Marvin A. Geller

SOLAR INFLUENCES ON CLIMATE

The development of this review article has evolved from work carried out by an international team of the International Space Science Institute (ISSI), Bern, Switzerland, and from work carried out under the auspices of Scientific Committee on Solar Terrestrial Physics (SCOSTEP) Climate and Weather of the Sun‐Earth System (CAWSES‐1). The support of ISSI in providing workshop and meeting facilities is acknowledged, especially support from Y. Calisesi and V. Manno. SCOSTEP is acknowledged for kindly providing financial assistance to allow the paper to be published under an open access policy. L.J.G. was supported by the UK Natural Environment Research Council (NERC) through their National Centre for Atmospheric Research (NCAS) Climate program. K.M. was supported by a Marie Curie International Outgoing Fellowship within the 6th European Community Framework Programme. J.L. acknowledges support by the EU/FP7 program Assessing Climate Impacts on the Quantity and Quality of Water (ACQWA, 212250) and from the DFG Project Precipitation in the Past Millennium in Europe (PRIME) within the Priority Program INTERDYNAMIK. L.H. acknowledges support from the U.S. NASA Living With a Star program. G.M. acknowledges support from the Office of Science (BER), U.S. Department of Energy, Cooperative Agreement DE‐FC02‐97ER62402, and the National Science Foundation. We also wish to thank Karin Labitzke and Markus Kunze for supplying an updated Figure 13, Andrew Heaps for technical support, and Paul Dickinson for editorial support. Part of the research was carried out under the SPP CAWSES funded by GFG. J.B. was financially supported by NCCR Climate–Swiss Climate Research.

The SPARC Intercomparison of Middle-Atmosphere Climatologies

An updated assessment of uncertainties in ‘‘observed’’ climatological winds and temperatures in the middle atmosphere (over altitudes ;10‐80 km) is provided by detailed intercomparisons of contemporary and historic datasets. These datasets include global meteorological analyses and assimilations, climatologies derived from research satellite measurements, historical reference atmosphere circulation statistics, rocketsonde wind and temperature data, and lidar temperature measurements. The comparisons focus on a few basic circulation statistics (temperatures and zonal winds), with special attention given to tropical variability. Notable differences are found between analyses for temperatures near the tropical tropopause and polar lower stratosphere, temperatures near the global stratopause, and zonal winds throughout the Tropics. Comparisons of historical reference atmosphere and rocketsonde temperatures with more recent global analyses show the influence of decadal-scale cooling of the stratosphere and mesosphere. Detailed comparisons of the tropical semiannual oscillation (SAO) and quasibiennial oscillation (QBO) show large differences in amplitude between analyses; recent data assimilation schemes show the best agreement with equatorial radiosonde, rocket, and satellite data.

A Comparison between Gravity Wave Momentum Fluxes in Observations and Climate Models

Forthefirsttime,aformalcomparisonismadebetweengravitywavemomentumfluxesinmodelsandthose derivedfromobservations. Althoughgravitywavesoccuroverawiderangeofspatialandtemporalscales,the focusofthispaperisonscalesthatarebeingparameterizedinpresentclimatemodels,sub-1000-kmscales.Only observational methodsthatpermitderivationofgravitywavemomentumfluxesoverlargegeographical areas are discussed, and these are from satellite temperature measurements, constant-density long-duration bal- loons,andhigh-vertical-resolutionradiosondedata.Themodelsdiscussedincludetwohigh-resolutionmodels in which gravity waves are explicitly modeled, Kanto and the Community Atmosphere Model, version 5 (CAM5), and three climate models containing gravity wave parameterizations, MAECHAM5, Hadley Centre Global Environmental Model 3 (HadGEM3), and the Goddard Institute for Space Studies (GISS) model. Measurements generally show similar flux magnitudes as in models, except that the fluxes derived from satellite measurements fall off more rapidly with height. This is likely due to limitations on the observable range of wavelengths, although other factors may contribute. When one accounts for this more rapid fall off, the geographical distribution of the fluxes from observations and models compare reasonably well, except for certain features that depend on the specification of the nonorographic gravity wave source functions in the climate models. For instance, both the observed fluxes and those in the high-resolution models are very small at summer high latitudes, but this is not the case for some of the climate models. This comparison between gravity wave fluxes from climate models, high-resolution models, and fluxes derived from observations in- dicates that such efforts offer a promising path toward improving specifications of gravity wave sources in climate models.

A Computation of the Stratospheric Diabatic Circulation Using an Accurate Radiative Transfer Model

Abstract The global diabatic circulation is computed for the months of January, April, July and October over the altitude region 100 to 0.1 mb using an accurate troposphere-stratosphere radiative transfer model, SBUV and SME ozone data, and NMC temperatures. There is high correlation between the level of wave activity and the local departure of the atmosphere from radiative equilibrium. For example, the summer lower stratosphere is close to radiative equilibrium while the winter is not. We find much greater heating in the upper stratosphere at low latitudes in the summer hemisphere, and roughly a factor of two less heating in the lower stratosphere at low latitudes, than did Murgatroyd and Singleton. An excess in the globally averaged net stratospheric heating from 40 to 50 km is computed for all months, and a deficit from 50 to 60 km is computed during solstice. Roughly a 20% uniform reduction in ozone from 40 to 50 km, or a temperature perturbation with an increase of 5 K at 1 mb, will bring the atmosph...

