Variations Of Meteorological Parameters Research Articles

Simulation of the interannual variations of tropospheric ozone over China: Roles of variations in meteorological parameters and anthropogenic emissions

Abstract We quantify the interannual variations (IAVs) of tropospheric O3 over China for the years 2004–2012 by using the one-way nested-grid version of the global three-dimensional Goddard Earth Observing System chemical transport model (GEOS-Chem). The roles of variations in meteorological fields and anthropogenic emissions of O3 precursors are examined separately and together through sensitivity simulations. With variations in both meteorological parameters and emissions, simulated seasonal mean surface-layer O3 concentrations over North China (NC, 110–120°E, 32–42°N) exhibit the largest IAVs in June–July–August (JJA). The regionally averaged absolute percent departure from the mean (APDM) values over NC are 0.7%, 3.2%, 3.9%, and 2.1% in December–January–February (DJF), March–April–May (MAM), and September–October–November (SON), respectively. Over South China (SC, 110–120°E, 22–32°N), the IAVs of O3 are found maximum in MAM, and minimum in JJA; the APDM values are 2.7%, 3.7%, 1.4%, and 2.6% in DJF, MAM, JJA, and SON, respectively. With respect to the IAVs of O3 over the Sichuan Basin (SCB, 102–110°E, 27–33°N), the APDM values are simulated to be 2.7–3.8% throughout the year. The IAVs in surface-layer O3 by variations in meteorological fields are simulated to be larger than those by variations in anthropogenic emissions throughout the year in NC and SC except for JJA in SC. The relatively more important role of variations in anthropogenic emissions is simulated in SCB in all seasons. Process analyses are performed to identify key meteorological parameters that influence the IAVs of O3 over NC, SC, and SCB. Over all of these regions, variations in winds are found to have the largest impact on the IAVs of O3, followed by those in temperature and specific humidity. Considering that the APDM values represent the IAVs averaged over 2004–2012, the magnitudes of IAVs of O3 for specific years can be more significant than the numbers reported here. Our results have important implications for the effectiveness of short-term air quality control strategies in China.

Analysis of meteorological parameters for dense gas dispersion using mesoscale models

The current study focuses on characterizing the atmospheric details required for dense gas dispersion analysis resulting from release of cryogenic liquids like LNG. The study investigates the effectiveness of coupling the prognostic MM5 mesoscale model with the CALMET diagnostic model for producing meteorological conditions that is characteristic of dry and arid regions like Qatar, with non-neutral boundary conditions. MM5-CALMET wind fields and temperature data are compared with the meteorological field observations from the Doha International Airport (DIA) on a monthly basis, daily basis and hourly basis to study the effect of different averaging periods. The monthly averages replicate the annual patterns of meteorological parameters very well. However difference in observation and model are observed for wind speed and wind direction variable. The daily averages obtained from the model are in good agreement with the observation for wind speed and temperature. For hourly averaging, the model is found capable of mimicking the temperature of a given location, but not wind speed and direction. The prediction of wind direction parameter using MM5-CALMET is moderate for any averaging period. The sub-optimal performance of wind direction variable is attributed to grid resolution of vertical and horizontal layers of MM5-CALMET model. Additionally a case study is performed to illustrate the effect of variation of meteorological parameters on the lower flammability limits (LFL) resulting from flammable dense gas release of LNG. The case study demonstrates the issues that arise in a risk analysis study when “wrong” meteorological data could be used. The overall study indicates that utilizing the coarsest prognostic meteorological model output in a diagnostic model provides an effective option for generating meteorological inputs for dispersion studies.

Impact of Meteorological Parameters and Gaseous Pollutants on PM2.5 and PM10 Mass Concentrations during 2010 in Xi’an, China

ABSTRACTMass concentrations of PM2.5 and PM10 from the six urban/rural sampling sites of Xi’an were obtained during two weeks of every month corresponding to January, April, July and October during 2010, together with the six meteorological parameters and the data of two precursors. The result showed that the average annual mass concentrations of PM2.5 and PM10 were 140.9 ± 108.9 µg m–3 and 257.8 ± 194.7 µg m–3, respectively. Basin terrain constrains the diffusion of PM2.5 and PM10 concentration spatially. High concentrations in wintertime and low concentrations in summertime are due to seasonal variations of meteorological parameters and cyclic changes of precursors (SO2 and NO2). Stepwise Multiple Linear Regression (MLR) analysis indicates that relative humidity is the main factor influencing on meteorological parameter. Entry MLR analysis suggests that SO2 from local coal-burning power plants is still the primary pollutant. Trajectory cluster results of PM2.5 at BRR indicate that the entrained urban pollutants carried by the westerly or winter monsoon forms the dominant regional pollution sources in winter and spring. Ultraviolet (UV) aerosol index verified the source and pathway of dust storm in spring.

