Changes of precipitation pattern in China: 1961–2010

Theoretical and Applied Climatology - Based on the precipitation records of 2474 meteorological stations, this study investigated precipitation characteristics and trends in China from 1961 to...     

A decision‐analytic study of the joint value of seasonal precipitation and temperature forecasts in a choice‐of‐crop problem

Abstract

A static decision‐analytic method is used to investigate the economic value of bivariate ‐ precipitation and temperature ‐ seasonal forecasts of the form currently issued by the U.S. National Weather Service. This method is applied to a corn versus spring wheat choice‐of‐crop decision‐making problem by considering a transect of four counties across the northwestern margin of the North American corn belt. Numerical results indicate that seasonal forecasts of current quality can be of appreciable value (≥$1/ha) for some locations when the optimal action chosen on the basis of climatological information is only marginally preferred to another action. Increases in forecast value follow from hypothetical increases in the quality of both the precipitation and temperature components of the forecasts in the spring wheat region, whereas forecast value increases primarily as a function of the quality of the precipitation forecasts alone in the corn belt region. The results are very sensitive to absolute and relative crop prices.     

Application of the delta‐Eddington method to the absorption of solar radiation in the atmosphere

Abstract

A model to compute rapidly the absorption of solar radiation in the atmosphere is described. The model is based partially on the parameterization of Lacis and Hansen and also makes use of the delta‐Eddington method. In addition to absorption by ozone and water vapour, and scattering by air molecules and clouds, the mode1 includes absorption and scattering by aerosols. Good agreement is found in comparison with the Lacis and Hansen parameterization in the absence of clouds and aerosol. The present model represents an improvement in the treatment of scattering by clouds. Its main advantage though, is in its flexibility in allowing for interactions with the atmospheric aerosol.     

Reply to comments on and addenda to “some properties and comparative performance of the semi‐lagrangian method of Robert in the solution of the advection‐diffusion equation”

Abstract

Droughts are major natural disasters for many parts of the world. Dry areas, where the precipitation pattern is markedly seasonal, or is otherwise highly variable, are the most susceptible. The Canadian Prairies, together with the U.S. Great Plains, are one such area. While immediate loss of life is seldom a feature of most droughts, malnutrition and even starvation do follow severe droughts in some parts of the world. In Canada, economic losses, particularly in the agricultural sector, may reach several hundred millions of dollars in a drought year, with major socio‐economic repercussions affecting the entire region. Environmental damages include soil degradation and erosion, vegetation damage, slough and lake deterioration and wildlife loss. Unlike most other natural disasters, drought onset is difficult to identify. Droughts develop slowly, and until human activity begins to be affected by an on‐going reduction of precipitation, their existence is unrecognized. Development and application of specific soil moisture and drought indices based on cumulative precipitation deficits have enhanced drought monitoring programs. These in turn provide guidance on the need for mitigative measures that can be initiated early in the course of a drought. Any improvement in the timely application of these measures is, however, strongly dependent on being able to determine the drought's course, extent and likely severity at the earliest stage possible. The identification of precursor conditions for past drought has raised the possibility that the likelihood of a drought occurring in a particular year or growing season might be predictable. Teleconnections between North American precipitation patterns and ENSO events and other surface boundary conditions in the North Pacific have been detected. Forecasting seasonal temperature and perhaps precipitation anomalies appears to be potentially feasible using a suitable merging of precursor parameters and modelling methodologies. Clearly, future research must focus both on those precursors that have been identified and on a search for possible new ones. Development of better forecasting methodology is also essential. Research activity to identify and evaluate new mitigative measures should also be increased to keep pace with the prospects of drought predictability.     

