Cloud Transmission Estimates of UV-B Erythemal Irradiance

Summary Two UV-Biometer 501A instruments were used to estimate global erythemal irradiance at two locations in southwest Sweden; the Earth Sciences Centre, University of G?teborg (57.69° N; 11.92° E) and the island of Nordkoster, 200 km to the north (58.83° N; 10.72° E). A semi-empirical radiative transfer model was used to calculate the global erythemally effective irradiance under clear skies. A ratio of the hourly measured to clear-sky modelled irradiance was then derived for zenith angles 35–70°. Subsequent comparisons were then made with routine measurements of sunshine duration at G?teborg and sunshine duration, cloud cover, type and height at Nordkoster. Cloud transmission of UV-B irradiance decreases with increasing solar zenith angle, with cloud attenuation being 8% stronger at Nordkoster Island for zenith angles >>;60°. Transmission also decreases with increasing cloud cover such that overcast cloud conditions reduce transmissions by an average of 75%. In addition, cloud type affects the amount of ground incident irradiant flux. Fractus cloud afforded the least UV-B transmission (0.16), while cirrus filaments afforded the most (0.95). The spatial and temporal distribution of clouds appears tobe non-random. Under conditions of 1 to 3 octas, sky cover, clouds appear to be concentrated in line with the sensor and Sun on more occasions than that expected given a random cloud distribution. The same cloud cover condition also resulted in many instances of ground incident irradiance above clear-sky values. The presence of cumuliform clouds appears to increase the likelihood of the latter phenomena. Received January 4, 1998     

The relationship between lightning activity and surface wet bulb temperature and its variation with latitude in Australia

Summary Convective Available Potential Energy (CAPE) is the driving force for thunderstorm development. CAPE is closely controlled by wet bulb temperature. The lightning activity measured by a network of ten lightning flash counters widely distributed across continental Australia was studied as a function of wet bulb temperature. At each of the stations, the monthly total of lightning ground flashes, N, increased sharply with the increase of the monthly mean daily maximum wet bulb temperature, T_w, max. The dependence was strongest in the tropics and became less pronounced at temperate latitudes. In Darwin (latitude 12° S), the lightning ground flash activity increased by over three orders of magnitude over a 7 °C range of T_w, max. The corresponding increases for Coffs Harbour (latitude 30° S) and for Melbourne (latitude 38° S) were about one and a half orders of magnitude and about half an order of magnitude, respectively, each over a 10 °C range of T_w, max. Power law approximations were derived for each of the ten stations and showed that the logarithm of N was directly proportional to the power, P, of T_w, max. The value of P showed a sharp exponential decrease with increasing latitude away from the equator.     

Estimating solar radiation on tilted surfaces with various orientations: a study case in Karaj (Iran)

Summary The aim of this study is the evaluation of models that estimate daily global solar radiation on tilted surfaces from that measured on horizontal surfaces. Global solar radiation incident on a tilted plane consists of three components: beam radiation, diffuse radiation and reflected radiation from the ground. The Klein (1977) method, modified by Andersen (1980), was used for estimating direct solar radiation incident on tilted surfaces and an isotropic model was used for estimating reflected solar radiation incident on a tilted plane. In contrast models for the diffuse radiation component show major differences, which justifies a validation study which has been done. Eight models for derivation of daily slope diffuse irradiance from daily horizontal diffuse irradiance were tested against recorded slope irradiances at Karaj (35°55′ N; 50°56′ E), Iran. The following models were included: Badescu (2002), Tian et al. (2001), Reindl et al. (1990), Skartveit and Olseth (1986), Koronakis (1986), Steven and Unsworth (1980), Hay (1979) and Liu and Jordan (1962). All the models use the same method for calculating beam radiation as well as ground reflected radiation. However, only diffuse component of radiation was compared. Statistical indices showed that Reindl’s model gives the most accurate prediction for the south-facing surface and Koronakis’s model performs best for the west-facing surface. The Relative Root Mean Square Errors (%RMSE), except for Steven and Unsworth’s model that has unacceptable results, for whole data range from 1.02 to 10.42%. In general, Reindl’s model produces the best agreement with the measured tilted data.     

