Session 6

Role of water from the ground to the upper atmosphere

12/11 – Thrusday


14:30 - 14:35 Various aspects of the role of water from the ground to the upper atmosphere in the terrestrial atmosphere (Takuji Nakamura )

  1. Takuji Nakamura (NIPR)

Water in the Earth`s middle atmosphere is a minor constituent, and very small in amount, but play important roles. It is recently known that latent heat released
by cumulus convection in the troposphere play important role in generating atmospheric waves, such as gravity wave and tides, which go up to the mesosphere and even thermosphere and ionosphere up to a few hundred km above ground, transporting momentum and energy, and driving the atmosphere circulation and variations of ionosphere. Water vapor is also one of greenhouse gases and the trend in the middle atmosphere is of interest. At mesopause, water becomes ice in summer polar region and forms noctiluscent clouds or PMC. The increasing trend of such clouds is a hot issue related to the global warming. Molecules related to water, such as OH, are emitting visible and infrared radiation as an airglow, which severely interference the astronomical observations from the ground, but very useful for remote sensing of the mesosphere lower thermosphere region to understand dynamical and chemical features of the terrestrial atmosphere. This talk will introduce various aspects of the water from the ground to the upper atmosphere, as the target of the session 6.

14:35 - 14:55 Precipitable Water and rainfall variabilites over the Amazon Basin region using the GPS Radio Occultation data, Tropical Rainfall Measuring Mission data and station data (Pablo Llamedo)

  1. Pablo Llamedo (Universidad Austral)
  2. Rodrigo Hierro (Universidad Austral)
  3. Alejandro De La Torre (Universidad Austral)
  4. Peter Alexander (Universidad de Buenos Aires)

The Amazon basin (AB) region (0-20S and 75W-45W), constitutes the largest extent of
tropical rainforest on Earth. The annual mean regional precipitation becomes the most important heat source for the tropical atmosphere providing almost 15 % of the global water discharged to the oceans.
The precipitable water content (PW) and specific humidity (q) obtained by the Global Positioning System (GPS) Radio Occultation (RO) technique (2006-2014), daily accumulated rainfall data (3B42 v7 product) obtained by the Tropical Rainfall Measuring Mission (TRMM) (1998-2013) and daily rainfall station data (Brazilian water agency) were used to study the variabilities in climate signal over the AB.
A multivariate linear regression is applied to time series to study the deppendace of longer signals like ENSO and possible trends. The correlations between PW and rainfall is analized. Also, a continuous wavelet transform is applied to PW and rainfall to investigate the temporal and spatial modes of oscullation.

14:55 - 15:15 Dynamical processes and transport influencing the water vapour budget in the upper troposphere / lower stratosphere (UTLS) (Martin Riese)

  1. Martin Riese (Forschungszentrum Jülich GmbH)
  2. Mengchu Tao (Forschungszentrum Jülich GmbH)
  3. Felix Ploeger (Forschungszentrum Jülich GmbH)
  4. Paul Konopka (Forschungszentrum Jülich GmbH)
  5. Rolf Mueller (Forschungszentrum Jülich GmbH)

Changes and variability of UTLS composition are major drivers of surface climate change (e.g. Solomon et al., 2010). Even small changes of spatially highly variable concentrations of greenhouse gases such as water vapor (H2O) have significant effects on the atmospheric radiation balance. Improved projections of chemistry-climate models (CCM) therefore rely on a realistic representation of physical and chemical processes affecting UTLS composition. This is problematic, because UTLS composition is governed by the complex interactions of various physical and chemical processes that operate at a wide range of temporal and spatial scales (local to global).

We analyze important underlying processes based on multi-annual simulations by the Chemical Lagrangian Model of the Stratosphere (CLaMS), in combination with satellite observations. Our results indicate that the Asian monsoon plays a crucial role for transporting moist air from the tropical troposphere into the extra-tropical lowermost stratosphere during boreal summer. In the tropics, transport of water vapour into the deep stratosphere, which is associated with the ascending branch of the large-scale Brewer-Dobson circulation, is significantly influenced by the Quasi Biennial Oscillation and by Major Stratospheric Warming events during boreal winter.