Areal distribution and precipitation–altitude relationship of heavy short-term precipitation in the Czech Republic in the warm part of the year

The article presents an analysis of heavy short-term precipitation for the warm part of the year in the Czech Republic (CR). Precipitation data are prepared for the years 2002–2007 with a horizontal resolution of 1 km and a temporal resolution of 1 h. A method merging radar and daily rain gauge measurements is applied to calculate basic hourly precipitation. Two types of 1-, 2-, 3-, and 6-h precipitation data, derived from the basic hourly precipitation, are investigated from the viewpoint of precipitation–altitude relationships and areal distributions of heavy precipitation. The first type of data consists of sums of hourly precipitation, where the summation is performed for all data regardless of whether the summed hourly precipitation is a part of a longer precipitation event or if some hours are without precipitation. The second type of data contains temporally bounded precipitation events. This type predominantly includes convective precipitation. The results show that for both types of data, 1-h precipitation with high rain rates is without apparent dependence on altitude. For the first type of data and for precipitation durations of 2 and 3 h, the impact of altitude on precipitation maps can be identified for low and high rain rates. The impact of mountains is evident for the 6-h precipitation because it includes large scale precipitation events. However, the second type of data does not depend on altitude for heavy precipitation. Heavy precipitation of the second type shows, especially for 6-h, an increased frequency of occurrence in the south to central CR.     

Climatological responses of winter precipitation in Turkey to variability of the North Atlantic Oscillation during the period 1930–2001

Summary Climatological responses of winter (DJFM) precipitation at 78 stations of Turkey to variability of the North Atlantic Oscillation (NAO) were investigated for the period 1930–2001. The analysis was performed with respect to relationships between precipitation and three different NAO indices (NAOIs) and composite precipitation changes corresponding to the extreme phases of the NAOIs, and individual wet conditions and drought events linked to the extreme NAOI events. Main conclusions of the study can be evaluated as follows:(a) The Ponta Delgada–Reykjavik (PD–R) NAOI is superior among the three NAOIs compared, followed by the Lisbon–Stykkisholmur/Reykjavik NAOI, with regards to its ability to control year-to-year variability in winter precipitation series and composite precipitation conditions corresponding to the extreme NAOI phases in Turkey. (b) Variability of winter precipitation at most stations in Turkey is significantly correlated with variability of the three NAOIs. Negative relationships are stronger over the Marmara, the Mediterranean Transition and the Continental Central Anatolia regions, and the Aegean part of the Mediterranean region. (c) Composite precipitation analysis exhibited an apparent opposite anomaly pattern at the majority of stations between the weak and strong phases of the NAOIs. Composite precipitation means corresponding to the weak NAOI phase are explained mostly by wetter than long-term average conditions, whereas composite precipitation responses to the strong NAOI phase mostly produce drier than long-term average conditions. (d) Composite wet (dry) conditions during the weak (strong) phase of the NAOI are significant at about 32% (69%) of 78 stations for the PD–R NAOI, and about 38% (55%) for the L–S(R) NAOI. The dry signals from the strong NAO phases are stronger and show a larger spatial coherence over Turkey. The significant signals are evident in the west, centre and south of the country. (g) Widespread severe droughts in 1943, 1957, 1973, 1974, 1983, 1989, 1990, 1992, 1993 and 1994, and widespread strong wet conditions in 1940–1942, 1956, 1963, 1966, 1969 and 1970 were linked to the extreme high- and low-index events of at least two NAOIs, respectively.     

Application of a coupled ice‐ocean model to the Labrador Sea

Abstract

The steady, coupled ice‐ocean circulation model of Willmott and Mysak (1989) for a meridional channel is applied to the Labrador Sea for the winter season. The model consists of a thermodynamic reduced‐gravity ocean combined with a variable thickness ice cover that is in thermal equilibrium. Upon specifying the forcing fields of surface air temperature, wind stress and water temperature along the open southern boundary, the winter climatological ice‐edge position, ice thickness, ocean circulation and temperature fields are determined in the channel domain. The sensitivity of the results to the various model parameters is examined. In particular, the optimum heat exchange coefficients for the interfaces of air‐water, ice‐water and air‐ice are found.