Derivation of Cloud Index from Geostationary Satellites and Application to the Production of Solar Irradiance and Daylight Illuminance Data

Summary  We investigate in the present paper the relationship between satellite count, global irradiance and other solar and illumination resource components, bringing a particular attention to low solar elevation situations (below 20 °) which are very important in northern latitudes. Our investigation is based on data from two geostationary satellites, METEOSAT and GOES, backed by ground measurements in Switzerland and the northeastern USA. The study of different clear sky normalizations lead to the conclusion that a linear correlation between the global clearness index and the irradiance (like the heliosat method) would be inaccurate for low solar elevations, and therefore for high latitude regions. We developed a model that directly relates an elevation dependent clearness index to the could index. This methodology presents a definite advantage because it can be generalized to address the clearness index of other solar radiation components, besides global irradiance, such as direct irradiance, diffuse illuminance, etc. The correlations described in this paper were developed on the data from Geneva (in the frame of the EC program “Satellight”) and evaluated on two other independent data sets (Albany, USA and Lausanne, Switzerland). Their precisions, on a hourly basis, are respectively 30%, 40% and 60% for the global, diffuse and beam components) (90,55 and 95 W/m²). The use of independent data for thederivation and the validation of the models shows thatthose can be used in a wide range of locations, even if the applicability has to be assessed for very different climates. Received June 27, 1998 Revised February 26, 1999     

Vertical ozone distribution characteristics deduced from ∼ 44,000 re-evaluated Umkehr profiles (1957–2000)

Summary Umkehr observations taken during the 1957–2000 period at 15 stations located between 19 and 52° N have been reanalyzed using a significantly improved algorithm-99, developed by DeLuisi and Petropavlovskikh et al. (2000a,b). The alg-99 utilizes new latitudinal and seasonally dependent first guess ozone and temperature profiles, new vector radiative transfer code, complete aerosol corrections, gravimetric corrections, and others. Before reprocessing, all total ozone values as well as the N-values (radiance) readings were thoroughly re-evaluated. For the first time, shifts in the N-values were detected and provisionally corrected. The re-evaluated Umkehr data set was validated against satellite and ground based measurements. The retrievals with alg-99 show much closer agreement with the lidar and SAGE than with the alg-92. Although the latitudinal coverage is limited, this Umkehr data set contains ∼ 44,000 profiles and represent the longest (∼ 40 years) coherent information on the ozone behavior in the stratosphere of the Northern Hemisphere. The 14-months periods following the El-Chichon and the Mt. Pinatubo eruptions were excluded from the analysis. Then the basic climatological characteristics of the vertical ozone distribution in the 44–52° N and more southern locations are described. Some of these characteristics are not well known or impossible to be determined from satellites or single stations. The absolute and relative variability reach their maximum during winter–spring at altitudes below 24 km; the lower stratospheric layers in the middle latitudes contain ∼ 62% of the total ozone and contribute ∼ 57% to its total variability. The layer-5 (between ∼ 24 and 29 km) although containing 20% of the total ozone shows the least fluctuations, no trend and contributes only ∼ 11% to the total ozone variability. Meridional cross-sections from 19 to 52° N of the vertical ozone distribution and its variability illustrate the changes, and show poleward-decreasing altitude of the ozone maximum. The deduced trends above 33 km confirm a strong ozone decline since the mid-1970s of over 5% per decade without significant seasonal differences. In the mid-latitude stations, the decline in the 15–24 km layer is nearly twice as strong in the winter-spring season but much smaller in the summer and fall. The effect of including 1998 and 1999 years with relatively high total ozone data reduces the overall-declining trend. The trends estimated from alg-99 retrievals are statistically not significantly different from those in WMO 1998a; however, they are stronger by about 1% per decade in the lower stratosphere and thus closer to the estimates by sondes. Comparisons of the integrated ozone loss from the Umkehr measurements with the total ozone changes for the same periods at stations with good records show complete concurrence. The altitude and latitude appearances of the long-term geophysical signals like solar (1–2%) and QBO (2–7%) are investigated. Received April 12, 2001 Revised September 19, 2001     

