John J. Bates

Trends in Global Cloud Cover in Two Decades of HIRS Observations

The frequency of cloud detection and the frequency with which these clouds are found in the upper troposphere have been extracted from NOAA High Resolution Infrared Radiometer Sounder (HIRS) polar-orbiting satellite data from 1979 to 2001. The HIRS/2 sensor was flown on nine satellites from the Television Infrared Observation Satellite-Next Generation (TIROS-N) through NOAA-14, forming a 22-yr record. Carbon dioxide slicing was used to infer cloud amount and height. Trends in cloud cover and high-cloud frequency were found to be small in these data. High clouds show a small but statistically significant increase in the Tropics and the Northern Hemisphere. The HIRS analysis contrasts with the International Satellite Cloud Climatology Project (ISCCP), which shows a decrease in both total cloud cover and high clouds during most of this period.

Radiance and Jacobian Intercomparison of Radiative Transfer Models Applied to HIRS and AMSU Channels

The goals of this study are the evaluation of current fast radiative transfer models (RTMs) and line-by-line (LBL) models. The intercomparison focuses on the modeling of 11 representative sounding channels routinely used at numerical weather prediction centers: 7 HIRS (High-resolution Infrared Sounder) and 4 AMSU (advanced microwave sounding unit) channels. Interest in this topic was evident by the participation of 24 scientists from 16 institutions. An ensemble of 42 diverse atmospheres was used and results compiled for 19 infrared models and 10 microwave models, including several LBL RTMs. For the first time, not only radiances but also Jacobians (of temperature, water vapor, and ozone) were compared to various LBL models for many channels. In the infrared, LBL models typically agree to within 0.05-0.15 K (standard deviation) in terms of top-of-the-atmosphere brightness temperature (BT). Individual differences up to 0.5 K still exist, systematic in some channels, and linked to the type of atmosphere in others. The best fast models emulate LBL BTs to within 0.25 K, but no model achieves this desirable level of success for all channels. The ozone modeling is particularly challenging. In the microwave, fast models generally do quite well against the LBL model to which they were tuned. However, significant differences were noted among LBL models. Extending the intercomparison to the Jacobians proved very useful in detecting subtle or more obvious modeling errors. In addition, total and single gas optical depths were calculated, which provided additional insight on the nature of differences.

Interannual Variability of Upper-Troposphere Water Vapor Band Brightness Temperature

Abstract A method for the intercalibration of the high-resolution infrared sounder (HIRS) upper-tropospheric water vapor band brightness temperature data is developed and applied to data from 1981 to 1993. Analysis of the adjusted anomaly time series show the location and strength of both the large-scale ascending and descending circulations in the Tropics as well as water vapor anomalies. Comparison of these HIRS data with outgoing longwave radiation and sea surface temperature anomalies reveals that both convection and increased upper-tropospheric moisture occur over anomalously warm water in the deep Tropics. The development and movement of deep convection and increased upper-tropospheric moisture can clearly he traced during the El Nino/Southern Oscillation warm events. These HIRS data are particularly useful in monitoring upper-tropospheric water vapor variability between the Tropics and subtropics.

Trends in upper‐tropospheric humidity

Water vapor is the most radiatively active greenhouse gas, and the process of water-vapor feedback may significantly amplify global warming induced by anthropogenic greenhouse gasses. Satellite radiance observations from the past 20 years, which are sensitive to the water vapor and temperature of the upper troposphere, provide the first global observations of trends in upper-tropospheric humidity. These decadal trends are strongly positive in the deep tropics, negative in the Southern Hemisphere subtropics and midlatitudes, and of mixed sign in the Northern Hemisphere subtropics and midlatitudes. The trends are shown to be consistent with atmospheric circulation changes observed in the past 20 years, including a tendency toward more El Nino-Southern Oscillation warm events and changes in transient eddy activity in the subtropics.

U.S. temperature and drought: Recent anomalies and trends

The spring and summer (March through August) of 2011–2012 set many new climatological records across the contiguous United States, including the hottest month in the instrumental record: July 2012. Various measures of temperature extremes and drought severity serve to put this period into historical perspective (1895 to present) and to assess to what extent the recent anomalies are consistent with observed trends. During spring and summer, anomalously high temperatures can combine with unusually dry conditions to amplify temperature and drought feedbacks. Observational data from 2011 and 2012 are strongly suggestive of such an amplification and reveal a number of significant trends for various measures of high temperatures in the United States.