Decadal trend and interannual variation of outflow of aerosols from East Asia: Roles of variations in meteorological parameters and emissions

We apply a global three-dimensional Goddard Earth Observing System (GEOS) chemical transport model (GEOS-Chem) to quantify the decadal trend and interannual variation of aerosol outflow from East Asia. Simulations of aerosols are performed for years 1986–2006, driven by the NASA/GEOS-4 assimilated meteorological fields. The impacts of variations in meteorological parameters and emissions are imposed separately and together by numerical experiments. With variations in both meteorological parameters and anthropogenic emissions, simulated annual outflow of PM2.5 (sum of sulfate, nitrate, ammonium, black carbon, and organic carbon) from East Asia increased by 6.0 Tg (or 53%) over years 1986–2006, in which the outflow fluxes of sulfate, nitrate, and ammonium aerosols had the largest contributions with decadal trends of +1.2, +0.8, and +0.7 Tg decade−1, respectively. Simulated outflow fluxes of aerosols also exhibited large interannual variations; the absolute percent departure from the mean (APDM) values of the annual outflow fluxes of sulfate, nitrate, ammonium, black carbon, organic carbon, and PM2.5 were 5.9%, 7.9%, 5.4%, 5.8%, 4.2%, and 5.2%, respectively, as variations in both meteorological parameters and anthropogenic emissions were considered. Model sensitivity studies show that, for outflow fluxes of aerosols from East Asia, the decadal trends were driven by variations in anthropogenic emissions whereas the interannual variations were dominated by variations in meteorological parameters. The increases in anthropogenic emissions alone explained about 86% of the decadal trend in outflow of PM2.5. Although variations in meteorological parameters can influence the interannual variations in aerosol outflow by changing both aerosol concentrations over East Asia and zonal winds, the latter is identified to be the key factor because of the high positive correlation coefficient between the annual outflow flux of PM2.5 and zonal wind at 700 hPa (the altitude with the maximum outflow fluxes) for years 1986–2006.

Effects of meteorology and secondary particle formation on visibility during heavy haze events in Beijing, China

The causes of haze formation in Beijing, China were analyzed based on a comprehensive measurement, including PBL (planetary boundary layer), aerosol composition and concentrations, and several important meteorological parameters such as visibility, RH (relative humidity), and wind speed/direction. The measurement was conducted in an urban location from Nov. 16, 2012 to Jan. 15, 2013. During the period, the visibility varied from >20km to less than a kilometer, with a minimum visibility of 667m, causing 16 haze occurrences. During the haze occurrences, the wind speeds were less than 1m/s, and the concentrations of PM2.5 (particle matter with radius less than 2.5μm) were often exceeded 200μg/m3. The correlation between PM2.5 concentration and visibility under different RH values shows that visibility was exponentially decreased with the increase of PM2.5 concentrations when RH was less than 80%. However, when RH was higher than 80%, the relationship was no longer to follow the exponentially decreasing trend, and the visibility maintained in very low values, even with low PM2.5 concentrations. Under this condition, the hygroscopic growth of particles played important roles, and a large amount of water vapor acted as particle matter (PM) for the reduction of visibility. The variations of meteorological parameters (RH, PBL heights, and WS (wind speed)), chemical species in gas-phase (CO, O3, SO2, and NOx), and gas-phase to particle-phase conversions under different visibility ranges were analyzed. The results show that from high visibility (>20km) to low visibility (<2km), the averaged PBL decreased from 1.24km to 0.53km; wind speeds reduced from 1m/s to 0.5m/s; and CO increased from 0.5ppmv to 4.0ppmv, suggesting that weaker transport/diffusion caused the haze occurrences. This study also found that the formation of SPM (secondary particle matter) was accelerated in the haze events. The conversions between SO2 and SO4 as well as NOx to NO3− increased, especially under high humidity conditions. When the averaged RH was 70%, the conversions between SO2 and SO4 accounted for about 20% concentration of PM2.5, indicating that formation of secondary particle matter had important contribution for the haze occurrences in Beijing.