Effect of clouds on UV and total irradiance at Paradise Bay, Antarctic Peninsula, from a summer 2000 campaign

Summary ?The analysis of ground-based measurements of solar erythemal ultraviolet (UV) irradiance with a Solar Light 501 biometer, and total (300–3000 nm) irradiance with an Eppley B&W pyranometer at the Argentine Antarctic Base “Almirante Brown”, Paradise Bay (64.9° S, 62.9° W, 10 m a.s.l.) is presented. Measurement period extends from February 16 to March 28 2000. A relatively high mean albedo and a very clean atmosphere characterise the place. Sky conditions were of generally high cloud cover percentage. Clear-sky irradiance for each day was estimated with model calculations, and the effect of the cloudiness was studied through the ratio of measured to clear-sky value (r). Two particular cases were analysed: overcast sky without precipitation and overcast sky with rain or slight snowfall, the last one presenting frequently dense fog. Total irradiance was more attenuated than UV by the homogeneous cloudiness, obtaining mean r values of 0.54 for erythemal irradiance and 0.30 for total irradiance in the first case (without precipitation) and 0.27 and 0.17 respectively in the second case (with precipitation). Mean r values for the complete period were 0.58 for erythemal irradiance and 0.43 for total irradiance. Erythemal and total daily insolations reduce quickly at this epoch due to the increase of the noon solar zenith angle and the decrease of daylight time. Additionally, they were strongly modulated by cloudiness. Measured maxima were 2.71 kJ/m² and 18.42 MJ/m² respectively. Measurements were compared with satellite data. TOMS-inferred erythemal daily insolation shows the typical underestimation with respect to ground measurements at regions of high mean albedo. Measured mean total daily insolation agrees with climatological satellite data for the months of the campaign. Received August 9, 2002; revised January 4, 2003; accepted January 28, 2003 Published online May 20, 2003     

The Siberian High and climate change over middle to high latitude Asia

Summary The Siberian High is the most important atmospheric centre of action in Eurasia during the winter months. Here its variability and relationship with temperature and precipitation is investigated for the period 1922 to 2000. The pronounced weakening of the Siberian High during the last ∼ 20 years is its most remarkable feature. Mean temperature, averaged over middle to high latitude Asia (30° E–140° E, 30° N–70° N), is correlated with the Siberian High central intensity (SHCI) with correlation coefficient of − 0.58 (1922–1999), and for precipitation, the correlation coefficient is − 0.44 (1922–1998). Taking the Arctic Oscillation (AO), the SHCI, the Eurasian teleconnection pattern (EU), and the Southern Oscillation (SO) index into account, 72 percent of the variance in temperature can be explained for the period 1949–1997 (for precipitation the variance is 26 percent), with the AO alone explaining 30 percent of the variance, and the Siberian High contributing 24 percent. The precipitation variance explained by the Siberian High is only 9.8 percent of the total. Received January 2, 2001 Revised November 24, 2001     

Forecasting the equatorial Pacific sea surface temperatures by neural network models

