U. von Zahn

Size distributions of NLC particles as determined from 3‐color observations of NLC by ground‐based lidar

From June to August 1998 the ALOMAR Rayleigh/Mie/Raman lidar, located at 69°N and 16°E in Northern Norway, repeatedly observed noctilucent clouds (NLCs) overhead the lidar. Due to a recent upgrade in detector technology, the lidar was able to obtain 151 hours of NLC observations, simultaneously at 355, 532, and 1064 nm. For the 11 strongest NLC events, we have calculated size distributions for the NLC particles from the backscatter ratios measured at the 3 wavelengths and using the assumptions of spherical ice particles with a monomodal lognormal size distribution. For all events evaluated at the layer maxima, we obtain well-defined median radii rmed, width parameters σ, and particle number densities NNLC for the NLC particle distributions. Mean values for 10 out of the 11 events are rmed = 51 nm, σ = 1.42, and NNLC = 82 cm−3.

Simultaneous and common‐volume observations of noctilucent clouds and polar mesosphere summer echoes

Joint operations of the ALOMAR Rayleigh/Mie/Raman (RMR) lidar and ALOMAR SOUSY radar (located at 69°N latitude) let us obtain a first series of simultaneous and common-volume observations of noctilucent clouds (NLC) and polar mesosphere summer echoes (PMSE). We present the results of 22 examples of simultaneous NLC and PMSE observations made during the summers 1994 until 1997. These observations show a strong correlation of NLC with PMSE and they lead us to a classification (3 types) of the observed events. Furthermore, we conclude that, in all probability, there are common causes for the two types of layers.

DROPPS: A study of the polar summer mesosphere with rocket, radar and lidar

DROPPS (The Distribution and Role of Particles in the Polar Summer Mesosphere) was a highly coordinated international study conducted in July, 1999 from the Norwegian rocket range (Andoya, Norway). Two sequences of rockets were launched. Each included one NASA DROPPS payload, containing instruments to measure the electrodynamic and optical properties of dust/aerosol layers, accompanied by European payloads (MIDAS, Mini-MIDAS, and/or Mini-DUSTY) to study the same structures in a complementary manner. Meteorological rockets provided winds and temperature. ALOMAR lidars and radars (located adjacent to the launch site) monitored the mesosphere for noctilucent clouds (NLCs) and polar mesosphere summer echoes (PMSEs), respectively. EISCAT radars provided PMSE and related information at a remote site (Tromso, Norway). Sequence 1 (5–6 July) was launched into a strong PMSE with a weak NLC present; sequence 2 (14 July) occurred during a strong NLC with no PMSE evident. Here we describe program details along with preliminary results.

A note on record‐high temperatures at the northern polar stratopause in winter 1997/98

A series of lidar temperature soundings from the ALOMAR observatory in northern Norway indicated an extreme warming of a descending stratopause in February 1998. The maximum temperature recorded during this event was +49°C at 40 km altitude. This stratospheric warming is described by means of SSU satellite radiance data and of stratospheric analyses from the Free University Berlin. Comparisons are made to a number of historical events with similar temperature observations from rocket soundings and to results from the Berlin general circulation model. It turns out that in all cases the highest stratopause temperatures occur close to the 40 km altitude level.