Over the contiguous United States, precipitation, temperature, streamflow, and heavy and very heavy precipitation have increased during the twentieth century. In the east, high streamflow has increased as well. Soil wetness (as described by the Keetch–Byram Drought index) has increased over the northern and eastern regions of the United States, but in the southwestern quadrant of the country soil dryness has increased, making the region more susceptible to forest fires. In addition to these changes during the past 50 yr, increases in evaporation, near-surface humidity, total cloud cover, and low stratiform and cumulonimbus clouds have been observed. Snow cover has diminished earlier in the year in the west, and a decrease in near-surface wind speed has also occurred in many areas. Much of the increase in heavy and very heavy precipitation has occurred during the past three decades. Abstract Over the contiguous United States, precipitation, temperature, streamflow, and heavy and very heavy precipitation have increased during the twentieth century. In the east, high streamflow has increased as well. Soil wetness (as described by the Keetch–Byram Drought index) has increased over the northern and eastern regions of the United States, but in the southwestern quadrant of the country soil dryness has increased, making the region more susceptible to forest fires. In addition to these changes during the past 50 yr, increases in evaporation, near-surface humidity, total cloud cover, and low stratiform and cumulonimbus clouds have been observed. Snow cover has diminished earlier in the year in the west, and a decrease in near-surface wind speed has also occurred in many areas. Much of the increase in heavy and very heavy precipitation has occurred during the past three decades.

Collocated global atmospheric temperature, humidity, and refractivity profiles from radiosondes and from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation data for April 2008 to October 2009 are compared for two purposes. The first is to quantify the error characteristics of 12 radiosonde types flown in the global operational network, as a function of height and for both day and nighttime observations, for each of the three variables. The second is to determine the effects of imperfect temporal and spatial collocation on the radiosonde‐COSMIC differences, for application to the general problem of satellite calibration and validation using in situ sounding data. Statistical analyses of the comparisons reveal differences among radiosonde types in refractivity, relative humidity, and radiation‐corrected temperature data. Most of the radiosonde types show a dry bias, particularly in the upper troposphere, with the bias in daytime drier than in nighttime. Weather‐scale variability, introduced by collocation time and distance mismatch, affects the comparison of radiosonde and COSMIC data by increasing the standard deviation errors, which are generally proportional to the size of the time and distance mismatch within the collocation window of 6 h and 250 km considered. Globally, in the troposphere (850–200 hPa), the collocation mismatch impacts on the comparison standard deviation errors for temperature are 0.35 K per 3 h and 0.42 K per 100 km and, for relative humidity, are 3.3% per 3 h and 3.1% per 100 km, indicating an approximate equivalence of 3 h to 100 km in terms of mismatch impact.

Automated Surface Observation Systems (ASOS) were widely introduced to replace manned weather stations around the mid-1990s over North America and other parts of the world. While laser beam ceilometers of the ASOS in North America measure overhead clouds within the lower 3.6 km of the atmosphere, they do not contain cloud-type and opacity information and are not comparable with previous cloud records. However, a network of 124 U.S. military weather stations with continuous human observations provides useful information of total cloud cover over the contiguous United States, thus lessening the disruption caused by the ASOS. Analyses of the military cloud data suggest an increasing trend (∼1.4% of the sky cover per decade) in U.S. total cloud cover from 1976 to 2004, with increases over most of the country except the Northwest, although large uncertainties exist because of sparse spatial sampling. Thus, inadequacies exist in surface observations of global cloud amounts and types, especially over th... Abstract Automated Surface Observation Systems (ASOS) were widely introduced to replace manned weather stations around the mid-1990s over North America and other parts of the world. While laser beam ceilometers of the ASOS in North America measure overhead clouds within the lower 3.6 km of the atmosphere, they do not contain cloud-type and opacity information and are not comparable with previous cloud records. However, a network of 124 U.S. military weather stations with continuous human observations provides useful information of total cloud cover over the contiguous United States, thus lessening the disruption caused by the ASOS. Analyses of the military cloud data suggest an increasing trend (∼1.4% of the sky cover per decade) in U.S. total cloud cover from 1976 to 2004, with increases over most of the country except the Northwest, although large uncertainties exist because of sparse spatial sampling. Thus, inadequacies exist in surface observations of global cloud amounts and types, especially over th...

