Anning Huang

Evaluation of multisatellite precipitation products by use of ground‐based data over China

Five satellite precipitation products, including Climate Prediction Center Morphing Technique (CMOPRH), Precipitation Estimation From Remotely Sensed Information Using Artificial Neural Network (PERSIANN), Tropical Rainfall Measuring Missing (TRMM) Multi-satellite Precipitation Analysis (TMPA) version 7 products 3B41RTV7, 3B42RTV7, and 3B42V7, are systematically evaluated by comparing to the daily precipitation data collected from ~2400 gauge stations over China during January 2000 to December 2014. Satellite estimates generally capture the overall spatial-temporal variation of precipitation over China with relatively better ability in warm seasons than in cold seasons. Meanwhile, satellite precipitation estimates also tend to show better agreement with gauge observations over humid regions than over arid and alpine regions. Analysis of the systematic and random error components suggests that the uncertainties in both TRMM3B42RTV7 and TRMM3B42V7 precipitation estimates are significantly reduced over most parts of China compared to the other 3 satellite products. Among the five products, the research product TRMM3B42V7 with bias adjustments agrees the most with the gauge observation in terms of spatio-temporal variation, amplitude and pattern of variability, occurrence of rainy events, and probability distribution function of the precipitation amount for different rain rates over most parts of China; the near-real-time product TRMM3B42RTV7 with the application of improved retrieval algorithms and more satellite data performs the second best over most sub-regions of eastern China. The improvements of TRMM3B42RTV7 without bias adjustments over eastern China relative to CMORPH, PERSIANN and TRMM3B41RTV7 are encouraging and favorable for the operational applications.

Simulated precipitation diurnal cycles over East Asia using different CAPE-based convective closure schemes in WRF model

Closure assumption in convection parameterization is critical for reasonably modeling the precipitation diurnal variation in climate models. This study evaluates the precipitation diurnal cycles over East Asia during the summer of 2008 simulated with three convective available potential energy (CAPE) based closure assumptions, i.e. CAPE-relaxing (CR), quasi-equilibrium (QE), and free-troposphere QE (FTQE) and investigates the impacts of planetary boundary layer (PBL) mixing, advection, and radiation on the simulation by using the weather research and forecasting model. The sensitivity of precipitation diurnal cycle to PBL vertical resolution is also examined. Results show that the precipitation diurnal cycles simulated with different closures all exhibit large biases over land and the simulation with FTQE closure agrees best with observation. In the simulation with QE closure, the intensified PBL mixing after sunrise is responsible for the late-morning peak of convective precipitation, while in the simulation with FTQE closure, convective precipitation is mainly controlled by advection cooling. The relative contributions of different processes to precipitation formation are functions of rainfall intensity. In the simulation with CR closure, the dynamical equilibrium in the free troposphere still can be reached, implying the complex cause-effect relationship between atmospheric motion and convection. For simulations in which total CAPE is consumed for the closures, daytime precipitation decreases with increased PBL resolution because thinner model layer produces lower convection starting layer, leading to stronger downdraft cooling and CAPE consumption. The sensitivity of the diurnal peak time of precipitation to closure assumption can also be modulated by changes in PBL vertical resolution. The results of this study help us better understand the impacts of various processes on the precipitation diurnal cycle simulation.

An evaluation of boreal summer intra-seasonal oscillation simulated by BCC_AGCM2.2

The intra-seasonal oscillation (ISO) is a prominent feature of the East Asia summer monsoon. The Beijing Climate Center model is one of the IPCC models participating in the Coupled Model Inter-comparison Project (CMIP) 3 and CMIP5 experiments. This paper presents a systematic evaluation of ISO simulated by the Beijing Climate Center atmospheric general circulation model version 2.2 against observations. The model reasonably simulates some salient features of BSISO in terms of temporal spectrum, leading EOF modes, and vertical structure, however limitations are also evident. The strength of the BSISO is overestimated and the northward propagating rain belt is tilted southwest-northeast, which is also different from the observation. The model tends to produce unrealistically strong but shallow convection associated with the ISO, leading to a northward shift of the Western Pacific Subtropical High and the main rain band compared to observations. Process studies show that the anomalous convective heating associated with the wet model bias drives a Gill-type response, resulting in the northwesterly biased position of Western Pacific Subtropical High. The study has revealed how the interaction of moist processes and large-scale dynamics can lead to model bias in simulating the east Asian regional climate system and its variability (ISO in particular). Future improvements in model resolution and convection parameterization are expected to reduce such errors.