The model ice‐edge position compares favourably with the 50% winter climatological ice concentration isoline obtained from an analysis of 32 years (1953–84) of sea‐ice concentration data. The simulations of the ocean temperature and ice thickness are also quite realistic according to the observed records available. The model is also applied to two specific winters (1981 and 1983) during which anomalous sea‐ice and weather conditions prevailed in the Labrador Sea.     

The life cycle of the intense IOP‐14 storm during CASPII. Part I: Analysis and simulations

Abstract

In this study, a 5‐day life‐cycle of the IOP‐14 storm during CASP II is examined using conventional observations and numerical simulations with a mesoscale version of the Canadian Regional Finite‐Element (RFE) model. Observational analysis reveals that the IOP‐14 storm forms from a lee trough, occurring along a strong baroclinic zone with an intense frontogenetic deformation, that interacts with an upper‐level travelling short‐wave trough across the Canadian Rockies. Then the storm experiences a slow, but nearly steady, growth while traversing the North American continent. It deepens explosively as it moves into the Atlantic Ocean. It appears that i) the enhanced large‐scale baroclinicity due to land‐sea temperature contrasts, ii) the tremendous latent heat release due to the transport of high‐θ_e air from the marine boundary layer, Hi) the decrease of surface drag and iv) the favourable westward tilt of the low with an amplifying trough all contribute to the explosive deepening of the storm.

Two consecutive simulations covering a total of 102 h during the storm development are carried out with a grid size of 50 km. The RFE model reproduces very well the formation of the surface low on the lee side of the Rockies, the track and deepening rates, the explosive development and decay of the storm, and various mesoscale phenomena (e.g., a “bent‐back” warm front, a “T‐bone” thermal pattern, a cold frontal “fracture”, an upper‐level “eye” and warm‐core structures), as verified by conventional observations, satellite imagery, flight‐level and dropsonde data from a research aircraft. It is found from potential vorticity (PV) analysis that the storm reaches its peak intensity as the upper‐level dry PV anomaly, the low‐level moist PV anomaly and surface thermal warmth are vertically superposed. PV inversions reveal that these anomalies contribute about 60%, 30% and 10%, respectively, to the 900‐hPa negative height perturbation. It is shown that the warm‐core structure near the cyclone centre is produced by advection of warmer air ahead of the cold front, rather than by adiabatic warming associated with subsidence.     

Documentation of a highly ENSO‐related sst region in the equatorial pacific: Research note

Abstract

A new ENSO SST index is documented that is strongly correlated to the core ENSO phenomenon. The SST anomaly in much of the east‐central and eastern tropical Pacific is closely related to ENSO. However, the anomaly from approximately the centre of the eastern half of the equatorial Pacific westward to near the date line is suggested to be most strongly ENSO‐related when data spanning the most recent several decades are used. This is the case both with respect to (1) strength of association with other oceanic/atmospheric ENSO‐related anomalies (both simultaneously and as a time‐delayed predictand), and (2) impact on remote worldwide climate anomalies. This observational insight was lacking in the early 1980s when the four “Niño” regions were developed. While a firmer dynamical foundation for this regional preference still needs to be established, the region straddling Niño 3 and Niño 4 may be regarded as an appropriate general SST index of the ENSO state by researchers, diagnosticians and forecasters. A dataset of this index, called “Niño 3.4” (5°N‐5°S, 120–170°W), is maintained on the Internet, shown in the Climate Diagnostics Bulletin, and provided in the Appendix of this note.     