A Climatology of the Water Vapor Band Brightness Temperatures from NOAA Operational Satellites

Abstract Measurements of brightness temperature from the water vapor band channels of the National Oceanic and Atmospheric Administration polar satellites from 1981 through 1988 are analyzed. Only clear and cloud-cleared measurements from the operational sounding product are used to produce averages for bins of 2.5° latitude by 2.5° longitude and 5 days. The standard deviations of random errors for these bins are estimated. A unique feature of this dataset is its ability to identify the dry regions in the middle and upper troposphere with unprecedented detail. Results agree with the known climatology in the tropics.

The Influence of Sea Surface Temperature Gradients on Stratiform Cloudiness along the Equatorial Front in the Pacific Ocean

Abstract Satellite observations of visible cloudiness and sea surface temperature (SST) are used to test the hypothesis that the configuration of cool low-level winds blowing across a sharp SST front in the equatorial eastern Pacific gives rise to stratiform clouds on the warm (downstream) side of the front. The results show that there is a maximum in low clouds over the equatorial front during the cold season of 1988 when the front and cross-isotherm winds were strong. The low-cloud maximum was reduced in the warm El Nino year of 1987, consistent with the weakening of the front. Instability waves along the equatorial front were pronounced during the summer and autumn of 1988. The results show a strong association between visible cloud and the SST waves, with enhanced (reduced) cloudiness in the warm troughs (cold crests) of the waves.

An intercomparison of radiation codes for retrieving upper-tropospheric humidity in the 6.3-μm band: A report from the first GVaP workshop

Abstract An intercomparison of radiation codes used in retrieving upper–tropospheric humidity (UTH) from observations in the n2 (6.3 mm) water vapor absorption band was performed. This intercomparison is one part of a coordinated effort within the Global Energy and Water Cycle Experiment Water Vapor Project to assess our ability to monitor the distribution and variations of upper–tropospheric moisture from spaceborne sensors. A total of 23 different codes, ranging from detailed line–by–line (LBL) models, to coarser–resolution narrowband (NB) models, to highly parameterized single–band (SB) models participated in the study. Forward calculations were performed using a carefully selected set of temperature and moisture profiles chosen to be representative of a wide range of atmospheric conditions. The LBL model calculations exhibited the greatest consistency with each other, typically agreeing to within 0.5 K in terms of the equivalent blackbody brightness temperature(Tb). The majority of NB and SB models ag...

Variability of tropical upper tropospheric humidity 1979–1998

We update the time series of upper tropospheric humidity observations, begun in 1979 through May 1998, which includes the major El Nino event of 1997–1998. The intercalibration of different satellites is updated and compared to a physically based intercalibration. The results show excellent agreement and indicate that the main source of intersatellite bias is the known filter response function of the different instruments. Interannual variability of spatial fields is dominated by the major El Nino events in the 1979–1998 time period. Tropical average anomaly time series of upper tropospheric humidity, however, are dominated by a pronounced seasonal preference in extremes. Large deviations from the anomaly time series are twice as likely to occur in boreal winter and spring as in boreal summer and fall. During boreal winter and spring, the tropical basic state circulation permits the opening of a westerly wave duct such that midlatitude Rossby waves can propagate into the subtropics and tropics. We hypothesize that variation in the Rossby wave activity modulates the vertical water vapor flux and is responsible for large variations in the tropical upper tropospheric humidity time series.

Estimating Bias of Satellite-Based Precipitation Estimates

Abstract Systematic biases in satellite-based precipitation estimates can be the dominant component of their uncertainty. These biases may not be reduced by averaging, which makes their evaluation particularly important. Described here are several methods of evaluating the biases and their characteristics. Methods are developed and tested using monthly average precipitation estimates from several satellites. Direct estimates of bias are obtained from analysis of satellite–gauge estimates, and they indicate the general bias patterns and magnitudes over land. Direct estimates cannot be computed over the oceans, so indirect-bias estimates based on ensembles of satellite and gauge estimates are also developed. These indirect estimates are consistent with direct estimates in locations where they can be compared, while giving near-global coverage. For both bias estimates computed here, the bias uncertainty is higher than nonsystematic error estimates, caused by random or sampling errors and which have been prev...