Diurnal cycle of precipitation over Fujian Province during the pre-summer rainy season in southern China

Precipitation diurnal cycle over Fujian in the pre-summer rainy season has been revealed based on the hourly rain gauge data during 2009–2013. The precipitation amount (PA) over northwestern Fujian and most southeast coasts shows relatively small diurnal variability. This is in contrast to large diurnal variations in the mountainous areas. Regional differences in precipitation diurnal cycles are obviously noted among the coastal, valley, hilly, and mountainous areas. The precipitation diurnal cycles are significantly affected by the terrain elevation and distance to coast, PA and precipitation frequency (PF) show much more pronounced double diurnal peaks with the terrain elevation and distance to coast increased. However, the precipitation intensity (PI) basically shows one distinct late afternoon diurnal peak for different elevations and distances to coast. Four typical patterns of precipitation diurnal cycle are further identified by cluster analysis. The four typical PF patterns show relatively apparent morning peaks over coasts, inland mountains, and hills in addition to distinct late afternoon maxima. Low PF with weak diurnal amplitude is mainly located over the coastal areas, while high PF with strong diurnal amplitude is found over the valley, hilly, and mountainous regions. The PA exhibits a weak early morning peak and a relatively strong late afternoon peak over coastal, hilly, or mountainous areas and windward slopes but only one distinct late afternoon peak over the valley regions and leeward slopes. The amplitude of PA diurnal cycle is the weakest over the coastal areas but the strongest over the valley regions or leeward slopes among the four PA patterns. The four PI diurnal cycle patterns consistently show distinct afternoon peaks.

Evaluation of the precipitation seasonal variation over eastern China simulated by BCC_CSM model with two horizontal resolutions

The performance of Beijing Climate Center climate system model (BCC_CSM) with two horizontal resolutions in simulating the precipitation seasonal variation over eastern China has been evaluated. The possible reasons related to the differences in the simulations of BCC_CSM1.1 m model with fine resolution and BCC_CSM1.1 model with coarse resolution also have been addressed and discussed. Results show that the improved simulation of the timing and amount of precipitation in dry seasons except for larger biases during rainy seasons can be noted in BCC_CSM1.1 m model relative to BCC_CSM1.1 model. The occurrence time of the precipitation annual peaks in BCC_CSM1.1 m model shows better agreements with the observation compared to BCC_CSM1.1 model. Mechanism analysis indicates that BCC_CSM1.1 produced earlier East Asian summer monsoon (EASM) onset and northward jump of western Pacific subtropical high (WPSH), leading to the earlier start of the rainy seasons and occurrence time of the precipitation annual peaks over eastern China comparing with the observation and BCC_CSM1.1 m simulation. The improved EASM onset and northward jump of WPSH in BCC_CSM1.1 m model resulted in better simulation of precipitation seasonal transition and occurrence time of the precipitation annual peaks. However, compared to BCC_CSM1.1 model, the much more underestimated summer precipitation over most eastern China in BCC_CSM1.1 m model is mainly due to the weakly simulated northeastward water vapor transport, which is resulted from the much stronger WPSH with farther northwest location and weaker land-sea thermal contrast.