We used neural network models to seasonally forecast the tropical Pacific sea surface temperature anomalies (SSTA) in the Ni?o 3.4 region (6 ^°S–6 ^°N, 120 ^°W–170 ^°W). The inputs to the neural networks (i.e., the predictors) were the first seven wind stress empirical orthogonal function (EOF) modes of the tropical Pacific (20 ^°S–20 ^°N, 120 ^°E–70 ^°W) for four seasons and the Ni?o 3.4 SSTA itself for the final season. The period of 1952–1981 was used for training the neural network models, and the period 1982–1992 for forecast validation. At 6-month lead time, neural networks attained forecast skills comparable to the other El Ni?o-Southern Oscillation (ENSO) models. Our results suggested that neural network models were viable for ENSO forecasting even at longer lead times of 9 to 12 months. We hypothesized that at these longer leads, the underlying relationship between the wind stress and Ni?o 3.4 SSTA became increasingly nonlinear. The neural network results were interpreted in light of current theories, e.g., the role of the “off-equatorial” Rossby waves in triggering the onset of an ENSO event and the delayed-oscillator theory in the development and termination of an ENSO event. Received: 31 October 1995 / Accepted: 25 July 1996     

Performance reduction of solar irradiance parametric models due to limitations in required aerosol data: case of the CPCR2 model

Summary Knowledge of the partition of global solar irradiance in its diffuse and direct beam components is required in different areas of applied meteorology. In the absence of solar irradiance measurements parametric approaches have to be used instead. In the present work, the parametric CPCR2 model has been analysed at Granada (37.18° N, 3.58° W, 660 m a.m.s.l), an inland location, covering a period greater than three years. Only cloudless conditions are analysed. Angstr?m’s α and β coefficients have been computed from measurements carried out with a sunphotometer. As the study reveals, the best performance of the parametric model is conditioned to the availability of appropriate information on aerosols, especially when the interest is focused on the direct and diffuse irradiance. Received October 18, 1999/Revised December 18, 2000     

Effective Accuracy of Satellite-Derived Hourly Irradiances

Summary  Estimates of hourly global irradiance based on geostationary satellite data with a resolution of several (2 to 10) kilometres reproduce ground-measured values with a Root Mean Square Error (RMSE) of typically 20% to 25%. The different components of this RMSE have been enumerated by several authors but, due to the lack of adequate measurements, their respective importance is not well settled. In the present study we attempt to quantify these components from a practical point of view, that is from the point of view of users having to rely on time/site specific irradiance data. We conclude that the intrinsic, or “effective” RMSE is more along the line of 12%. This effective RMSE is the measure of the methodological imprecision (satellite-to-irradiance conversion models). The remaining part of the overall RMSE is the amount by which spatially averaged satellite-derived estimates are, by their very nature, bound to differ from ground-measured local insolation. Received August 15, 1997 Revised March 4, 1998     

Principal component analysis of satellite-observed outgoing long-wave radiation during the monsoon period (June–September) over India

Summary In this study, Principal Component Analysis (PCA) has been used to identify the major modes of the outgoing long-wave radiation data for the period (1979–2002) during the Indian monsoon period (June–September), using seasonal mean values over the Indian region covering 143 grid points (5° N–35° N and 70° E–95° E at 2.5° Longitude–Latitude intervals. The five principal components explain up to 98.0% of the total variance. The first principal component explains 60% of the total variance with a pronounced variation in the outgoing long-wave radiation over the region 10° N to 25° N. It appears that the major reason for the monsoon variability is the intensity and associated fluctuations in the two major semi-permanent seasonal systems. This is largely indicative of strong seasonal shift of the major area of cloudiness associated with convergence zone. The second principal component explaining 20% of the total variance exhibits higher positive component loadings along 25° N and east of 80° E. The possible reason for this could be the synoptic systems such as monsoon depression/lows over the north bay and trough/vortices off the west-coast in the Arabian sea.     