Circulation effect: response of precipitation δ18O to the ENSO cycle in monsoon regions of China

Inter-annual variation in the ratio of ¹⁸O to ¹⁶O of precipitation (δ¹⁸O_p) in the monsoon regions of China (MRC, area approximately east of 100°E) has not yet been fully analyzed. Based on an analysis of the relationships between the time series of amount-weighted mean annual δ¹⁸O in precipitation (δ¹⁸O_w) and meteorological variables such as temperature, precipitation as well as atmospheric/oceanic circulation indices, it is recognized that the El Niño-Southern Oscillation (ENSO) cycle appears to be the dominant control on the inter-annual variation in δ¹⁸O_p in the MRC. Further analysis shows that the trade wind plays a role in governing δ¹⁸O_w through affecting the intensity of the different summer monsoon circulations which are closely linked to the weakening (weaker than normal) and strengthening (stronger than normal) of the trade wind and gives the δ¹⁸O_w different values at or over inter-annual timescales. The southwest monsoon (SWM) drives long-distance transport of water vapor from Indian Ocean to the MRC, and along this pathway increasing rainout leads to more negative δ¹⁸O_w via Rayleigh distillation processes. In contrast, the southeast monsoon (SEM), which is consistent with the changes in the strength of the West Pacific subtropical high, drives short-distance water vapor transport from the West Pacific Ocean to the MRC and leads to less negative δ¹⁸O_w. Therefore, the δ¹⁸O_w value directly reflects the differences in influence between the SWM, which is strong when the SE trade wind is strong, and the SEM, which is strong when the SE trade wind is weak. In addition, the South China Sea Monsoon also transports local water vapor as well as plays a role in achieving the synchronization between the δ¹⁸O_w and ENSO. The author thus terms the δ¹⁸O_p rhythm in the MRC the “circulation effect”. In turn, the δ¹⁸O_p variation in the MRC has the potential to provide information on atmospheric circulation and the signal of δ¹⁸O_p recorded in natural archives can then be used to deduce a long-term behavior of the tropical climate system.     

Decadal‐to‐interdecadal fluctuations of arctic sea‐ice cover and the atmospheric circulation during 1954–1994

Abstract

The relationship between the Arctic and subarctic sea‐ice concentration (SIC) anomalies, particularly those associated with the decadal‐scale Greenland and Labrador Seas “Ice and Salinity Anomalies (ISAs) “, and the overlying atmospheric circulation fluctuations is investigated using the singular value decomposition (SVD) and composite map analysis methods. The data analyzed are monthly SIC and sea level pressure (SLP) anomalies, which cover the northern hemisphere poleward of 45°N and extend over the 41‐year period 1954–1994.

The SVD₁ (first) mode of the coupled variability, which accounts for 57% of the square covariance, is for the most part an atmosphere‐to‐ice forcing mode characterized by the decadal timescale. The aforementioned ISA anomalies are clearly captured by this mode whose SIC anomalies are dominated by a strong dipole across Greenland. However, as part of the same mode, there is also a weaker SIC dipole in the northern North Pacific which has opposite‐signed anomalies in the Sea of Okhotsk and the Bering Sea. It is also shown that there exists a significant negative correlation between the decadal SIC variability in the Greenland‐Barents Seas region associated with this mode and the North Atlantic Oscillation, whose spectrum also exhibits a quasi‐decadal signal.

The SVD₂ mode accounts for 12% of the square covariance and shows no evidence of a dominant forcing field of either SIC or SLP. This SVD mode exhibits very low frequency (interdecadal) variability, and its co‐variability is mainly concentrated in the northern North Pacific. It appears to be a high‐latitude extension of the recently investigated interdecadal North Pacific Oscillation. The spatial structure of the second mode complements the case of the first SVD mode whose co‐variability mainly occurs in the northern North Atlantic.     