On the relationship between the Madden‐Julian Oscillation and 2 m air temperature over central Asia in boreal winter

Linear regression is used to explore the relationship between the Madden-Julian oscillation (MJO) and 2-meter air temperature (T2M) over Central Asia in boreal winter during 1979-2012. During MJO phases 3 and 4 (7 and 8), T2M anomalies exhibit a significantly strong, negative (positive) response to the MJO from the Arabian Sea to northwestern China. The anomalies of T2M are essentially influenced by surface net downward long (Ldown) and short wave radiations, which are caused by the changes in total cloud cover (TCC) and low-level tropospheric air temperature. The anomalies of Ldown that are caused by TCC account for 20-65% of total Ldown. The remaining anomalies of total Ldown are explained by low-level air temperature changes. 850-hPa air temperature (T850) tendency is mainly affected by the vertical motion over Central Asia during MJO phases 1, 2, 4-6, and 8, as well as over northern India during phases 3 and 7. Over Saudi Arabia, Afghanistan, Pakistan, Kazakhstan, and northwestern China, the anomalies of T850 tendency are mainly explained by the temperature advection during phases 3 and 7. TCC and vertical motion are affected by the evolution of the MJO event. The cyclonic (anticyclonic) circulation related to the MJO over Central Asia during phases 3 and 4 (7 and 8) causes the transport of cold (warm) air over Central Asia. The MJO can be a useful intraseasonal signal to predict winter T2M over Central Asia, where temperatures would be colder (warmer) than normal during MJO phases 3 and 4 (7 and 8).

Annual distributions and variations of dust weather occurrence over the Tarim Basin, China

The annual distribution and variations in dust weather occurrence (DWO) have been analyzed using monthly DWO data from 26 stations over the Tarim Basin during the period of 1961 to 2010. The results show that the DWO presents a significant decreasing trend for different parts of the Tarim Basin in recent decades. The monthly DWO has two peaks in the east and west. In the first half of the year, the peak is in April, but in the second half of the year, the peak is in September. According to the concentration period and concentration degree (CD) of DWO, we can find that the maximum DWO occurs in April in the eastern, western, and northern parts of the basin, but it occurs in May in the southern part. The dust weather season is shorter for the northern and eastern parts of the basin than those of the remaining parts. On average, the dust weather season initiates in April in the northeast and in May for the rest of the region. As an indicator for the length of dust weather season, the CD is significantly related to DWO, with a correlation coefficient of −0.51, revealing an interesting feature of regional climate change with declining DWO and declining dust weather season over the Tarim Basin. The correlation analysis exhibits that all the Arctic Oscillation, Antarctic Oscillation, and North Atlantic Oscillation have a negative relation with the DWO but a positive relation with the length of dust weather season.

Effects of the ground surface temperature anomalies over the Tibetan Plateau on the rainfall over northwestern China and western Mongolia in July

A significantly negative interannual relationship is identified between the ground surface temperature (GTS) over the Tibetan Plateau (TP) and the rainfall over northwestern China and western Mongolia (NWC-WM) through analyzing the Chinese weather station data, GPCP precipitation, and ERA-Interim reanalysis in July during 1980–2012. This relationship is verified by the model sensitivity experiments carried out by using RegCM4.1 during 1982–2011. The positive/negative GTS forcing of three different magnitudes is added in two key regions over the TP in RegCM4.1. One of the key regions covers the central and eastern TP (denoted as TPC). The other covers the northern and north slope of the TP (denoted as TPN). The model results suggest that when the GTS anomalies in either of the two key regions are negative (positive), the rainfall anomalies over NWC-WM are positive (negative), which is consistent with observations. Furthermore, rainfall anomalies over NWC-WM are more sensitive to the GTS anomalies over the TPN region than those over the southern TP. The model results also reveal that the negative (positive) GTS anomalies over region TPN mainly cause the decrease (increase) of the latent heat release related to rainfall (surface sensible heat) and descent (ascent) over the TPN region but ascent (descent) to the north of the TP between 40° and 50° N. In addition, the specific humidity between 40° and 50° N is increased (decreased). Therefore, the increase (decrease) in specific humidity and the ascent (descent) between 40° and 50° N cause the increase (decrease) in the rainfall over NWC-WM.