Simulation of the interannual variations of aerosols in China: role of variations in meteorological parameters

Abstract. We used the nested grid version of the global three-dimensional Goddard Earth Observing System chemical transport model (GEOS-Chem) to examine the interannual variations (IAVs) of aerosols over heavily polluted regions in China for years 2004–2012. The role of variations in meteorological parameters was quantified by a simulation with fixed anthropogenic emissions at year 2006 levels and changes in meteorological parameters over 2004–2012. Simulated PM2.5 (particles with a diameter of 2.5 μm or less) aerosol concentrations exhibited large IAVs in North China (NC; 32–42° N, 110–120° E), with regionally averaged absolute percent departure from the mean (APDM) values of 17, 14, 14, and 11% in December-January-February (DJF), March-April-May (MAM), June-July-August (JJA), and September-October-November (SON), respectively. Over South China (SC; 22–32° N, 110–120° E), the IAVs in PM2.5 were found to be the largest in JJA, with the regional mean APDM values of 14% in JJA and of about 9% in other seasons. The concentrations of PM2.5 over the Sichuan Basin (SCB; 27–33° N, 102–110° E) were simulated to have the smallest IAVs among the polluted regions examined in this work, with APDM values of 8–9% in all seasons. All aerosol species (sulfate, nitrate, ammonium, black carbon, and organic carbon) were simulated to have the largest IAVs over NC in DJF, corresponding to the large variations in meteorological parameters over NC in this season. Process analyses were performed to identify the key meteorological parameters that determined the IAVs of different aerosol species in different regions. While the variations in temperature and specific humidity, which influenced the gas-phase formation of sulfate, jointly determined the IAVs of sulfate over NC in both DJF and JJA, wind (or convergence of wind) in DJF and precipitation in JJA were the dominant meteorological factors to influence IAVs of sulfate over SC and the SCB. The IAVs in temperature and specific humidity influenced gas-to-aerosol partitioning, which were the major factors that led to the IAVs of nitrate aerosol in China. The IAVs in wind and precipitation were found to drive the IAVs of organic carbon aerosol. We also compared the IAVs of aerosols simulated with variations in meteorological parameters alone with those simulated with variations in anthropogenic emissions alone; the variations in meteorological fields were found to dominate the IAVs of aerosols in northern and southern China over 2004–2012. Considering that the IAVs in meteorological fields are mainly associated with natural variability in the climate system, the IAVs in aerosol concentrations driven by meteorological parameters have important implications for the effectiveness of short-term air quality control strategies in China.

Effect of inter and intra seasonal variability in meteorological parameters on rice productivity in central Punjab

A study was conducted to ascertain the role of meteorological parameters on year to year variability in rice yield in Punjab using 12 years (2000-11) data of Ludhiana district. The rice growing season was divided into three stages (entire rice season, vegetative stage and reproductive stage) and the meteorological data during these stages were correlated with the rice yields. Highly significant (p=0.05) positive correlation was noticed between grain yield and sunshine hours received during entire rice season and vegetative stage of the crop. The maximum temperature during entire rice season and vegetative stage was significantly (p=0.10) and positively correlated with grain yield. During all three stages maximum relative humidity had significantly negative correlation with grain yield. Rainfall during vegetative stage and number of rainy days during reproductive stage were significantly and negatively correlated with grain yield. After studying the deviation of meteorological parameters from respective normals during high and low yield years and the correlation of meteorological parameters with rice yield it can be concluded that in the central parts of the Punjab sunshine hours play a major role in determining the productivity of rice.

Precipitable water vapor estimation in India from GPS-derived zenith delays using radiosonde data

One of the most recent applications of global positioning system (GPS) is the estimation of precipitable water vapor (PWV). It requires proper modeling to extract PWV from zenith wet delay (ZWD). The existing global models take no account of latitudinal and seasonal variation of meteorological parameters in the atmosphere. In fact, they ignore the atmospheric conditions at a specific location. Therefore, site-specific PWV models have been developed for five stations spread over the Indian subcontinent, using 3-year (2006–2008) radiosonde data from each of these stations. Furthermore, a similar regional PWV model is also developed for the Indian region. The purpose of the developed site-specific as well as regional model was to convert ZWDs into PWV without using surface meteorological parameters. It has been found that the developed regional and site-specific PWV models show about mm-level accuracy in estimating PWV using derived ZWD from radiosonde as input. The developed site-specific, regional models were also used to extract PWV from GPS-derived ZWD at Bangalore and New Delhi. The accuracy of the developed site-specific and regional model is of the same level. The PWV accuracy obtained with the developed regional model is about 6.28, 6.6 mm in comparison to radiosonde PWV at Bangalore and New Delhi, respectively.