MANTRA ‐ A Balloon Mission to Study the Odd‐Nitrogen Budget of the Stratosphere

Abstract

The Middle Atmosphere Nitrogen TRend Assessment (MANTRA) series of high‐altitude balloon flights is being undertaken to investigate changes in the concentrations of northern hemisphere mid‐latitude stratospheric ozone, and of nitrogen and chlorine compounds that play a role in ozone chemistry. Four campaigns have been carried out to date, all from Vanscoy, Saskatchewan, Canada (52°01'N, 107°02'W, 511.0 m). The first MANTRA mission took place in August 1998, with the balloon flight on 24 August 1998 being the first Canadian launch of a large high‐altitude balloon in about fifteen years. The balloon carried a payload of instruments to measure atmospheric composition, and made measurements from a float altitude of 32–38 km for one day. Three of these instruments had been flown on the Stratoprobe flights of the Atmospheric Environment Service (now the Meteorological Service of Canada) in the 1970s and early 1980s, providing a link to historical data predating the onset of mid‐latitude ozone loss.

The primary measurements obtained from the balloon‐borne instruments were vertical profiles of ozone, NO₂, HNO₃, HCl, CFC‐11, CFC‐12, N₂O, CH₄, temperature, and aerosol backscatter. Total column measurements of ozone, NO₂, SO₂, and aerosol optical depth were made by three ground‐based spectrometers deployed during the campaign. Regular ozonesonde and radiosonde launches were also conducted during the two weeks prior to the main launch in order to characterize the local atmospheric conditions (winds, pressure, temperature, humidity) in the vicinity of the primary balloon flight. The data have been compared with the Model for Evaluating oZONe Trends (MEZON) chemical transport model, the University of California at Irvine photochemical box model, and the Canadian Middle Atmosphere Model (CMAM) to test our current understanding of model photochemistry and mid‐latitude species correlations. This paper provides an overview of the MANTRA 1998 mission, and serves as an introduction to the accompanying papers in this issue of Atmosphere‐Ocean that describe specific aspects and results of this campaign.     

Low-frequency oscillations of the East Asia–Pacific teleconnection pattern and their impacts on persistent heavy precipitation in the Yangtze–Huai River valley

Based on the daily reanalysis data from NCEP NCAR and daily precipitation data from the China National Meteorological Information Center,an ensemble empirical mode decomposition method is employed to extract the predominant oscillation modes of the East Asia Pacific(EAP) teleconnection pattern.The influences of these low-frequency modes on persistent heavy precipitation in the Yangtze Huai River(YHR)valley are investigated.The results indicate that the EAP pattern and rainfall in YHR valley both exhibit remarkable 10 30- and 30 60-day oscillations.The impacts of the EAP pattern on the YHR persistent heavy precipitation can be found on both the 10 30- and 30 60-day timescales the 10 30-day scale for most cases.Composite analysis indicates that,on the 10 30-day timescale,formation of the EAP pattern in the lower and middle troposphere is determined by convective systems near the tropical western Pacific;whereas in the middle troposphere,the phase transition is jointly contributed by both the dispersion of zonal wave energies at higher latitudes and convective systems over the South China Sea.In the context of the10 30-day EAP pattern,the anomalously abundant moisture is transported by an anomalous subtropical anticyclone system,and strong moisture convergence results from that anomalous anticyclone system and a cyclonic system in the midlatitude East Asia.Such a combination of systems persists for at least three days,contributing to the formation of persistent heavy precipitation in the YHR valley.     

Are band-pass variance statistics useful measures of storm track activity? Re-examining storm track variability associated with the NAO using multiple storm track measures

Over the past few decades, band-pass filtered (BP) variance statistics have been widely used as indicators of storm track activity. A recent study suggested that these statistics may be subjected to biases related to Doppler shifting of variance into and out of the fixed frequency band, in the process perhaps greatly exaggerating the correlation between BP variance and mean flow variability. In this study, BP statistics are examined together with other storm track measures to assess whether BP variances are useful indicators of the patterns of storm track activity. Storm track variability related to the North Atlantic Oscillation, as well as the five leading EOFs of 300 hPa BP filtered variance statistics, have been examined. Results presented here suggest that BP variance statistics are useful measures of the patterns of storm track activity. Firstly, BP variance statistics largely reflect changes in total unfiltered transient eddy variance as well as spatially filtered statistics. Secondly, different BP statistics all give qualitatively similar patterns. Thirdly, patterns derived from BP statistics are well correlated (spatially) with precipitation anomalies. In addition, BP statistics are straightforward to compute, and easily reproducible. Moreover, BP variance and covariance statistics are closely related to how storm tracks interact with the large scale circulation. However, results shown in this paper support the suggestion that some biases may be caused by the Doppler effect, especially for variations such as the NAO which are tightly tied to changes in the background flow speed. Thus it is argued that BP statistics should be examined together with other measures of storm track activity to obtain a broader perspective on storm track variations.     