15:15 - 15:45 Dehydration processes inside the Antarctic polar vortex (Yoshihiro Tomikawa)

  1. Yoshihiro Tomikawa (National Institute of Polar Research)

Interannual variations of stratospheric water vapor have a large impact on the surface temperature as well as the stratospheric temperature. The stratospheric water vapor concentration is primarily controlled by dehydration processes in the tropical tropopause layer and methane oxidation in the stratosphere. However, the water vapor concentration inside the stratospheric polar vortex, especially in the Antarctic, is affected by additional dehydration, because the lower stratosphere in the polar vortex becomes colder than the tropical tropopause. Thus it is inferred that the stratospheric water vapor, which is one of primary greenhouse gases, over the Antarctic changes in a different way from other latitude regions. In order to examine how much the stratospheric water vapor concentration varies due to the dehydration and any other processes unique to the Antarctic stratosphere, a trajectory-based analysis is applied to the stratospheric water vapor data of the Microwave Limb Sounder (MLS) onboard the Aura satellite. It can give a minimum saturation mixing ratio of water vapor on each trajectory, which should be identical with the observed water vapor mixing ratio if it is determined by the dehydration during the trajectory period. This analysis will provide quantitative estimates of the dehydration and any other processes contributing to the variation of water vapor concentration in the Antarctic stratosphere.

15:45 - 16:05 Water vapour and ion chemistry in the mesosphere and lower thermosphere - a model study (Holger Winkler)

  1. Holger Winkler (Institute of Environmental Physics, University of Bremen, Germany)
  2. Justus Notholt (Institute of Environmental Physics, University of Bremen, Germany)

The ion chemistry of the Earth’s mesosphere and lower thermosphere (MLT) region is affected by the concentration of water vapour. In particular, the height-distribution of proton hydrates (PHs) and non-proton hydrates (NPHs) depends on the water profile. Due to the fact that PHs and NHPs as well as molecular ions possess different reactivities, the ion composition of the D-region is linked to water. We present model simulations of hydrogen species and ions in the MLT region. For this purpose, a detailed ion-chemistry model is used in combination with a one-dimensional atmospheric chemistry and diffusion model. Additionally, water profiles from satellite observations are considered. The model is applied to quiet ionospheric conditions as well as to solar particle events.

17:00 - 17:30 Trends in Mesospheric Ice Layers in the Northern Hemisphere during 1961-2013 (Uwe Berger)

  1. Uwe Berger (IAP Kuehlungsborn, Germany)
  2. Franz-josef Luebken (IAP)

We have performed trend studies in the mesosphere in the period 1961–2013 with Leibniz-Institute Middle Atmosphere (LIMA) model driven by European Centre for Medium-Range Weather Forecasts reanalysis (ERA-interim) below approximately 45 km. LIMA adapts temporal variations of CO2 and O3 according to observations, and observed daily Lyman alpha fluxes.
The simulation of the thermal state at the summer upper mesosphere allows to investigate the impact on the morphology of ice particle related phenomena such as polar mesosphere clouds (PMC). The PMC characteristics deduced from LIMA are validated with various data sets from satellite (NOAA-SBUV, AIM-SOFIE) observations. Generally good agreement is found between the modeled long-term PMC variations and that derived from SBUV observations.
We investigate the role of trends in mesospheric water vapor and temperature that mainly force PMC trends. We show that water vapor and temperatures in the stratosphere/meso- sphere/lower thermosphere vary none-uniformly with time. Especially, we analyze the contribution of varying concentrations of CO2 and O3 to the temperature trend in the mesosphere. It is important to distinguish between trends on pressure altitudes and geometrical altitudes, where the latter includes the effect of shrinking due to cooling at lower heights. As a highlight, we will present first results in analyzing the very first appearance of NLC in 1885 observed after the volcanic eruption of Krakatao in August 1883 that injected a tremendous mass of water vapor into the stratosphere.