Measurements of ozone and its precursor nitrogen dioxide and crop yield losses due to cumulative ozone exposures over 40 ppb (AOT40) in rural coastal southern India

Measurements of ground level ozone (O3), nitrogen dioxide (NO2) and meteorological parameters (air temperature, relative humidity and wind speed and direction) has been made for 3 years from March 2007 to February 2010 at Nagercoil (8.2°N, 77.5°E, 23 m above sea level), an equatorial rural coastal site of southern India. The monthly average of daytime maximum of O3 concentrations ranged from 28 to 50 parts per billion (ppb) with an annual average of 19.8 ppb. Similarly, monthly average of NO2 concentration ranged from 3.4 ppb to 7.7 ppb with an annual average of 5.3 ppb. The monthly variation of meteorological parameters shows the little changes being a coastal site. The estimated summer crops yield losses by 1.1–15.6 % from present O3 concentration level associated with AOT40 index 3.1–5 ppm h.

Total water vapor content retrieval from sun photometer data

Simulation of Sun photometer measurements for two regions of Russia is made and total water vapor content retrieval errors, caused by variations in meteorological parameters and the application of empirical formulas used in AERONET, are estimated.

Variations in the quasi-static electric field in the near-Earth’s atmosphere during geomagnetic storms in November 2004

The effects of the geomagnetic storms of November 8 and 10, 2004, in variations in the strength and power spectra of the electric field in the near-Earth’s atmosphere in Kamchatka were studied, together with the meteorological and geophysical phenomena observed simultaneously. A sequence of strong solar flares was shown to cause an anomalous increase in air temperature and humidity. This resulted in the excitation of anomalously strong thunderstorm processes in the atmosphere during the storm of November 8 and made it impossible to distinguish the effects associated with cosmic rays on this background. During the storm of November 10, on the background of weak variations in meteorological parameters, an increase in the strength and intensity of power spectra of the electric field on the day before the storm of November 10 was detected; it was followed by an attenuation of these parameters on the date of the storm. These effects were supposed to be associated with the action of cosmic rays on currents of the global electric circuit. It was shown that the influence of the Forbush effect of galactic cosmic rays in the power spectrum of the electric field first of all shows as the amplification of the component with the period T ∼ 48 h; in variations in humidity, the effect shows as the amplification of the component with T ∼ 24 h. Cause-and-effect relationships between variations in the electric field strength and the horizontal component of the geomagnetic field were shown to be absent both under the conditions of “fair weather” and during the storm of November 10. A diurnal negative-difference atmospheric pressure was detected on the second day after the geomagnetic storms of November 8 and 10.

The wind chill temperature effect on a large‐scale PV plant—an exergy approach

ABSTRACTIn this paper, a detailed exergetic analysis based on the variation of meteorological parameters was performed for a solar power generation system. All wind and solar energy and exergy characteristics were examined in order to identify the variables that affect the power output of the photovoltaic (PV) system. Atmospheric variables such as air temperature, humidity and wind speed and their effects, shadow effects, tracking losses, and low radiation losses of the PV power output were investigated aiming at identifying the real and net solar energy output. It was shown that some usually disregarded atmospheric variables in planning new PV plants, in fact, do play a significant role on the plant's overall exergetic efficiency as wind chill temperature. The solar potential around a windy coastal hilly area was studied and presented on the basis of field measurements and simulations. Understanding atmospheric parameters variation appears to be of great importance for estimating correctly and trustworthy the energy yield, and special focus was given to that in this paper. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Peculiarities of approximation of meteorological characteristics having vertical gradient discontinuities close to the tropopause

Carried out is an analysis of errors of different approximation methods for separating the long- and short-wave parts of the spectra of the vertical distribution of meteorological variables and gas components in the areas of dramatic variations of their vertical gradients close to the tropopause. Proposed is an integrated approach using the polynomial, piecewise-linear, and spectral filtration and enabling to minimize the errors of approximation of long- and short-wave components of profiles of meteorological characteristics in the troposphere and stratosphere including the tropopause area. The method is useful for analyzing the mean values and mesoscale variations of meteorological parameters measured by the modern balloon and satellite systems.