Sensitivity of the CRCM atmospheric and the Gulf of St. Lawrence Ocean‐Ice models to each other

Abstract

The sensitivity of the Canadian Regional Climate Model (CRCM), developed at the Université du Québec à Montréal, and the Gulf of St. Lawrence Ocean Model (GOM), developed at the Institut Maurice‐ Lamontagne, to each other is tested with an ensemble of simulations over eastern Canada from 1 November 1989 to 31 March 1990. The goal of this study is to investigate the interaction of the CRCM and GOM with respect to each other's forcing fields. In the first part of the experiment, a series of simulations were performed using an iterative strategy, where both models run separately and alternately, using variables from the other model to supply the needed forcing fields for the computation of surface fluxes. The runs are iterated several times over the same period from the output of the previous run to allow the atmosphere and the ocean to interact several times with each other and to study the evolution of the solutions from one iteration to the next. In the second part of the experiment, a two‐way coupled simulation is performed over the same period. The results indicate that on a monthly or longer timescale, the CRCM is not very sensitive to the details of the oceanic fields from GOM, except locally over the Gulf of St. Lawrence (GSL). However, GOM is quite sensitive to the differences in atmospheric fields from the CRCM. The results of several iterations converge to a unique solution, suggesting that the CRCM and GOM reach equilibrium with respect to each other's forcing fields. Furthermore, the results of the coupled run also converge to this same solution.     

Sensitivity of precipitation to sea surface temperature over the tropical summer monsoon region—and its quantification

Over the tropical oceans, higher sea surface temperatures (SST, above 26 °C) in summer are generally accompanied by increased precipitation. However, it has been argued for the last three decades that, any monotonic increase in precipitation with respect to SST is limited to an upper threshold of 28–29.5 °C, and beyond this, the relationship fails. Based on this assessment it has often been presumed that, since the mean SSTs over the Asian monsoon basins (Indian Ocean and north-west Pacific) are mostly above the threshold, SST does not play an active role on the summer monsoon variability. It also implies that increasing SSTs due to a changing climate need not result in increasing monsoon precipitation. The current study shows that the response of precipitation to SST has a time lag, that too with a spatial variability over the monsoon basins. Taking this lag into account, the results here show that enhanced convection occurs even up to the SST maxima of 31 °C averaged over these basins, challenging any claim of an upper threshold for the SST-convection variability. The study provides us with a novel method to quantify the SST-precipitation relationship. The rate of increase is similar across the basins, with precipitation increasing at ~2 mm day^?1 for an increase of 1 °C in SST. This means that even the high SSTs over the monsoon basins do play an active role on the monsoon variability, challenging previous assumptions. Since the response of precipitation to SST variability is visible in a few days, it would also imply that including realistic ocean–atmosphere coupling is crucial even for short term monsoon weather forecasts. Though recent studies suggest a weakening of the monsoon circulation over the last few decades, results here suggest an increased precipitation over the tropical monsoon regions, in a global warming environment with increased SSTs. Thus the signature of SST is found to be significant for the Asian summer monsoon, in a quantifiable manner, seamlessly through all the timescales—from short-term intraseasonal to long-term climate scales.     

Is the Western Himalayan region vulnerable with respect to downscaled precipitation?

Theoretical and Applied Climatology - Statistical downscaling is the technique of linking large-scale predictors and local-scale predictands through a relationship that is assumed to be helpful to...