[1] The drift of radiosonde balloons during their ascent has generally been considered a negligible factor in applications involving radiosonde observations. However, several applications envisioned for observations from the Global Climate Observing System (GCOS) Reference Upper Air Network (GRUAN) require estimates of balloon drift. This study presents a comprehensive global climatology of radiosonde balloon drift distance and ascent time, based on 2 years of data from 419 stations, with particular attention to GRUAN stations. Typical drift distances are a few kilometers in the lower troposphere, ∼5 km in the midtroposphere, ∼20 km in the upper troposphere, and ∼50 km in the lower stratosphere, although there is considerable variability due to variability in climatological winds. Drift distances tend to increase with height above the surface, be larger in midlatitudes than in the tropics, be larger in winter than in summer, and vary with wind (and consequent balloon drift) direction. Most estimates of elapsed time from balloon launch to various pressure levels, due to vertical balloon rise, have median values ranging from about 5 min at 850 hPa to about 1.7 h at 10 hPa, with ranges of about 20% of median values. Observed elapsed times exceed those estimated using assumed 5 or 6 m/s rise rates.

A new daily latent and sensible flux product developed at the Woods Hole Oceanographic Institution (WHOI) with 1° × 1° resolution for the Atlantic Ocean (65°S–65°N) for the period from 1988 to 1999 was presented. The flux product was developed by using a variational objective analysis approach to obtain best estimates of the flux-related basic surface meteorological variables (e.g., wind speed, air humidity, air temperature, and sea surface temperature) through synthesizing satellite data and outputs of numerical weather prediction (NWP) models at the National Centers for Environmental Prediction (NCEP) and the European Centre for Medium-Range Weather Forecasts (ECMWF). The state-of-the-art bulk flux algorithm 2.6a, developed from the field experiments of the Coupled Ocean–Atmosphere Response Experiment (COARE), was applied to compute the flux fields. The study focused on analyzing the mean field properties of the WHOI daily latent and sensible heat fluxes and their comparisons with the ship-base... Abstract A new daily latent and sensible flux product developed at the Woods Hole Oceanographic Institution (WHOI) with 1° × 1° resolution for the Atlantic Ocean (65°S–65°N) for the period from 1988 to 1999 was presented. The flux product was developed by using a variational objective analysis approach to obtain best estimates of the flux-related basic surface meteorological variables (e.g., wind speed, air humidity, air temperature, and sea surface temperature) through synthesizing satellite data and outputs of numerical weather prediction (NWP) models at the National Centers for Environmental Prediction (NCEP) and the European Centre for Medium-Range Weather Forecasts (ECMWF). The state-of-the-art bulk flux algorithm 2.6a, developed from the field experiments of the Coupled Ocean–Atmosphere Response Experiment (COARE), was applied to compute the flux fields. The study focused on analyzing the mean field properties of the WHOI daily latent and sensible heat fluxes and their comparisons with the ship-base...

The relationship between cloud cover and near-surface air temperature and its decadal changes are examined using the hourly synoptic data for the past four to six decades from five regions of the Northern Hemisphere: Canada, the United States, the former Soviet Union, China, and tropical islands of the western Pacific. The authors define the normalized cloud cover–surface air temperature relationship, NOCET or dT/dCL, as a temperature anomaly with a unit (one-tenth) deviation of total cloud cover from its average value. Then mean monthly NOCET time series (night- and daytime, separately) are area-averaged and parameterized as functions of surface air humidity and snow cover. The day- and nighttime NOCET variations are strongly anticorrelated with changes in surface humidity. Furthermore, the daytime NOCET changes are positively correlated to changes in snow cover extent. The regionally averaged nighttime NOCET varies from −0.05 K tenth−1 in the wet Tropics to 1.0 K tenth−1 at midlatitudes in wint... Abstract The relationship between cloud cover and near-surface air temperature and its decadal changes are examined using the hourly synoptic data for the past four to six decades from five regions of the Northern Hemisphere: Canada, the United States, the former Soviet Union, China, and tropical islands of the western Pacific. The authors define the normalized cloud cover–surface air temperature relationship, NOCET or dT/dCL, as a temperature anomaly with a unit (one-tenth) deviation of total cloud cover from its average value. Then mean monthly NOCET time series (night- and daytime, separately) are area-averaged and parameterized as functions of surface air humidity and snow cover. The day- and nighttime NOCET variations are strongly anticorrelated with changes in surface humidity. Furthermore, the daytime NOCET changes are positively correlated to changes in snow cover extent. The regionally averaged nighttime NOCET varies from −0.05 K tenth−1 in the wet Tropics to 1.0 K tenth−1 at midlatitudes in wint...