In situ measurements of radon levels in water and soil and exhalation rate in areas of Malwa belt of Punjab (India)

Radon concentration levels in water and soil gas from 36 locations pertaining to some areas of Malwa region of Punjab have been measured on an in situ basis using a continuous active radon detector (AlphaGuard, Model – PQ 2000 PRO, Genitron instruments, Germany). Exhalation rate measurements have also been carried out at these places, using a closed-circuit technique. The radon concentrations in soil and water varied from 1.9 to 16.4 kBq m−3 and 5.01 to 11.6 kBq m−3, respectively. The exhalation rate (E Rn) ranged between 7.48 and 35.88 mBq m−2 s−1 with an average value of 18.17 mBq m−2 s−1. Annual dose rates have been calculated for water radon concentrations. The minimum to maximum values of dose rates were found to be 13.42–31.08 μSv y−1. The recorded values of radon concentration in water are within the safe limit of 11 Bq l−1 recommended by the US Environment Protection Agency [National Research Council, Risk Assessment of Radon in Drinking Water (Academy Press, Washington, DC, USA, 1999)]. All measurements were made in similar climatic and environmental conditions to ensure minimal variations in meteorological parameters. An intermediate correlation coefficient (0.5) was observed between radon exhalation rates and soil gas values.

Aerosol optical thickness and the total carbon monoxide content over the European Russia territory in the 2010 summer period of mass fires: Interrelation between the variation in pollutants and meteorological parameters

The spatial and temporal variabilities of the aerosol optical thickness (AOT) and the total carbon monoxide content (CO) in the period of development and weakening of mass forest and peatbog fires in the European Russia territory (ERT) in the summer of 2010 are investigated from data of the AOT and CO satellite observations. The intensities of aerosol and CO emissions in the period of mass fires and the ratio of the emission factors of aerosol particles and CO are estimated on the basis of calculations of the smoke and CO masses over the ERT. The interrelation between variations in the levels of the regional pollution by combustion products and the variability of meteorological parameters is investigated. Various aspects of the manifestation of radiation effects of aerosols are discussed. The synchronization of weekly signals of the AOT, CO, and meteorological parameters in the period of mass fires is noted.

How barley growing conditions and its output change in Hungary

There is no doubt that climate change has started. It is very important to make effort in developing impact analyses and adaptation strategies. First we were investigated how the production risk of winter barley is changing with time using the E,V efficiency criterion. Based on the regional yearly production data of the crop, we can conclude that beside other non-climatic effects, the changing climate has considerable impact on crops yield; its variability is increasing with the variability of meteorological parameters. We have used production data from 1951 to nowadays. Next, using comparison analyses for climate scenarios, we predict what we can expect in the future. For detecting the reasons of risk increase in the past, and forecasting the potential main points of future risk we have analysed statistically whether the climate needs of winter barley will be satisfied or not in its important periods of growing. Frequency calculations were made based on the daily meteorological data. The situation doesn’t show big change, but It is no doubt that the anomalies of the indicators have been becoming more and more frequent. The more frequent the extreme weather events are, the more we can be convinced of uncertainty.

Characteristics of major secondary ions in typical polluted atmospheric aerosols during autumn in central Taiwan

In autumn of 2008, the chemical characteristics of major secondary ionic aerosols at a suburban site in central Taiwan were measured during an annually occurring season of high pollution. The semicontinuous measurement system measured major soluble inorganic species, including NH4+, NO3−, and SO42−, in PM10 with a 15 min resolution time. The atmospheric conditions, except for the influences of typhoons, were dominated by the local sea-land breeze with clear diurnal variations of meteorological parameters and air pollutant concentrations. To evaluate secondary aerosol formation at different ozone levels, daily ozone maximum concentration (O3,daily max) was used as an index of photochemical activity for dividing between the heavily polluted period (O3,daily max ≧80 ppb) and the lightly polluted period (O3,daily max<80 ppb). The concentrations of PM10, NO3−, SO42−, NH4+ and total major ions during the heavily polluted period were 1.6, 1.9, 2.4, 2.7 and 2.3 times the concentrations during the lightly polluted period, respectively. Results showed that the daily maximum concentrations of PM10 occurred around midnight and the daily maximum ozone concentration occurred during daytime. The average concentration of SO2 was higher during daytime, which could be explained by the transportation of coastal industry emissions to the sampling site. In contrast, the high concentration of NO2 at night was due to the land breeze flow that transport inland urban air masses toward this site. The simulations of breeze circulations and transitions were reflected in transports and distributions of these pollutants. During heavily polluted periods, NO3− and NH4+ showed a clear diurnal variations with lower concentrations after midday, possibly due to the thermal volatilization of NH4NO3 during daytime and transport of inland urban plume at night. The diurnal variation of PM10 showed the similar pattern to that of NO3− and NH4+ aerosols. This indicated that the formatted secondary aerosols in the inland urban area could be transported to the coastal area by the weak land breeze and deteriorated the air quality in the coastal area at night.