On the use of a cloud modification factor for solar UV (290–385 nm) spectral range

Summary  Knowledge of ultraviolet radiation is necessary in different applications, in the absence of measurements, this radiometric flux must be estimated from available parameters. To compute this flux under all sky conditions one must consider the influence of clouds. Clouds are the largest modulators of the solar radiative flux reaching the Earth’s surface. The amount and type of cloud cover prevailing at a given time and location largely determines the amount and type of solar radiation received at the Earth’s surface. This cloud radiative effect is different for the different solar spectral bands. In this work, we analyse the cloud radiative effect over ultraviolet radiation (290–385 nm). This could be done by defining a cloud modification Factor. We have developed such cloud modification Factor considering two different types of clouds. The efficiency of the cloud radiative effect scheme has been tested in combination with a cloudless sky empirical model using independent data sets. The performance of the model has been tested in relation to its predictive capability of global ultraviolet radiation. For this purpose, data recorded at two radiometric stations are used. The first one is located at the University of Almería, a seashore location (36.83° N, 2.41° W, 20 m a.m.s.l.), while the second one is located at Granada (37.18° N, 3.58° W, 660 m a.m.s.l.), an inland location. The database includes hourly values of the relevant variables that cover the years 1993–94 in Almería and 1994–95 in Granada. Cloud cover information provided by the Spanish Meteorological Service has been include to compute the clouds radiative effect. After our study, it appears that the combination of an appropriate cloudless sky model with the cloud modification Factor scheme provides estimates of ultraviolet radiation with mean bias deviation of about 5% that is close to experimental errors. Comparisons with similar formulations of the cloud radiative effect over the whole solar spectrum provides evidence for the spectral dependency of the cloud radiative effect. Received November 15, 1999 Revised September 11, 2000     

Intense rainfall events over the west coast of India

Summary The west coast of the Indian peninsula receives very heavy rainfall during the summer Monsoon (June–September) season with average rainfall over some parts exceeding 250 cm. Heavy rainfall events with rainfall more than 15 cm day⁻¹ at one or more stations along the west coast of India occur frequently and cause considerable damage. A special observational programme, Arabian Sea Monsoon Experiment, was carried out during the monsoon season of 2002 to study these events. The spatial and temporal distributions of intense rainfall events, presented here, were used for the planning of this observational campaign. The present study using daily rainfall data for summer monsoon season of 37 years (1951–1987) shows that the probability of getting intense rainfall is the maximum between 14° N–16° N and near 19° N. The probability of occurrence of these intense rainfall events is high from mid June to mid August, with a dip in early July. It has been believed for a long time that offshore troughs and vortices are responsible for these intense rainfall events. However, analysis of the characteristics of cloud systems associated with the intense rainfall events during 1985–1988 using very high resolution brightness temperature data from INSAT-IB satellite shows that the cloud systems during these events are characterized by large spatial scales and high cloud tops. Further study using daily satellite derived outgoing longwave radiation (OLR) data over a longer period (1975–1998) shows that, most of these events (about 62%) are associated with systems organized on synoptic and larger scales. We find that most of the offshore convective systems responsible for intense rainfall along the west coast of India are linked to the atmospheric conditions over equatorial Indian Ocean.     

Estimating the annual mean screen temperature empirically

Summary We have examined station data from around the world to study the separate effects of the latitude (between 60° N–40° S), elevation and distance inland, on the annual-mean screen temperature. In the first 200–400 km from some west coasts, screen temperatures (after adjustment for elevation) rise inland, reaching a maximum called the ‘thermal-ridge temperature’ Tr. The rise of temperature within this littoral fringe (of width F) depends mainly on the difference between the sea-surface temperature off the west coast and the zonal mean. Further inland than such a fringe, adjusted temperatures generally decline eastwards, approximately linearly, at a rate C. The rate is related to hemisphere and latitude. Empirical relationships between latitude and the observed coastal sea-surface temperature, the near-shore screen temperature, Tr, C and F for each continent are used to estimate annual mean temperatures on land. Independent estimates of this kind for 48 places, using a look-up table, differ overall by only 0.7 K from the actual long-term average annual mean temperatures. This is less than half the error resulting from an assumption of zonal-mean temperatures. Basing estimates on coastal sea-surface temperatures, instead of the look-up table, results in an average error of 1.0 K for the 48 places. The errors are comparable with the standard deviation of annual mean temperatures during 30 years or so. Received March 6, 2001 Revised July 30, 2001     