17:30 - 18:00 Observations of Polar Mesospheric Clouds from Space and Their Scientific Implications (Scott Bailey)

  1. Scott Bailey (Virginia Tech)
  2. James Russell (Hampton University)

Observations of Polar Mesospheric Clouds (PMCs), also called Noctilucent Clouds, were first reported in 1885 by the amateur astronomer Robert Leslie. Since that time there has been a growing public and scientific interest in these beautiful, iridescent clouds. This is most probably because they can be easily seen from the ground at latitudes above about 55 degrees and in addition numerous papers have reported quantitative cloud properties from space borne measurements. In recent years the focus on PMCs has intensified as a result of satellite measurements that show increasing cloud brightness and frequency of occurrence over the last ~ 27 years. Also, while not conclusively shown, it seems that there are more frequent cloud sightings at lower latitudes, e.g. 40 N, than have been reported in the past. Finally, there is the unproven but plausible theory that the observed changes in cloud properties are connected with global change due to the buildup of the greenhouse gases, CO2 and CH4, in the atmosphere.

This paper will present an overview of space-based observations of PMCs and scientific implications of the data. The clouds have been extensively observed by a number of satellite experiments. AIM is the first mission dedicated to the study of PMCs with the overall goal being to understand why they form and vary. PMC temporal variability on time scales of a solar cycle and the 27-day solar rotation have been reported. We also now know that PMCs are highly variable from orbit-to-orbit and day-to-day with significant complex structure. Other analyses show that temperature change is a dominant factor in controlling season onset, variability during the season and season end. Rising water vapor levels at the beginning and falling values at the end also play a key role in season initiation and cessation. Structures seen in the clouds look very much like complex features seen in tropospheric clouds including large regions of near circular ice voids. Planetary waves modulate PMC occurrence and can effectively extend the PMC season by providing several days of localized regions of saturated air in the troughs of the waves. By contrast, gravity waves appear to locally diminish PMC frequency even though global scale gravity wave drag is acknowledged as the prime cause of the cold polar summer mesopause. Satellite results also provide evidence that interhemispheric coupling, from the winter hemisphere to the summer hemisphere affects PMC variability.

18:00 - 18:20 - Effects of cosmic rays on clouds and snow-fall in Antarctica (C. P. Anil Kumar)

  1. C. P. Anil Kumar (Indian Institute of Geomagnetism, Navi Mumbai – 410 218, India.)
  2. Balan Nanan (INPE, DAE, Sao Jose Dose Campos, SP, Brazill, CEP 12227-010)

We present the fair-weather air-earth current density (Jz) and meteorological parameters measured at the Indian Antarctic station Maitri (70º45’S, 11º43’E) for nine years covering solar maximum (2001-2002) and long deep solar minimum (2006-2009). The data at Maitri together with the equivalent galactic cosmic ray (GCR) flux measured by the neutron monitors at the American station McMurdo (77º51’S, 166º40’E), solar cosmic ray (SCR) flux measured by ACE (advanced composition explorer) satellite and meteorological data obtained from other Antarctic stations such as Vostok (78º27’S, 106º52’E), Scott Base (77º51’S, 166º46’E) and Antarctic Data base are also used to check the possible effects of cosmic rays on clouds and snow-fall in Antarctica. The observations show that the (1) current density Jz on the whole decreases from ~3.5 pA in 2001 to ~2.0 pA in 2006 and remains at ~2 pA during the long solar minimum (2007-2009) indicating that Jz is contributed more by SCR than by GCR; (2) Jz also shows peaks at specific UT hours corresponding to the thunderstorm times in continents. (3) Low level cloud coverage (pressure >680 hPa) and snowfall seem positively but weakly correlated to cosmic rays; and (4) highest correlations (0.34 for low level clouds and 0.14 for snow-fall) are obtained at the long deep solar minimum (2007-2009).