Variation of meteorological parameters over Saudi Arabia (1990‐2006)

The annual and seasonal variation of meteorological parameters has been studied for twenty stations in Saudi Arabia. The contour maps showed temperature and rainfall increasing and wind speed decreasing trends with decreasing latitudes. The mean temperature varied between a minimum of 8.4°C and a maximum of 34.61°C while overall mean was 23.95°C. The Mean, minimum and maximum values of pressure were 932.12, 923.3 and 944.6mb, respectively. The corresponding relative humidity values were 42.7, 78.5 and 21.5%, respectively. The empirical models developed for the prediction of monthly mean values of individual parameters were able to estimate the values with acceptable accuracy

Water-soluble organic compounds at a mountain-top site in Colorado, USA

Water extracts of atmospheric particulate matter (PM 2.5) collected at the Storm Peak Laboratory (SPL) (3210 MSL, 40.45° N, 106.74° W) were analyzed for a wide variety of polar organic compounds. The unique geographical character of SPL allows for extended observations/sampling of the free tropospheric interface. Under variable meteorological conditions between January 9th and January14th 2007, the most abundant compounds were levoglucosan (9–72 ng m −3), palmitic acid (10–40 ng m −3) and succinic acid (18–27 ng m −3). Of 84 analytes included in the GC–MS method, over 50 individual water extractable polar organic compounds (POC) were present at concentrations greater than 0.1 ng m −3. During a snow event (Jan. 11th–13th), the concentrations of several presumed atmospheric transformation compounds (dicarboxylic acids) were reduced. Lower actinic flux, reduced transport distance, and ice crystal scavenging may explain this variability. Diurnal averages over the sampling period revealed a higher total concentration of water extractable POC at night, 211 ng m −3 (105–265 ng m −3), versus day, 160 ng m −3 (137–205 ng m −3), which suggests a more aged nighttime aerosol character. This may be due to the increased daytime convective mixing of local primary emissions from the Yampa Valley. XAD resin extracts revealed a gas-phase partitioning of several compounds, and analysis of cloud water collected at this site in 2002 revealed a similar compound abundance trend. Levoglucosan, a wood smoke tracer was generally found to be the most abundant compound in both aerosol and cloud water samples. Variations in meteorological parameters and local/regional transport analysis play an important interpretive role in understanding these results.

Effect of inter- and intra-seasonal variations in meteorological parameters on wheat yields in Punjab

A study was conducted to evaluate the effect of variations in meteorological parameters on wheat (Triticum aestivum L. emend. Flori &amp; Paol) yields during 1970-2005 and also as simulated with CERES-wheat model. The technology trend model of historical wheat yields in Punjab indicated that over the past 2 to 3 decades, at Ballowal Saunkhri, Amritsar, Ludhiana, Patiala and Bathinda the wheat yields have increased @ 64.2, 76.3, 62.8, 87.3 and 71.1 kg/ ha/year respectively. An analysis of historical meteorological data and past wheat yields revealed that for January, February and March the most favourable maximum temperatures for wheat yields were in the range of 16.1-18.0 oC, &lt;21.0 oC and 28.1-30.0 oC respectively while minimum temperatures were in the range of 3.1-5.0 oC, 5.1-7.0 oC and 11.1- 13.0 oC respectively. The simulation study using CERES-wheat model revealed that the temperature increase mostly affected the early (October) sown crop during fourth week of January up to first fortnight of March; the timely (November) sown crop during February and March; the late (fourth week of November) sown crop during March; and very late(December) sown crop during March and first week of April. An analysis of historical wheat yields and weekly meteorological parameters at Ludhiana revealed that during the high yield (&gt;5 000 kg/ha) crop years, the maximum and minimum temperatures remained near normal (+ 2oC); the rainfall was also normal or slightly above/below normal under assured irrigated conditions. From mid-February to March, dry and clear weather proves beneficial for grain filling in wheat. On the other hand, during low yield (&lt;4 600 kg/ha) crop years, although the temperatures were favourable but very heavy rainfall showers were received during the anthesis and grain-filling period of wheat crop. The weather also remained cloudy and sunshine hours were invariably below or near normal while the relative humidity remained above (3-10 %) or near normal during most part of the crop season. Hence, these conditions were ascertained to be the most pertinent reason for relatively low-wheat yields.