The Characteristics of Cold Air Outbreaks over the Eastern Highlands of Kenya

Summary Climatological statistics of extreme temperature events over Kenya are established from the analysis of daily and monthly maximum temperatures for a representative station (Nairobi Dagoretti Corner) over the period 1956–1997. The months of June to August were shown to be the coldest with a mean monthly maximum temperature of less than 22 °C. Seasonal (June to August) mean maximum temperature was 21.5 °C. Using this seasonal mean temperature for the period 1967–1997 delineated 1968 as the coldest year in this series and 1983 as the warmest year. Spectral analysis of the seasonal data, for both the coldest and the warmest years, revealed that the major periods were the quasi-biweekly (10 days) and the Intraseasonal Oscillations (23 days). Secondary peaks occurred at periods of 4–6 and 2.5–3.5 days. A temperature threshold of 16.7 °C during July was used to define cold air outbreaks over Nairobi. This threshold temperature of 16.7 °C was obtained from the mean July maximum temperature (20.9 °C) minus two standard deviations. Notable trends include a decrease in the frequency of station-days, between 1956 and 1997, with temperatures less than 16.7 °C during July. Surface pressure patterns indicate that the origin of the cold air is near latitude 25° S and to the east of mainland South Africa. The cold air near 25° S is advected northwards ahead of the surface pressure ridge. Received July 19, 1999 Revised January 11, 2000     

Intraseasonal variability of the Tropical Easterly Jet

Summary By analyzing 12-year (1979–1990) 200 hPa wind data from National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis, we demonstrate that the intraseasonal time scale (30–60 days) variability of the Tropical Easterly Jet (TEJ) reported in individual case studies occurs during most years. In the entrance region (east of ∼70° E), axis of the TEJ at 200 hPa is found along the near equatorial latitudes during monsoon onset/monsoon revivals and propagates northward as the monsoon advances over India. This axis is found along ∼5° N and ∼15° N during active monsoon and break monsoon conditions respectively. Examination of the European Centre for Medium Range Weather Forecasts reanalysis wind data also confirms the northward propagation of the TEJ on intraseasonal time scales. During the intraseasonal northward propagations, axis of the TEJ is found about 10°–15° latitudes south of the well-known intraseasonally northward propagating monsoon convective belts. Because of this 10°–15° displacement, axis of the TEJ arrives over a location about two weeks after the arrival of the monsoon convection. Systematic shifting of the locations by convection, low level monsoon flow and TEJ in a collective way during different phases of the monsoon suggests that they all may be related.     

Determination of radiation amplification factor of atmospheric aerosol from the surface UV irradiance measurement at Gwangju, Korea

Summary This study investigated the impact of atmospheric aerosols on surface ultraviolet (UV) irradiance at Gwangju, Korea (35°13′N, 126°50′E). Data analyzed included surface UV irradiance measured by UV radiometers from June 1998 to April 2001 and the aerosol optical depth (AOD) in the visible range determined from a rotating shadow-band radiometer (RSR). The radiation amplification factor (RAF) of ozone for UV-B (280–315 nm) at Gwangju was 1.32–1.62. Values of the RAF of aerosols (RAF_AOD) for UV-A and UV-B were 0.18–0.20 and 0.22–0.26, respectively. Authors’ addresses: Jeong Eun Kim, Advanced Environmental Monitoring Research Center (ADEMRC), Gwangju Institute of Science and Technology (GIST) and Korea Meteorological Administration (KMA); Seong Yoon Ryu, Advanced Environmental Monitoring Research Center (ADEMRC), Gwangju Institute of Science and Technology (GIST) and Division of Metrology, Korea Research Institute of Standards and Science (KRISS); Young Joon Kim, Advanced Environmental Monitoring Research Center (ADEMRC) Gwangju Institute of Science and Technology (GIST), 1 Oryong-dong, Buk-gu, Gwangju 500-712, Republic of Korea.     

