (pattern) directly related to surface anomalous weather events, while total fields can obscure the visualization of anomalous features due to the climatic background. The advantage is noticeable in basic atmospheric variables, but is marginal in nonconservative diagnostic parameters and i...

Interannual and interdecadal variabilities in SST anomaly over the eastern equatorial Pacific

The global sea surface temperature (SST) anomaly data from 1950 to 1996 were used to analyze spatial characters of interdecadal SST variations. A wavelet transform was made for the equatorial eastern Pacific SST anomaly time series. Results show that there are three remarkable timescale SST variations: 130-month interdecadal variation, 57-month interannual variation and 28-month quasi2-a variation. Based on this result, an EI Niño event was predicted in the early part of 1997.

Monsoonal oscillation revealed by the upper-troposphere water vapor band brightness temperature

The measurements of brightness temperature (BT) from the upper-troposphere water vapor channel 12 of the National Oceanic and Atmospheric Administration polar satellites from 1979 through 1995 are used to analyze the interannual variations of the global monsoon strength. Results show that in the interannual time-sclae the BT variability in the equatorial eastern Pacific (EEP) is out of phase with the BT variabilities in other four regions, i. e. South Asia, tropical south American, two subtropical areas in the South and North Pacific. The BT interannual variation mode may be called monsoonal oscillation (MO). The MO is the result of the atmospheric circulation anomaly in the troposphere.

Long‐term trends of the Polar and Arctic cells influencing the Arctic climate since 1989

The strengthening and broadening trends of the Hadley cell have been revealed, while the existence of the Arctic cell has also been confirmed in previous studies. This study extends previous strengthening trend analyses of the Hadley cell to the Polar and Arctic cells in the Northern Hemisphere and explores their climate influences. Results show that the Polar cell experienced an abrupt change from a slow to a rapid strengthening trend in 1989, while the Arctic cell showed an insignificant strengthening trend and a significant weakening trend successively. The strengthening subsidence flow associated with the Polar and Arctic cells can partly explain the warming surface air temperature and declining sea ice concentration through the increasing tropospheric height and temperature trends. These results provide new insights for understanding the interdecadal relationship between atmospheric circulation and climate change in the Arctic region.