Cooling trend of the tropical cold point tropopause temperatures and its implications

Operational sounding data (1973–1998) were used to determine cold point tropopause (CPT) characteristics. A cooling trend (−0.57±0.06 K/Decade during 1973–1998) in tropical CPT temperatures has been found, which is opposite to what has been hypothesized to explain the trend in stratospheric water vapor. Given this trend, the annual averages of the CPT saturation mixing ratios (SMRs) inferred from the analysis of the 1994–1997 data in the work of Dessler [1998] are substantially smaller than those from data before the mid-1990s. This implies that while Newell and Gould-Stewarts “stratospheric fountain” might not have been necessary to explain stratospheric water vapor during the mid-1990s, it was necessary in most years before that. Changes in tropical convection occurrence frequency and/or strength are suggested to explain the cooling trend in the CPT temperatures. It is suggested that the observed positive trend in stratospheric water vapor is probably due to changes in the residual circulation.

Rethinking reactive halogen budgets in the midlatitude lower stratosphere

Current stratospheric models have difficulties in fully explaining the observed midlatitude ozone depletion in the lowermost stratosphere, particularly near the tropopause. Such models assume that only long-lived source gases provide significant contributions to the stratospheric halogen budget, while all the short-lived compounds are removed in the troposphere, the products being rained out. Here we show this assumption to be flawed. Using bromine species as an example, we show that in the lowermost stratosphere, where the observed midlatitude ozone trend maximizes, bromoform (CHBr3) alone likely contributes more inorganic bromine than all the conventional long-lived sources (halons and methyl bromide) combined.

The Response of Soil Moisture to Long-Term Variability of Precipitation

Abstract Soil hydrology is a widely recognized low-pass filter for the interaction between land and atmosphere. However, the lack of adequate long-term measured data on soil moisture profiles has precluded examination of how soil wetness responds to long-term precipitation variations. Such a response can be characterized by its amplitude damping, phase shifting, and increasing persistence with soil depth. These should be correlated with the climate spectra through the interactions between the land and the atmosphere. The major objective of this study is to investigate how precipitation signals are manifested in vertical soil moisture profiles in the context of timescales. Thus, the natural variability of soil moisture profiles is documented using 16 yr of field observational data of soil moisture measured at 11 levels of various depths down to 2.0 m at 17 locations over Illinois. Detailed statistic analyses are made of the temporal variations of soil moisture profiles and concurrently measured precipitati...

Planetary Wave Coupling between the Troposphere and the Middle Atmosphere as a Possible Sun-Weather Mechanism

Abstract The possibility of planetary wave coupling between the troposphere and solar-induced alterations in the upper atmosphere providing a viable mechanism for giving rise to sun-weather relationships is investigated. Some of the observational evidence for solar-activity-induced effects on levels of the upper atmosphere ranging from the thermosphere down to the lower stratosphere are reviewed. It is concluded that there is evidence for such effects extending down to the middle stratosphere and below. Evidence is also reviewed that these effects are due to changes in solar ultraviolet emission during disturbed solar conditions. A theoretical planetary wave model is then used to see at what levels in the upper atmosphere moderate changes in the mean zonal wind state would result in tropospheric changes. It is concluded that changes in the mean zonal flow of ∼20% at levels in the vicinity of 35 km or below would give rise to changes in the tropospheric planetary wave pattern that are less than but on the ...

Spatial and Temporal Variations of Gravity Wave Parameters. Part I: Intrinsic Frequency, Wavelength, and Vertical Propagation Direction

Abstract Five years (1998–2002) of U.S. high vertical resolution radiosonde data are analyzed to derive important gravity wave parameters, such as intrinsic frequencies, vertical and horizontal wavelengths, and vertical propagation directions in the lower stratosphere and troposphere. Intrinsic frequencies ω increase with increasing latitude, with larger values in the troposphere. In the lower stratosphere, ω is higher in winter than in summer, especially at mid- and high latitudes. Intrinsic frequencies divided by the Coriolis parameter f are ∼4 in the troposphere, and ∼2.4–3 in the lower stratosphere. The lower-stratospheric ω/f generally decreases weakly with increasing latitude. The latitudinal distributions of the lower-stratospheric ω/f are explained largely by the propagation effects. The seasonal variations of ω in the lower stratosphere are found to be related to the variations of the background wind speeds. Dominant vertical wavelengths decrease with increasing latitude in the lower stratos...

Troposphere-Stratosphere (Surface-55 km) Monthly Winter General Circulation Statistics for the Northern Hemisphere-Four Year Averages

Abstract Monthly mean Northern Hemisphere general circulation statistics are presented for the four-year average December, January and February months of the winters 1978–79 through 1981–82. These calculations start with daily maps for eighteen pressure levels between 1000 and 0.4 mb of Northern Hemisphere temperature at 1200 GMT that are supplied by NOAA/NMC. Geopotential height and geostrophic wind are constructed using the hydrostatic and geostrophic relationships, respectively. Fields presented in this paper are zonally averaged temperature, mean zonal wind, and amplitude and phase of planetary waves with zonal wave-numbers 1-3. Diagnostic quantities, such as the northward fluxes of heat and eastward momentum by standing and transient eddies along with their wavenumber decomposition and Eliassen-Palm flux propagation vectors and divergences by the standing and transient eddies along with their wavenumber decomposition, are also given. The observations indicate that polar temperatures in the lower stra...