Cause-effect relationships between sea surface temperature, precipitation and sea level along the Bangladesh coast

Summary  The Bangladesh coast, which lies on the confluence of three mighty rivers, the Ganges, the Brahmaputra and the Meghna, with the Himalayas to the north and the Bay of Bengal to the south, is an ideal zone for sea level rise due to enhanced rainfall during the monsoon season from June to September. An attempt has been made here to look into the cause-effect relationships between observed trends in sea surface temperature (SST) over the Bay of Bengal and the trends in monsoon rains and sea level in Bangladesh. The study utilizes the 14-year satellite-derived SSTs over the Bay of Bengal for 1985–1998, the tide gauge stations data along the Bangladesh coast for 1977–1998 and the 31-year monsoon rainfall data for Bangladesh, 1961–1991. Received October 20, 2000     

A Diagnostic Study of the Global Distribution of Contrails Part II: Future Air Traffic Scenarios

Summary  The global distribution of the contrail coverage is computed for several scenarios of aviation in the years 2015 and 2050 and compared to 1992 using meteorological analysis data representative of present temperature and humidity conditions and assuming 0.5% cover in a reference region 30° W–30° E, 35° N–75° N covering parts of western Europe and the North Atlantic. The mean contrail coverage of the Earth is computed to increase by a factor of about three compared to 1992 and to reach 0.25% in 2015. For three different scenarios of aviation and for constant climatic conditions, the global mean contrail coverage reaches values between 0.26% and 0.75% for 2050. Contrail coverage increases more strongly than total fuel burn mainly because of more traffic in the upper troposphere and because of more efficient engines with cooler exhaust. The overall efficiency of propulsion is expected to grow from about 0.3 in the fleet average of 1992, to 0.4 in 2015, and to 0.5 in 2050. The expansion of air traffic makes Canada, Alaska, the North Pacific route from North America to Japan and most of the Asian continent new regions where contrails are expected to cover more than 0.5% on average. Received September 7, 1998 Revised January 4, 1999     

Interpretation of recent temperature and precipitationtrends observed in Korea

Summary  The possibility of climate change in the Korean Peninsula has been examined in view of the general increase in greenhouse gases. Analyses include changes in annual temperature and precipitation. These analyses are supplemented with our observations regarding the apparent decrease of forest areas. It was found that there was a 0.96 °C (0.42 °C per decade) increase in annual mean temperature between 1974 and 1997. The increase in large cities was 1.5 °C but only 0.58 °C at rural and marine stations. The difference in the mean temperature between large cities and rural stations was small from 1974 to 1981. However, the difference increased from 1982 to 1997. In particular, the warming appears most significant in winter. Prior to 1982, the lowest temperatures were often −18 °C in central Korea, and since then the lowest temperatures have been only −12∼−14 °C. Recently, the minimum January temperature has increased at a rate of 1.5 °C per decade. It is estimated that the increase of1 °C in annual mean temperature corresponds to about a 250 km northward shift of the subtropical zone boundary. The analysis of data from 1906 to 1997 indicates a trend of increasing annual precipitation, an increase of 182 mm during the 92-year peirod, with large year-to-year variations. More than half of the annual mean amount, 1,274 mm, occurred from June to September. Meteorological data and satellite observations suggest that changes have occurred in the characteristics of the quasi-stationary fronts that produce summer rain. In recent years scattered local heavy showers usually occur with an inactive showery front, in comparison with the classical steady rain for more than three weeks. For instance, local heavy rainfall, on 6 August 1998 was in the range of 123–481 mm. The scattered convective storms resulted in flooding with a heavy toll of approx. 500 people. The northward shift of the inactive showery front over Korea, and of a convergence zone in central China, correlate with the increase in temperature. It has been suggested that the decrease in forest areas and the change in ground cover also contribute to the warming of the Korean Peninsula. Received March 16, 2000